THE END

OF

ASTRONAUTS

Why Robots Are the Future of Exploration

Donald Goldsmith and Martin Rees

THE BELKNAP PRESS of HARVARD UNIVERSITY PRESS

Cambridge, Massachusetts & London, England      2022

Copyright © 2022 by Donald Goldsmith and Martin Rees

All rights reserved

Design by Oliver Munday

978-0-674-27621-5 (EPUB)

978-0-674-27622-2 (PDF)

978-0-674-25772-6 (cloth)

The Library of Congress has cataloged the printed edition as follows:

Names: Goldsmith, Donald, author. | Rees, Martin J., 1942- author.

Title: The end of astronauts : why robots are the future of exploration / Donald Goldsmith and Martin Rees.

Description: Cambridge, Massachusetts : The Belknap Press of Harvard University Press, 2022. | Includes bibliographical references and index.

Identifiers: LCCN 2021040946

Subjects: LCSH: Space robotics—United States. | Outer space—Exploration—United States.

Classification: LCC TL1097 .R44 2022 | DDC 629.47—dc23

LC record available at https://lccn.loc.gov/2021040946

Introduction

From Fireworks to Spaceflight

Astronauts are heroes. They perform technical, engineering, and scientific feats in an environment of weightlessness even as they must deal with the nausea, disorientation, and potential long-term medical consequences of that weightlessness. They risk cancer and other physical damage from the assaults of high-energy particles from the sun and the deeper universe. Astronauts perform excursions from their spacecraft, relying on complex suits of armor that prevent their bodies from exploding. They rescued the Hubble Space Telescope from failure and prolonged its lifetime by decades on five different missions to upgrade its instrumentation.¹

The authors belong to a generation old enough to remember the Apollo lunar landings of 1969–1972; we can hardly look at the moon without being reminded of Neil Armstrong and Buzz Aldrin. Their exploits, which seem even more heroic as we recall their dependence on primitive computers and untested equipment, remind us that humans have traveled into space for more than sixty years, not from necessity but in response to our desire to send them there and then bring them back to Earth.

Future decades will continue to test how much we want, and how much we need, to send astronauts into Earth orbit, on to the moon, and to Mars. Preceding any human journeys, our robots have explored these locales, scouting distant terrain after testing their launch and landing systems. No one doubts that our ever-improving machines can perform in space more efficiently, less expensively, and more safely than humans can. But can they equal human explorers’ abilities? And does this question miss a more important issue: how can we maintain public interest and inspiration, or fulfill our destiny as humans, without visiting our celestial neighbors in person?

Neither of these questions has an obvious answer, not least because we act in response to emotion as much as to logic. This book describes current and future plans for human and robotic investigations, presenting the argument for using only automated robots and fabricators, at least through the coming decades, beyond orbits close to Earth, in order to save public money, to avoid the loss of life, and to protect the moon and Mars so far as possible from pollution caused by our activities. The book also examines different non-technological motivations for supporting or opposing the presence of humans in space. Whether or not readers find themselves convinced as to the soundness of our reasoning, the following chapters also offer a survey of our spaceborne future.

ROCKETING INTO SPACE

Long before we had coherent plans to send humans into space, we engaged in hurling projectiles across large expanses, both in warfare and for fun. Contemporaneously with the European Middle Ages, technologists of the Chinese Song dynasty built gunpowder rockets that sent “nine-dragon arrows” and a “flock of bee arrows” high into the atmosphere. Gunpowder technology then became the rocket standard until the modern era. A century ago, the eccentric engineer and inventor Robert Goddard, inspired as a boy by the science fiction of H. G. Wells and a student of rocket dynamics as developed by Konstantin Tsiolkovsky in Russia, spent two decades creating and improving a succession of several dozen liquid-fueled rockets, some of which rose more than a mile above the hills of central Massachusetts. Goddard also introduced successful multistage rockets and invented two-axis guidance systems, gaining a fame that led the National Aeronautics and Space Administration (NASA) to name its space flight center in Maryland after him.²

Goddard’s final years saw his work upgraded to become the foundation of an enormous government effort to transform rocketry from its experimental stages into the production of rockets with a practical use. Unfortunately, that government had Adolf Hitler at its head, and the practical use entailed rockets that could deliver bombs beyond any defensive capability. Under the scientific leadership of Wernher von Braun, the Nazis developed the V-1, an uncrewed jet airplane, and the famed V-2, a true rocket that carried the oxygen required to ignite its liquid ethanol fuel. This allowed the V-2 to rise above most of the atmosphere and to travel at many times the speed of sound. Although the V-2 had only a primitive guidance system and often missed its target, its explosive payloads delivered many fatal blows to the British population, descending so rapidly that its only “warning” consisted of the explosion itself. (The V-1, also called the “buzz bomb,” terrorized through the sound that it made before anyone knew just where it would land.)

After World War II, the most prominent Nazi rocketeers surrendered to the Allies, hoping—quite correctly, in the event—that the Americans in particular would judge them so useful that their wartime activities would be overlooked. Under interrogation, von Braun cited as their inspiration not only the Nazis’ own rocket man, Hermann Oberth, but also Robert Goddard, saying, “Don’t you know about your own rocket pioneer? Dr. Goddard was ahead of us all.”³

Brought to America by Operation Paperclip, which resettled about 1,600 Nazi scientists and engineers in the United States, von Braun helped to launch the remaining V-2 rockets for scientific purposes, and in 1950 he became the leader of a rocket team at the US Army’s Redstone Arsenal in Alabama that developed new rockets with liquid-fueled engines for military use.

In October 1957, the Soviet Union stunned the entire world, and a complacent America even more, by launching Sputnik, the first artificial satellite of Earth. Americans suddenly realized that their chief enemy had gained superiority in producing rockets that could not only send satellites into orbit but also carry nuclear weapons from one continent to another. To the public, and presumably to leaders in Washington, the United States desperately needed highly visible feats in space exploration. Aware that entrusting the task to a military rocket development team led by a former Nazi might lead to bad publicity, the government commissioned a commercial firm to manufacture non-military Vanguard rockets, more modest in size and thrust than their military cousins. But after that commercial firm’s first attempt in December 1957 ended in a launch pad explosion, von Braun’s team stepped in and used the Jupiter-C missile, which they had designed as a military weapon, as the first stage of a rocket that launched the first United States satellite eight weeks later.

During the following decades, a tremendous arms race between the two great Cold War powers, the United States and the Soviet Union, centered on attempts to design and to build ever more powerful rockets, primarily for the delivery of nuclear weapons but secondarily as launch vehicles for improved satellites and human-occupied vehicles. Improvements in rocket technology led to the first human orbit of Earth (by the Soviet cosmonaut Yuri Gagarin, who made the first such orbit in April 1961), followed in February 1962 by the first American astronaut to orbit the Earth, John Glenn. Other Soviet firsts soon followed: the first woman to orbit in space (a seventy-hour flight by Valentina Tereshkova in June 1963) and the heroic first spacewalk by Alexei Leonov in March 1965. These feats owed their success to the eminent Soviet rocket innovator Sergei Korolev, whose name was kept from the public until he died; before then, he was known only as the “great designer.” Failures of Korolev’s later rockets slowed Soviet efforts in space and allowed the United States to win the “race to the moon” with six astronaut journeys between July 1969 and December 1972.

In September 1962, President John F. Kennedy, who had won election in 1960 in part by proclaiming that a “missile gap” prevailed between the United States and the Soviet Union (after the election, the “gap” was shown to exist only as a projection of future numbers), called for American astronauts to reach the moon in a race that “we intend to win.” Fourteen months later, an assassin’s bullets took his life. Nevertheless, Kennedy’s vision of sending humans to the moon was eagerly adopted by his successor, Lyndon Johnson, who had become an early advocate of crewed spaceflight and had played a key role in the 1958 creation of NASA. Johnson’s policies ensured that NASA’s Texas center would provide the hub of human spaceflight planning in the United States. For the next decade, those plans revolved around human missions to the moon, with eventual triumphant success.⁴

Today the Johnson Spaceflight Center near Houston retains its central role in the United States’ efforts to promote human spaceflight, but the five decades since astronauts last touched the lunar surface testify to how geopolitics have warped the application of reason to these efforts. Once the United States won the race to the moon, plans for further astronaut exploration foundered on the twin rocks of overwhelming expense and marginal returns. Beyond the moon, the hundred-times-longer journey to Mars lacked feasibility, and no other targets existed to offer a stunning reward for our efforts.

Instead, the space race assumed a calmer, more appropriate form. Both world powers sent automated probes to Venus, Mars, Mercury, and the four giant planets of the solar system, Jupiter, Saturn, Uranus, and Neptune. These journeys began in earnest soon after the Apollo program had taken astronauts to the moon. They revealed a stunning array of surprises, from Mercury’s heavily cratered surface to Valles Marineris, known as the Grand Canyon of Mars, and from the sulfur-laden volcanoes of Jupiter’s moon Io to the ethane-rich lakes on Titan, Saturn’s largest moon. Looking back at the last quarter of the twentieth century, one cannot help but be impressed by the brilliant, ever more miniaturized exploring spacecraft that were developed by NASA, the European Space Agency (ESA, created in 1975), and the Japanese Aerospace Exploration Agency (JAXA, created in 2003). In tandem with these robotic voyagers, the three agencies also designed, built, and operated a host of automated spaceborne observatories, which provided humanity with an array of marvelous results, from studies of the radiation left over from the earliest epochs of the universe to the discovery of the “dark energy” that permeates the cosmos and overwhelms the amount of energy in all other forms. These outstanding achievements have continued into the present era and will extend into the future.

THE FUTURE OF ASTRONAUTS: A BRIEF SURVEY

Chapter 1 of this book examines public support, both rational and emotional, for sending astronauts into space. The next five chapters outline the situations that face astronauts and robots in different regions of our cosmic surroundings. During the past five decades, astronaut activities have transpired solely in near-Earth orbits. Humans will likely continue to operate within this easily accessible domain, although most of what they do, such as manufacturing specialized items under weightlessness conditions, can be accomplished more effectively by robots. Space tourism (far better described as space adventurism because of its dangers) could prove a lucrative enterprise, a joy for the rich and in some ways an inspiration to everyone—but only if the risks remain sufficiently low.

Beyond the first few hundred miles above the Earth’s surface, a thousand times farther into space, the moon beckons to those who seek to search its surface for clues to the formation of the solar system, to others who hope to mine the lunar surface for valuable resources, and to still others who plan to establish habitats for long-term residence or moon bases for longer-range travel, using the moon’s underground water for drinking and to release breathable oxygen. Automated explorers can undertake the first two pursuits more efficiently, more safely, and less expensively than humans can. The third mission raises the question of why we should or should not plan for long-term human residence beyond the Earth. This issue will run through later chapters until we confront the more distant future’s prospect of creating free-floating space colonies that could permanently house millions of people, or even more.

For the easily foreseeable future, the foremost aspect of astronaut exploration will center on Mars, the most fascinating world beyond our own. Any analysis of the desirability of sending human explorers to the red planet naturally begins from the impressive, even amazing successes of our robot explorers during the past fifty years. Their current culmination in the Perseverance rover and prototype Ingenuity helicopter presage still more marvelous robots in the near future. For now, however, even these marvels’ capabilities fall short of humans’ abilities. This fact may argue for haste in sending trained geologists to Mars while they can still outperform our machines, or, conversely, for waiting a while longer until we develop automated extensions of our abilities that can effectively equal our best bodily efforts.

Most of the discussion in this book deals with attitudes and plans within the United States, the longtime leader in space exploration. But in recent years other countries—China, Russia, Japan, India, and many European nations—have been investing more heavily in automated space probes and in plans for astronaut journeys. In addition, corporations now play increasingly prominent and significant roles, typically under the leadership of charismatic individuals of immense wealth with their own plans for spaceborne activities. Chapter 9 examines the extremely modest international legal constraints that regulate actions in space and the potential rules for any such governance.

Many people find their imaginations fueled by the amazing reports from space travelers to other worlds, and enjoy picturing themselves taking a trip through the solar system. Human evolution has led us to understand situations by mentally projecting ourselves into them. Coupled with the delight of adventure, this projection often provides the basic method to comprehend journeys of exploration, even if they are undertaken by robots.

These considerations have influenced space agencies’ plans and budgets for six decades. Resting as they do on basic human impulses, these plans seem unlikely to change significantly, no matter how convincing the arguments for reconsideration may seem. In writing this book, however, we aim to persuade readers that matters could and should be different. In the authors’ opinion, people should focus less on how we may raise our spirits by sending astronauts to our closest celestial neighbors. Instead, we should inquire more about how we may best use space technology for human benefit and how we may most effectively explore the cosmos, near and far, to gain an understanding of our celestial environment.

One general conclusion about human actions deserves thoughtful consideration. David Spergel, an astrophysicist who is now the head of the Simons Foundation, has summarized this with the pithy observation that “our history as humans has shown that first we screw things up, and then we make some things right.”⁵ Spergel’s dictum, well verified by human exploration of the moon, should incite us to keep in mind the dangers of a hasty approach to large issues.

The arguments in this book point to one striking conclusion and a second, much softer one. We do not need astronauts as space explorers. Continual advances in our technological abilities and the development of artificial intelligence allow us to create ever more competent robots, while human bodies remain—until the time that they too may include important robotic components—subject to the constraints that limited our pre-spacefaring ancestors. For decades to come, these limitations, along with the enormously greater sums required to send humans rather than machines on long journeys into space and to bring them safely back to Earth, should militate in favor of automated explorers. Still, whether astronauts nonetheless perform a valuable inspirational role remains an open question, although public opinion and the decades-long hiatus between the end of moon landings and the present time provide some useful information. Aside from inspiration, astronauts appear to many people as the natural extension of a human desire to explore, a desire that we should support rather than discourage. Emotions have a powerful appeal to all of us, but they should hardly prove decisive in reaching decisions of great importance.

Readers who disagree with the conclusions in this book will, we hope, enjoy considering which arguments carry more weight than others. Even in democratic nations, we remain far from a situation in which individual opinions directly determine the resolution of this question and other relevant issues. Rather, society has evolved a complex system to make such decisions. Issues that fail to rank as politically important become provinces of those strongly involved in their outcomes—politicians with special ties and interests, businesses with direct economic stakes, and affinity groups with an axe to grind. The authors belong to this last group: astronomers and astrophysicists who spend their lives attempting to improve our understanding of the cosmos. Although we approach the astronaut issue from this perspective, we aim to present a scientifically oriented, pro-and-con balance in the discussion that follows. We also remain fully mindful of the ways in which space technology—for communication, weather and environmental monitoring, innovation and miniaturization, satnav, and so forth—has improved everyone’s daily lives. Before reaching scientifically based arguments, however, we should examine what may prove the most significant of all factors: how people feel about astronaut journeys to distant worlds.

CHAPTER 1

Why Explore?

Do we need humans in space? Many members of the public reply with a definitive answer: Of course we do! A variety of assertions underlie this nearly automatic conclusion: “Curiosity is in our DNA.”¹ “Humans have evolved to explore.”² “If we cease our exploration, we shall cease to be truly human.”³ Humans working in space “demonstrate American military superiority”⁴ (a theme that President Donald Trump repeatedly simplified by asserting that “America will land the first woman on the moon—and the United States will be the first nation to plant its flag on Mars”).⁵ “As pioneers, we seek to blaze the trail for others, establishing a presence that leads to economic progress and broad societal benefit.”⁶ “We must inspire young people and future generations, which only astronauts can do.”⁷ “Mars beckons us.”⁸ “Mars is within our grasp.”⁹ “When humanity is living and working on Mars, it will change everything.”¹⁰ “We must send humans into space to prove that we can.” The last of these is an argument embraced by President Kennedy in his September 1962 speech that urged the nation to send astronauts to the moon:

But why, some say, the moon? Why choose this as our goal? And they may well ask why climb the highest mountain? Why, 35 years ago, fly the Atlantic? Why does Rice play Texas? We choose to go to the moon. We choose to go to the moon in this decade and do the other things, not because they are easy, but because they are hard, because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one which we intend to win, and the others, too.¹¹

The preceding quotations, drawn from dozens of similar ones made both by ordinary people and by experts in various fields, primarily emphasize the emotional basis for supporting the human exploration of space. They also focus attention on the public’s chief target in space today, the fascinating planet Mars. Chapter 5, which provides a detailed discussion of the prospects for exploring Mars with robots or humans, includes an examination of the scientific arguments for and against sending astronauts there, which hinge on whether humans can explore much more efficiently than robots—an issue with an obvious past answer (yes!) that remains arguably correct today but provides at best a highly uncertain prediction for the future. Among other uncertainties, we know not when astronauts may reach Mars, nor which countries will send them, nor whether the first “Marslings” will be funded by governments, corporations, or rich individuals.

To some, these distinctions have little importance. Our emotional preference for human rather than robotic explorers rests on sentiments that each of us formed before we ever attempted to use reason as a guide. These attitudes will persist, hardly capable of change or refutation whatever outcome we may desire. Nevertheless, claims for the superiority of astronauts over robots deserve closer examination through several approaches.

First, to paraphrase the philosopher James S. J. Schwartz, the desire to explore is not our destiny, nor in our DNA, nor innate in human cultures.¹² The first assertion has only mysticism in support, the second has no genetic evidence, and the third encounters negative evidence around the world. If sending humans to Mars were “our destiny,” we would have no reason to hurry down this path, as many insist we must, since we would be sure to get there eventually. If our DNA someday revealed a genetic bias toward exploration, this could have resulted from natural selection in the descendants of those who had engaged in exploration and survived. And while some cultures have proven enthusiastic adventurers and explorers, many others have not. For example, Polynesians of past centuries were fearless explorers, while their Chinese contemporaries found satisfaction remaining within the Middle Kingdom.

Second, we do not need to vanquish our challengers in a race to Mars. Competition between nations motivated the push to send humans to the moon; the fifty years after that have shown that a rational exploration program would have made far more sense and yielded far more useful results. The imperative to “beat the Russians” to the moon opened the funding floodgates for the Apollo program, which might never have gotten off the ground had there been no “space race,” to use the common term from the 1960s. Both rational examination and simple common sense suggest that the best way to go to Mars would proceed from a worldwide effort, not only because such an effort would have positive implications for our civilization but also because it would offer a greater chance of success. Unfortunately, such an effort may prove no more likely now than its moon equivalent did fifty years ago. As happened then, a nation may undertake the challenge in order to show its supremacy in space by planting its flag on Mars. In addition, unlike the situation of the 1960s, private funding may undertake the challenge to reach Mars first, thanks to a willingness to accept much higher risks than most nations would, including the possibility of much less expensive one-way journeys (plenty of volunteers already exist). Either pathway for sending humans to Mars will involve tremendous difficulties and expense—more than those envisaged by wealthy individuals whose past history might lead them to believe that they can overcome anything.

A multinational effort—or, even better, a multinational effort that received substantial funds from individuals rather than taxpayers—not only would make more sense but also could inspire the better angels of our nature (though this consideration alone hardly justifies the mammoth effort). Some supporters of astronauts emphasize the “soft power” that their achievements will generate for democratic governments, a proposition that is difficult to confirm and would be subject to countereffects from the possibilities of catastrophe that inevitably accompany all space exploration.

Third, humans on Mars will not change everything. Even if we united humanity to accomplish this task, our problems on Earth will remain much as they are today. This argument reappears (in spades) in Chapter 7’s discussion of giant colonies in space, whose supporters imagine improved societies, freed from the constraints that weigh us down on Earth. A far more likely outcome would demonstrate that humans bring their problems with them no matter where they go.

Fourth, although astronauts do help to inspire students as well as adults to learn about science, they are hardly necessary to achieve this result. The landing of the Perseverance rover on Mars in 2021 demonstrated that spectacular images and astonishing scientific results can elicit a powerful response. Today’s generation of students, who possess far greater knowledge and acceptance of virtual reality than their predecessors, have correspondingly superior abilities to project themselves mentally to other worlds without losing sight of where they are.

Fifth, in contradiction to President Kennedy’s words six decades ago, the argument that we should accomplish a feat in order to prove that we can makes no more sense than climbing Mount Everest simply because it is there. This justification works only for those who regard planting the flag as the prime reason for going to Mars.

The preceding discussion addresses only the most commonly offered justifications for astronauts. A complete treatment would have to deal with the wider range presented by the science writer Oliver Morton, who wrote that people may want to go to the moon not only to mine its resources but also for “tourism, self-gratification, inspiration, ego jousting, the denting of the universe, preserving and enhancing the future of humankind, having fun, showing off, and experiencing the sublime.”¹³

Surveys of public attitudes tend to show that three rationales for supporting human spaceflight rise highest:

Humans in space can do more, and more efficiently, than robots can.

Humans must satisfy their impulse to explore new frontiers.

Humans in space add to our understanding of the cosmos and ourselves.

These three arguments draw on different types of explanation for human activity. The first assesses human abilities, the second draws on our inner urges, and the third posits a desirable goal for our civilization. Before turning to additional motivations for human spaceflight, we may note that the discussion throughout this book centers on disproving the first assertion, which grows steadily weaker as time moves forward; focuses less on investigating the second as possibly determinative of the issue of astronauts versus robots; and wholeheartedly adopts the third, which supports the use of automated as well as human explorers.

We should note that even though astronauts who venture to Mars would take heroic risks, we would make an error in calling them “explorers” and comparing them to the famed European explorers of the fifteenth and sixteenth centuries. Long ago, the first humans to travel to distant regions entered true terra incognita, lands unknown to them before their arrival. Astronauts who reach Mars will touch down on regions previously explored by robots in detail (including, in all likelihood, the analysis of samples returned to Earth) and will be able to communicate with Earth. (At least they are likely to avoid the shock of discovering native inhabitants who already knew all about their “newfound” land.)

If the United States and other countries decided to prioritize sending humans to Mars to the same degree as the Apollo program, few would disagree that astronauts could reach Mars well before 2050, and probably by 2040. However, the prevailing political and commercial reality creates a large gulf between what can be done and what will be done. Consider that the Concorde, the first supersonic airliner, which entered service four months before the first Apollo landing on the moon, made its final flight almost twenty years ago, with no detailed plans for any successor.

NASA’S JUSTIFICATION FOR HUMAN SPACE EXPLORATION

Those who turn to the NASA website “Beyond Earth: Expanding Human Presence into the Solar System” will find that the section “Why We Explore” includes the assertion that “curiosity and exploration are vital to the human spirit and accepting the challenge of going deeper into space will invite the citizens of the world today and the generations of tomorrow to join NASA on this exciting journey.” The site’s “Why Mars?” section ends with this statement:

A mission to our nearest planetary neighbor provides the best opportunity to demonstrate that humans can live for extended, even permanent, stays beyond low Earth orbit. The technology and space systems required to transport and sustain explorers will drive innovation and encourage creative ways to address challenges. As previous space endeavors have demonstrated, the resulting ingenuity and technologies will have long lasting benefits and applications. The challenge of traveling to Mars and learning how to live there will encourage nations around the world to work together to achieve such an ambitious undertaking. The International Space [S]tation has shown that opportunities for collaboration will highlight our common interests and provide a global sense of community.¹⁴

Beyond the unchallengeable assertion that sending humans on long journeys will prove that they can indeed perform them, nothing in this statement distinguishes any benefits of human visits from those flowing from robotic exploration.

PSYCHOLOGICAL ASPECTS OF SUPPORT FOR SPACE EXPLORATION

A complete discussion of the pros and cons of sending astronauts on journeys that range in distance from the few hundred miles needed to reach a comfortable orbit around the Earth through the quarter-million-mile distance to our moon and on to the hundreds of millions of miles to Mars must explore not just the solar system but also the human psyche, in some ways a more difficult proposition. In contrast to a cost-benefit analysis of the different approaches to space exploration, which has the virtue of reliance on numbers, an assessment of the nature and significance of exploration’s psychological and emotional underpinnings remains far more uncertain. Yet a large portion—perhaps the major portion—of our support for space exploration depends on how we feel about particular programs, rather than on the scientific knowledge, mineral wealth, or other visible results that they may produce.

Any examination of humans’ emotional and psychological attitudes toward space exploration should recognize that members of the public often fail to keep in mind the significant differences between human and automated investigators of the cosmos emphasized in this book. When asked directly, many people will insist that humans must or should engage in space exploration, but their reactions, typically springing from emotional considerations, often soften or eliminate the human / robot distinction, so all exploration strikes a positive chord.

In contrast to these feelings, scientists and engineers remain vividly aware of the differences between the two approaches to exploration. Over the decades their efforts have featured two distinct methods, on rare occasion intermingled, for studying the universe. We can send astronauts farther and faster than before, allowing them to reach the closest objects in our solar system and to probe them in person. Or, as we have done repeatedly, we can design and build robots. One type of robot makes journeys to worlds within the solar system, performing far more cheaply what humans could do, plus many other accomplishments. The other type of robot, even more important to astronomers, carries and maintains telescopes and similar instruments far above the blurring and absorbing effects of Earth’s atmosphere, which gives us life but significantly clouds our vision. These robotic instruments allow us to study, far more effectively than earthbound observatories can, stars and galaxies trillions of times farther from us than the moon and planets.

In theory, both human and robotic exploration make sense; properly planned, they may even complement each other. The most celebrated human-robot hybrid project, the Hubble Space Telescope, has received five different astronaut visits during its forty-year lifetime.¹⁵ Although each visit markedly upgraded the telescope’s capabilities (and the first rescued it from an otherwise fatal manufacturing defect), the director of the Space Telescope Science Institute, which manages the mighty instrument, has said that the total cost of the five astronaut repair missions would have paid for building and launching seven replacement telescopes. The comparison reminds us that our “sunk costs” prejudice would prevent us from choosing the replacement option so long as the repair option, even if somewhat more expensive, remained viable.

In practice, for the investigation of our neighbors in the solar system, astronauts’ requirements raise their costs per useful output many times over the corresponding expense for automated spacecraft, which yield far more comprehensive scientific results than astronauts can. (See Chapter 8 for a closer examination of the costs and results of the two approaches to space exploration.)

Why, then, do so many of us long to see astronauts on Mars, often ignoring the fact that we are on Mars right now, with amazing robotic explorers that map the planet’s surface from orbit and even more amazing rovers that examine the surface in detail, rock by intriguing rock? And why do astronomers such as the authors of this book imagine that they can shift this attitude toward recognizing the superiority of studying the solar system and beyond with robots rather than by sending humans to faraway places?

Our evolutionary and social histories have produced sizable psychological differences in the way we react to human explorers and to exploring adventures that take place without humans. During the past six decades, our civilization has devoted immense resources to the creation of systems to send both human and automated explorers into space. While members of the public have celebrated the successes and mourned the failures of both types of exploration, the emotional connections that we naturally feel with our fellow humans mean that astronauts get far more attention than robots. The first humans to land on the moon excited the world at a deeper level than the first probes to reach Venus, Mars, Jupiter, Saturn, or Pluto ever could; in 1986 and 2003, the losses of astronauts sent to orbit the Earth moved us far more deeply than any of the numerous losses of our automated spacecraft.

These differences in emotional response and attachment may reasonably be judged to be permanent. Automated explorers may well arouse our feelings of connection, as happened with the Sojourner, Spirit, and Curiosity robot explorers on Mars, still more for their more capable successor Perseverance, and even for the plucky New Horizons spacecraft that secured our first good view of Pluto and its moons. Still, decades ago, scientists and engineers who sought funding for future missions to solar system objects coined the slightly cynical adage “No Buck Rogers, no bucks.”¹⁶ (Today, younger generations may not realize that for half a century after the character’s first appearance in 1929, Buck Rogers and his twenty-fifth-century adventures—seen in comics, magazines, books, radio, television, and movies—brought new concepts of space exploration to millions of Americans and inspired a host of imitators and variations.)

In monetary terms, we should quickly note that in the United States, human exploration programs have never consumed as much as 4.5 percent of the national budget, and rose above 4 percent only for two years during the mid-1960s.¹⁷ Since its creation in 1958, NASA has spent about 60 percent more on human exploration than on robotic investigation of the cosmos (see details in Chapter 7). We should note that the human exploration of space has so far extended only to the moon, whereas automated spacecraft not only have traveled thousands of times farther to investigate all the major objects that orbit the sun but also have also made literally billions of observations of much more distant objects in our own galaxy and far beyond the Milky Way.

EXISTING DATA ON PUBLIC ATTITUDES TOWARD SPACE EXPLORATION

What are the current public attitudes toward space exploration and research? As the nation with the most ambitious program, and one deeply engaged in public surveys of all types, the United States provides the richest trove of data on this subject. We may hope that these polls can serve, at least for the time being, as a proxy for opinion in most European countries. On the other hand, public opinion in China remains a mystery, along with the related question of how much the opinions of individual Chinese citizens affect the decisions taken by the Chinese government. Like Americans, Chinese presumably have a range of attitudes regarding the importance of direct human involvement in space exploration. Despite the lack of Chinese data, and without proof that the US results reflect opinions in other developed countries, we shall take the risk of applying the conclusions drawn from the United States data to much of the rest of the world’s population. Should it turn out that these data truly reveal only the opinions of US residents concerning the issues involved in space exploration, they would still retain significance in light of the deep involvement of the United States in a host of efforts to send astronauts and automated spacecraft to nearby portions of the solar system.

Before we delve into the data from surveys of public attitudes, we should recognize that a sizable majority of the general public has comparatively little interest in any aspect of space exploration. Those who do express some interest vary in self-assessment from “modestly” to “extremely” interested. In the broader political and social contexts, space exploration ranks far below the best-known terrestrial issues, from abortion to environmental concerns. This comes as no surprise: earthbound problems confront us every day, while space abides. A 2020 analysis of four different public-opinion polls concluded that Americans can be divided into roughly three groups: those highly interested in NASA and space exploration (10–20 percent), those not interested at all (about 20 percent), and those who are interested to varying degrees (60–70 percent).¹⁸ A related section of the analysis revealed that the public “seems conflicted on the role of crewed missions in space exploration, with the ‘interest’ groups again making their difference apparent.” Opinions about governmental spending on space exploration followed a similar trend: 32 percent of respondents in one survey judged spending levels too low, and 21 percent thought they were too high.

In 2014, a wide-ranging report produced by the National Research Council assembled data from previous public opinion polls from 1980 onward.¹⁹ Members of the public were asked about the depth of their interest in space, and about how well-informed they felt they were regarding space exploration. Their answers fluctuated over time, with interest and information levels reaching their highest values in the early 1980s with the first flights of the space shuttle, and their lowest ones during the second half of the decade 2000–2009. Those who were “very interested” fell from a high of 33 percent to below 20 percent; those who were “well informed” declined from 16 percent to 7 percent; and those who were “attentive to space” dropped from 10 percent to 5 percent. The survey’s authors correctly noted that “the level of public interest in space exploration is modest relative to that in other public policy issues.”²⁰

The opinion surveys just described dealt with public attitudes toward “space” generally or NASA, and did not distinguish between human exploration and robotic exploration. This mingling of largely separate avenues of activity remains prominent in discussions of space exploration, blurring the primary issue presented in this book. A similar confusion often arises in discussions of extraterrestrial life, which fail to distinguish between the possibility that life exists elsewhere within the solar system or within the Milky Way galaxy and the possibility that intelligent aliens exist. Further chapters will extend this analysis.

In 2019, a C-SPAN poll commissioned to mark the fiftieth anniversary of the first lunar landing by humans found that only 13 percent of respondents thought that returning astronauts to the moon should rank as a top priority for NASA.²¹ A larger number, 18 percent, thought a human mission to Mars should be a top priority. A far higher proportion—fully 63 percent—gave “top priority” status to a focus on satellite monitoring that could allow us to understand environmental changes on Earth, and 47 percent assigned “basic scientific research to increase knowledge of space” to this category. (Respondents could assign “top priority” status to more than one activity.)

THE NATIONAL ACADEMY OF SCIENCES SURVEY OF STAKEHOLDERS

The National Academy study, led by Jonathan Lunine, a prominent astronomer, and Mitch Daniels, former governor of Indiana and head of the US Office of Management and Budget and now the president of Purdue University, also included its own poll. This surveyed not the general public but about two thousand members of eight different “stakeholder groups,” including individuals involved in industry, space science, education, defense, foreign policy, science popularization, and space-exploration advocacy.²² When respondents were asked to provide what they thought was the single strongest reason for space exploration in general, two answers predominated: increasing our knowledge and scientific understanding (mentioned by 60 percent) and the human drive to explore new frontiers (cited by 21 percent).²³

The report states that “in the case of human spaceflight, no rationale drew a majority of responses as very important even when respondents were given the list in a closed-ended format. Inspiring young people to pursue STEM careers (47%) and satisfying a basic human drive to explore new frontiers (45%) were the rationales that were most frequently cited as very important, followed by driving technological advances (40%) and expanding knowledge and scientific understanding (37%), but no rationale was viewed as a very important reason for human spaceflight by a majority of the respondents.”²⁴

It is worth emphasizing that the stakeholders’ reasons for supporting space exploration differ from their reasons for supporting human spaceflight, except for the basic human drive to explore new frontiers, which receives identical percentages in both lists. On the other hand, improving knowledge and scientific understanding was cited more than twice as often for supporting space exploration than for human spaceflight. Neither the potential economic rewards of being in space nor the search for life on other worlds drew more than 2 percent support.²⁵

The National Academy of Science’s report usefully categorized rationales for human spaceflight as either pragmatic (economic activity, national security, national stature and pride, education and inspiration, and scientific discovery) or aspirational (long-term human survival on other worlds, our shared destiny, the desire to explore). The report pointed out that even though robotic missions can go farther sooner and at less cost, robots cannot at present match humans’ ability to improvise and respond quickly—though “such constraints may change some day.” Regarding the aspirational rationales, the report judged that we cannot now decide whether off-Earth settlements could outlive the human presence on Earth and lengthen our species’ survival. And “while not all share [the view that our destiny is to explore space], for those who do it is an important reason to engage in human spaceflight.”²⁶

The survey committee then grasped the nettle and pronounced a key conclusion: “No single rationale seems to justify the value of pursuing human spaceflight.” On the other hand, when taken together, these rationales have more force: “Aspirational and inspirational rationales and value propositions, however, are more closely aligned with the enduring questions and when ‘added’ to the practical benefits do, in the committee’s judgment, argue for continuations of NASA human spaceflight programs [with, of course, suitable provisos].”²⁷

These carefully couched statements, which may well represent the best judgments of the most knowledgeable experts, imply that while our emotions tend to mislead us when we are considering the important issue of future space exploration by humans, when we combine those emotions with rationality in our analysis and approach, we may well decide to proceed with a plan to send astronauts into space.

The chapters that follow examine the pros and cons of human spaceflight in greater detail, and we will lay out our reasons for favoring robotic over human investigation. But we also present some of the latest discoveries and future plans for exploring the solar system. These reveal a fair amount about what we have accomplished, and what we hope to achieve, in our attempts to decipher what the cosmos has to tell us.

CHAPTER 2

Organizing Space

Space travel, whether by astronauts or autonomous robots, requires enormous efforts and monetary outflows, which pose impediments to all great enterprises, either of virtue or mischief. In considering our efforts to overcome these impediments, this book asks a fundamental question: could robots rather than humans accomplish these endeavors more efficiently, more safely, and at far lower cost?¹

SIX SPHERES OF EXPLORATION

A comparison of human and automated space exploration rationally begins with the scientific technique of classifying the subjects of investigation. In assessing our present and future undertakings in space, we may usefully locate them within one of the following six spheres of activity:

Near-Earth orbits (also called low-Earth orbits), which so far represent the chief domain of spaceborne activities

Scientific investigation of, and habitat construction on, the moon

Missions to the closest planets, primarily to Mars

Investigation, mining, and possible capture of asteroids

Construction of freely orbiting, permanent habitats in space

Long-term journeys to the sun’s outer planets, and perhaps in later centuries to other planetary systems

The order in which these six activities are listed roughly corresponds to the time sequence in which they have been achieved or may be realized in the future. The first two—near-Earth orbits and lunar exploration—began more than sixty years ago. The benchmarks of this era include the first artificial satellite (1957), the first cosmonaut to orbit the Earth (1961), and the first astronauts to land on the moon (1969).² The third initiative began with probes that orbited Mars and Venus during the early 1970s and the first spacecraft to land on another planet (in 1971, with the brief survival of the Soviet Mars 3 lander, followed in 1976 by the two successful Viking landers). Astronaut landings on the moon will probably resume during the coming decade. Astronauts could land on Mars within a relatively few years if the United States made this an Apollo-style national priority, but given current conditions, this may take decades longer. Asteroid investigators have now secured close-up images from three different objects, with sample material taken from two of them and brought to Earth (the first in 2020, the second scheduled for 2023). Serious mining operations on asteroids have generated lively discussion, but nothing appears likely to occur on this front for at least another half decade.

Automated exploration of the outer solar system has been a mainstay of NASA and its partners since the late 1960s; the ESA began parallel efforts soon afterward. The nine robotic visitors sent to the four giant planets and the minor planet Pluto during the past five decades include two multiyear orbiters, one around Jupiter (Juno) and the other around Saturn (Cassini). Despite the appeal of searching for life beneath the icy surfaces of Jupiter’s moon Europa and Saturn’s moon Enceladus, or in the ethane-rich lakes of Saturn’s giant moon Titan, no viable plans currently exist for any astronaut involvement in these endeavors. The feasibility of space habitats has likewise fascinated humanity for half a century or more, but so far there has not been even a formal proposal for a specific project.

The difficulty of accomplishing the missions listed within each of the six categories depends primarily on their distance from us. Because almost all astronomy involves distances and numbers far beyond our everyday experience, the use of distance ratios rather than the distances themselves may provide easier understanding. Following this principle, we can expand our description of the six regions of activities in space as follows:

Near-Earth orbits occupy the region a few hundred miles above Earth’s surface. Geostationary orbits, which allow a satellite to remain stationary above a point on the Earth’s equator as our planet rotates, lie nearly a hundred times higher, 22,236 miles above the Earth’s surface.

The Earth-moon distance averages 239,000 miles, close to a thousand times farther than objects in near-Earth orbit, and about eleven times the distance to a geostationary satellite.

Venus and Mars, our closest neighbor planets, approach Earth within about 30 million miles. However, an energy-efficient trajectory to reach them must cover about 300 million miles, more than a thousand times the distance to the moon.

Most of the asteroids orbit the sun between Mars and Jupiter, at nearly twice Mars’s distance from the sun. A small minority of asteroids have orbits that take them somewhat closer to Earth, and a few have orbits that cross the Earth’s (producing a—fortunately small—probability of catastrophic impacts).

Concepts for large habitats in space concentrate on the L4 and L5 points of the Earth-moon system.³ These points, with one preceding and the other following the moon in its orbit, create equilateral triangles that place the Earth and moon at the triangles’ other two vertices. Objects at one of these points can orbit with comparative stability without being pulled into different orbits by the other planets, and can maintain the same distance from Earth as from the moon.

The sun’s four giant planets—Jupiter, Saturn, Uranus, and Neptune—and their retinues of large and small satellites orbit the sun at distances five to thirty times the Earth-sun distance, from just under half a billion miles to 2.8 billion miles—a few thousand times the distance from Earth to the moon. If we contemplate travel to the nearest stars and their planetary systems, we must leap upward by another large factor: their distances from us are about 40,000 times greater than Jupiter’s.

It is difficult to make predictions, especially about the future (a remark often attributed to the great Danish physicist Niels Bohr, or, alternatively, to Yogi Berra).⁴ If we have learned anything from history, it is that we should continue to expect the unexpected. Some future events will occur with near certainty: the sun will rise tomorrow, and it will undergo a total eclipse on August 2, 2027.⁵ We can have a high degree of confidence in the likelihood of others because of our past experience. In contrast, events whose first appearance lies in the future carry varying degrees of uncertainty. In assessing the probability that astronaut journeys set in categories 3 through 5 will occur, or in assigning a time scale to any of them, we must keep this uncertainty in mind, together with the emotion that we bring in assessing the probability of these future outcomes.

In comparing astronaut journeys with robotic spacecraft travel, a notable difference resides not in the distances to be traveled but in their implications for human survival. Once launched into space, an automated spacecraft that is supplied with energy from solar collectors or a nuclear generator and shielded against high-energy particles can easily survive for decades, as our probes of the outer planets have long demonstrated. In contrast, every day that astronauts spend in space requires additional oxygen, water, and food, as well as much stronger protection against particles from the sun and from outer space; in the longer term, sickness and old age pose additional barriers. We shall meet these issues in greater detail in Chapter 4, which describes journeys to Mars, and in Chapter 7, which examines multigenerational, self-contained ecosystems that could either orbit the sun or travel to the stars.

FINDING THE ENERGY TO ESCAPE FROM GRAVITATIONAL WELLS

Part of the challenge presented by travel through space depends, of course, on the distance to be covered. There is also a second, somewhat subtler factor: the depth of the “gravitational well” that inhibits escape from any sizable object. The concept of gravitational wells usefully connects with Einstein’s concept of space as a three-dimensional version of a two-dimensional sheet of fabric: it is flat almost everywhere, and objects with mass bend it to produce gravitational dimples or “wells.” Any spacecraft traveling from Earth must expend the energy needed to climb out of our planet’s gravitational well, plus additional energy to avoid falling too rapidly into the gravitational well at its destination. Deeper wells require more energy for escape, and more massive spacecraft likewise demand more energy than less massive ones do.

We can attempt to describe the depth of an object’s gravitational well by specifying the energy with which a projectile of standard mass would have to be fired to escape from it completely. This number provides only a crude measure of the energy needed for a realistic rocket, because a real rocket accelerates gradually, decreases its mass as it exhausts its fuel, and must expend extra energy to pass through a thicker atmosphere. Bearing these facts in mind, we may note that Earth has an escape velocity of 7 miles per second, while Mars’s is 3.1 miles per second and the moon’s is just 1.5 miles per second. At the other end of a space journey, escape velocity plays a role of equal importance as a rough description of the energy required to land safely on a celestial object rather than crash into it.

For escape from celestial objects with the same average density of matter, Newton’s laws show that the escape velocity scales in direct proportion to the objects’ diameters.⁶ The moon, Mars, and Earth have diameters whose ratios roughly equal 1:2:4, respectively. Because these objects have different densities, the actual escape velocities have the ratios 1:2.1:4.7. Ceres, the largest asteroid, with a diameter 27 percent of the moon’s, has 21 percent of the moon’s escape velocity because of its notably lower density. Mars has two tiny moons, Deimos and Phobos, with diameters of four and seven miles; their escape velocities are measured not in miles per second but in miles per hour (12 mph for Deimos and 25 mph for Phobos)—meaning that a hypothetical astronaut bicyclist could ride up a ramp and escape into space. These moons’ low escape velocities and proximity to Mars make them near-ideal observing platforms to support complex instruments for surveying the red planet.

IMPLICATIONS FOR SPACE TRAVEL AND CONSTRUCTION

For any particular journey in the solar system, the fundamental facts of distance and escape velocity determine how long the journey will take with a particular propulsion system and how much energy will be required. Beyond the energy analysis roughly expressed with escape velocity, we need to consider the extra energy requirements imposed by each additional step of a journey. For example, leaving near-Earth orbit to reach a much larger geostationary one requires about one-quarter of the energy needed to leave Earth’s surface and enter that near-Earth orbit. Departure from that much larger geostationary orbit for a journey to the moon or elsewhere, then, calls for a much more modest energy expenditure (though we should note that different trajectories prescribe different energy requirements).

These applications of physical law imply that if we aim to create a base of operation from which to launch matter toward faraway objects, a smaller celestial object will serve better as a base than a larger one. Sending material to Mars will require far less energy if we direct it from the moon rather than from Earth, even though the journeys cover the same distance. This holds true, of course, no matter where the material goes.

The single greatest impediment to spaceflight resides, all too literally, in the fuel required for escape from a gravitational well, either into orbit or (with still more fuel) onto an escape trajectory. Because chemical fuel provides an inefficient method for storing energy, any rocket must leave Earth carrying fuel that weighs several times more than its structure or payload. Multistage rockets deal with this problem as best they can, by jettisoning their first stage and booster rockets once their fuel has been exhausted. Spacecraft could avoid this obstacle, at least as far as reaching orbit around the Earth, by keeping their power source on the ground. For example, a carbon-fiber cable rising 30,000 miles above the Earth’s surface, held in place by the centrifugal force from the Earth’s rotation, could provide a “space elevator” for cargo or astronauts to ride on a smooth ascent. (The manufacturing techniques needed to produce a sufficiently strong cable—for instance, by weaving a “rope” from a multitude of carbon fibers—remain futuristic.)

A more conventional improvement, broadly speaking, would consist of improved fuels, most notably nuclear-based ones. By itself, a nuclear-powered spacecraft probably couldn’t generate the thrust needed to escape from the Earth’s surface, but once in space it could generate a low, continuing thrust—slow acceleration followed by slow deceleration—throughout its journey, achieving a higher average speed. Nuclear propulsion could, for example, cut the travel time to Mars from six to three months, halving the dangers from astronauts’ exposure to radiation and their long-term confinement in cramped quarters. Today, the limitations of chemical fuel require that spaceflight must be carefully pre-planned to limit any maneuvers that would consume additional fuel. But with abundant fuel supplies, astronauts could engage directly in midcourse maneuvers, opening their journeys to human rather than computer control.

For robotic cargo shipments, distances matter less than the depths of gravitational wells because high speeds are less important. An object that has escaped from the well of a planet or a moon will coast comparatively freely through space, slowed only by the sun’s gravitational force if it moves outward through the solar system. For instance, the energy required to send a laboratory toward Mars is almost enough to carry it to an asteroid more than twice as far away. While the trip to the asteroid may well take more than twice as long, this hardly matters for the transfer of inanimate matter.

Living systems face a different calculus. An astronaut traveling to the asteroid belt will require approximately twice as much food, water, and oxygen as one on the way to Mars, even if the energy requirements for each of the two trips are roughly equal. The requirement for more of these essentials adds to the mass of the spacecraft, which in turn increases the energy required. To take the simplest example, each astronaut stay in near-Earth orbit requires that supplies be sent some 250 miles above the Earth. The necessary energy expenditure, converted into current dollar figures, amounts to at least $1,250 per pound. The combination of human requirements and launch costs produces a total cost of $7.5 million for each day that an astronaut spends in the International Space Station.⁷

For inanimate material sent to distant locations, the energy required for escape likewise factors directly into the energy (and thus the monetary) expense. Because the Earth has an escape velocity more than four and a half times the moon’s, it is far less expensive to send anything to destinations far from the Earth-moon system if we launch them from the moon rather than the Earth. As we contemplate the creation of bases elsewhere in the solar system, the energetic bottom line remains: if you need raw materials somewhere, send them from the moon if you can.

Still better, to be sure, is to find the raw materials where you need them, leaving only the problem of moving them over the surface of an object—an operation humans have long performed on Earth, as happened more than 4,000 years ago when the Egyptians built their pyramids, and, on a less gigantic scale, when the builders of Stonehenge in Britain moved the heaviest stones from a quarry 25 miles away and a set of three-ton boulders more than 150 miles from an even older sacred site in Wales.⁸ The essential requirement for creating a base on the moon consists of finding almost everything needed for its construction and maintenance on the moon itself. For example, the astronomers Roger Angel and Nick Woolf have suggested that the loose rocks and soil above the lunar bedrock could be made into bricks and used to build a dome-like structure that would recall ancient Rome’s Pantheon, which still stands strong in the Italian city’s center after two millennia.⁹

Before we turn to the prospects for a human return to the moon, we must examine the domain with which astronauts have become familiar: near-Earth (or low-Earth) orbit. Triumph and tragedy have marked this realm a few hundred miles above the Earth, where hundreds of men and women have learned how to adjust to conditions unfamiliar to our planet’s surface-dwellers.

CHAPTER 3

Near-Earth Orbit

At the risk of overconcentrating on the United States, we can summarize human involvement in space exploration during the past five decades by citing the achievements of NASA and its worldwide partners. During that time, NASA devoted approximately half of its annual budget (currently about $23 billion) to humans in space, and roughly another 30 percent to scientific activities.¹ The chief accomplishment on the human side today, the International Space Station, allows astronauts to live for months on end and to perform a host of experiments, many of which deal with aspects of living in space. The roster of those who have orbited the Earth now includes astronauts from many countries around the world, as well as some comparatively untrained ordinary people, a few legislators, and even some “space tourists” who have paid impressively large sums for the thrill of orbiting the Earth. One of the legislators, Senator Bill Nelson from Florida, who flew in the space shuttle in 1986, was nominated as NASA administrator thirty-five years later, in 2021.

After the two great space shuttle disasters, the Challenger explosion upon takeoff in 1986 (ten days after Nelson returned to Earth in the Columbia) and the Columbia disintegration upon reentry in 2003, participation in space travel has tended to be limited mostly to trained astronauts.² With a total of 135 space shuttle launches, these two disasters created a failure rate of less than 2 percent—a rate entirely acceptable to astronauts, sports enthusiasts who engage in hang gliding and other risky pursuits, and test pilots, though unacceptable to ordinary air travelers, whether tourists or businesspeople. NASA had promoted the Challenger’s last flight as an opportunity to deepen popular support for the space program by selecting Christa McAuliffe, a secondary-school teacher from New Hampshire, to represent the public as one of the seven members of the crew. Each of the two space shuttle failures led to a long hiatus while costly efforts were made, with very limited effect, to reduce the risks of spaceflight. Nevertheless, the lure of space travel remains sufficiently strong among the well-heeled public that plans now exist to create a more extensive commercial program, which will almost certainly be marketed as an adventure for thrill-seekers rather than as routine tourism.

Until China sent its first astronauts into space in 2003, only the United States and the Soviet Union (Russia after 1989) had launched astronauts. They traveled in a series of ever-improved spacecraft, including the Soviet Union’s Vostok (1961–1963), Voskhod (1964), Salyut (1971–1986), and Mir (1986–2001), and the United States’ Mercury (1958–1963), Gemini (1961–1966), Apollo (1961–1972), Skylab (1973), and space shuttle (1981–2011; the final versions of the shuttle carried the European Space Agency’s Spacelab module in its cargo bay between 1983 and 1998).

THE INTERNATIONAL SPACE STATION AND THE FUTURE OF ASTRONAUTS IN NEAR-EARTH ORBIT

These missions paved the way for the International Space Station (ISS), created by five different space agencies involving twenty-six countries. Made with modules added one by one since 1998 and permanently crewed since 2001, the ISS weighs about 1 million pounds, includes a pressurized interior volume of 32,000 cubic feet, and spans more than two football fields in width.³ Operation of the ISS has tested and verified many important aspects of human space flight. First, astronauts have demonstrated that they can assemble sizable habitats in space. Second, they have shown that humans can survive many months under the weightless conditions that prevail in space; the issues and problems that arise in spaceflight can nonetheless prove to be serious, and will be discussed later in this chapter. Third, their stays on the ISS have highlighted the advantages and limitations of humans in space. Overall, astronauts aboard the ISS devote about 15 percent of their time to research activities, with the remainder spent on sleep, meals, exercise, and keeping their spaceborne environment in proper condition. To be sure, humans on Earth typically manage quite well in life while spending not much more than 20 percent of their time doing paid work. Still, that 15 percent figure reminds us that practical results from having humans in space will remain hard won, even before we consider the additional extra effort required for comparatively rare excursions outside the ISS.⁴

With a total cost surpassing $150 billion, the ISS ranks as probably the single most expensive artifact that humans have ever made. (There is some double billing here: the space shuttle program, which cost $195 billion in total, flew 36 of its 135 missions to the ISS, and its costs of $1.5 billion per mission are included in the $150 billion ISS total.) Although the ISS has produced scientific and technical results, its return on investment has been far less than the payoff from robotic missions. As those of older generations can readily testify, the inspiration that astronauts once provided to the public has steadily decreased. Supporters of the ISS could argue that this fact proves how successful the ISS has been, making news only from difficulties such as a malfunctioning space toilet in 2019 or from stunts such as the Canadian astronaut Chris Hadfield’s rendition of a David Bowie song with guitar accompaniment in 2020.⁵

The ISS has provided far more data on how spaceflight affects humans than journeys beyond near-Earth orbit have. In the more than five decades after Yuri Gagarin launched from Kazakhstan in 1961 to become the first human in space, just twelve humans have walked on the moon. Fifty times that many, from forty-one different countries, have orbited the Earth, spending more than 57,000 days in space; most of these space travelers have been Russian nationals (30,000 or so) or Americans (about 23,000). Valery Polyakov holds the longest single-stay record of 438 days in orbit; Scott Kelly, now a United States senator (the third astronaut to serve in the Senate), comes in fifth with 340 days in orbit. Those two records were, of course, set on the ISS, on which more than 400 astronauts have stayed as members of a rotating seven-person crew.⁶

This comparison implies that future as well as current human activities in space will occur in near-Earth orbit, the region a few hundred miles above the Earth’s surface and high above all but the flimsiest parts of the atmosphere. Recent improvements in modern rocketry, both technological and economic, have come more from private projects than from governmental efforts, and in particular from Elon Musk’s SpaceX corporation, which has developed the capability of recovering the massive casing of a rocket’s first stage for reuse. SpaceX currently charges the United States government $1,250 per pound to send cargo to the International Space Station.⁷ Though this price may not reflect the true cost, since SpaceX seeks to secure government contracts for the future, it represents a good number to bear in mind. SpaceX’s success with its Falcon rockets contrasts markedly with NASA’s repeated problems with its next-generation SLS launch system, currently still in development while its efficacy remains in doubt.⁸

In summary, just as expected, experience and the geography of space have rendered access to near-Earth space fairly reliable, as well as considerably less expensive than travel to the distant objects that populate the solar system. Nonetheless, strong arguments can be made that most of what goes on in near-Earth orbit can be accomplished without humans.⁹

While later in this chapter we will examine the reasoning behind this conclusion, three exceptions immediately suggest themselves. First, almost all the complex experiments needed to determine how humans can best survive their exposure to space travel naturally need to be carried out in space. Second, the desire to watch how humans behave in space likewise requires astronauts in orbit. Third, space adventuring, a developing industry seeking new income streams and the broadening of spaceborne involvement, by definition involves journeys into space. Some of these adventure flights may be suborbital, taking participants to the “edge of space,” some sixty miles above the Earth’s surface, while others, more substantial, more expensive, and more thrilling, will provide the full experience of orbit.

Counterarguments to these exceptions spring easily to mind. As for the first exception, citing the need to learn how humans fare in space as a reason to send humans into space amounts to circular reasoning: it’s essential if we decide this travel should occur, fully optional if not. As for the second, we’ve already discussed (in Chapter 2) our desire to see humans in space. The third exception, however, has no real rebuttal: if some of us are willing to pay enough for an exhilarating experience, and that adventure proves feasible, someone will probably provide the means to satisfy that urge. Arguments to the contrary hinge on the general issues involved in near-Earth orbits—for example, the danger of overcrowding, leading to possibly fatal collisions. (All such dangers will, of course, bring lawyers and the damage waivers they create into the space arena.)

ADVANTAGES OF WEIGHTLESSNESS FOR RESEARCH AND FABRICATION

By far the most significant gain from the hundreds of astronauts who have collectively spent a hundred thousand hours in orbit consists of detailed knowledge of how humans can survive and thrive in a spaceborne environment. Increasing our knowledge of space physiology and biology justifies itself because of its direct link to astronaut journeys or sojourns in future space habitats. Numerous studies of how well various species of animals and plants can live under weightlessness conditions likewise relate to maintaining astronauts, since we are unlikely to make plans to grow wheat or raise animals in space if there are no humans in space. (The exception lies in the spaceborne generation of biological material for applications on Earth, which brings us into the realm of space manufacturing; we’ll discuss this later.) Similarly, the production in space of items designed for astronauts, including myriad components that a new generation of improved 3-D printers could make for their use in orbit, make no sense without actual astronauts.

Quite apart from human occupation, fabricating specialized crystals and other materials in space makes good sense, as does producing certain cell cultures. But do they justify the enormous investment in the International Space Station? As early as 1990, fourteen scientific organizations, including the American Physical Society, the American Chemical Society, and the American Crystallographic Association, concluded that the useful scientific knowledge gained in this way could not justify constructing the ISS. Undaunted, NASA proceeded with its experiments. It devoted particular attention to growing protein crystals under weightlessness conditions, despite the American Society for Cell Biology’s judgment that the experiments were unlikely to make serious contributions to our understanding of protein structure.

Nevertheless, the production of certain specialized materials in near-Earth orbit makes good sense. An intriguing material called ZBLAN offers an excellent example of the advantages of space manufacturing.¹⁰ Discovered by accident in 1974, this fluorozirconite glass consists primarily of fluorine and zircon, together with smaller amounts of four other elements: barium, lanthanum, aluminum, and sodium (their chemical symbols are the basis of the acronym ZBLAN). Glass with this composition can transmit not only all the colors of visible light but also ultraviolet and part of the infrared spectrum. Properly heated, ZBLAN can be spun into the fiber-optic cables thinner than human hairs that now connect the components of the digital world, carrying billions of data bits every second across thousands of miles of distance. These signals inevitably suffer loss in transmission because no glass offers perfect transparency. Signals carried by conventional fiber-optic cables composed of silicon dioxide (silica) undergo a hundred times more loss per mile than they do when carried by ZBLAN. However, the process of manufacturing ZBLAN cables can be tricky; it involves melting fluorozirconite, then stretching it into long, incredibly thin fibers. As the glass cools, it can develop tiny crystals that impede the passage of signals flashing from place to place. Making ZBLAN under weightlessness conditions notably reduces the frequency of these flaws, however. In 2019, this key spaceborne advantage received operational testing when a cargo flight carried a suitcase-sized manufacturing platform to the International Space Station. For two months, controllers at the Marshall Space Flight Center in Alabama supervised the platform’s operation remotely. A SpaceX Dragon then brought it home with the first optical fibers made in space.

This single example shows that space manufacturing already exists and can proceed without human intervention. For the ZBLAN made in 2019, astronauts had to receive the platform, install it, and then remove it for its return journey, but these operations could be accomplished with even simpler automation than what was needed for the manufacturing platform. What works for ZBLAN should work for other materials to be produced in space: astronauts will not be needed, and their presence only adds an element of danger if a catastrophe should occur with the manufacturing process.

OTHER COUNTRIES ACTIVE IN SPACEBORNE ACTIVITIES

After the first five decades of space exploration, dominated by the Soviet Union and by the United States with its European and Japanese partners, advances in technology, especially the development of less expensive launch vehicles, have allowed numerous countries to join the exploration of near-Earth orbital space. China, the most significant new participant, has by far the widest ambitions, including plans to send astronauts to the moon and possibly also to Mars, where a Chinese orbiter and rover arrived in 2021. In addition to the satellites produced by these countries and by the European Space Agency, some of whose member countries have acted as individuals, India, Israel, Iran, North Korea, and Ukraine have demonstrated launch capabilities. However, any country (or sufficiently wealthy individual) can purchase that capacity, as the United Arab Emirates did from Japan when it sent its own spacecraft to Mars. The discussions of missions to the moon and Mars that follow this chapter include some results from space endeavors around the world, all of which respond to an analysis similar—except, perhaps, for the legal aspects—to the one made for the United States’ efforts.

SPACE ENTREPRENEURS

A notable development in space exploration involves the recent emergence of immensely wealthy individuals as prime movers in attempts to find more efficient avenues to launch vehicles into space and, in the not so distant future, to return to the moon, send astronauts to Mars, and gather resources on the moon and metal-rich asteroids. These efforts pose direct questions about the proper role of nongovernmental actors in space, which in turn raises the unresolved issue of how civilization may eventually determine what roles are assigned to (or seized by) different countries, corporations, well-funded groups, or particular individuals.

Three individuals stand out most prominently for their attempts to create private space exploration spacecraft: Elon Musk, Jeff Bezos, and Richard Branson. Each of them gained fame during the 1990s through their close association with at least one visionary enterprise: Bezos, born in 1964, began Amazon as an online bookstore before expanding to, well, everything; Musk, born in 1971, became PayPal’s largest shareholder when that company merged with his financial services company, shortly before eBay bought PayPal for $1.5 billion in stock; and Branson, born in 1950, founded the Virgin empire, most known for its airline and its package holidays.

As the twenty-first century opened, each of these double-alpha, enormously wealthy males added a deep involvement with space exploration to their other pursuits. Musk took the helm of the Tesla Motor Company in 2004 and plunged into making electrically powered vehicles, pursuing this effort so vigorously that Tesla teetered on the verge of bankruptcy until the rising public demand for electric cars made Musk one of the wealthiest US citizens, along with Jeff Bezos and Bill Gates. SpaceX, established by Musk in 2002 to manufacture launch vehicles, has produced the Dragon and Falcon spacecraft, workhorses for NASA’s missions to send supplies, and to send and return astronauts, to the International Space Station. Musk’s new, super-heavy Starship launch system aims for Mars, where, he has said, he would like to die, “just not on impact.” Steve Jurvetson, Musk’s longtime friend and collaborator, has said that Musk believes that by 2035 thousands of rockets will be taking a million people to Mars to create a self-sustaining colony. Musk has repeatedly publicized overly optimistic timelines for his grand projects, including the introduction of Tesla electric cars, but he has overcome numerous setbacks to deliver on his promises and deserves his acclaim. The arguments against the desirability of mass emigration to Mars emphasize that creating a million-person habitat there would prove more difficult than establishing a million people at the South Pole or on the bed of the Pacific Ocean.

Jeff Bezos’s Blue Origin corporation also concentrates on improving systems to launch astronauts far beyond the Earth. In contrast to Musk’s determination to colonize Mars, Bezos centers his immediate goals on creating lunar colonies, declaring in 2019 that “it’s time to go back to the moon, this time to stay.” In 2020, NASA’s Artemis program awarded a contract worth $579 million to a Blue Origin consortium that includes the aerospace giants Lockheed Martin and Northrop Grumman for the development of an integrated system to land astronauts on the moon and bring them back to Earth. Unlike Musk’s vision of a large population on Mars, Bezos’s vision of the future looks toward the free-floating space colonies described in Chapter 7, where even heavy industries could proceed without polluting any planet.

Richard Branson’s plans for his Virgin Galactic company seem more modest, since they extend only to the edge of Earth’s atmosphere. They would, however, allow risk-taking enthusiasts to touch the edge of space, often defined as the region fifty to sixty miles above the Earth’s surface. Branson’s SpaceShipTwo rides underneath a carrier aircraft to an altitude of about ten miles, then uses its rockets to soar five times higher, providing its occupants with about six minutes of weightlessness. In July 2021, Branson and three others made the first such voyage, suggesting that before long, flights on SpaceShipTwo will become available to the public. They will clearly cost much less and offer much less than voyages to the moon on Bezos’s Blue Origin or to Mars on Musk’s Starship. They could, however, introduce comparatively large numbers of would-be adventurers to the basic experience of space travel: weightlessness for a few minutes, accompanied by panoramic views of the Earth stretching below for more than a thousand miles, out to a curved horizon beneath a black sky.

Those who venture into space expose themselves to cosmic hazards. We will turn to an examination of these dangers, with the knowledge that they grow progressively more severe on progressively longer journeys—to the moon, and then to Mars, a hundred times farther. For now, we will begin with the scientific classification of the perils of spaceflight, which arise within two well-defined spaces, those inside the spacecraft and those outside.

HAZARDS WITHIN THE CABIN

Inside a spacecraft, an astronaut must deal with the sensation of weightlessness—something never previously experienced during our evolutionary history, and forever unknown on Earth save for parachutists before they open their chutes, base jumpers, and those in a few other special situations.

Problems inside the spacecraft can be divided into two types: psychological and physiological. Among the former, psychosocial difficulties familiar to explorers or submariners on Earth invariably arise among a small group of humans confined within a limited volume for long periods of time. In his autobiography, the Soviet cosmonaut Valery Ryumin, who twice spent six months in orbit, quoted the American writer O. Henry’s maxim from one of his short stories: “If you want to instigate the art of manslaughter, just shut two men up in an eighteen-by-twenty-foot cabin for a month. Human nature won’t stand it.”¹¹ (O. Henry, regarded as an anticapitalist, was one of the most widely read authors in the Soviet Union.) A study of Russian and American astronauts aboard the Mir space station found a partial solution, also familiar to stressed workers on Earth: the “displacement of tension and negative emotions from crewmembers to mission control personnel and from mission control personnel to management.” In other words, complaining to your boss can partially relieve tension. This approach works far better for astronauts in near-Earth orbit than for the problems arising on longer journeys, which, the study noted, “will include increased crew autonomy, more dependence on onboard technical resources, communication delays with the Earth, increased isolation and monotony, and the Earth-out-of-view phenomenon.”

Some astronauts have undergone adverse reactions upon their return to Earth, including anxiety, depression, alcohol abuse, and marital difficulties, treated in some cases with psychotherapy and psychoactive medication. Buzz Aldrin, the second man to land on the moon, detailed his experience with these problems in his memoir; in his case, they may have partly stemmed from the void left after an intense wave of fame had washed over him and passed on.

Physiological problems involved in spaceflight loom larger than the psychological ones. They include the temporary physical strains imposed upon takeoff by the spacecraft acceleration, which generates forces several times the normal force of gravity; similar forces occur upon return to Earth. Still more serious problems arise in orbit, as astronauts deal with a variety of challenges, either continuous or transitory, which begin with the phenomenon called weightlessness. Astronauts in orbit find themselves in free fall, akin to the experience of a parachutist, but an astronaut falls around the Earth, not toward it. Because an astronaut’s weight—the amount of gravitational force exerted by the Earth—does not change, the term “weightlessness” falls short of complete accuracy. The even worse term “zero-g” implies that the gravitational force on an astronaut disappears; in fact, only the sensation of that force vanishes.

Weightlessness’s myriad effects on a human body begin to appear a few minutes after launch. Mike Massimino, a scientist-astronaut who flew into space twice on missions to repair and upgrade the Hubble Space Telescope, described some of them:

Your sense of motion is all messed up. You feel crazy and out of control at first.… And you feel horrible, absolutely terrible … The first thing that happens is the fluid shift. There’s tons of fluid in our body: blood, plasma, water, mucus. On Earth, gravity keeps it pushed down. In space, it’s free to float up to our head … Then there’s the nausea. “Stomach awareness” is the official term.… The more you move around, the worse it gets.… In space there is no up or down.… So if you spin around or flip upside down, the sensation is not that you’ve spun or flipped around. What you feel is that the room is spinning and flipping around you while you’re staying perfectly still, which causes the worst vomit-inducing feeling of vertigo you’ve ever experienced. After a couple of days you get used to it.¹²

Saying that astronauts “get used to” weightlessness refers to their perception, but the experience nevertheless creates longer-term physical problems, usually but not always undiagnosed until they return to Earth’s gravity. Some of these affect all astronauts, whereas others appear in only half or fewer of them. Prolonged living in an environment of weightlessness leads to a loss of bone and muscle mass, which can be partially avoided through regular exercise. Actual skeletal deterioration, however, also occurs, and it does not recover so easily. In addition, weightlessness changes humans’ cardiovascular function, their production of red blood cells, and their eyesight (astronauts have a higher likelihood of early-onset cataracts). Sleep difficulties often arise in space, largely from the disruption of Earth’s familiar day-and-night cycle. Serious blood flow complications, including blood clotting, have affected some astronauts on the International Space Station. And weightlessness understandably creates slight changes in the position of an astronaut’s brain within the cranium. Data on all these issues continue to mount with the increase in the number of astronauts and the duration of the time that they spend in space.

HAZARDS OUTSIDE THE CABIN: COSMIC DANGERS TO ASTRONAUTS

Anyone who passes beyond our planet’s atmosphere and magnetic field encounters a harsh cosmic environment. Streams of atomic nuclei, most notably protons, continuously bombard the spacecraft, requiring that astronauts be protected against them. On our planet’s surface, Earth’s atmosphere and magnetic field block or divert most of the subatomic particles that continuously assault our planet. But high-altitude fliers such as military and civilian pilots or flight attendants are more vulnerable—a few five-hour flights at 35,000 feet expose an individual to as much radiation as that from a typical chest X-ray.

These streams of particles arrive from two different sources: the sun and the cosmos in general. The sun produces a steady flow of high-energy particles, engagingly named the “solar wind”—mainly protons, electrons, and the nuclei of helium atoms. Life on Earth has evolved with a tolerance for the small amount of this incoming flux that penetrates to ground level, but on occasion the sun produces giant clouds of much more energetic, more dangerous subatomic fragments. These coronal mass ejections (CMEs), typically signaled by blazes of light called solar flares, erupt from the solar corona, the layer of highly rarefied, million-degree gases above the sun’s surface. Although the particles of CMEs have speeds measured in millions of miles per hour, those directed toward our planet require several days to reach the Earth, where they disrupt radio communications and even the electric grid, while also stimulating stunning auroral displays. A traveler in space would need thick, heavyweight shielding to avoid serious damage or death from a powerful CME.

Astronomers who observe the light from a solar flare, which takes only eight minutes to reach us, could alert astronauts in near-Earth orbit, who would have sufficient warning of the impending “storm” of particles to return to Earth. Planning for a trip to the moon or beyond requires a different approach, either trusting to luck that a CME would not occur during the journey or outfitting a spacecraft with heavy shielding (adding so much weight to the spacecraft would have consequences for energy consumption, of course).

Beyond the solar system, the cosmos teems with “cosmic rays”—a name assigned by historical accident that misrepresents their essence. Cosmic rays consist of solid particles, generated by exploding stars throughout our Milky Way galaxy and the entire cosmos. Almost all these particles are nuclei of the most common elements. The bulk of them consist of single protons (nuclei of hydrogen, the most common element in the universe); others include the nuclei of helium (next in line in terms of cosmic abundance) and more massive nuclei, mainly of carbon, nitrogen, oxygen, and iron. Higher-energy particles tend to be rarer than lower-energy ones, a fortunate circumstance since higher energies imply greater capacity for damage. Measured in units of MeV (1 million electron volts), ordinary solar wind particles have energies around 1 / 1000 MeV. Solar storm particles have energies close to 1 MeV, and the particles from coronal mass ejections come in at 10 to 100 MeV. Cosmic ray particles, potentially the most damaging, appear in the 100–1000 MeV range. Thus the particles’ energies differ by factors as large as 1 million. For every cosmic ray particle with an energy of 1000 MeV that arrives at Earth, more than a billion ordinary particles arrive in the solar wind.

Deprived of the protective blanket of Earth’s atmosphere, astronauts in space face a steady barrage from solar wind and cosmic ray particles, as well as the possibility of increased danger from CMEs. High-energy solar radiation in the form of x rays and gamma rays poses an additional hazard (likewise blocked in large part by our atmosphere); however, the outer surface of a spacecraft, especially if backed by polyethylene, provides an effective barrier to these massless photons, with only extravehicular excursions (spacewalks) posing a problem that requires protective gear. In contrast to x rays or gamma rays, high-energy particles have far greater penetrating power, capable of passing through many inches of solid shielding (though it depends on the precise energies involved). When these particles strike the molecules at the centers of the cells that form human bodies, they can cause mutations that increase the risk of cancers, most notably of the lung, colon, breast, liver, or stomach.

Long aware of these issues, NASA has attempted to limit astronauts’ risk from spending time outside the atmosphere. The most straightforward approach limits the time in orbit in order to keep the risk of cancer below a predetermined level. NASA currently aims to make sure that no more than 3 percent of all astronauts will die from cancers caused by exposure to solar wind and cosmic ray particles. Trying to ensure this result on the basis of theoretical analysis alone has clear drawbacks. By now, however, significant data from actual astronauts have become available. A 2019 study of 418 Russian, European, and American astronauts, after an average interval of twenty-four years following their time in orbit, found that almost 30 percent of deaths arose from cancer.¹³ The study concluded that “we again fail to find evidence sufficient to conclude that historical doses of space radiation pose an excess mortality risk for astronauts and cosmonauts. However, it is important to note that future missions of deep space exploration will likely offer much greater doses of space radiation than have historical doses, which will lead to a different risk profile for future astronauts and cosmonauts.”

ONE MORE DANGER: COULD NEAR-EARTH ORBIT BECOME OVERCROWDED?

The fact that near-Earth space contains the easiest trajectories for spacecraft to reach, as well as the orbits most useful for many purposes, has made it prime real estate for various types of satellites. These include satellites developed for military uses, for weather observations, and for general surveys of our planet’s land masses and oceans. Equally useful, and now more abundant, are small satellites used to relay messages and data, for surveillance, and to bring rapid broadband service to remote parts of the world.

Advances in miniaturization and changing economics have now enabled the launch of entire flotillas of small satellites—as many as one hundred on a single rocket. These satellites enable companies such as California’s Planet Labs to obtain daily images of the entire globe with a resolution sufficient to reveal road traffic, building sites, land use, and related information. Even greater advances lie in the near future, as SpaceX envisages that its Starlink project will place up to 40,000 satellites in orbit to create a network for enhanced global broadband communication.¹⁴ Other companies, including Amazon, have announced similar plans. In principle, these are exciting and welcome developments, the more so if they establish broadband internet connectivity in places currently without it, including many parts of Africa.

Unsurprisingly, however, programs such as these carry a downside: a host of satellites—far more than the total launched to date—would seriously interfere with astronomers’ view of the cosmos. The number 40,000 approximates the number of square degrees on the sky. If you hold a small coin at arm’s length, it will cover a square degree, and if you imagine a moving bright spot in every such patch of sky, you can visualize the situation shortly before sunrise or after sunset, when sunlight will glint from each satellite in orbit hundreds of miles above an observer’s horizon. Skywatchers would find the familiar stars augmented by hundreds or thousands of bright spots in motion across the sky. Professional astronomers observing a single celestial object would find these “rogue lights” a minor irritant, but they would prove an enormous hindrance to ongoing projects that continuously monitor or search large areas of the sky for transient events such as exploding stars or still more exotic cosmic outbursts. Particular confusion would arise when part of a satellite catches the sun and reflects like a mirror. Pointed toward a telescope, the beam of light would mimic a faraway explosion. This difficulty would especially impede the ongoing search for small asteroids like those described in Chapter 6.

There’s more. Astronomers have developed sensitive instruments to detect and analyze microwave radiation, the portion of the spectrum with wavelengths similar to those used in familiar kitchen appliances. Microwaves reveal the details of how young stars and protoplanets form, as well as the types of atoms and molecules that provide their raw material. Microwaves also transmit the uplink and downlink data from satellites, so a host of satellites would effectively “pollute” this portion of the spectrum all day and all night. Astronomers have carefully positioned their radio telescopes (including those designed to study microwaves) in radio-quiet regions of the globe, but no telescope can hide from a profusion of satellite-linked microwaves. (The exception lies on the far side of the moon, which would be an excellent site for telescopes, as described in Chapter 4.)

The issue of satellite swarm clearly has two sides. Spreading broadband worldwide has genuine benefits. The mega-enterprises behind these efforts recognize the problem of having so many satellites in near-Earth orbit and attempt to minimize it by blackening the satellite surfaces and choosing the transmission wavelengths carefully. This represents serious progress since the days when other corporations proposed that giant advertisements could orbit the Earth to enlighten the buying public. We should not forget, however, that it’s not only astronomers and space enthusiasts who have a stake in the outcome. The night sky’s “vault of heaven” offers the sole feature of our environment that humanity has shared—and wondered at—throughout our history on this planet. We have already diminished its impact with our city lights, and we should deplore anything that degrades it further, much as we bar telephone wires and bright lights in our national parks.

The proliferation of small satellites will inevitably produce collisions between some of them, along with disruptive impacts with existing space debris. In 2009, a communications satellite’s collision with a defunct Russian satellite produced almost 2,000 pieces of debris at least 4 inches across, plus thousands of smaller pieces. Most of this litter will orbit the Earth for years on end.¹⁵ The growing satellite swarm threatens to generate a “Kessler effect,” named after a NASA expert in space detritus, David Kessler, who predicted a self-reinforcing cascade when the remnants of collisions themselves collide to generate still more debris.¹⁶ The Kessler effect would mimic the current situation of seaborne waste, whose interactions follow a fractal process that produces ever-smaller particles of metal and plastic. Although three-quarters of the mass of oceanic detritus consists of pieces more than two inches across (and thus potentially recoverable, albeit with a mammoth effort), the remaining 25 percent consists of microplastics less than 1 / 25 of an inch in size, which are almost impossible to remove from the ocean.¹⁷ These tiny particles account for almost 95 percent of the estimated trillions of pieces of trash floating within the Great Pacific Garbage Patch, located in the North Pacific between North America and Japan.

The Kessler effect could make near-Earth orbit difficult or impossible to utilize during the decades before the development of a satisfactory cleanup technique. The problem, which affects both astronauts and automated satellites, reminds us that human advances often carry unanticipated consequences. We would do well to bear this rule in mind as we examine the prospects for astronaut journeys far beyond their now-familiar near-Earth environment. These naturally will begin with a resumption, after half a century, of visits to the moon.

CHAPTER 4

The Moon

Astronomers of centuries past looked to the moon as they sought to resolve a long-running mystery: the basic nature of heavenly bodies. Instead of the perfect and unsullied orb that philosophers had imagined, improved observations eventually revealed that the moon fundamentally resembles the Earth, a solid object with a wrinkled exterior. When Galileo turned his first telescope toward the moon in 1609, he immediately saw a cratered surface, which we now know incorporates a history of change rather than of eternal perfection. Although Galileo misinterpreted the moon’s broad, dark plains of frozen lava, calling them maria or “seas,” his designation likewise implied a changeable world. If the moon resembles the Earth, Galileo argued, the planets must do so as well.

With the moon’s surface subject to detailed inspection, thoughts of voyages through space naturally tended toward our closest celestial neighbor. The first science fiction story, written by Galileo’s great contemporary Johannes Kepler though published only after Kepler’s death, carries the title “Somnium” (Dream). Its protagonist travels in a dream to Levania, the moon (in Hebrew, the name connotes the whiteness of the full moon), where he notes correctly that one-half of the moon’s population, because they inhabit the side of the moon that always faces away from the Earth, never has the chance to see our blue planet. In the century after Kepler’s time, Isaac Newton and other astronomers established that Earth’s natural satellite has only 27 percent of Earth’s diameter, 1 / 50 of its volume, and 1 / 81 of its mass.

WHY GO TO THE MOON?

Astronomically speaking, the moon orbits in our own backyard; Mars and Venus lie a hundred times farther from us, on average. As the brightest object in the nighttime sky, the sole celestial object with a surface visible to unaided eyes, the moon has fascinated humans ever since they began to observe the heavens. The moon naturally became the initial goal of our voyages in space, whether real or imaginary, and has remained a prime target ever since actual journeys began.

Today, more than fifty years after astronauts first landed there, the moon beckons us for at least six different, though interrelated, purposes:

Investigating the formation and early history of the solar system

Creating lunar habitats and possible bases for longer journeys

Constructing astronomical observatories

Discovering and utilizing the water buried in the lunar soil

Securing valuable lunar substances (most notably the rare isotope of helium called helium-3) or material for construction on the moon itself

Sending lunar rocks into space to construct free-floating colonies that could support hundreds of thousands of inhabitants

The first four endeavors would proceed entirely on the lunar surface. The fifth would almost certainly involve the return of helium-3 to Earth. The sixth, a much mightier project for the future, is discussed in Chapter 9. A closer examination of these lunar projects allows us to consider the extent to which on-site astronauts will be worthwhile and cost-effective for each of them.

STUDYING THE LUNAR SURFACE IN DETAIL

Like all the surfaces of other solar system objects, the moon’s continues to intrigue astronomers and geologists, who plan to survey, in far greater detail than possible from the Earth, the lava plains, rills, ridges, hills, mountains, and other aspects of lunar topology, with the goal of uncovering the story of how our satellite achieved its present condition. The essence of the moon’s features, and the primary reason for astronomers’ interest in them, resides in their age. During the first hundred million years or so after the Earth and moon had formed, 4.6 billion years ago, they both suffered bombardment from remnants of material similar to that which had formed them. These impacts melted the rocks on their surfaces, in a sense completing their assembly. After the onslaught had run out of material, the cooling of the moon’s surface left behind the alternating dark and light features that Westerners see as the “man in the moon” and people in Asian countries see as the “rabbit in the moon.” These areas, along with the remainder of the lunar surface, have lain frozen and basically unaltered for 3 to 4 billion years, presenting us with a moonwide fossil record of the solar system’s early history. During those eons, Earth’s much larger size gave rise to tectonic activity, weathering, oceanic changes, and other natural events that have buried or destroyed the corresponding geological record.

During the early years of the space race between the Soviet Union and the United States, both countries devoted large outlays of money and effort to the task of sending humans to the moon and returning them safely. The success of the six Apollo lunar landing missions overshadowed important results from robotic spacecraft that came before and enabled these landings, and from others that have continued throughout the following five decades.

Close-up lunar exploration began in 1959, when the Soviet Union and the United States each sent spacecraft past the moon. In the years since then, more than five dozen automated probes have crossed the Earth-moon divide; some of them have orbited the moon or landed on its surface. Lunar orbiters created by five countries and the European Space Agency have mapped the moon’s surface in detail. These include NASA’s Lunar Orbiter (1966–1967), Clementine (1994), Lunar Prospector (1998–1999), and Lunar Reconnaissance Orbiter (2009–present), as well as the seven orbiters of the Soviet Union’s Luna program (1966–1974), ESA’s Smart-1 (2004–2006), Japan’s SELENE (2007–2010), China’s Chang’e 1 (2007–2009), and India’s Chandrayaan-1 (2008–2009).¹

Landing safely on the moon calls for even greater precision than entering lunar orbit. In 1966, the Soviet Union, beating the United States’ Surveyor 1 by four months, achieved the first soft lunar landing with Luna 9, whose number testified to the failure of many of its predecessors. Improved probes brought samples of lunar soil to Earth, with Luna 16 in 1970, Luna 20 in 1972, Luna 23 in 1974, and Luna 24 in 1976. After a hiatus of more than four decades, Russia restarted the Luna program with Luna 25, sent to the moon in October 2021 to participate in the now-intense quest to find ice beneath the moon’s surface. In all, five NASA Surveyors preceded the Apollo landings of 1969–1972, after which NASA has sent only orbiting spacecraft to the moon.²

The Chang’e 3 mission placed China’s first rover on the moon in 2003, and its Chang’e 4 made the country’s first soft landing on the moon’s far side in 2018. This spacecraft carried an improved, solar-powered rover, Yutu-2 (“jade blossom” in Chinese), which broke the previous longevity record for lunar operation. In December 2020, China’s Chang’e 5 spacecraft landed on the moon and returned to Earth with the first sample of lunar soil in forty-four years.

As part of its active lunar exploration program, China apparently intends to send astronauts to the moon in the near future. The United States’ Artemis program plans to follow suit soon thereafter—though, as discussed later in this chapter, debate continues over using the moon primarily as a way station for a crewed mission to Mars or as an exploration site for astronauts.

BRINGING LUNAR MATERIAL TO EARTH

Proponents of sending astronauts on further voyages of lunar exploration can effectively argue that our finest achievements in space exploration have occurred on the moon’s surface: the selection of lunar rocks for return to Earth and the discovery of the moon’s orange soil. Both these accomplishments, achieved half a century ago, deserve recognition today. Scientific motivation for reaching the moon has long centered on the desire to analyze samples of lunar rock and soil in order to reveal the details of their composition, formation, and subsequent history. The samples brought to Earth by automated landers and in far larger amounts by the Apollo astronauts represent the enduring scientific legacy of the first fifty years of lunar exploration.

In the same epoch when the Apollo astronauts explored the moon and removed some of it for terrestrial examination, the Soviet Union’s robotic spacecraft achieved the first fully automated sample returns to Earth. During the early 1970s, each of three Soviet Luna missions drilled about fourteen inches into the lunar soil, placed its haul into a capsule, and brought it back to Earth, where they parachuted their precious cargo into Kazakhstan for easy recovery. The three missions brought a total of 325 grams (about 11 ½ ounces) to Earth.

The six Apollo missions brought about 1200 times more than this, some 845 pounds of material, home with them. The amounts from the individual missions ranged from 49 pounds from Apollo 11’s first landing on the moon to 211 pounds from the final lander, Apollo 17. Today some of this moon matter appears on the open market at impressively high prices, not least because ownership of rock from the moon remains illegal in the United States (if you did not gather it on the moon yourself). Meteorites made from lunar material that strikes the Earth belong to a different, entirely legal category; in both cases, proof or disproof may be a bit tricky.

In November 2020, forty-four years after Luna 24 brought moon matter to Earth, China launched Chang’e 5, an automated spacecraft, to gather more lunar samples. Building on the success of Chang’e 4’s first soft landing on the moon’s far side a year earlier, Chang’e 5’s lander collected about four pounds of lunar material and placed it into an ascent vehicle. A rendezvous with another spacecraft in lunar orbit allowed the transfer of the cargo for return to Earth. Examination of the material in 2021 revealed the material’s surprisingly young age: less than 2 billion years, in contrast to the 4 billion years of most moon rocks.

From one point of view, the amount of lunar material returned by automated means via Chang’e 5 was a sixfold increase over the total from the three Luna missions. From another, the total mass returned by Chang’e 5 equals just 1 / 200 of the Apollo total, collected by humans. More significantly, humans have demonstrated clear superiority over robots in identifying and selecting lunar material. In considering future sample return missions to the moon, to Mars, and to the asteroids, the history of lunar sample returns argues strongly in favor of astronauts. To reverse this judgment requires the conclusion that future spacecraft will be able to identify significant rocks as well as or even better than humans—at least in a cost-benefit analysis. While this discussion awaits future developments, we should examine an even finer example of human intelligence exercised on our celestial neighbor: the orange soil on the moon.

THE DISCOVERY OF THE LUNAR ORANGE SOIL

Scientists’ peak success in on-the-spot lunar exploration occurred in December 1972, during the final Apollo mission to the moon, soon after Harrison Schmitt, a trained geologist, stepped onto the lunar surface. Accompanied by Apollo 17’s pilot, Eugene Cernan, Schmitt drove in their battery-powered Lunar Roving Vehicle to Shorty Crater, a modest depression about 120 yards across. There Schmitt made the discovery that would bring him the fame that helped him get elected to the United States Senate four years later. (Six years after that, his opponent denied him reelection while deploying the slogan “What on Earth has he done for you lately?”)

Having stopped to examine a large boulder on the crater rim, Schmitt and Cernan suddenly saw soil with an orange coloration—so familiar to those who have spent a career examining rocks and dirt that Schmitt excitedly radioed, “It looks just like an oxidized desert soil” and “It’s all over! Orange!” On Earth, volcanic eruptions rich in water vapor create most of the planet’s oxidized rock. Brought to Earth for analysis along with 240 pounds of other samples, the orange soil proved to have a volcanic origin and an age of 3.7 billion years.³ Continuing study has strengthened the conclusion that today’s nearly bone-dry moon had a water-rich surface during the early existence of the solar system.

WATER ON THE MOON FOR ASTRONAUT HABITATS AND EXPLORATION BASES

Water buried in lunar rocks, especially those near the moon’s north and south poles, could provide a crucial resource to any future lunar explorers, or a supply for missions to more distant objects. These prospects have strengthened as the result of the improvements in astronomical instruments and observing techniques that have allowed automated spacecraft to reveal a host of new information about the moon. In 1994, NASA’s Clementine spacecraft spent two months in lunar orbit, using its seven different instruments to map the moon and examine its surface, including the lunar far side and both its poles. Much closer to home, the SOFIA aircraft, flying higher than commercial airplanes in order to avoid the infrared-blocking effect of our atmosphere, confirmed that small amounts of water exist on the moon’s surface. In 2008, the Indian Space Research Organization’s Chandrayaan-1 spacecraft used an imaging spectrometer provided by NASA to discover that water ice speckles the walls and floors of some of the craters near the south pole.⁴ Further confirmation arrived in 2009, when NASA’s automated LCROSS mission executed a planned crash of its booster rocket into the moon’s south pole. The orbiting spacecraft analyzed the plume of ejected material and discovered that it included water molecules.

During the moon’s slow rotation, most of its surface alternately bakes for two weeks at temperatures above water’s boiling point before descending into a two-week-long nighttime with temperatures hundreds of degrees colder than anywhere on Earth. However, sunlight never reaches the interiors of craters near the moon’s poles, whose walls block the constant but extremely low-angled sunlight. There temperatures of the soil and subsoil remain below -400 degrees Fahrenheit, creating super-cold, super-hard ice, analogs of the ice on the surface of Pluto, which orbits forty times farther from the sun than the Earth and moon. The super-cold lunar ice makes the south pole of the moon a potential hot property, rich in a highly valuable resource for astronauts who plan long stays on the moon. The only problem is that we don’t know how much ice exists, or how easily it can be extracted.

Both the United States and China plan to investigate this super-cold ice with spacecraft that can drill into the polar soil, extract samples of the ice, and bring them to Earth. China has announced a successor to the Chang’e 5 robot that will return lunar rocks from the polar regions. In 2022, NASA plans to send two landers to the south pole, to be followed in late 2023 by VIPER (Volatiles Investigating Polar Exploration Rover), capable of finding ice below the surface and drilling a yard into it.⁵

Confirmation that ice exists in abundance on the moon will raise several important questions. How much ice lies buried there? Who has the rights to use it? How long will it last? The oxygen locked into the ice has tremendous value for liquid rocket fuel, which otherwise must be sent from the Earth’s much deeper gravitational well, and for human respiration.

Furthermore, how can we exploit this icy resource without destroying its greatest significance for science, the historical record locked within it? Planetary scientists seeking to understand the early history of the Earth-moon system remain handicapped by the fact that, as noted earlier in this chapter, Earth’s plate tectonics and weather have hidden or destroyed that entire geological record on our end of the system, leaving only a few rocks older than 4 billion years. But the moon’s lack of erosion and tectonic activity has preserved ancient records on its surface, including, astronomers reasonably assume, the evidence needed to answer a fascinating question: How did the Earth and the moon get their water? Did it arrive from cometary bombardment? Or from volcanic explosions? Or from particles in the solar wind? Though the moon has failed to retain most of its original water, the ice that remains could presumably reveal its origins. Should we make sure that whoever extracts lunar ice does not contaminate it so far that we can no longer read its long-locked-away messages? How could we impose the necessary rules? Chapter 9 examines the last issue but (spoiler alert) does not find a solution.

LUNAR RESOURCES FOR HABITATS IN THE BEST LOCATIONS

The hazards to humans in space that Chapter 3 described also apply to the moon’s surface, which lacks the protection that Earth provides with an atmosphere and magnetic field that block or divert incoming high-energy particles. Without these, shielding against dangerous particles requires a thick layer of rock or metal. Abundant rocks on the moon’s surface would furnish natural building material for stone shelters and larger structures; in addition, most of the raw materials required for post–Stone Age habitats could be derived from the metal ores that form part of the moon’s outer layers. Although not so metal-rich as our home planet, the moon’s surface layers include plenty of iron, copper, nickel, and other metal ores, ready for prospecting and mining.

In addition to buried ice and metal ores, some of the craters in the moon’s polar regions possess a resource much rarer in the solar system: nearly constant light on a solid surface. At the moon’s south pole, some points on the rims of craters bathe in essentially perpetual sunlight, in a situation similar to what prevails at each of the Earth’s poles during about half of each year. But whereas the tilt of the Earth’s rotation axis gives non-equatorial regions periods of longer and shorter sunlit hours over the course of a year, the moon’s rotation axis has almost no similar tilt but instead “stays upright” at all times, so the moon’s surface has no large seasonal variations. The south pole’s sunlit pinnacles, sites where the temperature varies far less than in other lunar regions, could prove ideal locations for solar collectors designed to provide solar power to a base for extracting ice from the nearby crater floor. These “peaks of eternal light,” named a century and a half ago by the astronomer and prolific author Camille Flammarion, could develop into “peaks of eternal conflict,” not only among nations but also between rival entrepreneurs. For instance, the interior of the 13-mile-wide Shackleton Crater lies in perpetual darkness near the lunar south pole, but parts of its 2 ½-mile-high rim bask in near-constant sunlight.⁶ Chapter 9 discusses attempts to create rules for activities beyond the Earth that could conceivably deal effectively with territorial (more properly “selenorial” or just plain “lunar”) issues that make conflict more likely.

THE FAR SIDE OF THE MOON: A PREMIER TELESCOPE SITE

Just as the lunar poles harbor a valuable resource for human consumption, so the lunar far side offers two great advantages for astronomical investigations. First, it provides a solid surface upon which to construct large instruments to collect light, radio waves, and all the other types of radiation that bring information from the cosmos to eager astronomers. Second, it offers special advantages to radio astronomers, whose increasingly sensitive receivers now can detect the emission from a single mobile phone at the Earth-moon distance, because the moon’s bulk can shield their telescopes from the vast quantities of emissions produced on the nearby Earth. The appeal of the moon’s far side (the popular term “dark side” is not accurate, since all sides of the moon pass two weeks in sunlight followed by two weeks in darkness) rises so high in some astronomers’ future plans that some among them who decry other uses of astronauts in space carve out an exception for building lunar far-side observatories. Even these observatories, however, could be constructed before long by sufficiently capable robots.

In 2020, Saptarshi Bandyopadhyay presented a basic concept for a 1-kilometer-wide radio dish, to be constructed in a far-side lunar crater whose shape would make the support system easier to build. On Earth, the largest single-dish radio telescopes—the 300-meter Arecibo dish, which collapsed in 2020, and the 500-meter Chinese FAST radio reflector—likewise sit in natural limestone bowls. Radio astronomers dream of ever-larger instruments not only for their greater ability to gather waves from faint sources but also because long, low-frequency radio waves cannot be well observed unless the collecting reflector has a diameter many times their wavelengths. The concept promoted by Bandyopadhyay, a robotics technologist at the Jet Propulsion Laboratory in Pasadena, California, which for more than sixty-five years has had a leading role in the design, manufacture, and guidance of spacecraft that explore the solar system, embraces the placement of a wire-mesh reflecting surface by wall-climbing robots.⁷ Once in operation, the 1-kilometer dish could observe radio waves from the early universe emitted by atomic hydrogen (the most common element in the cosmos) that the cosmic expansion has stretched to the point that they now have wavelengths between 10 and 50 meters. Radio waves with these wavelengths require an enormous dish to receive them with any accuracy.

Another type of radio telescope uses an array of smaller dishes spread over a wide area. By combining and analyzing the signals that reach each dish, astronomers can create an interferometer that uses a type of triangulation to produce images as sharp as those that would come from a single dish as wide as the full spread of the array. On Earth, astronomers are creating similar arrays; the most ambitious example, the Square Kilometer Array [SKA] project, will spread dozens of dishes, whose combined area equals a square kilometer, over desolate areas in Western Australia and South Africa.⁸ Linked electronically, radio maps made with the SKA will have a resolution of detail equal to that available from a dish the size of the Earth. Before long, robotic construction of a similar array should prove entirely feasible, even on the far side of the moon, from where a satellite in synchronous orbit above the array could relay observations to Earth.

HELIUM-3: HELIUM’S ELUSIVE AND USEFUL ISOTOPE

The fifth lunar project listed earlier in this chapter refers to a commodity extremely rare on the moon but rarer still on Earth: nuclei of helium-3, each made of two protons and one neutron.⁹ As originally emphasized by Harrison Schmitt, the hero of the lunar orange soil, these nuclei could, in theory, provide a possible fuel for abundant, entirely clean nuclear energy both on Earth and for activities on the moon.

Almost all of the helium that occurs naturally throughout the universe is helium-4, whose nuclei each incorporate two protons and two neutrons. Nuclear fusion, the melding of nuclei that powers the stars and made the elements, follows the laws of nuclear physics, and these laws discriminate mightily between the two types of helium: nuclei of helium-3 fuse easily, while those of helium-4 rank as the most fusion-resistant of all nuclei.

Most stars, including our sun, employ a three-step process to release energy through nuclear fusion that turns hydrogen nuclei (protons) into nuclei of helium-4. In the first step, two protons fuse together to make a nucleus of deuterium (heavy hydrogen) plus two other particles, a positron and a neutrino. The second step fuses another proton with the deuterium nucleus, producing a nucleus of helium-3 and a high-energy photon. Finally, two helium-3 nuclei fuse to produce a nucleus of helium-4 and two protons. The three steps turn four protons into one helium-4 nucleus and some additional particles, plus additional energy that appears primarily as motion of the helium-4 nucleus. Thus, although the production of energy in the sun creates enormous numbers of new helium-3 nuclei (almost a hundred billion billion billion billion of them) every second, essentially all of them promptly disappear. Similar numbers describe the birth and death of helium-3 nuclei in stars that resemble our own, all of which face an eventual energy crisis as they exhaust their stores of protons in their nuclear-fusing cores.

The first few minutes after the big bang produced even more staggering numbers of helium-3 nuclei, but their easy fusion reduced their numbers to the point that today they constitute only about one-millionth of all helium nuclei. Furthermore, while stars have sufficient gravitational force to retain their primordial helium, lightweight helium has largely escaped from smaller objects such as the Earth and moon, leaving us to search for pockets of helium gas trapped within rocky deposits. And when we do find helium on Earth, less than one nucleus in a million turns out to be helium-3 rather than helium-4. This leaves us without much hope of profiting from the fact that fusing helium-3 nuclei can release new energy without producing any dangerous radiation or radioactive nuclei, the bane of the nuclear fission reactors that we now use to generate electricity. Access to abundant amounts of helium-3 nuclei could prove a great boon to humanity.

Compared to Earth, the moon teems with helium-3. Instead of one helium-3 nucleus for every million helium-4 nuclei, moon rocks have an abundance ratio ten to a hundred times higher, the result of billions of years of bombardment by the same high-energy particles that pose a danger to astronauts beyond our protective atmosphere and magnetic field. Helium-fusion enthusiasts regard the moon as the promised land, chock full of the matter that could solve our most pressing energy and pollution crises.

This would, of course, require serious exertions. For one thing, helium-3 nuclei still amount to only a few parts in every billion parts of lunar surface material. For another, any effort to gather helium-3 would require serious strip-mining of the lunar regolith (the loose rocks and soil above the bedrock), accomplished in a way that does not liberate helium gas, which would promptly escape into space. In addition, maintaining helium-3 fusion would require entirely new machines to confine gases at the enormously high temperatures that would allow energy release. Finally, without serious intervention through other costly processes, helium-3 fusion will produce other types of nuclei that effectively gobble up helium nuclei in other fusion processes, thereby preventing continuous helium fusion. Frank Close, an expert in particle physics, has labeled the notion of generating electricity through helium-3 fusion as “moonshine.”¹⁰ Others disagree heartily.

Whatever the likely outcome of helium-3 mining on the moon, consideration of its prospects provides a prototype for analyzing future mining efforts on other worlds: they all require strenuous, long-term efforts, serious damage to the local environment, and, in many cases, new technology such as the one that would allow nuclear fusion to proceed continuously on the moon. The terrestrial history of balancing the costs and benefits of such projects does not imply that rationality will always triumph.

HUMAN VERSUS ROBOT EXPLORERS, NOW AND IN THE FUTURE

Proponents of exploration with astronauts often cite Cernan and Schmitt’s discovery of the lunar orange soil as proof that humans can use their experience, insight, and mental agility in ways that no robot ever could. We must note, however, that our human brains’ marvelous capacities will remain basically static until we reengineer our biology, whereas our robots’ abilities increase every year, with no end in sight. (Some futurists predict that the “end” will arrive with robots taking control of our society and eventually dispensing with humans altogether. These potential situations lie beyond the time range discussed in this book.) Fifty years ago, a comparison between Harrison Schmitt on the moon and his counterpart in Houston directing an automated lunar rover would have been close to laughable. Even though such a rover could have been directed in almost real time (radio signals require only 2 ½ seconds for the round trip between the Earth and the moon), it was obvious that people on the moon could achieve insights from surveying their surroundings more quickly, more efficiently, and with deeper insight than a person at an earthbound control desk.

Today things look different, both on the moon and on celestial objects too distant for real-time guidance from Earth, as demonstrated by the Perseverance rover on Mars, described in Chapter 5. An automated lunar rover could deploy its own “brain”—the algorithms that embody its experiential learning—as it traveled over the lunar surface. By now, improvements in artificial intelligence (AI) have roughly equalized human and robot abilities to recognize prominent geological features. Further AI advances will continue to tilt the balance in favor of robots. For some years, humans may maintain their advantage in determining the broad contours of their activities (as opposed to carrying out specific tasks), but eventually this too will diminish as automated explorers improve.

AI has proven indispensable for an enormous range of industrial and computer-based activities. The speed with which computers can process information gives them a huge advantage—almost beyond thought of a competition—in many situations involving vast amounts of data, such as controlling electrical grid networks or traffic flow. AI can analyze more images in an hour than a human expert could in a lifetime. Perhaps its most evident benefits have appeared in the medical world, especially in radiography and diagnosis. The Association for the Advancement of Artificial Intelligence, based in Menlo Park, California, has established the AAAI Squirrel AI Award for Artificial Intelligence for the Benefit of Humanity.¹¹ Regina Barzilay, the first winner of this million-dollar prize, created an algorithm to analyze mammograms in order to predict whether a patient is likely to develop breast cancer in the future. Another algorithm to identify molecules likely to lead to new medications has led to the development of halicin, an antibiotic apparently effective in killing antibiotic-resistant bacteria, now undergoing clinical trials. AI is likely to yield numerous additional successes in the next few years. Among other areas, AI will continue to improve at controlling large robots (see the videos of robot dancing, available by easy search of the internet) as well as miniature ones used in microsurgery; at language recognition, already evident to those who speak with Alexa, Siri, and Google Assistant; at facial recognition (if persons with criminal intent deploy these abilities, this reminds us that not all technological advances are entirely positive); and in producing videos of all sorts.

These developments may seem to leave us some distance from an autonomous lunar rover that can determine the trajectory most favorable to potential discovery, follow it while surveying the moonscape, and collect soil samples or drill into the surface for analysis either on the spot or back at its home base. However, predictions of the most significant improvements coming from artificial intelligence during the next decade or so show a significant overlap between terrestrial and lunar tasks. Transportation on Earth seems likely to receive the greatest impact from AI, as the replacement of our existing road vehicles with self-driving cars and trucks improves the safety of highway travel, free from accidents caused by human distraction and poor judgment. Excessively dangerous activities such as firefighting and underground mining will be largely performed by robots. Their ability to judge and to navigate complex situations will mimic what robots on the moon must apply on a larger scale of operation. Few people doubt that machines will gradually surpass or significantly enhance more and more of our distinctively human capabilities. Disagreements center on the time scale on which this will occur. Some AI enthusiasts say that this will take only a few decades, while more cautious predictions suggest that at least a century will be required.

Ian Crawford, a planetary scientist and astrobiologist at the University of London, presented a contrary view in his 2012 article entitled “Dispelling the Myth of Robotic Efficiency.”¹² As Crawford emphasized, if astronauts can achieve their goals—for example, the assessment of a Martian landscape—in far less time than a robot can, then even though astronauts may cost far more per hour, the net cost of a particular discovery could turn out to be equal, or even favor the astronaut.

Crawford’s analysis compared humans and robots with respect to eighteen different skills on a scale ranging from “total advantage to humans” to “total advantage to robots.” Some of these skills could be measured objectively, others only subjectively. They included strength, endurance, precision, cognition, perception, detection, sensory acuity, speed, response time, decision-making, reliability, adaptability, agility, versatility, dexterity, fragility, expendability, and maintainability. The last of these produced the only tie. Of the remaining seventeen, robots prevailed in four: precision, sensory acuity, reliability, and expendability. Humans won the other thirteen, including speed (humans are “able to cover great distances quickly”), cognition (they are “creative and limited only by prior training”), agility (they are “limited only by design or exoshell”), fragility (humans are “generally robust but total system failure can be caused by small effects,” whereas robots are “generally very fragile, especially attendant instrument suites”), and endurance (humans are “limited by available consumable and physical tolerances,” while robots are “limited by design and environmental decay”).

For our purposes, Crawford’s analysis has value not for his assessment a decade ago but for its use in predicting the skill-contest outcomes during the 2031–2040 decade. Current trends in artificial intelligence suggest that of the thirteen categories judged to favor humans in 2012, humans will remain on top in only a couple of them twenty to thirty years later: cognition and decision-making. Even those two could favor robots before much more time would elapse. On Earth, for example, within a decade or two, robots may quite likely make better surgical decisions than humans.

WHAT’S NEXT IN LUNAR EXPLORATION AND UTILIZATION?

During the remainder of this decade, two groups of countries will proceed to the moon, quite possibly to the same south polar region, with plans to explore the surface, develop its resources, and employ both the moon and artificial lunar satellites as potential bases for expeditions to Mars.

In February 2021, Russia and China announced a joint program to create the International Lunar Research Station (ILRS) near the moon’s south pole by deploying numbers 6, 7, and 8 of the continuing series of China’s Chang’e spacecraft.¹³ After its initial construction as a fully robotic base, the station could include astronaut explorers and a long-term robotic presence in the early 2030s. During the 2036–2045 decade astronauts could spend many months at the ILRS. The two founding countries anticipate collaboration with others as their plans mature.

The decision to collaborate directly with China followed Russia’s choice not to join the Artemis Accords, the more fully developed plan of their competitors. The Artemis program includes NASA and commercial spaceflight companies contracted by it, together with the space agencies of Europe, Japan, Australia, the United Kingdom, the United Arab Emirates, Brazil, and Ukraine. Artemis, named after the god Apollo’s twin sister, the goddess of the moon and more, has undergone many revisions during the past decade, because the United States, its primary proponent and funder, has a tendency to alter important decisions as governmental majorities change. This would not work for the twenty-two countries of the European Space Agency, which has a history of sticking with decisions once they have been made. The Biden administration has expressed basic support for the Artemis program as shaped first by the Obama administration and then by the Trump administration, although the accelerated timeline insisted upon by the latter will not be followed.

Designed with the goal of landing “the next man and the first woman” near the moon’s south pole, the Artemis program involves establishing a lunar base camp and creating a moon-orbiting space station, the Deep Space Gateway, from which astronauts can perform observations and travel to the lunar surface or onward to Mars.¹⁴ In 2020, in its “Plan for Sustained Lunar Exploration and Development,” NASA stated that “the Moon is more than a physical destination. A core focus of Artemis is to extend the nation’s geo-strategic and economic sphere to encompass the Moon with international partners and private industry.”¹⁵ Except for the private partners, one may reasonably assume that China and Russia likewise aim at “encompassing” the moon. Calling for “a predictable and safe process for the extraction and use of space resources under the auspices of the Outer Space Treaty” (the treaty is described in Chapter 9), the plan emphasizes the tremendous rewards to the human psyche that will flow from human activity on the moon and human journeys to Mars: “For millennia humanity has looked at the Moon in wonder and awe.… [O]ur presence on the Moon will serve as a constant reminder of the limitless potential of humanity. It will continue to inspire humanity as we seek ever more distant worlds to explore—starting with Mars. The first human mission to Mars will mark a transformative moment for human civilization.… Most importantly, the accomplishment of the Moon to Mars approach will assure that America remains at the forefront of exploration and discovery.” The call for a “transformative moment” captures the fundamental driver of astronaut programs, discussed in Chapter 1: they make us feel better, more connected, and more engaged in our success as a country, perhaps as a civilization. Though such results are not to be sneered at, they should be weighed against their possible drawbacks, largely involving money and risk.

While considering this issue, we should note how deeply the Artemis program depends on automated operation. This raises the question of whether the program could achieve its goals of exploring the moon, employing its surface for construction and for astronomical observations, and then proceeding to explore Mars with advanced methods and equipment without bringing humans along. Consider, for instance, that the Gateway, designed to provide a platform in orbit thousands of miles above the lunar surface, will at first be operated autonomously in order to demonstrate its capability and reliability. In addition, the Gateway will house Commercial Lunar Payload Services, which will deliver material, including automated rovers, to the moon’s surface. The first of these rovers will study water molecules frozen beneath the south pole. The NASA plan points out that “rovers will be used to explore the surface more extensively, carrying a variety of instruments.… These robotic efforts will unleash a broad array of inquiry and scientific investigations.… The far side of the Moon … harbors resources, such as water, that are among the rarest and most precious commodities in space, offering potential sustenance and fuel for future explorers.”

The plan’s reference to the “rarest and most precious commodities” again raises a question that could become urgent if the two grand consortia come to establish outposts, whether robotic or human, at the moon’s south pole: who has the right to such commodities, especially if they could be quickly exhausted? If the United States and its partners compete with China, Russia, India, or other countries in efforts to establish themselves in this key lunar regions, the situation seems to beg for a regime, or at least an agreement, that will avoid open conflict. As said at the beginning of this chapter, Chapter 9 examines this issue—without, however, reaching a definitive answer.

SHOULD WE FEAR WHAT ALIEN ORGANISMS MIGHT DO TO EARTH?

Are we in danger of importing dangerous viruses or living organisms from the moon? Sixty years ago, plans for the first landings on the moon transformed contamination between celestial objects from a theoretical problem to a practical one. For understandable reasons, primary attention within the media, along with concern among scientists, put a spotlight on the danger that lunar pathogens could arrive with the astronauts. In response to this concern, as well as from the less-publicized fear of contaminating the lunar soil, NASA decided that the three Apollo 11 astronauts would spend three weeks in quarantine both before their journey and afterward. The quarantines aimed mainly to ensure that the astronauts would leave in perfect health, thus eliminating the possibility of returning with an illness that could cause the public to panic over “moon germs” reaching the Earth, and to demonstrate, after the journey, that this had not occurred. (President Nixon almost spoiled the pre-flight quarantine with his desire to have breakfast with the astronauts before their flight, but NASA officials managed to divert him from this plan.)

SHOULD WE FEAR WHAT OUR ORGANISMS MAY DO TO OTHER WORLDS?

To some scientists, the problem of contamination centers on a different issue, familiar to us on Earth: human-borne pollution. How did NASA deal with the more likely, if not more exciting, challenge of ensuring that the astronauts and their lander did not contaminate the moon? The particular pollution that causes restless nights in some astronomical circles involves a four-letter word: life.

Astrobiologists—those who spend their careers investigating the possibilities of extraterrestrial life—dream of finding living creatures on other worlds. They keep their dreams realistic by confining themselves, in almost all cases, to microscopic life, not much to look at but loaded with information about life’s origin and distribution in space. All life on Earth, from the deepest oceans to the atmospheric heights, relies on a single method of transmission from one generation to the next: the DNA molecules that encode the description that future life will follow. The possible discovery (may it come soon!) of life on another world, or even of life-forms floating through interplanetary space, would pose the fundamental question of astrobiology in the solar system: do those alien life-forms use the same DNA that ours do? A positive answer would strongly suggest a common origin and later distribution from place to place, while a negative one would imply separate origins on different worlds.

It’s certainly possible that we may never find life beyond the Earth. The full current of our ever-improved knowledge, however, runs in the opposite direction, toward a realization of life’s ability to survive, and presumably to originate, under conditions that we call “hostile” for their alien characteristics. This realization has sprung from the discovery of living organisms in terrestrial locations previously judged incapable of supporting life. For example, within the last few years researchers have found bacteria that live in tiny crevices of volcanic rocks hundreds of feet below the deep-sea floor. These bacteria don’t simply live but thrive, packed into communities as dense as those in the human gut, with 10 billion cells per cubic centimeter.

All scientific discussions of the issue of possible human contamination of other parts of space hark back to the 1960s, when the object to be visited was our moon. The moon, you say? Surely a dead world, devoid of atmosphere, with a surface baked and frozen, an uneroded surface barely changed for millions of years, bombarded by high-energy particles and deadly solar ultraviolet radiation that the Earth’s ozone layer absorbs. The rebuttal to this easy conclusion raises three separate issues that arise from our lack of knowledge and apply everywhere that we may visit. First, we do not know whether life may exist in environments that appear totally hostile. Second, we may learn that what seemed initially to be a hostile environment turns out to be comparatively favorable to life, thanks to circumstances we never suspected. Third, we must confront the issue of “back contamination”: bringing back to Earth forms of life that could create a pandemic or similar misfortune over the globe that we inhabit.

These concerns have always been evident to scientists. How seriously to take them, however, has never had a simple answer. The conservative approach—take care, so far as possible, to sterilize our intrusion, whether in person or by machines, and to sterilize anything that returns to Earth—makes eminent sense. But as we well know, nothing works perfectly, leaving open the question of how hard we must try. What level of cleanliness and sterilization will suffice, both to protect ourselves and to preserve any extraterrestrial ecological system as it was before we arrived?

BERESHEET AND THE TARDIGRADES

On April 11, 2019, the spacecraft Beresheet approached the moon, one representative of the increasing pace of uncrewed lunar exploration. Built by the Israeli space company SpaceII and named after the opening word of the book of Genesis, this probe aimed for a controlled descent onto the lunar surface. Failure of its gyroscopes, however, led to the shutoff of the main engine and a violent crash.

Beresheet carried a payload notable from a space-contamination viewpoint: a “time capsule” that contained the Torah and many other writings, an Israeli flag, 30 million pages’ worth of data, and—held within sheets of epoxy—human genetic samples and a few thousand tardigrades.

Tardigrades, also called “water bears,” are eight-legged micro-animals about 1 / 50 of an inch long. They are often described as the most resilient life-form on our planet, where they have been found to survive at high altitudes and miles under the sea, at temperatures hundreds of degrees below zero and above water’s boiling point, through ten years devoid of any water, and under bombardment by radiation and particles that will kill almost anything else. The private company that decided to send tardigrades to the moon presumably had an interest in determining how long they could abide there. If future expeditions reach the site of the Beresheet crash, they may determine the lower bound of this parameter, while adding crash-survival ability to tardigrades’ repertoire.¹⁶

But what if tardigrades from this or any other terrestrial probe reached the moon and established themselves there? A chance exists that their burial put the Beresheet in contact with underground material with enough water molecules to satisfy a group of water bears. If, a century from now, investigations find tardigrades in the area, they would presumably determine with relative ease that these tardigrades came from Earth, as they would have nearly identical DNA, only slightly altered, if at all, by adaptation to life on our satellite. But a few more centuries after that, the tardigrades of the moon might have evolved, in response to natural selection within a lunar setting, to life-forms not so clearly with an origin on Earth. And if not these tardigrades, what about others, sent by other private enterprises, perhaps as further experimentation, perhaps to join the tardigrade hall of fame?

A SCIENTIFIC RESPONSE FROM FIFTY YEARS AGO

The moon may yet prove so hostile to life that fears of biological contamination in either direction will turn out to have been unjustified. Of course, this hardly argues in favor of abandoning attempts to avoid any contamination. Prudence rules—or certainly should rule—when we contemplate destroying our hopes of determining whether or not a lunar life-form qualifies as indigenous.

The problem appeared in scientists’ considerations as soon as spacecraft landing on Mars approached reality, first achieved by the Soviet Union’s Mars 3 in May 1971. (The spacecraft ceased transmission after fifteen seconds on the surface.) Thirteen years earlier, the International Council of Scientific Unions, a long-standing nongovernmental organization many decades old, had established the Committee on Space Research (COSPAR). COSPAR’s triennial meeting in 1964 included a debate on acceptable levels of contamination, and the participants included a group of eminent scientists, of whom Carl Sagan became the best known. In 1968, Sagan, along with Elliott Levinthal and Joshua Lederberg (who in that year won the Nobel Prize in Physiology or Medicine for discovering that bacteria can mate and exchange genes), published their analysis of the situation in Science magazine.¹⁷ COSPAR’s efforts in attempting to set contamination rules represented grew out of the concepts that had been incorporated in the Outer Space Treaty of 1967.

In their paper, the three authors attempted to rebut other estimates by other experts that only a small probability existed that terrestrial organisms could be released by a Martian lander, and that the probability of reproduction of any such contaminant was negligible. In those bygone days, the only spacecraft under consideration would come from the United States or the Soviet Union. Using the sort of pithy language that Sagan would later make famous, the authors stated that Soviet efforts embodied a misunderstanding of the purpose of planetary quarantine: “It is not an immigration program designed to keep the total number of migrants matched to the resources of the target planet. It is a quarantine program designed to minimize the possibility that the planet will be infected with a single viable organism that might propagate now or in the future.” They posed a useful analogy involving a dry forest in tinderbox conditions: “If the individual in front of us throws a lighted match into the forest, it does not follow that we may throw large numbers of lighted matches as well, particularly if we are seeking out the driest parts of the forest. His match might not ignite the forest; ours might. Also, if we are cautious with matches, the need for caution and the method of achieving it might be grasped by our companion.”

Today, while numerous state and private entities have replaced the sole “companion” of the 1960s and 1970s, nothing has changed about the basic problem that Sagan, Levinthal, and Lederberg considered—except for growing much worse and passing out of control. On the one hand, any sort of life on the moon appears highly unlikely, although the presence of water makes our satellite seem a bit less hostile to microorganisms. On the other, it’s far clearer now than it was when Sagan and Lederberg engaged in their research that several planets and moons clearly offer potentially excellent habitats, thanks to abundant liquids on their surfaces or below a layer of ice. The presence there of even the simplest living creatures, or of their fossils from billions of years ago, could provide one of the most significant scientific discoveries of all time.

Acting through billions of years, Darwinian evolution has taken Earth life from its simplest forms to the marvelously intricate biosphere within which we live today. But the actual origin of life—the crucial transition from increasingly complex molecules to the first metabolizing and reproducing entities that we call “alive”—remains a mystery despite the increasing attention that it receives. Because we possess only the single example of Earth life, we remain ignorant of whether we represent a fluke or whether life tends to arise in any environment that meets basic requirements (it remains to be determined what those requirements are, but we could define these as being roughly similar to Earth’s situation). If life has arisen elsewhere, we don’t know whether Earth life’s fundamental DNA / RNA mechanism has such special properties that we should expect to find it elsewhere, or whether extraterrestrial life employs different molecules for metabolism and reproduction.

Perhaps the most exciting advance (so far) in twenty-first-century astronomy resides in the demonstration that the Milky Way, and presumably the entire universe, teems with planets that provide a panoply of possible worlds, differing in their sizes, temperatures, distances from their stars, rotation rates, atmospheric composition, and other properties that affect the likelihood of life upon them. These planets shine so faintly by the light that they reflect from their overpowering parent stars that astronomers must await a generation of more powerful telescopes to analyze that light, even from planets orbiting nearby stars, in sufficient detail to reveal telltale signs of life. Does a planet have land masses and oceans? Does oxygen exist in its atmosphere? Is there evidence for vegetation? As the search progresses, we may hope that biologists will develop other diagnostics to search for life on these worlds. For now, our best hopes for discovering the pivotal second example of life, whose comparison with Earth life could reveal the similarities and differences between two life-bearing worlds, remain within the solar system. The discovery of another form of life that clearly differs from ours in its origin would eliminate the possibility that Earth life represents a rare fluke of nature, and would imply that life in its different forms populates millions and billions of other worlds. The search for extraterrestrial organisms, either living or fossilized, supplies humanity with the best reason—far better than the desire to celebrate human or national achievement—for exploring other objects in the solar system. In this pursuit, the prime target has always been our neighbor Mars, the font of inspiration and fascination for generations of would-be space travelers.

CHAPTER 5

Mars

The moon’s size and brightness make it the most prominent object in the night sky. Mars’s appeal, though subtler, has dominated the attention given to the sun’s family of planets. For millennia, observers around the world followed its complex motions against the backdrop of stars and admired the rust-red color that evoked bloody conflict. Before artificial illumination and electrically based entertainment, these phenomena made an impact on society far beyond today’s earthlight-hampered views of the skies.

Telescopes finally revealed the natures of the sun’s planets. Jupiter and Saturn turned out to be great balls of gas, hardly conducive to imaginary or practical exploration; Mercury revealed a pockmarked surface akin to the moon’s; Venus, similar to the Earth in size and mass, wraps its solid exterior within an eternal opaque shroud. But Mars, which approaches Earth almost as closely as Venus does, has a surface reminiscent of our own continental surfaces, with craters, plains, polar caps, sand dunes, ancient river deltas, and an enormous canyon system that’s often called the Grand Canyon of Mars.

Speculation about life on Earth’s smaller cousin shifted into high gear in 1877, when the Italian astronomer Giovanni Schiaparelli, observing Mars with a modest 8-inch refracting telescope at the Brera Observatory in the heart of Milan, announced that the lighter and darker regions seen on Mars must be oceans and land, and that on the “land” he could see canali.¹ In Italian, canali denotes “channels” that may or may not be artificial, but English translations promptly opted for “canals,” which are definitely not natural features. (To be fair to the translators, Schiaparelli concluded that water from Mars’s polar regions spreads through these channels, offering widespread life a chance to thrive.)

Schiaparelli’s contemporary Camille Flammarion had a lifelong interest in astronomy and psychical research, helped to create the French Astronomical Society, and became the leading popularizer of astronomy in late nineteenth-century France. He wrote more than a dozen books on astronomical topics, plus many more on psychic research and related investigations. In 1892, Flammarion published Mars and Its Habitability Conditions, asserting that Martian canals and seas implied that the planet could be inhabitable by “a race superior to ours.”² Interest in Mars rose even higher after Percival Lowell, from a long-established and distinguished Boston family (his brother was the longtime president of Harvard College and his sister was a famous poet), grew interested in astronomy. Stimulated by Schiaparelli’s observations and Flammarion’s descriptions, Lowell built his own observatory in Flagstaff, Arizona, at the close of the nineteenth century. He purchased a 24-inch refracting telescope from the Alvan Clark firm of Cambridgeport, Massachusetts, which had become the primary American telescope maker by manufacturing the 26-inch refractor for the Naval Observatory in Washington, D.C. In Flagstaff Lowell spent long nights observing Mars through clear skies. He confirmed the existence of Schiaparelli’s canals and traced a still more complex canal network—which, he claimed, must have been built by a Martian civilization in order to bring water from the polar caps to the arid deserts near the equator.³

To bring his discoveries to the public, Lowell wrote four books about Mars with a literary flair that might have reminded readers that his great-uncle had been the first editor of The Atlantic Monthly. He presented his years-long observations as definitive and detailed proof of intelligent beings on Mars: the network of canals, together with Mars’s general suitability as a possible habitat for life, elevated the planet to the prime candidate for finding other beings. Decades later, improved observations demonstrated that Lowell’s (and Schiaparelli’s) canals had been optical illusions, and that Mars’s polar caps, much thinner than Earth’s, consist almost entirely of frozen carbon dioxide (dry ice). Nevertheless, Mars has remained fixed in the public’s mind as the “abode of life” that provided Lowell’s book titles. In the broadest sense, the likelihood of ancient life on a water-rich Mars confirms Lowell’s most fundamental thought: we now search for life on Mars not in its fictional canals but in the river valleys and lakes that dried up billions of years ago, perhaps leaving evidence of long-vanished Martian microbes, or even harboring them underground.

Fiction, as it often does, promptly added to Lowell’s asserted proof. Two years after Lowell’s first book, H. G. Wells’s science fiction novel The War of the Worlds introduced technologically superior Martian invaders of Earth, advancing invincibly until they succumbed to our home-grown bacteria. A decade later, Edgar Rice Burroughs wrote a series of novels in which the hero, John Carter, struggled against monsters on Barsoom, a thinly fictionalized Mars. Burroughs’s series of books inspired a generation of science fiction writers and fascinated a young Carl Sagan, who attributed his early interest in astronomy to them.⁴ One might claim that from Lowell to the present day, dreams about Mars have exerted as much force on our planet’s culture as Mars’s gravity has applied to our orbit. Cartoons rarely feature “moon men” or “Saturnian overlords,” but a host of them have made Martians of various dispositions familiar at a glance.

We now live in an age of Martian exploration that justifies Mars’s starring role in our imaginations, even though we have had to abandon any hope of discovering a Martian civilization or much hope of finding larger-than-microscopic forms of life. The existence of small amounts of water on Mars, the presence of surface temperatures not far below Earth’s, and especially the clear evidence that water flowed in abundance eons ago have combined to stimulate our desire to land on Mars, examine its topography, drill below the soil to search for life underground, test the Martian soil chemically and biologically, spend months or years traversing the hills and valleys on its surface, deploy orbiting spacecraft to map the planet and its two tiny moons, and bring samples of Mars to Earth for analysis in our finest laboratories.

All of these efforts have borne fruit, at least in their preliminary stages. We have achieved amazing successes through the design, creation, launch, safe landing, and years-long maintenance of our marvelous robotic Martian investigators. Half a dozen spacecraft have flown past Mars, and fifteen others have orbited the planet; seven have landed on Mars, and half a dozen rovers have traversed part of the Martian surface. Nearly two dozen spacecraft destined for Mars have failed in their efforts, some on the launch pad, some in interplanetary space, and some on the Martian surface. The first Martian fly-by (1964), the first Martian orbiter (1971), the first Martian landers (1976), and the first Martian rover (1996) testify to our stubbornness and problem-solving abilities in overcoming the obstacles to exploring another planet.

These successes may tend to obscure the most significant obstacle of missions to Mars, especially those that require providing life support to astronauts for months on end: it’s a long way to the red planet. As Mars and Earth orbit the sun, the distance between them varies by a factor of seven, from 35 million miles at their closest up to 250 million miles at their most distant. Reworking a simile provided by John McPhee, if you imagine the Earth-moon distance as a short fingernail clipping, the least Earth-Mars distance will run to your elbow, while the longest will span twice the width of your outstretched arms.⁵ The laws of gravity and planetary dynamics disfavor trips across the shortest path; instead, interplanetary travel to Mars typically covers 300 million miles, even more than the greatest distance to Mars, as the spacecraft swoops outward to overtake the planet. Using our best rocket technology, each journey requires nearly seven months.

These missions to Mars follow a rhythm imposed by the motions of the planets. The planetary lineup that results in minimal rocket fuel requirements recurs at regular intervals, spaced twenty-six months apart. Orbiting the sun at 1 ½ times the Earth’s distance, moving more slowly than Earth in response to the sun’s weaker gravitational force upon it, Mars completes each orbit in 687 days. At intervals of 780 days, Earth overtakes Mars to regain the previous orientation between the planets. The July 2020 launch window allowed three missions to leave Earth for their 300-million-mile journeys that brought them to the red planet six and half months later. These three spacecraft—sent by China, the United Arab Emirates, and the United States and its collaborators—rank as the most capable emissaries ever sent to another world.

From the Japanese space center at Kagoshima, the United Arab Emirates launched the Hope spacecraft, the first interplanetary mission from an Arab country, now in position to spend years in a fairly large orbit that allows it to observe Mars by day and by night. Hope should create the first global weather map of Mars, and will also devote particular attention to Mars’s upper atmosphere, seeking observational data that could help to determine how and why the planet lost much of its primordial atmosphere.

China demonstrated larger aims than Hope. Tianwen-1, its first Mars mission, is also the first from any country to reach the planet with a full trifecta: an orbiter, a lander, and a rover. These automated devices will, by different means, acquire images, subsurface radar measurements, spectroscopic observations, and atmospheric data; the orbiter will also map Mars’s magnetic and gravitational fields. Like the United States, China harbors the desire, and apparently nurtures a plan, to send “taikonauts” (from 太空 tàikong, meaning “space”) to Mars once the country has successfully achieved human exploration of the moon.

NASA sent Perseverance, its most ambitious rover, a notable improvement on both the InSight lander, which landed on Mars in late 2018, and its Curiosity rover, which remains operational nearly a decade after reaching Mars in August 2012. In addition to its weather station, radar system, and array of cameras, Perseverance is testing an apparatus engineered to liberate oxygen molecules from an atmosphere made almost entirely of carbon dioxide—a breakthrough for providing oxygen to astronauts on Mars. The spacecraft also brought along a miniature helicopter named Ingenuity, designed to test whether any such craft can fly in an atmosphere only 1 percent as thick as Earth’s at sea level. Ingenuity’s success lends impetus to the creation of more massive and capable helicopters that could expand our search capabilities many times over, helping to direct rovers toward the most promising locations for close-up inspection and surveying steep terrain, such as crater walls, where no rover can go. (In 2026, NASA plans to launch Dragonfly, a multirotor craft that will fly over Saturn’s moon Titan, where a thick atmosphere makes comparatively massive flying vehicles quite feasible.)

Profiting from the years-long on-site testing of Curiosity’s performance, NASA modified its basic design for Perseverance, which runs on six independently mounted wheels that are larger than Curiosity’s to allow the rover to traverse rough and rocky surfaces. Unlike its predecessor, Perseverance mounts six HazCams, four in the front and two in the rear, to identify hazards that lie in its path, whether ahead or behind. More significant differences appear in the rovers’ artificial brains: Curiosity required guidance from Earth, foot by foot and yard by yard, in order to avoid large rocks, sand dunes, or deep trenches that could have caused damage or left the rover stuck in one place. Perseverance, however, has basic autonomy in its motions in traversing the landscape, stopping at intervals to obtain stereo images that allow it to analyze different pathways, then choosing the best one. Perseverance can therefore follow overall directions from Earth without constantly requiring guidance. This ability foreshadows the creation for later Mars expeditions of truly autonomous robots that will study the landscape and choose the best routes on their own. Onboard “intelligence” and decision-making provide a crucial benefit because a message takes between 3 and 22 minutes to pass from Earth to Mars, depending on their relative positions in orbit. Round-trip communications naturally take twice as long.

For now, controllers at the Jet Propulsion Laboratory make all the larger decisions. In consultation with key scientists, they chose to land Perseverance on the alluvial delta fan in Jezero Crater, judged the best spot to search for fossils of ancient life. If all forms of life require some liquid to support chemical reactions, and if water indeed provides the most abundant and most useful liquid, then the golden rule of exobiology becomes “follow the water.” Perseverance’s front-mounted HazCams allow its controllers to direct its highly capable, seven-foot-long robotic arm, equipped with spectrometers to determine the chemical composition of rocks and soil and a drill to remove samples.

More than forty-five years ago, two Viking landers brought modest laboratories to the Martian surface to look for signs of life. Their ambiguous results, interpreted as positive before being reanalyzed to reach the opposite conclusion, helped to convince those seeking evidence of microscopic extraterrestrial life that the most efficient methods will rely on bringing samples to advanced laboratories on Earth. As Harry McSween, a planetary geoscientist at the University of Tennessee, summarized this plan, samples from a distant world represent “the gift that keeps on giving.”⁶

BRINGING SAMPLES OF MARS TO EARTH

Before examining our hopes of transferring part of Mars to Earth, we should give a nod to nature itself, which continually showers our planet with material from Mars. Thousands of Martian meteorites weighing more than a few grams each reach the Earth every year; a much smaller number have weights measured in kilograms (a United States pound equals 454 grams). The Viking landers’ measurements of slightly different element abundance ratios between Mars and Earth rocks allows us to determine which meteorites originated on Mars. The famous Martian meteorite known as ALH84001, or “the rock from Mars,” stunned the world when it seemed to contain fossilized evidence of tiny, long-vanished life-forms. Although this turned out not to be so, we may yet discover at least extinct Martian life from discoveries made on our own planet.

Martian meteorites found on Earth provide an extreme example of the correct approach to finding microscopic or extinct forms of life on Mars: choose the most promising samples and bring them to Earth for study in our finest laboratories. Decades will pass before we can construct anything similar a hundred million miles away; meanwhile, with care and luck, a few pounds of Martian material could reveal the secrets of Martian biology.

When may we expect to have carefully chosen samples of Mars safely in terrestrial laboratories? Perseverance carries forty-three sample tubes, with a system to load soil into each one (keeping four empty for comparison), tamp it down with a ramrod, and essentially weld the tube shut to create the hermetic seal required for a long wait on Mars. In collaboration with the European Space Agency, NASA has created the Mars Sample Return Mission, designed to locate the sample capsules, load them for interplanetary transfer, and carry them to Earth.⁷ The mission plan involves the transport of Perseverance’s samples to a NASA-built Mars Ascent Vehicle to lift them into orbit around Mars. An ESA-built Earth Return Orbiter would meet the NASA bus, place the samples into a secure compartment, and bring them to Earth at some point in the 2030s. The Mars Sample Return endeavor would mark a crucial stage in our exploration of the solar system, capable of revealing some of the history of ancient life on Mars—provided that this history lies within the rocks of Jezero, as most experts believe is likely.

HUMAN AND AUTOMATED EXPLORERS ON MARS

The advantages that human explorers now hold over robots will continue to diminish as advances in AI and technology increase the robots’ abilities. Future breakthroughs in artificial intelligence could lead to self-guided Martian robots that would follow general instructions while performing the same tasks that human explorers would. We may use Perseverance’s success on Mars to analyze the issue of how astronauts on Mars would improve the situation. What would change if we replaced a fully automated investigation with one with on-site humans? To take sample return as an example, the tasks involved include reaching Mars, choosing the best locations to sample, drilling into the rocks or soil at those locations, extracting material and sealing it for study, bringing the material to Earth, and examining the samples with the instruments best suited to that task. For all of these except the choice of drilling locations, robots rather than humans can perform more safely, more easily, and less expensively. They cannot match the brain of an experienced geologist—for now. Although our robots will continue to increase their artificial intelligence, no one knows when, if ever, they can match us humans, though we must beware of a bias in assessing our own proficiency.

As we’ve noted, for some people the idea of having humans on the ground provides the paramount reason for space exploration. In that context, the history of our efforts to study Mars appears as a sixty-year prelude to the epoch when humans reach Mars and colonize it. Marvelous though this era will be, the issue discussed throughout this book remains not whether we want it as soon as possible but whether we need it as soon as possible. Consider this heartfelt exclamation from Jeffrey Hoffman, one of the scientist-astronauts who repaired the Hubble Space Telescope. After five missions in space, Hoffman has no hesitation in saying, “I want to know what it’s like being on Mars!” For those of us who are not going there, the desire to put humans on Mars resides not in our own journey but in relishing the views and news from those who do reach the planet. Hoffman himself summarizes the robot / human issue by saying, “If it can be done robotically, do it.”⁸

The scientific rationale for sending astronauts to Mars centers on the expectation that the long experience and human flexibility of scientifically trained astronauts will allow them to search through new locales and to discern special, perhaps unexpected features far more rapidly than any robot can. Steve Swanson, who flew twice on the space shuttle and once to the International Space Station, points to the fact that Apollo 17’s astronauts covered twenty-two miles on the moon in three days, while the Curiosity rover on Mars traveled about twelve miles in more than six years.⁹ Quite so—but Perseverance will cover Martian ground far more rapidly, and its successors will do still better. The same objection applies to the statement that Steve Squyres, one of the chief scientists for Curiosity’s predecessors, Spirit and Opportunity, made in 2005: “The unfortunate truth is that most things our rovers can do in a perfect sol [one Martian day of 24 hours and 37 minutes], a human explorer on the scene could do in less than a minute.”¹⁰ In 2009, Squyres left academia to become the chief scientist at Jeff Bezos’s Blue Origin corporation, which plans to land cargo on the moon by 2023, and astronauts a year later.

Chris McKay, one of the leading astrobiologists involved in planning future missions to Mars, has spent years in the Arctic and Antarctic to study life under conditions as close to those on Mars as Earth offers. When will robots on Mars have abilities equal to those of a human field scientist? Not on the horizon, McKay says. What about abilities equal to those of a capable field assistant? That would require our robots’ current capabilities to be doubled at least five times, he thinks; he notes that at present each doubling requires more than a decade, “but innovations in the space biz may greatly shorten that.”¹¹

Those who want to make the strongest scientific case for astronauts on Mars should rely on McKay’s judgment to argue that in order to obtain the best result, we must send our best investigators: humans. The issue then becomes one of how much we are willing to pay for the advantages that humans can provide. Those who favor robots could stress that as more time elapses, the advantage humans hold over robots will continue to decline, eventually to the point that the scientific argument for astronauts disappears. Meanwhile, public enthusiasm for sending astronauts to Mars will persist, not so much because of the superiority of human geologists but instead because of the belief that we ought to go there.

THE HAZARDS OF TRAVEL TO MARS

One of the many reasons (though not the primary one) that we remain far from the day when we may launch astronauts to Mars is the dangers of interplanetary travel. As we’ve seen, if we use our best rocket technology and launch a spacecraft during the window for the best interplanetary lineup, it takes at least six months to travel to Mars. This interval, longer than a journey to the moon by a factor of fifty, reflects the impressively greater distances to even the closest planets. This fifty-fold increase roughly corresponds to the increase in the risks of a voyage to Mars over a trip to the moon.

The challenges of space travel discussed in Chapter 3 began with the effects of weightlessness: the initial problems of nausea and disorientation, followed by changes in human organs, especially the brain, heart, and central nervous system, that arise from long periods in the absence of gravity. Experience on the ISS has shown how to overcome these problems in part, though the long-term effects remain significant and still partially unknown. As the length of exposure beyond the atmosphere increases, however, the possibility of serious damage from radiation rather than from weightlessness tends to dominate the balance sheet of risks.

Radiation that poses a threat to long journeys through interplanetary space falls into three basic categories, as discussed in Chapter 3: constant solar wind particles, sudden fluxes of much higher-energy particles from the sun’s coronal mass ejections (CMEs), and a continuous flow of cosmic ray particles from the cosmos. As we saw when assessing hazards to astronauts in near-Earth orbit, the more damaging, higher-energy particles in the solar wind and cosmic rays tend to be rarer. The same analysis applies to interplanetary journeys: longer trajectories carry increased risks.

Marco Durante, a leading biophysicist who studies radiation damage, summarizes the effects of the regular flow of solar wind and cosmic ray particles: “One day in space is the equivalent of the radiation received on Earth for a whole year.”¹² Recent data indicate that an astronaut spending six months on the way to Mars would receive at least 60 percent of the total radiation dose recommended for a full career.¹³ Time on Mars plus a return trip would push this over the recommended limit, even without any sudden increase from solar storms or flares. As described in Chapter 3, astronauts in near-Earth orbit would have options to return to safety or to find shelter from heavyweight material lofted into space. For astronauts on the way to Mars, however, such shielding would raise the mass of a spacecraft significantly, and design limitations might mean that a spacecraft’s emergency shelter would have to be so small as to be barely tolerable.

Humans have always demonstrated a creative approach to problem-solving. The data derived from the experiences of astronauts on the International Space Station and after their return, together with continuing measurements of the numbers and energies of particles from CMEs, should eventually reveal accurate parameters for the hazards that would need to be overcome on any journey to Mars. Nuclear-powered rockets could cut the travel time to Mars in half, once they exist; in 2019, NASA allocated a modest $125 million toward their development, and it seems unlikely that we may have a working system before the mid-2030s at the earliest. Any journeys to the giant planets of the outer solar system would require such rockets.

Astronauts who travel to Mars face serious health risks from the time spent on long journeys to and from the planet, as well as on the Martian surface, which offers no atmospheric protection against solar and cosmic radiation. In 2013, a study by experts in space medicine stated that “using NASA’s models of risks and uncertainties, we predicted that the central estimates for radiation induced mortality and morbidity could exceed 5% and 10% with upper 95% [confidence intervals] near 10% and 20%, respectively, for a Mars mission.” Furthermore, “additional risks to the central nervous system (CNS) and qualitative differences in the biological effects of [galactic cosmic radiation] compared to terrestrial radiation may significantly increase these estimates, and will require new knowledge to evaluate.”¹⁴ In view of these sizable numbers, the key to travel to Mars despite these hazards could reside in the fact that some of us have a greater willingness to assume risks. One possibility would be to favor older astronauts, whose shorter remaining lifetimes reduce the time interval in which they might develop cancer or other afflictions. Some astronauts might simply decide that it’s worth the risk to make the journey to Mars, and some might be happy to travel to Mars and not return. The issue of risk seems destined to become central in a discussion of how and when to send the first humans to Mars.

MARS HABITATS

The concepts developed for planting humans on the moon for long-term stays also applies to Mars if we make key modifications that deal with the different natures of these objects. Colonizers’ basic needs can be met in part on the Martian surface, which will furnish various materials for building habitats. Its soil, so far as we know, contains little or no water, but as we have seen, there is evidence of water in a few areas, though the amounts are unknown. The thin Martian atmosphere provides a surface pressure equal to only 1 percent of that on Earth. Most of the atmosphere consists of carbon dioxide, with a 1 percent admixture of oxygen molecules and a tiny amount of water vapor. The polar caps are likewise mainly frozen carbon dioxide, but even if they are 1 percent water ice, that would total to significant supplies of this essential component of life. The low temperatures at the poles imply that astronauts would require a source of heat as well as supplies of food and oxygen.

With sufficient water and covered interior spaces, plus a source of energy for heating, astronauts could grow crops bionically, using solar energy as in a terrestrial greenhouse. Viewers of the 2015 film The Martian will recall that the most productive crops—potatoes, for instance—could keep astronauts alive. Plants in these Martian greenhouses could raise the oxygen level, eventually allowing continued habitation without the import of oxygen from Earth. One serious problem with this plan turns out to be the Martian soil, because experiments have shown that test plants—lettuce and the weed called Arabidopsis thaliana—cannot grow in synthetic Martian soil made from the components that NASA’s rovers and orbiters have discovered on Mars.¹⁵ After all, terrestrial soil has become rich in microbes and organic matter that promote growth, while Martian soil appears to be crushed rock. We might eventually find ways to make Martian soil amenable to terrestrial organisms, a task that could vary from location to location, but as the geochemist Laura Fackrell has summarized the situation, “It’s not quite as easy as it looks in The Martian.”¹⁶

To enthusiasts of human exploration and colonization on Mars, tasks such as improving Martian soil could well fall to hardworking robots, fundamentally there to support a continuing human presence on Mars. Future colonists would explore the red planet in detail; they would provide a key base for exploration of the worlds much farther from the sun and the Earth; and, in some visions, their population could eventually increase to a society of millions of people on a neighbor planet.

HOW CAN WE PROTECT OURSELVES FROM MARS, AND MARS FROM US?

Today no one doubts that there is a possibility—which some scientists would describe as a likelihood—of finding life on our planetary neighbor, nestling close to the water that percolates in small degrees at certain sites. Astronomers once judged Mars entirely lacking in water, except for small, transitory amounts at the fringes of the polar caps. Today, however, we observe rivulets of water—likewise transitory, to be sure—that pour over the edges of Martian craters. Most Mars experts believe that in many places, the Martian subsoil contains significant amounts of water. The Perseverance rover is presently exploring Jezero, a thirty-mile-wide crater whose topography identifies it as a former lake, fully filled with water 3.5 billion years ago. Lake Jezero may have borne hosts of flourishing organisms, whose descendants or fossils await our interest. Far better to examine them without muddying the waters, literally and metaphorically, by disturbing their calm existence either physically or biologically. Still better would be not to bring any home that could produce, in an outcome as unlikely as it would be unwelcome, a pandemic fatal to much of the life on Earth.

If we find rocks that may have lain on the bottom of long-vanished Martian lakes, bring them to Earth, crack them open, find bacteria inside, and discover that their DNA matches ours, what should we conclude? If we can rule out pollution, the conclusion follows that life has long existed on Mars, and that in the distant past, life-forms traveled from Earth to Mars, or from Mars to Earth, or from a third object to both Earth and Mars. But if we cannot be sure whether the bacteria in Mars rocks made their journey millions of years ago or only a few years earlier because of equipment that we humans brought to the planet, the confidence that we place in our conclusion shrinks drastically. Biologists could argue about the likelihood that bacteria could find their way into rocks only a few years after they landed on Mars; they could discuss the similarities and differences between terrestrial and Martian bacteria that could determine the possibility of interplanetary identity. What’s clear is that pollution by Earth life obviously and inevitably complicates any analysis of living organisms discovered beyond the Earth. Just as clearly, the prevention of such pollution presents a far greater challenge when a human expedition rather than a robotic explorer investigates Mars or any other planet.

Even the most modest exploratory missions necessarily bring a host of organisms from our planet. Fully aware of this fact, NASA and its partners, as we have seen, make significant attempts to sterilize spacecraft sent to the moon, the planets, and the asteroids. Their scientists know that even our best attempts cannot send completely organism-free probes to land on other solar-system objects. As we can easily perceive, the sterilization issue grows many times more difficult with spacecraft that allow humans to disembark, and many times more than that with colonies established for the long term.¹⁷

Why should this pose a serious obstacle? Leaving aside the moral issue of altering alien environments in ways that prevent them from ever regaining their pristine state, the most obvious problem arises in alien biology. One of the greatest motivations for exploring the solar system has always been the search for extraterrestrial life, either in fossil form or, far more appealing, in actual, thriving existence. On the moon or on the surface of asteroids, the prospects for finding life appear dim. Even there, however, we would be mistaken to assign a probability of zero to these chances. In addition, geologists would quickly point out a similar problem with rocks: once we begin to rip up a celestial object’s surface, the geological record there suffers, at first only a bit, but then more and more as we increase our activities.

Nevertheless, biology deserves the most attention. If we ever do find life on Mars, the most fundamental and significant question will be whether or not Martian life differs from Earth life. The difference or similarity would appear at the genetic level. If, for example, Martian life was found to use the same sort of DNA and RNA molecules, and in the same way, as we find on Earth, we would reasonably conclude that life did not arise independently on these two planets, but instead transferred itself from one planet to the other. But could we be sure that this transfer did not occur quite recently because we brought the “Martian” organisms with us? The more biological material we deposit on the planet, the greater this uncertainty will become. Only the hope that any life-forms on Mars either went extinct billions of years ago or have biological systems so different from Earth’s that confusion will never be likely can overcome this worry.

For all these reasons, the key question first raised in Chapter 3—could Earth life be unique?—cannot be settled by investigations on Mars unless and until we find life-forms there that are governed by a chemistry fundamentally different from that used by life on Earth. If we can’t do this, our search will turn toward the outer solar system, whose worlds, especially the most promising moons of Jupiter and Saturn, lie much farther from Earth than Mars, making the transmission of Earth life less likely—and exploration more difficult. The next stage on this front should come from the European Space Agency’s Jupiter Icy Moons Explorer (JUICE) mission, scheduled for launch in mid-2022.¹⁸

TERRAFORMING MARS

By the end of this century, a technologically reasonable projection foresees a human settlement on Mars, analogous in structure and functions to our current installation at the South Pole, though operating under much harsher circumstances. Some enthusiasts regard this as a preliminary stage in a grand, planetary-scale project to turn Mars into a planet more hospitable to human habitation, potentially capable of supporting a population equal to Earth’s. Although Mars has barely more than half the Earth’s diameter, its lack of oceans gives the red planet a total land area almost equal to Earth’s, so some may claim that the planet offers equal potential for maintaining a human population. Some envision “terraforming” Mars, transforming its environment into a near-duplicate of Earth’s. The crucial first step in this planet-wide engineering feat would give the planet a much thicker atmosphere by vaporizing the small amounts of water and much larger amounts of carbon dioxide that currently lie frozen within the polar caps. As we’ve seen, the surface atmospheric pressure on Mars is less than 1 percent of that on Earth’s surface, too low to allow liquid water to exist; any temporarily liquid water would promptly evaporate, and water ice would sublimate directly into water vapor without passing through a liquid state. By introducing, with considerable effort—and some irony, given humans’ role in climate change on Earth—sufficient quantities of heat-trapping gases or dust into the Martian atmosphere, we could alter the planet’s atmosphere enough to make liquid water possible there once again.¹⁹

Mars could then have lakes and streams, along with a cycle of evaporation and condensation that would mimic the long-vanished Martian past, whose running water and large pools have left clear markings to be read and interpreted billions of years later. Visionaries who look still farther into the future imagine growing enormous numbers of plants, which, after five hundred or a thousand years, could make the Martian atmosphere rich in oxygen. At that stage, Mars would resemble the Earth, offering (some advocates claim) potential refuge if terrestrial living becomes unsupportable. Both Jeff Bezos and Elon Musk have seriously advocated a future in which Mars supports an autonomous human society that numbers not in the thousands but in the millions. These innovative visions also embrace, and sometimes conflict with, concepts of giant, free-floating space colonies that could likewise serve as refuges for a time when Earth’s environment no longer works for us. A counterargument asserts that if we cannot solve the problems that we have created on Earth, we shall never do so by starting over. In any case, the project of implementing effective measures to stabilize Earth’s climate and biosphere so that the planet remains suitable for life is far less difficult than terraforming an entire planet to create an ecosystem from scratch. This comparison will appear again when we critique the possibility of space colonization in Chapter 7.

Here’s a straightforward challenge to those who dream of terraforming Mars: can you make a “Biosphere 3” that succeeds on Earth? Biosphere 2, a privately funded research station in the Arizona desert, aimed to create a self-contained biosphere, a precursor of colonies on Mars or in space, within which eight humans would live for two years without outside assistance, amid an agricultural area, grasslands, wetlands, and a rain forest. Two attempts during the early 1990s ended in failure that arose from diverse, simultaneous problems, including agricultural and atmospheric collapse as well as interpersonal difficulties.²⁰ Some of these were on the way to being overcome when the most serious problem of all—a cutoff in funding—terminated the project. Although the precise interpretation of Biosphere 2’s results remains controversial, an excellent concept to implement before setting out to create a viable, self-contained colony on Mars would be the creation of such a self-contained colony that can flourish on Earth. The larger issue, of course, is what human activity has already done to the Earth as a whole. The strongest argument against terraforming Mars remains the fact that we are doing a poor job of terraforming Earth.

A more modest, though potent, objection to terraforming Mars rests on the same grounds as the argument against Martian colonization in general: we don’t need to do it. All plans to change an entire planet necessarily involve wholesale contamination of another world. We would destroy our chances to examine in detail the conditions that have prevailed on Mars for billions of years, and quite possibly the clues to ancient life and its demise there. Furthermore, given human fallibility, we might not only ruin the “old” Mars but also fail in creating a successful “new” Mars.

VENUS

If the prospect of terraforming Mars is dubious, would other planets lend themselves to this concept more effectively? The scientist-astronaut John Grunsfeld has suggested that we consider Earth’s oft-neglected near-twin, the planet Venus.²¹ Much larger than Mars, Venus suffers both in the public mind and in considerations of human habitation from its thick, stifling, carbon-dioxide atmosphere, laced with sulfuric acid and other compounds that render the atmosphere opaque and allow its “greenhouse effect” to raise the planet’s surface temperature above 800 degrees Fahrenheit. Grunsfeld notes that if we introduced bacteria that could metabolize molecules made of hydrogen and sulfur, we could reduce Venus’s atmospheric opacity, allowing heat to escape more efficiently and thus cooling the planet’s surface to a possibly bearable temperature. This project would, of course, face the same technological and moral obstacles as the terraforming of Mars.

THE BODILY EXPERIENCE OF PLANETARY EXPLORATION

Let us for now set aside grandiose projects of modifying entire planets and return to a more basic question: how badly do we want to see humans on Mars? If you want to assess the strength of your own desire, try the following approach. Imagine that advances in technology could produce a superior form of virtual reality that would allow you to transport your senses to Mars, so that you could feel yourself walking on its surface, feeling the light Martian breezes, watching the sun set over Olympus Mons or Tharsis Tholus, or admiring temporary rivulets at the edge of the ice cap at the South Pole. How less satisfactory would this be than traveling to Mars in your actual body? And how much more important would it be for astronauts to reach Mars in person rather than by this advanced application of virtual exploration? If you believe that in-person exploration could reveal more than virtual exploration, you have judged that we need astronauts. But if you believe that we’re not really exploring Mars if we only do it virtually, then your stance reflects primarily your desire to see them on Mars.

Honesty compels us to admit that this type of virtual reality probably could never occur, not least because of the many minutes required for any transmission between Earth and Mars. But try the mental experiment not with Mars but with Mount Everest: how different would it be for you to experience everything that a climber does without being physically present on the mountain?

“Mars ain’t the kind of place to raise your kids,” Elton John famously sang in his song “Rocket Man.”²² A lot of people who want to see human settlement on our neighbor planet think he’s wrong. And yes, exploring Mars—understanding its geology, searching for traces of ancient life and for possible existing life in places where liquid water exists, uncovering Mars’s history and how it fits into the origin and evolution of the solar system, flying drones that can map the entire surface of the planet and discover individual locations of intense interest—is a marvelous goal that fascinates all of us. But to achieve this, we don’t need astronauts, whose presence inevitably degrades their surroundings—something that is of special concern if we hope to be sure that any life-forms we may discover are indeed Martian. When we send our ever-improved robots there, they confirm that we are indeed on Mars—not individual humans, but all of us, the earthly species that has the ability to explore another planet in an efficient and ecologically sound manner.

CHAPTER 6

Asteroids

Far beyond Mars, more than a third of the way from there to Jupiter, a swarm of smaller objects, forged as part of the solar system 4.6 billion years ago, continue to orbit the sun in the same direction that the planets do. As the solar system formed from interstellar gas and dust, Jupiter’s powerful gravitational force disrupted these objects’ tendency to create another planet. Today the fragments of this would-be planet have diameters that range from 600 miles for Ceres, the largest asteroid, to much less than a single mile. The self-gravitational forces within each of the largest asteroids pulled them into a nearly spherical configuration, but the smaller asteroids have random shapes. The distribution of asteroid sizes follows a pattern recurring in nature: the smaller the size, the more of them that exist. Fewer than a hundred asteroids have diameters greater than 100 miles, but a million or more exceed half a mile across.¹

A striking difference exists between public attitudes about astronauts on Mars and astronauts on asteroids. Although asteroids teem with mineral wealth and offer comparatively easy access because of their modest gravitational wells, you will wait a long time before anyone brings asteroids into a conversation about solar-system exploration, and even longer before you hear anyone insist that astronauts rather than robots should explore or exploit them. If they orbited between Earth and Mars, rather than between Mars and Jupiter, the importance of sending astronauts to explore the asteroids might provoke a serious debate. Instead, rousing an argument over this issue can prove difficult, even among those with a lively interest in these objects.

Part of this lack of interest arises from their distance to us. The hundred largest asteroids move in orbits 85 percent larger than Mars’s, and remain correspondingly more distant from us than the red planet does. An important minority of the smaller asteroids, however, have orbits that carry them much closer to the sun than the big ones, the result of perturbations by Jupiter as well as their mutual close encounters. Because some of their orbits cross the Earth’s, it’s possible that some of these smaller ones could collide with our planet. Sixty-six million years ago, a six-mile-wide asteroid collided with the Yucatán peninsula. The impact raised an enormous cloud of planet-girdling atmospheric debris, blocking the sun and settling to earth only over many months. The demise of dinosaurs, which occurred during the same epoch, may have been spurred by this event. Astronomers now seek to identify and follow the larger Earth-crossing asteroids carefully, though the odds that a catastrophic impact will occur during the next few millennia are very low—for example, astronomers assign a 1-in-2700 chance that the 500-yard-wide asteroid Bennu will strike the Earth during the last quarter of the twenty-second century.

Asteroids rank among the least altered objects in the solar system, unchanged by any geological processes over billions of years (except perhaps for the very largest asteroids) and comparatively unaffected by bombardment from the particles in the solar wind. Their surfaces, and still more their interiors, incorporate a pristine record of how the solar system formed. The moon’s cratered surface likewise carries a multibillion-year history of bombardment in our solar system neighborhood, including several giant impacts soon after the asteroids formed that created the lava lakes that froze to become the lunar “seas.” With their deep interiors more readily accessible than the moon’s, asteroids offer an easier route for uncovering the early history of how the solar system’s objects formed.

BRINGING SAMPLES TO EARTH: ITOKAWA AND BENNU

With far less fanfare than landing a rocket on Mars, the worldwide astronomical community has accomplished the first returns to Earth of material from asteroids—not from the larger, main-belt asteroids, but from two small Earth-crossing asteroids, Itokawa and Bennu. The comparative proximity of this duo, together with their small sizes and masses, which allowed easy approach and escape, made them excellent targets for these historic missions, the first to secure material from any objects beyond the moon.

In 2005, the Japanese Aerospace Exploration Agency brought its automated spacecraft Hayabusa into a matching orbit with Itokawa, a peanut-shaped object about a thousand feet long.² Itokawa is aptly described as a “rubble pile,” since it consists of rocks and boulders of various sizes that are only loosely held together. The probe landed briefly and collected some 1500 dust particles. After Hayabusa’s return to Earth in 2010, laboratory analysis showed that Itokawa’s composition resembles that of terrestrial rocks made mostly of silicon and oxygen, with a significant amount of water. In fact, asteroids like this one may have played a significant role in bringing water to Earth soon after our planet formed.

The second and more ambitious asteroid investigation bears the provocative acronym OSIRIS-REx (for Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer)—a deliberate and slightly clumsy match to the name of ancient Egypt’s god of fertility and resurrection.³ The spacecraft’s name refers to its ability to analyze light reflected from the asteroid’s surface (spectral interpretation) to determine its composition (resource identification), and to secure a sample from its regolith—the rock, rock fragments, and dust on its surface—for transport to Earth, where laboratory analysis can reveal the clues that the regolith offers about the details of the solar system’s formation.

Two key characteristics led NASA to choose Bennu as OSIRIS-REx’s target: its composition and its comparatively close approach to Earth. Bennu belongs to a small class of asteroids known as carbonaceous chondrites, objects rich in carbon and laced with tiny mineral grains called chondrules. Years of studying carbonaceous chondrite meteorites have shown that they contain the most primitive material in the solar system, barely altered through the past 4.6 billion years. These relics apparently once formed part of a sizable object, a planet-in-formation that shattered during the earliest years of our system’s history. Many carbonaceous chondrites contain amino acids, the small molecules that in Earth life collectively form much larger protein molecules, raising the possibility that life itself may have arisen in some of them.

Bennu, a roughly spherical object 1,600 feet in diameter, resembles an enormous carbonaceous chondrite meteoroid. However, Bennu has not been altered, as meteorites are, by high-speed passage through the Earth’s atmosphere, and its large size implies an interior structure far more complex than that within a meteorite. In September 2016, NASA commanded OSIRIS-REx to perform a series of complicated orbital maneuvers that brought it to Bennu twenty-seven months later. Throughout the following year, geologists studied the asteroid’s surface and chose a site to deploy the mechanism to procure a sample, which the spacecraft obtained in October 2020. Some material spilled out of the sampler head when its flap failed to close perfectly, but NASA confidently announced that more than a pound of Bennu is heading our way along a complex path that will carry it to us in September 2023, seven years after the spacecraft left the Earth.

BEYOND SCIENCE: WEALTH FROM ASTEROIDS

Beyond the successes of scientific investigation, certain asteroids command wide attention for the mineral wealth they contain, capable of inspiring dreams of wealth far beyond the appeal of simple avarice. Which ones? Not the largest ones, nor the great majority of the smaller ones, which almost certainly consist mostly rock with some metal ores mixed in. If space habitats become common, these asteroids could provide building material, as well as a supply of water from the ice frozen within their rocks. A minority among all asteroids, however, consist almost entirely of metal: not only iron or copper, but also more valuable elements such as platinum, plus many others essential in modern technology.⁴

These objects owe their metal-rich composition to their small sizes. Larger solar system objects, including the Earth, became differentiated as their internal plasticity allowed heavier elements to sink toward their centers, producing metal-rich inner regions and metal-poor outer regions. Asteroids seen as the richest potential prizes are the undifferentiated, metal-rich objects in the class of near-earth asteroids (NEAs), defined as asteroids that come comparatively close to Earth. Some NEAs may contain platinum at a concentration ten or twenty times higher than the richest platinum mines in South Africa.

Consider the asteroid Nereus, also known to astronomers as asteroid 4660. Roughly similar to Bennu in size, Nereus’s somewhat elongated shape gives it dimensions of 500 by 320 by 320 yards. From the way it reflects sunlight, astronomers have concluded that the mineral enstatite apparently forms the bulk of Nereus. Made mainly of silicon, oxygen, and magnesium, enstatite roughly resembles silicate rocks on Earth. Its high magnesium content offers significant value, with still greater benefit implied by the fact that on Earth magnesium often appears in conjunction with a host of less abundant elements such as manganese, cobalt, silver, and gold, together with less familiar and still rarer elements: molybdenum, osmium, platinum, tungsten, ruthenium, rhenium, and—currently the most valuable of all—palladium and rhodium, essential for automobiles’ catalytic converters.

Although the need for catalytic converters may soon vanish as electric vehicles become more dominant, modern civilization has developed a need for a wide variety of rare-earth elements with haunting names: praseodymium, promethium, erbium, terbium, cerium, yttrium, ytterbium, dysprosium, gadolinium, lanthanum, holmium, and neodymium. Without these elements, we would lack current models of computer hard drives, lithium-ion batteries, high-power magnets, smartphones, digital cameras, nuclear-reactor control rods, hybrid-car batteries, wind turbines, jet engines, solar panels, steel alloys, and a host of other modern conveniences. Some of these elements are mined on Earth only in dangerous locales, or in countries—China, for instance—that could shut off supplies at a moment’s notice. An asteroid rich in many of these elements—or even just a few of them—would represent a bonanza greater than anything from the gold found long ago in California and Alaska.

We may usefully compare Nereus with the largest discovered ore body in North America, discovered near Timmins, Ontario, in 1963.⁵ This deposit, roughly the same size as Nereus, contained about 30 million tons of material, including more than 12,000 tons of silver and more than 60 million ounces of gold. At current valuations (close to $1,800 per ounce for gold), the Timmins deposit held more than $100 billion of once-buried wealth.

All this and more resides in mineral-rich asteroids such as Nereus. In 2015, the futurist engineer Peter Diamandis predicted that the first trillionaire will be made in space.⁶ A year later, Neil deGrasse Tyson agreed: “It is likely that the first trillionaire will be the person who exploits the mineral resources of asteroids.”⁷ Two years after that, Senator Ted Cruz boldly stated, “I predict the first trillionaire will be made in space.”⁸ (But we could see the world’s first trillionaire well before anyone deploys a crewed mission to the moon, Mars, or an asteroid—a mere fivefold increase in Elon Musk’s or Jeff Bezos’s net wealth could take one of them over the trillion-dollar threshold.)

Less than forty years from now, in 2060, Nereus will approach within 750,000 miles—only about three times the moon’s distance—of our planet. For those seeking useful material for use elsewhere—for instance, to construct enormous structures in free space—Nereus possesses an additional advantage over the moon, and indeed over any sizable moon of another planet. These much larger objects have correspondingly deep gravitational wells that require large amounts of energy to remove any material from their surfaces. Nereus has a tiny well: its gravitational force upon objects on its surface equals only 1 / 3000 of the moon’s force on objects there. Mining operations on Nereus would require only modest amounts of energy to fling material into space.

FARTHER OUT: MINING THE MAIN-BELT ASTEROIDS

Those whose dreams carry them beyond the comparatively small Earth-crossing asteroids turn toward asteroids such as Psyche, a typical main-belt asteroid that forever remains at least a hundred times farther from Earth than Nereus. One of the dozen largest asteroids, but too small to pull itself into a spherical shape as the planets have done, Psyche measures 173, 144, or 117 miles across, depending on what axis one chooses as its diameter. This asteroid’s appeal stems from its rank as the largest object in the solar system made mostly of metal; perhaps once, 4 ½ billion years ago, it was the core of a potential planet that could never grow larger. Spectroscopic analysis shows that Psyche consists mainly of iron and nickel, as well as some associated elements. Psyche contains 20 million times more raw material than Nereus, offering the chance to reap enormous economic benefits. In orbiting the sun, Psyche follows an elongated path that keeps it 2.5 to 3.3 times farther from the sun than we are, so the distances over which we would bring material from Psyche to Earth span many hundreds of millions of miles. As shown in Chapter 2, additional distance requires more time, but not necessarily much more energy, so automated spacecraft for transferring wealth-bearing ore from Psyche to Earth seem likely to be a good choice.

Which of these prospects for obtaining asteroid-borne wealth seem capable of realization in the near future? Both governmental and private groups have studied the feasibility of securing this stuff that dreams are made on, initially from near-Earth asteroids and later from the much larger main-belt asteroids. In 2013 NASA initiated the Asteroid Redirect Mission (ARM), a program to develop an automated spacecraft that would remove a large boulder, laden with valuable ore, from a near-Earth asteroid. The plan also envisioned developing spacecraft able to manipulate part or all of an asteroid into an orbit around the Earth. Even a modest asteroid some 25 feet across could include a thousand tons of valuable ore from the birth of the solar system. But, as has happened before with other NASA programs, ARM was cancelled in 2017, leaving this project on hold for the time being.⁹

In the same year that NASA created ARM, private asteroid mining took a step forward in planning with the formation of Deep Space Industries (DSI), a privately held corporation aiming to create a robotic probe to test the technology required for asteroid mining.¹⁰ Headquartered in Luxembourg, which seems eager to become the center of the asteroid mining industry, DSI planned to develop its own automated vehicle to leave near-Earth orbit to visit near-Earth asteroids and secure some of their material. The company enjoyed a good run of publicity until its acquisition in 2019 by Bradford Industries, which announced that it would concentrate on space propulsion systems rather than asteroid mining. A few months earlier, Planetary Resources, a United States company founded in 2009 to create a trillion-dollar business in asteroid mining, became part of ConsenSys, which focuses primarily on bringing blockchain technology into space, presumably to avoid all governmental interference.¹¹ During the previous decade, Planetary Resources had deployed significant amounts of capital obtained from venture-capital luminaries such as Charles Simonyi (the only one of the seven wealthy individuals who have paid for trips to the International Space Station to have made two visits) and the founders of Google in order to launch two experimental satellites to search for the most promising asteroids. The failure to secure additional funding led to the company’s sale to ConsenSys.

GOLD RUSH 2049?

Although NASA and the companies just described have abandoned their plans for asteroid mining and asteroid retrieval, we may expect that future decades will see similar and more expansive plans to extract value from the primordial rock piles of the solar system. For now, as these plans remain in incubation, we may identify key differences from and resemblances to plans to send humans to Mars.

First, as noted at the start of this chapter, a vast chasm in public opinion distinguishes Mars from the asteroids. Plans to explore Mars only with robots fail to appeal to large segments of the population, whose desires have been stoked by visual imagery in films and continual reminders that Mars beckons as the next natural goal of our celestial journeys. In stark contrast, the public’s interest in mining asteroids remains minimal, starting with the fact that most people cannot describe the nature or location of these objects. Debates as to whether humans or robots provide the better means of exploiting the riches that some asteroids hold may eventually seize public attention, but for now, only a few among us have a strong opinion.

Those who do, however, tilt toward regarding humans who mine asteroids as exemplars of our species’s ability to conquer new worlds and gain value from them. The natural analogy on Earth, the colonization of the Americas and Australia by Europeans, provides an example of the benefits and drawbacks of a rapid rush for gain.

In science fiction, and potentially in the actual future, the initial human miners on asteroids would constitute a hardy bunch of misfits who would create a loosely organized society reminiscent of California, Australia, or Alaska during the nineteenth century. Space forces from different countries, or mercenaries hired by giant corporations, could vie for the figurative and literal gold contained within the host of asteroids. We can imagine the more powerful groups happily perched on the most remunerative sites, with their lesser rivals relegated to worlds with less metal and more rock. On at least the larger asteroids, the earliest robot explorers would be superseded by well-equipped, highly skilled humans guiding powerful, specialized machinery to extract minerals, prepare them for shipment, and direct them into spacecraft that will carry them to where they are needed.

Although such activities might seem dangerous only to those engaged in them, the same fact that promotes mining on asteroids—their modest gravitational wells—also allows the easy escape of dust and debris, or, even worse, the deliberate discard of the tailings from mining operations into space. The side effects may be acceptable for mining on the main-belt asteroids, but on those made attractive by their comparatively close approach to Earth, where our planet’s gravity exerts considerable force, some of the waste could affect activities in near-Earth orbit. In an extreme case, mining that involves explosive charges could change a small asteroid’s orbit, increasing the possibility of a collision with our home planet.

In addition to the risk of pollution, opposition to mining the asteroids invokes an ecological argument that embraces all exploration of the solar system. Do we have the right to do whatever we choose with the products of 4.6 billion years of cosmic evolution? Does this right depend on whether the objects might support life? Do future generations have the right to expect to find them at least mostly intact? Throughout human history, exploration has preceded exploitation. The Europeans who ventured to new continents encountered areas teeming with natural resources, as well as native populations who the Europeans thought could assist in their efforts, or be made to do so. From South America came gold and tin, from Africa enslaved people and rare minerals. Today, more enlightened in our views, we consider some of our forebears’ actions immoral, and we retroactively condemn the negative climatic and environmental consequences of their efforts to secure the coal, oil, iron ore, rare elements, and other raw materials on which modern civilization depends.

As we reach the end of our survey of the most likely near-term exploration targets, we may usefully refer to David Spergel’s perceptive remark, quoted in the first pages of this book: “Our history as humans has shown that first we screw things up, and then we make some things right.” An extreme expression of this view rebuts the statement attributed to the writer Larry Niven that “the dinosaurs died out because they didn’t have a space program” with the assertion that “dinosaurs survived for a hundred million years because they didn’t have a space program.”¹²

The prospects for future exploitation of the asteroids adds little fuel to the astronauts-versus-robots debate. Essentially none of those who seek to profit from asteroids’ mineral wealth care whether it arrives via purely robotic processes, or via humans with pickaxes and wheelbarrows, or via a population of robot slaves with a human overseer (a scenario sometimes seen in science fiction films). Although the asteroids’ ancient surfaces and interiors hold keys to understanding the solar system’s early history, the public interest in exploration of the solar system typically does not extend to them. For now, the debate over how best to proceed with exploration ends once we pass outward from Mars. As a reward for having come this far, readers may enjoy taking a deep dive into the future with projects that exceed even Martian colonization by millions of Earthlings: colonies in space.

CHAPTER 7

Space Colonization

The most far-reaching current projection of how best to use the solar system’s raw materials envisions giant colonies in orbit around the sun, far from the influence of any object whose gravitation, atmosphere, or unstable surface might inhibit our abilities to reconstruct reality as we choose. This vision understandably grips some people hard. Throughout history, philosophers aware of the failings of our current social structures have dreamed of far better systems. From the modest paradise of Eden through the fourth century’s Peach Blossom Spring, the Buddhist Ketumati, the medieval Land of Cockaigne and Schlaraffenland, Thomas More’s sixteenth-century Utopia, and on to more modern political communities from Brook Farm in Massachusetts to Arcosanti in Arizona, humans have dreamed of better realms on Earth. The twentieth century brought these mental projects into the celestial realm, as engineers and technologists supplanted philosophers with attempts to create better worlds, not metaphorically but in reality.

The vision of human space habitats traces its modern version to Konstantin Tsiolkovsky, a Russian astronautics pioneer at the start of the twentieth century, who insisted that “Earth is the cradle of humanity, but one cannot remain in the cradle forever.” Tsiolkovsky’s dictum received only passing attention for decades, even as scientists, rocket engineers, and warfare experts generated ever more powerful rockets, eventually capable of sending astronauts to the moon, and used them to launch Earth-orbiting laboratories where astronauts could explore how to live in space for months on end. In 1969, as the first moon landings captivated worldwide attention, a Princeton physicist named Gerard O’Neill introduced an idea that would become his lifetime obsession: the creation of space habitats where generations of humans would spend their lives.¹

O’Neill had an impressive record as an innovator of improvements for particle accelerators, including “storage rings” that greatly assisted experimenters in their efforts to impel elementary particles to high-energy records. Inspired by students who judged science harshly for its participation in creating weaponry for the Vietnam War but found notions of space colonization highly inspiring, he began to write and to organize conferences on this more appealing topic. His vision attracted a host of ingenious and enterprising young physicists, along with a wide sampling of the public, including Timothy Leary, then famed as a proselytizer for the use of LSD to perceive new realities. These advocates found a marvelous challenge in designing entirely new environments, and—for many—even more in envisioning how these environments could usher in a new era of human thought, interaction, and activity.

The engineering and scientific analysis carried out by O’Neill and his followers yielded a basic plan for space habitats. Picture an immense cylinder, a mile long and hundreds of yards wide, with its long sides made of solid material that alternates with transparent windows. The rotation of the cylinder produces an effect, popularly called centrifugal force, that impels people and objects outward, simulating Earth’s gravity along its long surfaces. Mirrors outside the large windows reflect and modify sunlight, allowing the solid surfaces inside the cylinder to host a town, parkland, and fields for agriculture.

During the late 1970s and the 1980s, the challenges and opportunities embodied in O’Neill’s concept attracted supporters with backgrounds ranging from hard-core engineering to furry freakdom. Some saw a refuge from a deteriorating Earth; others promoted a future that could allow each “tribe” to enjoy its own cultural creation; still others emphasized the healthy environments that could be created ab initio, leaving disease and ecological deterioration behind on our original planet. In 1988, when then-Representative Bill Nelson chaired the space subcommittee of the House Committee on Science, Space, and Technology, that year’s NASA authorization act included this provision: “Congress declares that the extension of human life beyond Earth’s atmosphere, leading ultimately to the establishment of space settlements, will fulfill the purposes of advancing science, exploration and development and will enhance the general welfare.”² Another provision required NASA to produce biannual reports on a number of subjects, including steps taken toward the creation of permanent space habitats. (After the first such report, NASA ceased their production, apparently because they were judged unnecessary.)

Artists often depict space colonies as exciting and attractive, resembling a holiday resort, a better-organized Manhattan, or some other realization of our hopes for a near-perfect environment. If we ask who would actually prefer confinement within one of these enclosed, fragile environments to the messiness of global society and the beauty of the natural world, we find that some people would and some would not (so human!). Those in the former group tend to overlook the difficulty and danger of maintaining a huge artificial structure in space, as well as the technical challenges involved in its construction. For example, the internal air pressure required for an Earth-like interior would require exterior walls with tremendous tensile strength. This would call for mining enormous amounts of material, which would then have to be refined, either at its source or at its destination. In either case, this issue raised the question of how great quantities of solid matter could be transported. O’Neill suggested that magnetically powered “mass drivers” could shoot matter from the moon toward wherever it was needed; this is not an impossibility, but it has yet to be implemented, even at a scale much more modest than would be required to fulfill O’Neill’s vision.

Suppose that (in what currently seems a highly unlikely scenario) bold pioneers overcame these challenges and that a few such colonies came into existence, attracted eager settlers, and somehow became economically viable. In that case, advocates for future space habitats would claim that the sky’s the limit and call for the creation of much larger colonies, perhaps ten miles long, likewise rotating to simulate gravity, but less rapidly than the smaller colonies because of their greater width. Instead of occupying regions near the Lagrange points of the Earth-moon system, which offer orbital stability, each of the colonies in the second generation could have its own orbit around the sun, far from any planets.

Although O’Neill’s vision dealt primarily with establishing a society in space colonies that would prove superior in its organization and rules to any on Earth, many of his supporters have stressed their belief that these colonies could preserve humanity once our planet becomes uninhabitable. Numerous high-profile individuals, including Elon Musk and Stephen Hawking, have projected their fear that this crisis will arrive within a century or so. As a result, they urge us to begin our efforts to colonize another planet to establish the nucleus of a new civilization that will survive Earth’s demise. In 2016, Musk told the International Astronautical Congress that we face a crucial choice between two outcomes: “One is that we stay on Earth forever and then there will be an inevitable extinction event. The alternative is to become a spacefaring civilization, and a multi-planetary species.”³ For Jeff Bezos and others, however, the path to avoid extinction on Earth leads not to Mars but into space colonies.⁴ Mars can offer only the same land area that Earth does, while space colonies could provide an enormously larger total—if we build them.⁵

Many who support O’Neill’s vision foresee a time when the multitude of new environments could embrace an equally vast multitude of differently ordered societies, with emigrants from Earth free to choose the social organization that best suits them. Taking the other side of the argument, the political scientist Daniel Deudney has categorized a host of factors that would predispose space colonies to “unfreedom.”⁶ A partial listing includes the predictions that in any colony, access to food, water, and air, along with the opportunity to enter or to leave the colony or to share information with other colonies, would be centrally controlled; that each colony’s small size would produce extreme pressure toward social conformity, often leading to the rise of cultish religions hostile to freedom; that for economic success, any colony would require collective efforts that prevent individual autonomy; that some individuals’ unpredictable and possibly criminal activities would require constant surveillance in order to avoid catastrophes that could cripple or destroy a colony; and that population growth would have to be strictly regulated. One might well add the possibility of space colonies with a hegemonic approach, eager to incorporate other colonies into their empires, eventually capable of attacking one another in a sad replay of past histories on Earth.

If we suppose that Deudney’s worries were to prove illusory and ask how many colonies, and how many inhabitants, could populate the nearly empty regions of the solar system, we can perform some straightforward calculations. A space habitat a mile wide and ten miles long, with a surface area of perhaps twenty square miles, could support a few million people at a population density similar to that in Manhattan. (In O’Neill’s more detailed plans, the agricultural regions would be located in separate regions beyond the central cylinder.) Thus a few thousand such habitats could contain the Earth’s population, and a million of them would allow a few trillion humans to spend their lives in space.

The two fundamental resources that constrain this scenario—raw materials and sources of energy—turn out to be far more plentiful than one might think. At our distance from the sun, we intercept about one part in a billion of the flow of energy from our star. If we could rely on solar power to support terrestrial civilization, as seems achievable, the total solar output could theoretically maintain a billion times more people than Earth does. And by constructing space colonies that have comparatively thin outer shells, we would find that the outer layers of the moon, or a few of the larger asteroids, could provide all that we might need in order to construct a vast array of habitats. With orbital dynamics correctly under control, these colonies could harvest a large fraction of the sun’s energy flow. Instead of 10 billion inhabitants on Earth in 2050, enthusiasts claim, many millennia from now the solar system could support a billion billion people!

Some find this vision appealing, while others find it appalling. In his 1997 book Mining the Sky, the cosmochemist John Lewis lamented that “as long as the human population remains as pitifully small as it is today, we shall be severely limited in what we can accomplish.” Lewis stressed that “human intelligence is the key to the future.… Having only one Einstein, one Hokusai, one Mozart, one da Vinci, one Shankara, one Poulenc, one Arthur Ashe, and one Bill Gates is not enough. We need—and can have—a million times as many.… Life is not a cancer of matter; it is matter’s transcendence of itself.… Intelligent life, once liberated by the resources of space, is the greatest resource in the solar system.”⁷

A notable inconsistency seriously weakens most scenarios for these grandiose space projects. Out of necessity, their supporters envisage them against the backdrop of present-day society. But even by the middle of this century, drastic geopolitical changes may have occurred—indeed, such changes underpin the argument for the rapid construction of space colonies. The economic systems of spacefaring nations may undergo enormous transformations, possibly toward an equalization of wealth, possibly in the opposite direction. These new developments make it unclear whether space colonization might be funded by governments, either separately or in collaboration, or by immensely wealthy buccaneers who aim to set themselves up as the rulers of new empires.

One factor that would affect any of these transitions is the certain appearance of new technologies that will shape how humans live on Earth. Just as today’s smartphones might have seemed nearly magical to Neil Armstrong, super-advanced computers will enable future transformations such as artificial intelligence and, of course, intelligent robots. Silicon chips, which have already remade our everyday objects and social interactions, will grow more powerful, creating (among many other worries) the capability to maintain constant surveillance of an entire population. On the more positive side, advances in propulsion systems and in the strength of materials may change the way that we think about spaceflight and construction in space.

Still more influential, if that seems possible, will be genomics as applied to our biological development. AI systems will prove capable of inferring the combinations of genes that optimize particular human (or animal) characteristics, and of synthesizing a genome with these properties. As a result, designer babies will become conceivable, in both senses of the word. Even with advanced genomics, we may encounter limits to how much we can enhance the size and processing power of human brains. But no limits constrain electronic computers (and even less, perhaps, quantum computers). “Thinking,” no matter how it is defined, will increasingly become the domain of artificial intelligence. We may be approaching the end of our traditional Darwinian evolution and the opening of an era of technological evolution of intelligent beings. Our progeny in the remote future may be cyborgs, rather than entirely flesh and blood.

Barring a catastrophe that arrives before we possess space refuges, most futurists agree that machines will gradually surpass and enhance more and more of our distinctively human capabilities, though they disagree over the timeline. Some enthusiasts predict that a few decades will bring this about, while more cautious projections look several centuries into the future. Both intervals represent an instant in comparison with the timescales of the Darwinian selection that led to humanity’s emergence. More relevant is that neither of them exceeds any realistic timescale for achieving Bezos’s vision of O’Neill-style colonies spreading throughout the solar system.

We may hope that the coming techniques for “human enhancement” will be heavily regulated on Earth, for prudential and ethical reasons. Emigrants to Mars habitats or space colonies will live far beyond the grasp of the regulators—one of the reasons, some of their supporters say, for creating them. The new environments of these brave new worlds will motivate, even compel, their settlers to redesign themselves for better harmony with their surroundings. To do so, they can harness the super-powerful genetic and cyborg technologies that will be developed in coming decades. We may wish them good luck in modifying their progeny for better adaption to alien environments, which could lead toward a divergence into new species. Those who welcome these spacefaring possibilities will populate the new outposts, leaving behind those more comfortably adapted to life on Earth.

Organic creatures almost certainly require the support of a surface or ocean on a planet or large moon, but if post-humans make the transition to fully inorganic intelligences, they will no longer require a surface or atmosphere. They may prefer weightlessness, especially if they seek to build massive structures. If so, deep space—not Earth, not Mars, not the interiors of rotating space colonies—will see the development of non-biological brains with powers that we humans cannot imagine. Back on Earth, where our evolution in symbiosis with all the planet’s other biota has, by definition, adapted us to living here, such enormous changes will occur more slowly, and in different ways, though we shall share with our free-living cousins the need to ensure that artificial intelligence remains benevolent.

Should these seemingly fantastic developments occur during the next few centuries, as seems entirely likely, they will refute the claim that “we” will spread ourselves throughout the solar system in a multitude of space colonies. Instead, the process of secular intelligent design, operating a thousand times more rapidly than Darwinian selection, will produce diverse varieties of post-humans, as variegated in appearance as in the lifestyles and occupations that they pursue.

Whether any of these space colonization scenarios comes to approach reality remains unpredictable. We can, however, state with confidence that they do not violate any fundamental laws of physics. Whatever the motivation of those who may aim to turn one or more of them into reality, and whatever motivators—global cooperation, powerful countries locked in rivalry, religious sects, or individuals with enormous resources—may generate them, we can judge their desirability. To the extent that a global catastrophe may not only destroy humanity but also foreclose the immense potential of a post-human future, space colonies and Martian settlements seem a definite plus. On the other hand, disturbing existing ecological systems has a downside. For now, this applies only to the presumably simple organisms that may exist elsewhere in the solar system. In the distant future, a similar analysis could apply to the danger of disturbing far more advanced organisms in neighboring planetary systems.

Even those who—like the authors—regard huge space colonies as unattractive or unfeasible have an affinity for a somewhat more limited scenario that Bezos has advocated: heavy and polluting industry could be relegated to orbital factories, perhaps with intensive agriculture as well. These facilities could be constructed and operated robotically, freeing the Earth to provide a more verdant home for humanity.

COLONIES TO THE STARS

While considering the possibilities of space colonies in the solar system, we may reasonably ask whether space colonies could serve as the model for journeys to the stars. Colonies enter this discussion because the closest stars and their planets lie so far from us that journeys to them will require more than a single lifetime for a long time to come. Even if humans develop propulsion systems capable of reaching speeds of, say, 10 or 20 percent of the speed of light—thousands of times greater than our best rockets today—interstellar travel will require dozens of years to reach the nearest planetary systems, and many times that to travel to a good sample of the sun’s neighbors. The natural plan for an interstellar spacecraft takes the generalized form of a space colony with a propulsion system, within which generations can embark on, and eventually complete, their journeys of decades or centuries. A look at the future shows that such journeys are not particularly well suited for human enterprises but could be better performed by creatures with extended life spans, and still better by electronically based entities. A million-year voyage, a daunting prospect even for an ongoing human colony, would appear far different to near-immortals. (We do well to bear this in mind when we consider possibilities for contact with other civilizations, if they exist, always remembering that an advanced civilization with no interest in being detected almost certainly possesses the means to avoid detection.)

These futuristic visions provide a good reminder of the limited scope of the argument made in this book—that we don’t need astronauts to explore the solar system, however much we may want them. Our assertion refers not to future centuries but to this one, and in particular to the next few decades. Our grandchildren, who will presumably welcome the twenty-second century as eagerly as many of us did the twenty-first, are likely to see astronauts on Mars. We should not deny them this opportunity by rushing to achieve this result as soon as possible. As demonstrated by the history of astronauts on the moon, calm reasoning often serves society better than a breakneck rush toward one particular result.

Calm reasoning, of course, goes only so far. We are human, not machines. On the other hand, we remain capable of recognizing what machines can do and when to employ them. Returning to the mundane tasks involved in planning our future exploration of space, we may turn to the least attractive of all: counting the money.

CHAPTER 8

The Global Costs of Space Exploration

Any discussion of human versus robotic space exploration raises the issue of their costs, or, more accurately, of a cost-benefit analysis. We have seen that evaluating the benefits of human explorers hinges largely on non-quantifiable factors, including the excitement and inspiration they may produce, the belief we can fulfill our destiny only by exploring in person, and the other factors described in Chapter 1.

The costs of these efforts lend themselves more naturally to numerical analysis. In determining their amounts, some difficulties arise in interpreting existing data, and far greater ones from the familiar problem of attempting to predict the future. Broadly speaking, the overarching factor in the relative costs of human and robotic exploration remains our human nature. We cost far more than robots to maintain, and we expect to return home. The maintenance problem endures through every moment of human spaceflight: on the months-long journey to a distant object, during weeks or months of exploration once safely landed there, and during the months of a return journey. The last of these requirements adds hugely to the costs, because we must create and deploy a rocket that is capable of launch from a distant object and carries the fuel needed to get back.

Short of the suspended-animation techniques prominent in science fiction films, the first set of problems has no solution beyond providing astronauts with oxygen, water, food, and living space for their journeys. Imaginative solutions for the return-journey requirement include finding volunteers who would remain at their destination instead of returning (apparently no shortage exists within the wider community, if not among those likely to be chosen as astronauts) or bringing machinery to extract fuel or oxygen (or both) from another planet’s soil (hydroponic farming, as seen in The Martian, would presumably have to wait for at least a second journey). For the present, the likely solution would mimic Apollo’s: send the major vehicle into orbit, and use a smaller one to descend to, and ascend from, the surface. This approach should work as well around Mars as around the moon; its drawback lies only in the extra mass for the entire transport system. At present, NASA’s plans track those of the Apollo program, setting an initial goal of placing astronauts in orbit around Mars before attempting a landing, as Apollo 8 and Apollo 10 did before Apollo 11’s first lunar landing.

HOW MUCH WILL AN ASTRONAUT MISSION TO MARS COST?

One factor in our attempt to determine the costs of robotic and human exploration to Mars is that we already have a good grasp of the costs of robotic missions from actual experience. In recent decades, each major mission has cost from $1 billion to several billion dollars. Spirit and Opportunity, the twin rovers launched in 2003, cost $1.1 billion: $744 million for their development and launch, and $336 million for 15 years of operation (Spirit ceased operation in 2011, Opportunity only in 2018). Curiosity, the next rover to travel over the Martian surface, reached the planet in 2012 and has performed for nearly a decade, with a total inflation-adjusted cost of about $3.2 billion. The Perseverance rover’s total cost is estimated at approximately $2.75 billion, spread over eleven years. Most of this amount, $2.2 billion, was spent on developing and constructing the rover itself. Another $243 million paid for the launch, and $291 million has been budgeted for mission operations through the summer of 2023, the rover’s nominal lifetime. If this estimate holds true, Perseverance will cost less than its less capable predecessor Curiosity, a tribute to engineers who learned from previous success.¹

The prediction that future rovers on Mars will each cost several billion dollars seems relatively secure. We naturally know far less about the costs of sending astronauts to Mars and returning them since we have yet to achieve any similar feat. On the low side, the group of enthusiasts known as Mars One evaluated the cost of the first crewed mission at a modest $6 billion, largely from reliance on their plan that “since the Mars One crew will stay on Mars, mission complexity and the weight of the hardware that needs to be sent to Mars are a lot lower compared to return Mars missions.”² On the higher end, in 2015 O. Glenn Smith, a former manager of shuttle systems engineering, and Paul Spudis, a staff scientist at the Lunar and Planetary Institute, envisioned a spacecraft capable of carrying astronauts to Mars as a “traveling space station,” essentially a smaller version of the International Space Station. They pointed out that

the most critical element needed for a trip to Mars is also the most expensive. A new vehicle must safely sustain the crew for two to three years without resupply and embody all the functions of the current ISS and be a lot better. These requirements include an environmental control and life support system that monitors and controls partial pressures of oxygen, carbon dioxide, methane, hydrogen and water vapor. It must filter out particulates and microorganisms, provide thermal control with external cooling loops and pumps, and distribute air. This system for Mars also must provide potable water and perform habitation functions, such as food preparation and production, hygiene, collection and stabilization of metabolic waste, laundry services and trash recycling. Waste management systems safeguard crew health, controlling odors and retarding the growth of microbes.

Other critical systems include electric power generation and control, communications and navigation, attitude control (control moment gyroscopes), exercise equipment, propulsion to dodge foreign objects, puncture repair kits, fire suppression equipment, medical equipment for first aid and continuing care of potentially sick or disabled crew, airlock, spacesuits for extravehicular activity, manipulator arm and control station, and food, extra supplies of oxygen, nitrogen, fuels and other expendables. Long-term exposure to space radiation in excess of levels encountered on the ISS will require significantly enhanced protection for the crew.

Every one of these systems must operate without resupply for the duration of the mission and do so with several times the reliability of its corresponding system on the ISS. They must be repairable in flight in the event of minor malfunctions. The National Research Council recently reported that U.S. and Russian systems on ISS demonstrate rates of hardware failures that would be unsustainable on a Mars mission.³

Drawing on their comparison with the ISS, Smith and Spudis estimated the cost of such a spacecraft at somewhat more than $100 billion, with a similar amount added for the propulsion system, to reach a total cost of $230 billion for the first crewed mission in 2035. A 2019 analysis by the Institute for Defense Analyses (IDA) estimated that a mission for astronauts to orbit the planet without landing on it would cost $117 billion through 2037.

Rejecting the Mars One cost-saving approach and taking into consideration the Smith / Spudis and IDA estimates, we can conclude that astronaut missions to Mars, at least during the next two decades, would likely carry about fifty times the cost of a robotic exploration. Although this hardly settles a debate about sending astronauts to the red planet, we should keep it in mind in judging both the strength of our desires and the likelihood of obtaining sufficient funding for a properly conceived and executed human exploration of Mars.

NASA EXPENDITURES AND THE ARTEMIS LUNAR PROGRAM

When attention turns toward the moon, much better data exist for estimating costs, thanks to the astronauts’ lunar landings more than fifty years ago. Because the creation of NASA in 1958 came as a direct response to the Soviet Union’s launch of the first artificial satellite of Earth, Congress was ready to approve a huge rise in spending to match and surpass the USSR’s present feats and future possibilities. After President Kennedy’s 1961 announcement that the United States intended to land a human being on the moon, NASA’s spending rose above 4 percent of the total federal budget in 1964 and 1965. As the Apollo program reached its conclusion, this fraction fell below 1 percent in 1975 and then below 0.5 percent in 2006, where it has remained there for nearly five decades.⁴

In actual dollars, the United States budgetary projections for the 2021 fiscal year envision expenditures of $23.1 billion for the Military Intelligence Program, of which some $10 billion apparently goes to the National Reconnaissance Office; $9.13 billion for the Military Defense Agency; and $15.2 billion for the Space Force.⁵ NASA’s 2021 budget totals $23.3 billion, of which 45 percent ($10.6 billion) goes to human spaceflight, 31.5 percent to science, 14.7 percent to facilities and overhead, 4.9 percent to technology, 3.5 percent to aeronautics, and 0.5 percent to education. The funds for human spaceflight include $6.56 billion for exploration; $4.91 billion for launch vehicles; $3.99 billion for operations; $2.94 billion for safety, security, and mission services; and $1.39 billion to smaller budget items.

NASA’s plans for astronauts to return to the moon reside in the Artemis program (outlined in Chapter 4), with the United States at the center of a multinational consortium.⁶ Artemis will incorporate the following key components:

The Space Launch System (SLS), a new propulsion system with even more power than the Saturn rockets that sent the Apollo astronauts to the moon.

The Orion capsule, which combines a crew module to carry astronauts, capable of returning for an ocean landing on Earth, with a service module, to be built by NASA’s European partners, that will power the spacecraft and store supplies of oxygen and water for the astronauts. Orion will use solar power, allowing longer missions than those possible with power supplied by fuel cells.

The Gateway lunar orbiter, where astronauts will transfer to vehicles that will take them to and from the lunar surface.

The Dragon XL spacecraft, created by Elon Musk’s SpaceX corporation to resupply the Gateway orbiter in a manner similar to how SpaceX’s Falcon Heavy rocket resupplies the International Space Station.

A Human Landing System (HLS), to carry astronauts from the Gateway orbiter to the lunar surface and return them to the Gateway. In April 2021, SpaceX won the competition with its rivals Blue Origin and the Dynetics Corporation to use its Starship rocket for an uncrewed landing and then for the first crewed landing, with later landings subject to further competition.

SpaceX’s Starship rocket also competes with the SLS, for which the Boeing corporation is the lead contractor, to provide the best new heavy-lift vehicle. Both rocket designs use liquid fuel (liquid hydrogen for the SLS, liquid methane for Starship), which combines with liquid oxygen upon ignition. SLS’s lower stage has four rockets similar to the three on the space shuttle, along with twin solid-fuel boosters that fall away after use. An intermediate-stage booster, modeled on NASA’s Delta workhorse, provides additional thrust, with the Exploration Upper Stage adding still more lifting power for later SLS flights. As has been the case with previous NASA programs, the SLS is several years behind schedule and several billion dollars over budget.

SpaceX’s more advanced approach envisions an upper stage for Starship that will be a fully operational, long-duration spacecraft eventually capable of traveling to Mars and back, and of landing vertically on Earth for comparatively easy refueling and reuse. Like the SLS, Starship should prove capable of lifting more than a hundred tons into near-Earth orbit and more than forty tons to the Gateway lunar orbiter. SpaceX has achieved remarkable success in reducing the cost of sending payloads into Earth orbit, and it may eventually succeed in bringing its approach not only to moon-bound astronauts but also to a human expedition to Mars. The company does, however, have a record of promising far more rapid success than it delivers; one may reasonably argue that what counts the most is that it does eventually deliver.

In February 2021, the Biden administration endorsed the Artemis framework, and projected a total cost for the fiscal years 2021–2025 of $85.7 billion. Serious doubt now exists as to whether the program can succeed in its stated goal of landing lunar astronauts by 2024, with 2028 often cited as more realistic, implying an increase in expenditure beyond the 2025 fiscal year. This gains more credence from the fact that important components of the framework described above have yet to be designed, let alone constructed. In addition, NASA must rely on its numerous foreign collaborators: the European Space Agency, the Japan Aerospace Exploration Agency, the Canadian Space Agency, the Italian Space Agency, the Australian Space Agency, the United Kingdom Space Agency, the United Arab Emirates Space Agency, the State Space Agency of Ukraine, and the Brazilian Space Agency. History demonstrates that coordination among such a large group of worldwide entities can prove challenging.

US support for the Artemis program has become more likely with the confirmation, in April 2021, of former Senator Bill Nelson as the new NASA administrator. In 1986, Nelson orbited the Earth on the Space Shuttle Columbia (lost in an accident in 2013), and he has been a devoted supporter of astronaut exploration of the solar system.

COSTS OF LAUNCH INTO NEAR-EARTH ORBIT

Much closer to home than the moon or Mars, near-Earth orbit has become a familiar locale for our extension into space, if only by a few hundred miles. Nevertheless, to send either astronauts or cargo into near-Earth orbit remains an expensive undertaking, simply because even partial escape from the Earth’s gravitational well requires reaching speeds of many miles per second, which in turn require an impressive expenditure of energy, along with a system to direct it properly.

In recent years, thanks in large part to the efforts of private entrepreneurs, the costs per pound of launch into near-Earth orbit have declined impressively. In the past, when only governments launched spacecraft, different approaches existed for calculating and presenting launch costs per pound. On occasion, NASA showed a tendency to quote only the direct costs of a launch, such as the fuel for a spacecraft, omitting the expenses incurred in its design and construction. The more accurate method, often used in the aircraft industry, describes the “unit flyaway cost,” which includes pretty much everything, such as indirect manufacturing costs and overhead, systems and program management, and non-recurring charges for tooling and engineering.

To avoid some of the complexities of these calculations, we may divide the total cost of an entire program by the total of its lifted cargo, or, for commercial enterprises, by noting the price charged for each pound sent into orbit. (The latter amount might reflect either a loss leader or a plan to make a profit.) A prime example is the space shuttle. Each flight could transport about 52,000 pounds to near-Earth orbit. Although many of the shuttle’s flights carried far less than this, if we use this upper bound and multiply by the 135 missions, we find that the 7 million pounds of potential cargo cost $195 billion (in today’s prices), or about $28,000 per pound.⁷ (We should reemphasize that because the actual cargo total was far less than the theoretical maximum, the actual per-pound costs were much higher; furthermore, the cost of operations was greatly enhanced because the shuttle was designed to carry humans.)

Later NASA missions have often been described as carrying a price tag of $10,000 per pound, a figure easy to remember. During the past few years, however, SpaceX has successfully aimed to reduce this number significantly. In 2020, NASA contracted with the company to pay $2.4 billion for six missions to the International Space Station, including both astronauts and cargo. Since SpaceX’s Falcon 9 rocket has a cargo capacity of 50,000 pounds, this implies a launch cost per pound—more precisely, the price charged per pound—of $8,000. However, the contract with NASA includes tasks associated with, for example, preparing the rocket to launch humans rather than cargo, and a pure cargo launch would almost certainly be considerably less expensive. Indeed, SpaceX projects future costs of $2,500 per pound or less.

To estimate the costs of maintaining astronauts into orbit, a task for which per-pound calculations are poorly suited, we may cite the $90 million that Russia charged for each “astronaut seat” to the International Space Station. (For a 200-pound astronaut, that comes to $450,000 per pound.) This may have involved some price gouging, but it is worth bearing in mind that every astronaut trip to and from the International Space Station costs many tens of millions of dollars. We may take a different approach to assessing the per-astronaut cost of the ISS beyond the costs of transport from and to the Earth. During the two decades since it began operations, the ISS has supported approximately 20,000 astronaut-days, typically with three to six astronauts aboard at any time and remaining for several months each. The ISS’s total cost of approximately $150 billion corresponds to about $7.5 million per astronaut-day, or about $675 million for an astronaut who stays aboard for three months.

WORLDWIDE FUNDING FOR SPACE RESEARCH AND EXPLORATION

From the dawn of the space age until now, governmental funding has dominated efforts in space research and exploration, with the United States the principal fount of support, easily exceeding the combined expenditures of all other nations. Only the Soviet Union in its heyday approached even half of the US total, though currency restrictions and secrecy made direct comparisons difficult. Today only China comes partway close to the United States, with similar difficulties arising from exchange rates and a lack of transparency on China’s part. In general, the second- and third-largest investors in space exploration, China and Russia, choose not to provide many aspects of information about their spending or to be transparent about how they allocate costs. We may nevertheless gain a useful perspective from a review of plans for space exploration beyond those centered on the United States.

CHINA

China’s rocket development began under the aegis of Qian Xuesen, a pioneering scientist who received his PhD from Caltech in 1939 and collaborated on the first rocket experiments at what became the Jet Propulsion Laboratory, where the project leader, Theodor von Kármán, called him an “undisputed genius.”⁸ During World War II, Qian worked on the Manhattan Project to develop the atomic bomb; afterward, he was sent to Germany to help question Wernher von Braun and other Nazi rocket engineers. In 1949, he became a professor at Caltech; in 1950, he announced his intention to return to China, and was arrested by US authorities; in 1951, he was placed under house detention, where he wrote the basic textbook on servomechanisms, Engineering Cybernetics. After Qian’s release in 1955, Undersecretary of the Navy Dan Kimball commented that his arrest “was the stupidest thing this country ever did. He was no more a Communist than I was, and we forced him to go.” Back in China, Xuesen became the leader of the program that made the Dongfeng ballistic missiles and the Long March space rockets, as well as part of the effort that produced the first Chinese atomic and hydrogen bombs. He also made numerous contributions to various scientific fields, including systematics and complexity science. He received Caltech’s Distinguished Alumni Award in 1979, thirty years before his death at age ninety-eight.

Current assessments of China’s budget for space exploration estimate annual expenditures of $11 billion, roughly half of NASA’s annual budget.⁹ Although this amount has to be considered as only approximate, it clearly indicates that China can compete with the United States, since China’s labor and other costs tend to be significantly lower.

Among countries active in space exploration, China arguably ranks highest in its willingness to claim property rights beyond the Earth. In 2015, Ye Peijian, the chief designer for lunar exploration projects, compared the moon and Mars to the contested Senkaku and Spratly Islands, stating that not exploring those celestial objects might result in a failure to protect China’s “space rights and interests.”¹⁰

China’s most notable successes in space exploration include the Chang’e 4 spacecraft, which made the first successful landing on the moon’s far side in January 2019. In order to relay communications to and from Earth, the lunar lander took advantage of the Queqiao spacecraft previously placed in orbit around the moon. Just under two years later, the Chang’e 5 landed on the moon, drilled a yard into the surface, collected almost four pounds of samples, and brought them to Earth in December 2020. In February 2021, the Tianwen-1 mission entered orbit around Mars, seeking to accomplish the first Martian trifecta of an orbiter, a lander, and a rover.

By the end of this decade, China plans to send robotic explorers to Venus and to Jupiter, as well as a second Mars mission that will build on the hoped-for success of Tianwen-1. For human exploration, China projects that in 2022 it will have a space station in near-Earth orbit to rival the International Space Station, although it will support only three astronauts during long-duration stays. Because international funding for the ISS remains uncertain past 2025, the director-general of the European Space Agency has expressed interest in collaborating with China on its space station as well as on missions to the moon and Mars. By the middle of the 2030s, China hopes to have a permanent base on the moon, as well as Earth-orbiting satellites designed to capture solar power and beam it to Earth. In all these activities, China hopes to overtake the United States not only in its actual accomplishments but in securing cooperation and respect from countries around the world. This challenge has induced some supporters of NASA’s efforts to seek an agreement with China for future activities in space. Pamela Melroy, who flew on three space shuttle missions, one as commander, and served on President Biden’s transition team, commented in 2021 that “trying to exclude [China] I think is a failing strategy … it’s very important that we engage.” On the other hand, Melroy also noted that China’s activities in the South China Sea created the apprehension that their efforts in space represent a “play for resources,” in essence echoing the remarks by China’s Ye Peijian in 2015.¹¹

THE EUROPEAN SPACE AGENCY

For decades, the now twenty-two-member European Space Agency has played key roles in exploring the solar system, from its workhouse Ariane rockets to its design and construction of crucial components of probes such as the Cassini-Huygens mission to Saturn. Because ESA typically ranks as NASA’s junior partner in funding, and because United States residents typically think almost entirely of NASA when they think of space, ESA’s contribution often receives little attention, even though projects such as the Hubble Space Telescope, the Infrared Space Telescope, and the soon-to-be-launched James Webb Space Telescope have relied on ESA throughout their history. Europe has contributed about 8 percent of the operational costs of the International Space Station, including the Columbus laboratory, the Cupola observatory, the Tranquility and Harmony modules, and the computers that collect data and provide navigation, communications, and operations capability for the Russian segment of the ISS.¹² ESA’s five Automated Transfer Vehicles (ATVs) were massive and versatile supply ferries that provided the ISS with supplies and boosted its orbit for increased stability. The ATV program has evolved into the European Service Modules that ESA will supply for NASA’s Artemis program, continuing the NASA-ESA collaboration beyond near-Earth orbit. ESA’s successes in exploring the outer solar system include the first landing on a comet (the Rosetta mission, which reached Comet Churyumov-Gerasimenko in 2014) and the first landing on another planet’s satellite in 2005, when the Huygens probe, released from the Cassini spacecraft, descended onto the surface of Saturn’s large moon Titan.

ESA’s multinational nature has naturally led to a decision process somewhat different from that in the United States. Whereas the latter can and does changes its mind on a year-by-year basis, ESA sticks to a decision once it has been agreed upon. In 2016, ESA’s Space Exploration Strategy summarized its ongoing discussions of space exploration’s future as “subject to intense debate throughout the last years, within Europe and internationally at [the] political level, as well as among space agencies and other stakeholders. This debate demonstrated broad consensus on the potential of space exploration to produce societal, intellectual and economic progress for the benefit of our citizens.”¹³ In response to this consensus,

the European Space Agency is pursuing an independent strategic planning process for consolidating a destination-driven space exploration strategy to low Earth orbit, the Moon and Mars. International cooperation is a key pillar of ESA’s strategy as it is considered both an enabler for realising the strategic interest of ESA and a benefit, opening new perspectives for addressing future challenges. International cooperation does not prevent competition, an essential factor for fostering innovation and for the future of space exploration. ESA has already developed some critical capabilities, identified its future focus areas for space exploration and invested in selected research and development areas with a view to secure attractive roles in the global space exploration endeavour.

So far as those “attractive roles” are concerned, the statement notes that “the development of new robotic techniques, together with human-assisted robotic instruments will bring data from new planetary locations.” ESA plans for its Rosalind Franklin probe to reach Mars in 2023, where it will release a Russian lander to descend to the surface and drill up to two meters into it to obtain samples that a later collaborative mission with NASA will bring to Earth.¹⁴ As the ESA statement summarizes: “The prospect of analysing returned samples in sophisticated terrestrial laboratories will allow the study of the physical processes underlying the evolution of our immediate environment in the Cosmos. The human exploration of Mars is the long-term objective of this programme, and it is therefore vital to embed the development of the necessary technologies for human spaceflight into this comprehensive strategy. This will provide both a means of achieving the Mars exploration goals and act as a focus for public engagement in this long-term international endeavour.”¹⁵

The rather anodyne reference to human exploration of Mars as the program’s long-term objective seems to make “embed[ding] the development of the necessary technologies” something of an afterthought. The statement continues with the pronouncement that “from all these discussions, three common mission goals for the next decades are emerging: [e]xploitation of human-tended infrastructures in Low Earth Orbit (LEO) beyond 2020 for advancing research and enabling human exploration of deep space; [r]eturning samples from the Moon and Mars; [e]xtending human presence to the Moon and Mars in a step-wise approach.” One may note the difference between ESA’s reference to “human exploration” and “extending human presence” and the opening sentence of NASA’s “Moon to Mars Overview,” which states that “human lunar exploration plans under the Artemis program call for sending the first woman and next man to the surface of the Moon by 2024 and establishing sustainable exploration by the end of the decade. The agency will use what we learn on the Moon to prepare for humanity’s next giant leap–sending astronauts to Mars.” This contrast may arise from the difference between a single country’s space agency and one that must respond to the approaches favored by twenty-two different countries. The ESA statement that “human missions to the lunar surface are a key component in reducing risks for human long-duration missions on the surface of Mars” touches on a subject that rarely appears in NASA’s discussions of human exploration of the solar system.

RUSSIA

During the period between the end of the space shuttle program in 2011 and October 2020, Soviet rockets offered the only means of carrying humans to and from the International Space Station. The creation of SpaceX’s Crew Dragon, capable of launching astronauts into near-Earth orbit, has produced a situation in which only Russian astronauts depart from the Baikonur launch facility in Kazakhstan. Late in 2021, Roscosmos, the Russian space agency, plans to achieve its first soft landing on the moon in forty-five years with Luna 25.¹⁶ This sixty-six-pound payload, basically a test for future lunar landers, will carry imagers, thermometers, and spectrometers to the lunar surface.

The joint program with China to create a base on the moon, described in Chapter 4, represents Russia’s only known plan for astronaut journeys beyond near-Earth orbit. In October 2020, the leader of Russia’s space program criticized NASA’s plans for sending astronauts to the moon as “too US-centric” and said that Russia would not participate unless the effort had stronger international cooperation.¹⁷

INDIA

The Indian Space Research Organization operates a large number of remote-sensing satellites, as well as two satellite navigation systems. In 2008, India placed the Chandrayaan-1 rocket into lunar orbit, from where the Moon Impact Probe made a planned crash descent into the Shackleton Crater at the moon’s south pole, revealing the presence of water beneath the lunar soil.¹⁸

In September 2014, the Mars Orbiter Mission, familiarly called “Mangalyaan,” entered orbit around Mars—the first time that a country succeeded in this effort on its first attempt. The Chandrayaan-2 moon mission, designed to land and then operate a lunar rover, failed in this attempt, though its orbiter remained functional. Future plans include a new launch vehicle for astronauts, a solar probe to study coronal mass ejections, an orbiter of Venus to study the planet’s atmosphere, a new Mars mission (Mangalyaan 2), and an international agreement with Japan’s space agency for a mission to search for water at the lunar south pole. India’s space research budget has doubled during the past seven years to 140 billion rupees ($1.93 billion).

JAPAN

In March 2021, near the end of the Japanese government’s fiscal year, the space budget for the new fiscal year 2021 rose by 23.1 percent to $4.14 billion.¹⁹ Nearly half of this amount, $2.04 billion, will go to that ministry that controls the Japan Aerospace Exploration Agency, with almost one-quarter of that amount ($472 million) to be applied to participation in NASA’s Artemis program.

CHAPTER 9

Space Law

Human civilization rests on our ability to maintain an acceptable degree of reconciliation and coordination among large numbers of individuals and groups, laden with conflicting attitudes and desires, that populate the globe almost to bursting. Divergences of cultural attitudes and national goals provide never-ending disagreements that, as history fully demonstrates, can quickly evolve into warfare or its near equivalent. Similar behavior on more local levels likewise sustains near-conflict situations in endless repetition. Successful societies avoid the most negative outcomes by following a code of behavior, embodied in written laws and traditions, together with a host of actions designed to enforce this code.

In space, whether they enter in person or by automated proxies, humans encounter a realm nearly devoid of traditions, norms, or codified rules, and almost absolutely lacking in enforcement capability. No widely agreed-upon principles govern how different state and individual actors may or should execute their plans. The extensive projects of Jeff Bezos, Elon Musk, and others, along with SpaceX’s demonstrated superiority to the US government in rocket manufacturing, raise issues about the proper role of nongovernmental actors in space. We may well ask how our civilization can determine the roles that may properly be assigned by governments—or that may be seized by various countries, corporations, well-funded groups, or wealthy individuals. For now, the sweeping expanse of space provides a domain of potentially eternal discord: a lawyer’s paradise—except that no courts exist to exert legal oversight.

THE SPROUTING OF SPACE LAW

Almost all legal systems have grown organically, the result of long experience that comes from changes in the political, cultural, environmental, and other circumstances of a society. The first sprouts of space law deserve attention from those who may participate in the myriad activities envisioned for the coming decades, as well, perhaps, from those who care to imagine how a Justinian law code could arise in the realm of space.¹

Those who travel on spacecraft, and to some degree those who will live on another celestial object, occupy situations analogous to those aboard naval vessels, whose laws offer precedents to deal with crimes or extreme antisocial behavior. These laws typically assign to a single officer or group of officers the power to judge and to inflict punishment, possibly awaiting review in the event of a return to a higher court. This model seems likely to reappear in the first long-distance journeys within the solar system and in the first settlements on other celestial objects, before the usual structure of court systems for larger societies appears on the scene.

As on Earth, however, most law is civil law, not criminal law. A far greater challenge than dealing with criminal acts lies in formulating an appropriate code of civil law that will apply to disputes, whether national or international, arising from spaceborne activities by nations, corporations, or individuals. For half a century, a small cadre of interested parties have developed the new specialty of “space law,” some of which already has the potential for immediate application. What happens if a piece of space debris launched by a particular country or corporation falls onto an unsuspecting group of people or onto their property? What happens if astronauts from different countries lay claim to parts of the moon or an asteroid? And most important in its potential importance, if not in its likelihood: who will speak for Earth if we should receive a message from another civilization?

Conferences on subject such as these have generated more interest than answers. Human exploration of the moon brought related topics to more widespread attention and argument. During the 1980s, the United Nations seemed the natural arena in which to hash them out, and those discussions eventually produced the outcomes described in this chapter. Today, one suspects, almost no one knows the documents that the United Nations produced, let alone has plans to support countries that obey the guidelines in those documents. Our hopes for achieving a rational means to define and limit activities beyond our home planet will require more extensive agreements, plus a means of enforcing them.

Non-lawyers who read existing and proposed agreements about the use of space should remain aware that lawyers typically define words relating to specialized situations as “terms of art,” giving them meanings other than those that a plain reading would suggest. For example, the word “recovery” in normal discourse refers to regaining the value of something that has been lost, such as the lost wages that arise from an injury. In more specialized usage, “resource recovery” refers to the act of recycling material that would otherwise go to waste. In the vocabulary of mining operations, however, “recovery” has nothing to do with losing what was once possessed; instead, it refers to the extraction of ore from the ground or the seabed. The word’s gentle nature contrasts with the more accurate term “exploitation,” which often implies disapproval, though in legal matters it often carries only a neutral meaning. For example, in 1982 the United Nations Convention on the Law of the Sea established an International Seabed Authority (ISA) to set rules for the large portion of the seabed that lies beyond the jurisdiction of any nation.² By now, 168 countries have signed on to the convention, but the United States has not. According to the ISA’s website, its Mining Code “refers to the whole of the comprehensive set of rules, regulations and procedures issued by ISA to regulate prospecting, exploration and exploitation of marine minerals in the international seabed Area.” In mining circles, no one blinks at plans to exploit a particular location by extracting its mineral resources. Discussions of space law, however, tend to avoid the term “exploitation” in favor of “recovery.”

THE ANTARCTIC TREATY AS A POTENTIAL MODEL FOR SPACE TREATIES

The Antarctic Treaty of 1959, the most successful international treaty dealing with unclaimed land, could potentially serve as the basis for space-based agreements. Eight decades ago, as World War II neared its end, large portions of Africa and Asia, rich in population and mineral wealth, “belonged” to the colonial empires of European countries. Continuing their colonial traditions, these colonizing countries and other nations had also asserted direct ownership of portions of the southernmost continent. A dozen countries had made territorial claims to triangular land areas that all came to a sharp point at the South Pole. The unsurprising overlap among many of these claims offered fertile grounds for conflict, and in fact a few military confrontations, with warning shots fired, suggested that significant problems lay ahead. During the early 1950s, attempts led by the United States to have the United Nations effectively govern Antarctica gained little traction, with the Soviet Union notably uninterested. Peaceful scientific investigations during the International Geophysical Year of 1957–1958 helped to motivate the search for another path to a peaceful resolution. A brilliant solution eventually appeared: without losing national pride by dropping a single word of their ownership claims, the nations primarily engaged in Antarctic activity agreed to suspend any attempt to enforce these claims and to forgo any activities that would assert further territorial rights. Responding to strong objections from Argentina, Chile, and the Soviet Union, the United States abandoned any right to conduct nuclear explosions on the southern ice. Other areas of disagreement yielded to a final resolution in December 1959, when a dozen nations, eventually joined by more dozens more, signed the Antarctic Treaty in Washington, D.C.³

The treaty forbids military activity; guarantees peaceful scientific investigations; bars nuclear explosions and the disposal of radioactive waste; calls for the free passage of observers, notice of proposed activities, and free inspection of facilities; and promotes supportive activities, including periodic meetings for consultation on further measures. The fact that more than sixty years have passed without major incident since the treaty went into force testifies to the widespread adoption of these declarations and their success in regulating conduct.

In considering how the Antarctic Treaty’s principles might best be applied to activities in space, diplomats and others who study the situation remained aware of the perhaps most difficult aspect of any agreement, whether among corporations or nations: how should enforcement proceed? The Antarctic Treaty requires that in the event of a dispute, the contracting parties “shall consult among themselves with a view to having the dispute resolved by negotiation, inquiry, mediation, conciliation, arbitration, judicial settlement or other peaceful means of their own choice.” If the conflict remains, any dispute “shall, with the consent, in each case, of all parties to the dispute, be referred to the International Court of Justice for settlement; but failure to reach agreement on reference to the International Court shall not absolve parties to the dispute from the responsibility of continuing to seek to resolve it by any of the various peaceful means referred to.”

The constructive spirit of these pronouncements works nicely in situations where parties have honest disagreements and welcome a reasonable means to resolve them. Understandably, situations involving less cooperative parties pose a greater challenge, and the treaty contains no enforcement mechanism beyond the prescriptions quoted above. This does not leave the continent with no paths of enforcement. In 1995, the United States, the chief actor in Antarctica, authorized the Antarctic Conservation Act, which imposes civil and criminal penalties for a range of activities that may disrupt the pristine environment, including the introduction of non-native plants and animals, taking native mammals or birds, and dumping pollutants into the sea. American summer visitors to Antarctica include deputy marshals ready to enforce the country’s criminal laws, such as those against murder, that apply outside the United States. No murders have yet been reported, and even reports of burglary and robbery barely exist, probably in part because of the localized difficulties of concealing and removing stolen goods. Notice, however, that the situation effectively takes a step backward from global cooperation through its application of US law rather than international law to dispute situations.

THE UNITED NATIONS OUTER SPACE TREATY

The Antarctic Treaty naturally served as a template for the United Nations’ attempt to create an international agreement to govern, or at least to restrain, countries’ activities in space. In 1959, the United Nations created COPUOS, the United Nations Committee on the Peaceful Uses of Outer Space, to govern (in those days not a word to draw derision) the exploration and use of space to aid humanity through international cooperation, encouragement of space research, and the study of legal problems in space.⁴ COPUOS, which meets annually in Vienna, played a significant role in the creation of the major United Nations success relevant to space exploration, the 1967 Outer Space Treaty (to use its familiar short title), which was in force during the years of the Apollo landings on the moon (1969 through 1972).

The Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including the Moon and Other Celestial Bodies remains the foundational document of space law.⁵ More than a hundred nations, including all those likely to be involved in space exploration and exploitation except Iran, have ratified this treaty since 1967. Key provisions of this agreement forbid the placement of nuclear weapons or other weapons of mass destruction on the moon, in orbit, or anywhere else in outer space, and require that all celestial bodies are to be used exclusively for peaceful purposes. The treaty proclaims that outer space, including all celestial bodies, is not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means, and that all parties to the treaty shall follow international law in their activities relating to the exploration and use of outer space. We should note that the treaty does not define the term “national appropriation,” potentially leaving fertile ground for disputes. The Outer Space Treaty understandably reflects attitudes toward space activities predominant during the first decades after the launch of Sputnik in 1957. It creates an agreement among nations that limits their activities and embodies the principles of their countries’ laws, including their adherence to international law.

Nongovernmental actors received little notice in the treaty, making their most notable appearance in Article VI’s requirement that adhering countries “shall bear international responsibility for national activities in outer space … whether such activities are carried on by governmental agencies or by non-governmental entities, and for assuring that national activities are carried out in conformity with the provisions set forth in the present Treaty.” Those provisions basically bar nations from asserting sovereignty over celestial objects. Private corporations and individuals who might appropriate what they can, when they can, and where they can will find themselves subject only to any restrictions that their own country might impose upon them. For example, the treaty’s bar of “national appropriation,” taken literally, would allow a corporation to move an asteroid and mine it into nullity, simultaneously forbidding any nation to claim ownership, if the responsible nation did nothing to stop it. A lasting principle of international law dates from a 1927 maritime collision case known as Lotus, in which the International Court of Justice ruled that for any restriction on a nation to be internationally recognized, it must be stated clearly, so “that which is not explicitly prohibited is thereby permitted.” A clever space lawyer could argue, with some justification, that the Outer Space Treaty allows each country to control its own citizens to the extent that it chooses. Among other possibilities, this approach could bring to space a near-duplicate of Earth’s hundreds of separate codes of law. This would hardly help to allow the rational regulation of activities in space and on particular objects.

THE MOON TREATY

Despite its modest reach and lack of enforcement procedures, most observers judge the Outer Space Treaty a success. Nations aspiring to activities in space have signed the treaty as a mark of their seriousness, and no nation has violated its limited precepts so far. We can ascribe this broadly positive result to the equally broad principles and language of the Outer Space Treaty. The general comity among nations soon confronted the nuts-and-bolts aspect of lunar exploration and the prospect of numerous missions to more distant objects. After long negotiation, in 1979 members of the United Nations did succeed in concluding the Agreement Governing the Activities of States on the Moon and Other Celestial Bodies” popularly called the Moon Treaty.⁶ In contrast to the Antarctic and Outer Space Treaties, this treaty has received no agreement from any country currently capable of reaching the moon—a mark of the difficulty of passing from principles to rules. If this were not so, the need for a moon treaty, which is much greater than the need for a treaty dealing with the remainder of the solar system, would have led to the adoption of the former and postponement of the latter.

The Moon Treaty, whose formal title includes specific reference to “states,” makes numerous references to the “use” as well as the exploration of the moon and other celestial objects. It requires each nation to conform to international law and the Charter of the United Nations; to use the moon solely for peaceful purposes; and to coordinate its activities with others, guided by the principles of cooperation and mutual assurance. The treaty’s more provocative provisions, which largely explain the agreement’s failure, specify that “the exploration and use of the moon shall be the province of all mankind and shall be carried out for the benefit and in the interests of all countries” and that “in exploring and using the moon, States parties shall take measures to prevent the disruption of the existing balance of its environment, whether by introducing adverse changes … by its harmful contamination … or otherwise.” The attempt to limit their activities on the moon led all actual and aspiring spacefaring nations to reject the Moon Treaty. Only seven countries have ratified the agreement, while a dozen more have “acceded.” Neither category includes a likely participant in lunar exploration.

The Moon Treaty also deals with the “other celestial bodies” of its title. Its terms apply to Mars, the asteroids, the giant planets and their moons, and interloping comets and Kuiper belt objects that orbit beyond Neptune; it exempts only the Earth and objects that strike the Earth as a result of natural causes. Imposing the United Nations Charter as the international law applicable to activities on other worlds, the treaty follows its promotion of activities benefiting humankind by allowing nations to collect lunar samples, to establish crewed or uncrewed lunar bases, and to move freely over or even under the moon’s surface. Furthermore, as in the Antarctic Treaty, “the moon is not subject to national appropriation by any claim of sovereignty”; activities on the moon create no rights of ownership; and nations agreeing to the treaty “hereby undertake to establish an international regime, including appropriate procedures, to govern the exploitation of the moon as such exploitation is about to become feasible.”

In broad outline, the Moon Treaty aims to establish an international regime on the moon that would supervise any nation making efforts in exploration and development; it is an attempt to create in space what remains only a dream on Earth. Even more difficult for moon-ranging nations to accept, the treaty states that participating nations “shall bear international responsibility for national activities on the moon, whether such activities are carried out by governmental agencies or by non-governmental entities,” and for ensuring that national activities conform to the treaty. Furthermore, the treaty states that each nation can assure itself that other nations’ activities are “compatible” with the treaty’s specifications, with access for inspection of other nations’ installations. If a country suspects another of violating the treaty, it has a right to a prompt consultation to seek a resolution. Should the consultation fail to reach an acceptable resolution, the treaty calls for other peaceful means to settle the dispute. If that fails, the aggrieved nation may apply directly to the secretary general of the United Nations.

Comparison of the Outer Space and Moon Treaties emphasizes the conflict between high-minded principles and the commercial exploitation of natural resources. Art Dula, a lawyer with half a century of experience in the theory of space law, has written, “Present space law … has been forged almost entirely out of high academic ideals in advance of a practical commercial reality.… Free enterprise institutions simply cannot make significant investments in space while they are under the threat of lawsuits over the meaning of treaty terms of ex post facto appropriation of their investments by a nebulous future international regime.”⁷

Dula’s analysis received immediate confirmation in the worldwide negative governmental reactions to the Moon Treaty. The minimum number of nations needed to bring the treaty into force, five, signed on almost immediately; during the next four decades, another dozen, including Australia, Turkey, and Saudi Arabia, joined them. Countries likely to engage in exploration of the moon and beyond, which remained unified in their rejection, typically shared an antipathy to rules that would subject their activities in space to international law. In the United States, President Carter’s favorable attitude toward the treaty was replaced by Ronald Reagan’s negative one after he became president in 1981. The ensuing decades, which saw only modest innovations in lunar exploration, brought increasing awareness of the possibilities of non-state actions in space.

THE UNITED STATES SPACE ACT

The past decade of legislative and executive action in the United States has demonstrated the weakness of the Outer Space Treaty in actual regulation of activities in space. In 2015, growing recognition of corporate and individual activities in space led the United States to enact the Spurring Private Aerospace Competitiveness and Entrepreneurship (SPACE) Act.⁸ Without mentioning the United Nations or the Outer Space Treaty, the SPACE Act denies that the United States asserts sovereignty over any cosmic objects, but specifically allows US citizens and corporations to engage in the commercial exploration and exploitation of “space resources,” which exclude any biological life forms that may exist in space. A final subsection emphasizes the role of private enterprise by stating that a “U.S. citizen engaged in commercial recovery of an asteroid resource or a space resource shall be entitled to any asteroid resource or space resource obtained, including to possess, own, transport, use, and sell it according to applicable law, including U.S. international obligations.”

During 2017 and 2018, the Trump administration followed the Space Act with three space policy directives that concentrated on issues arising from commercial involvement in sending humans into space.⁹ The first of these replaced earlier language about the country’s goals in space exploration by directing the government to “lead an innovative and sustainable program of exploration with commercial and international partners to enable human expansion across the solar system and to bring back to Earth new knowledge and opportunities. Beginning with missions beyond low-Earth orbit, the United States will lead the return of humans to the Moon for long-term exploration and utilization, followed by human missions to Mars by and other destinations.”

More recently, in April 2020, the U.S. government issued Executive Order 13914, entitled “Encouraging International Support for the Recovery and Use of Space Resources,” which states that

Americans should have the right to engage in commercial exploration, recovery, and use of resources in outer space, consistent with applicable law. Outer space is a legally and physically unique domain of human activity, and the United States does not view it as a global commons. Accordingly, it shall be the policy of the United States to encourage international support for the public and private recovery and use of resources in outer space, consistent with applicable law. The United States is not a party to the Moon Agreement. Further, the United States does not consider the Moon Agreement to be an effective or necessary instrument to guide nation states regarding the promotion of commercial participation in the long-term exploration, scientific discovery, and use of the Moon, Mars, or other celestial bodies. Accordingly, the Secretary of State shall object to any attempt by any other state or international organization to treat the Moon Agreement as reflecting or otherwise expressing customary international law.¹⁰

The 2015 Space Act and Executive Order 13914 together make clear that the United States does not welcome restriction on activities in space by its government or its citizens. Instead, the executive order speaks of a policy “to encourage international support for the public and private recovery and use of resources in outer space, consistent with applicable law” before it rejects the concept of space as a “global commons” and proclaims the rights of U.S. citizens without reference to other countries. By direct implication, the executive order vetoes an international approach to the exploitation of space resources in favor of opening a path for private individuals and corporations to procure what they can from our celestial neighbors. An accompanying fact sheet states that “supportive policy regarding the recovery and use of space resources is important to the creation of a stable and predictable investment environment for commercial space innovators and entrepreneurs, and it is vital to the long-term sustainability of human exploration and development of the Moon, Mars, and other destinations.” One might reasonably argue that the best approach to maintaining “a stable and predictable investment environment” for the commercial exploitation of space resources would involve agreement among those nations whose citizens may compete for those resources.

In October 2020, a few months after the issuance of the executive order, eight countries—the United States plus seven others potentially involved in space exploration, with the notable exclusion of China and Russia—signed the Artemis Accords, an agreement aimed to govern exploration and exploitation of the moon.¹¹ Russia rejected the agreement as “too US-centric,” while China, aware of a US law that bars that country from engaging directly with it on space projects, expressed no opinion. The accords state that countries have the right to the ownership and use of resources derived from the moon. James Bridenstine, then the NASA administrator, compared these resources to fish in an ocean, which become property once they have been caught.¹² An obvious difference lies in the fact that fishing, if properly managed, does not appreciably diminish the number of fish in the sea, whereas appropriation of an asteroid, for example, reduces the number available for others to exploit.

In response to the Artemis Accords, University of British Columbia astronomer Aaron Boley and political scientist Michael Byers wrote an essay in Science magazine that criticized NASA’s approach of bilateral cooperation, proposing instead that the use of space resources should be determined within the COPUOS framework.¹³ The authors noted that acceptance of the Artemis Accords would make the United States the de facto gatekeeper to the moon and other celestial objects. Furthermore, because international law often treats acquiescence as consent, the United States’ activities—for example, in mining, refining, and removing the lunar regolith—could become established as the norm. The authors noted that multilateral agreements require compromise and time to reach fruition, while the United States approach takes a “prisoner’s dilemma” approach, in which a powerful actor denies other participants the chance to communicate with one another, or, in this case, exerts a time pressure that makes communication more difficult. “NASA’s actions must be seen for what they are,” Boley and Byers wrote, “a concerted, strategic effort to redirect international space co-operation in favor of short-term U.S. commercial interests, with little regard for the risks involved.”

The Biden administration in the United States has so far shown little interest in modifying the policies and attitudes embodied in the Space Act and the executive order. A greater willingness to investigate and develop international collaboration for the exploration and exploitation of the moon and other objects may yet appear among the leaders of the United States if they are again touched by the better angels of our nature. If China maintains an attitude similar to that described above, only a strong international collaboration seems likely to provide a counterweight capable of bringing all human spaceborne activities under a rational and effective regime.

Realistically, all restrictions imposed by law or a code of morals are resented by some, or they would not be needed. It seems clear that space law will develop organically rather than from long-term agreements that all spacefaring nations and individuals will respect and follow. For now, whether or not most exploration involves humans in space, conflict lies just over the horizon—more precisely, wherever resources exist. Even the L4 and L5 points described in Chapter 2, where spacecraft can be “parked” in orbits that remain comparatively free from the perturbing forces that the planets exert at other locations, represent such a resource, because although they include thousands of cubic miles of space, increasing numbers of objects there will eventually produce collisions.

We possess no effective mechanism to deal with the overall problem beyond goodwill and pragmatism, which can take us only so far. Although the dangers from human conflict in space may never rise to equal those from accidents, we cannot ignore them. As with earthbound conflicts, we may hope that the negative effects of war inspire us to create institutions, such the United Nations, that could temper human nature and direct it toward positive outcomes. Any assessment of how well this has worked so far leaves us at a considerable distance from this desirable goal.

Humans will not cease exploring, as T. S. Eliot noted, though his conclusion that “the end of all our exploration will be to arrive where we began and to know the place for the first time” rings rather strange in space exploration circles.¹⁴ If we choose wisely, examine our motivations, and use our robotic emissaries for exploration, a better outcome awaits us than if we insist that humans must go into space.

Epilogue

Perspectives on Space Exploration in 2040—and Far Beyond

Astronomers are ever mindful of the vast timescales that stretch out in both directions, toward the past and toward the future. Our solar system is about 45 million centuries old. Life on Earth has taken most of that time to evolve—from its still-mysterious origins into the intricate biosphere within which we humans form a part. We’re extremely late arrivals, occupying an immensely thin sliver of the cosmic timeline. “Modern” humanoids appeared just a few thousand centuries ago. Communities that used technology to build the first cities and invent agriculture appeared only around 100 centuries ago. The last one or two centuries have brought an unprecedented rate of change in human societies, creating a fast-rising and interconnected global population empowered by transformative technologies. The emergence of spaceborne technology currently spans less than a single century among the 45 million of Earth’s history.

But the future stretches before us in a still more prolonged manner. We humans may not represent anything close to the halfway stage in the emergence of complexity on our planet. Our sun has yet to reach the halfway point of its life, while the cosmos will endure far, far longer than our solar neighborhood.

In Chapter 7, we ventured to speculate on our comparatively far-off future, and perhaps strayed into the realm of science fiction. But the timescales for the development and spread of space colonies, for pioneering interstellar voyages, and for the technological wonders that would allow them potentially take us into the future only a few thousand years—not millions, still less billions. We cannot accurately predict what could happen over the immense spans that might take us into remote post-human eras that our brains and imagination can’t conceive. But for now, always aware that global catastrophes within the next few decades could change our outlook, we may remain confident that our capabilities as spacefarers and our knowledge of the wider cosmos remain in infancy.

Let us shelve such long-term, all too seductive visions to refocus on this book’s primary theme: the role of astronauts in the foreseeable near-term future. Here experience and logic impose serious caveats. History shows us that we cannot reliably forecast technical breakthroughs, geopolitical upheavals, or changes in social attitudes even a few decades into the future. Inventions, trends, and vectors of change are difficult to foresee and often surprise us, while the rates at which changes will occur are even harder to predict.

As a result, even though we, the authors of this book, are astronomers who have grown comfortable with contemplating vast stretches of space and time, we remain diffident about making forecasts. We nonetheless predict with confidence that during the next few decades, robots and artificial intelligence will grow vastly more capable, closing the gap with human capabilities and surpassing them in ever more domains. These developments will surely reduce the need for astronauts in the exploitation of space, leaving us to choose whether humans ride along, viewing themselves as explorers, adventurers, or colonizers.

We feel most confident in forecasting trends in the space enterprise between now and the 2040s. This confidence stems largely from the fact that large space missions often span two decades or more, from their conception through their design, construction, travel time to the destination, and accomplishment of their goals after arrival. Let us therefore look forward to the 2040s to ask what our society’s efforts to explore the solar system will look like.

We venture three major predictions. If all three prove correct, we shall have a rate of success far better than average. On the other hand, these qualify as conservative predictions, and of course as short-term ones in the context of our civilization’s future.

First, we’re confident that Mars’s domination of space exploration in public support, and therefore to a large extent among funding agencies, will only increase. China may land astronauts on the moon and establish bases there, an outcome even more likely than similar efforts by the United States and its partners because it correlates with China’s desire to outshine other countries. Nevertheless, the fact that astronauts have already visited the moon will reduce the psychological impact of new efforts there. Even the construction of lunar habitats could well be regarded as developing the techniques necessary for astronauts to live on Mars. Actual conflict between lunar astronauts—for example, over property rights to the moon’s Peaks of Eternal Light—could change this attitude, but ordinary rivalry could intrigue the public without reducing interest in the primary goal: Mars.

Second, whether or not astronauts reach Mars by 2040, the search for life on the red planet will escalate, thereby drawing more attention among both the public and the community of exobiologists. These trends will grow impressively stronger, at least temporarily, if our robotic probes uncover strong evidence of fossil life, and will go through the roof if we find living Martian microbes. Both of these discoveries would almost certainly occur on Earth, within samples brought here from Mars, because the evidence for fossil or existing life would most likely reside in microscopic or even submicroscopic details. The crucial step in finding Martian life, however, would have been taken on Mars with the proper selection of samples. We therefore stand by our prediction that a decade or more from now, ongoing sample return programs will rely on ever more capable rovers to select and obtain the most promising material (and on the spacecraft that carry it to Earth), rather than on astronauts whose requirements for survival rise orders of magnitude beyond those needed for robotic explorers.

To the extent that members of the public and funding agencies recognize and accept this vision of the future, they will realize, possibly consciously, that the desire to see astronauts on Mars projects our desires to establish human societies on another planet. This may well occur at some point in the future, whether or not these societies represent either an adjunct to terrestrial civilization or the necessary escape pod promoted by Stephen Hawking and Elon Musk. This diaspora will not occur by 2040, however, unless the passions that once created a race to the moon bypass the rational approach of an international effort that respects the need to maintain a pristine Mars, so far as possible, in order to preserve our ability to discover Martian life and to assure that it has not been contaminated by life brought from Earth.

What of the deeply held desires of Elon Musk and Jeff Bezos to send humans to Mars despite the rationale expressed earlier? Here a rather cynical compromise may prove possible. If these men succeed in sending astronauts to the moon in an attempt to establish lunar colonies, that may partially slake their desires while simultaneously demonstrating the much greater difficulty of the reality compared to the planning stages of these efforts.

Third, whether or not we find life on Mars, the outer solar system will receive more attention and effort. This conclusion springs from the search for life on Mars. If we do find life there, the impulse to search for life on other objects in the solar system will naturally increase, and if we do not, human nature will likely call for increased attempts to look elsewhere.

Where would we look? Recent discoveries made by automated spacecraft have shown that each of four key objects beyond Mars have strong claims for our attention. Thanks to astronomical history, they bear names from ancient mythology: Ceres, Europa, Enceladus, and Titan. These are, respectively, the largest of the asteroids, with a diameter of 588 miles; the smallest of Jupiter’s four main moons (1940 miles in diameter); a strange little world around Saturn (just 313 miles in diameter); and Saturn’s much larger satellite, almost tied with Jupiter’s Ganymede as the largest moon in the solar system (3200 miles across).

These four moons share a common distinction: liquid. If life requires a liquid medium within which molecules can float, interact, and eventually produce living systems, then we should search for life on objects with liquids in abundance. The absence of liquid water flowing on Mars made this search appear hopeless until astronomers saw evidence of transient water on the surface and suggestions of water underground. Astrobiologists traditionally call for “following the water,” but other liquids may suffice, as the solar system demonstrates. The Dawn spacecraft, which orbited Ceres in 2015 and afterward, found that the largest asteroid has abundant underground water. Automated spacecraft to the Jupiter and Saturn systems made a similar discovery for Europa and Enceladus, but those objects guard their water beneath worldwide surfaces of solid ice. Titan also has liquid, not hidden beneath a frozen surface but in large ponds and lakes on its surface—not liquid water but instead liquid ethane, a hydrocarbon similar to terrestrial antifreeze.

Just as robots made these discoveries on the big four candidates, robots will search for life there. Ceres lies more than twice as far from us as Mars; Europa is almost twice as far as Ceres; and Enceladus and Titan are almost twice as distant as Europa. Visions of astronauts landing, for example, on Europa’s or Enceladus’s icy exterior and drilling—no one now knows how deeply—to reach the ocean below and to sample its contents have yielded to the more rational approach of sending more and better robot explorers there. Astronaut journeys to these worlds would require not months but years. They may occur someday, but not before 2040. Robots, however, can go boldly where humans rightly fear to tread.

These robotic probes are being developed by NASA, ESA, Russia, and China; multiple collaborations are involved, and other nations may enter the quest. An interesting perspective on the politics of future exploration came in 2021 from Mitch Daniels, the co-chair of the National Academy of Sciences study presented in Chapter 2. He emphasized that we should not forget how difficult it will be to send astronauts to Mars:

As dazzling as the Perseverance achievement is, it involves radiation-proof robots, not fragile humans, and a seven-foot, one-metric-ton craft, not the 40-metric ton, two-story system that a human landing, life support, and ascent vehicle would require. It will be exponentially harder for humans to fly safely to Mars, establish a sustained presence, and survive to return to Earth. To do so, our commission concluded, would require making the goal a central, single-minded priority of the U.S. space program; a relentless, unswerving multidecade commitment to a pre-agreed path to reach the goal; and constant investments in amounts well about the rate of inflation. American democracy is not very good at any of these things.… So if our system is ill-suited to the task, what kind of nation would be most likely to reach this next frontier? Oh, in theory, one with a patient, farsighted culture, accustomed by history to taking the very long view. A country with an authoritarian regime, capable of commandeering the massive resources necessary without making concessions to public opinion.¹

Daniels proceeded to pass over the question of the desirability of any country sending humans into space, and expressed his hope—as an American—that he would not have to spend the next half century watching Chinese astronauts or robots “boldly go where no man has gone before.” He hoped that this would not occur because, in his view, the political freedoms in the United States allow “nimble private companies, unencumbered by political realities, backed by private fortunes imbued with the explorer spirit and, in some cases, a dream of profits,” to ensure that “the first human on Mars, as on the moon, will be a free citizen of a free country.”

Many will share our belief that this echo of the Cold War space race represents an inappropriate posture for analyzing the desirability of humans in space. We must also remain agnostic about international relations and geopolitics even in the 2040s, and certainly during the second half of this century. We resonate, however, with this statement in the National Academy’s report:

The committee … acknowledges the possibility that over the half-century considered, advances in science and technology, in bioengineering, artificial intelligence and other fields may come far more quickly and unpredictably than the advance contemplated for the human spaceflight pathways proposed in this report. Breakthroughs in these other realms could serve to solve many of the large obstacles to exploration beyond [near-Earth orbit]. In particular, the line between the human and the robotic may be blurred more profoundly than simple linear extrapolations predict. In such an eventuality, exploration of the “last frontier” of space might well occur in a more rapid and far-reaching way than is envisioned in this report; indeed, whether it would still be accurately described as human exploration is unknowable.²

Let us hope that we pursue the quest to explore our cosmic neighborhood in a cooperative fashion and sets the tone for the centuries to come. We must remain mindful of the huge spans of time lying ahead, when our descendants, whether human or post-human, will surely witness ever more amazing ventures. To quote the author and visionary H. G. Wells, “The past is the beginning of the beginning, and all that has been is but the twilight of the dawn.”³

APPENDIX

Timeline of Key Events in Space Exploration

June 20, 1944    German V2 rocket makes the first journey into space, defined as reaching altitudes above 100 kilometers (62 miles).

1945–1952    V2 rockets used in test flights in Britain, the Soviet Union, and the United States (White Sands Proving Ground, New Mexico).

1952–1958    Redstone rockets, the first large US ballistic missiles, are developed and deployed under the leadership of German rocket scientists brought to the United States, with launches from the White Sands Proving Ground.

October 4, 1957    The Soviet Union launches the 184-pound Sputnik, the first artificial satellite of Earth.

February 1, 1958    The United States launches the 31-pound Explorer 1, its first artificial Earth satellite.

February 12, 1961    The Soviet spacecraft Venera 1 becomes the first probe to another planet, though it loses telemetry when not quite at Venus.

April 12, 1961    Soviet cosmonaut Yuri Gagarin becomes the first human to orbit the Earth.

February 20, 1962    John Glenn becomes the first American to orbit the Earth.

December 14, 1962    NASA’s Mariner 1 becomes the first spacecraft to pass close to another planet.

June 14, 1963    Soviet cosmonaut Valentina Tereshkova becomes the first woman to orbit the Earth.

November 28, 1964    The United States’ Mariner 4 makes the first flyby of Mars.

March 1, 1966    The Soviet Union’s Venera 3 makes the first crash landing on another planet.

April 3, 1966    The Soviet Union’s Luna 10 becomes the first spacecraft to orbit the moon.

June 2, 1966    NASA’s Surveyor 1 makes the first soft landing on the moon.

October 18, 1967    Soviet Union’s Venera 4 makes first observations from within Venus’s atmosphere.

October 7, 1968    NASA’s OSO-2 becomes the first spacecraft to make telescopic observations from space; the craft remains active for more than three years in orbit.

December 21, 1968    Apollo 8 becomes the first crewed spacecraft to leave near-Earth orbit and the first crewed spacecraft to orbit the moon.

July 20, 1969    The Apollo 11 lander brings two humans to the moon for the first time.

December 15, 1970    The Soviet Union’s Venera 7 makes the first soft landing on another planet.

April 19, 1971    Launch of the first Earth-orbiting space station, the Soviet Union’s Salyut.

May 28, 1971    The Soviet Mars 3 spacecraft makes the first soft landing on Mars and transmits for fifteen seconds.

May 30, 1971    NASA’s Mariner 9 becomes the first orbiter of Mars.

August 21, 1972    NASA’s OSO-3 satellite, renamed Copernicus, successfully observes sources of ultraviolet and X-ray emissions for more than eight years.

December 14, 1972    Apollo 17’s astronauts conclude the ninth human journey to the moon; the moon would remain unvisited by humans for more than fifty years after their departure.

December 3, 1973    NASA’s Pioneer 10 makes the first flyby of Jupiter, and later becomes the first artificial object to leave the solar system.

October 22, 1975    The Soviet Union’s Venera 9 becomes the first orbiter of Venus.

July 20 and September 3, 1976    Viking 1 and Viking 2 land on Mars, and later make the first tests for life in Martian soil.

October 9, 1978    The four probes of NASA’s Pioneer Venus Multiprobe enter Venus’s atmosphere; one probe survives for forty-five minutes on Venus’s surface.

March 5 and July 9, 1979    NASA’s Voyager 1 and Voyager 2 fly by Jupiter.

September 1, 1979    NASA’s Pioneer 11 makes the first flyby of Saturn.

November 12, 1980, and August 25, 1981    NASA’s Voyager 1 and Voyager 2 fly by Saturn.

January 24, 1984    NASA’s Voyager 2 makes a flyby of Uranus.

August 25, 1989    NASA’s Voyager 2 makes a flyby of Neptune.

April 24, 1990    Launch of NASA’s Hubble Space Telescope. Soon the mirror’s defective shape is discovered. Five astronaut missions (in 1994, 1997, 1999, 2002, and 2009) add corrective lenses, better detectors, and improved cameras.

December 4, 1996    NASA’s Mars Sojourner becomes the first rover on another planet.

November 20, 1998    Launch of the International Space Station.

November 2, 2000    First astronauts reach the International Space Station, which has been continuously inhabited since then.

February 12, 2001    NASA’s NEAR Shoemaker spacecraft makes the first landing on an asteroid.

January 2, 2004    NASA’s Stardust spacecraft collects the first particles from a comet’s immediate vicinity, returning them to Earth on January 15, 2006.

March 2, 2004    Launch of European Space Agency’s Rosetta spacecraft. It reaches Comet 67P / Churyumov-Gerasimenko on August 6, 2014, deploying its Philae lander module to make the first soft landing on a comet.

July 1, 2004    NASA’s Cassini spacecraft enters orbit around Saturn, carrying the European Space Agency’s Huygens probe.

June 14, 2005    The European Space Agency’s Huygens probe lands on Titan, Saturn’s largest moon.

November 19, 2005    The Japanese Hayabusa spacecraft lands on the asteroid Itokawa, returning to Earth with the first samples from an asteroid on June 30, 2010.

November 27, 2006    Launch of the European Space Agency’s COROT spacecraft, the first to be dedicated to searching for extrasolar planets.

November 5, 2007    Chang’e 1 becomes the first Chinese spacecraft to orbit the moon.

November 14, 2008    India’s Chandrayaan spacecraft’s Moon Impact Probe crashes onto the lunar surface near Shackleton Crater, close to the moon’s south pole, and finds evidence of water ice beneath the surface.

March 6, 2009    Launch of NASA’s Kepler spacecraft to search for exoplanets.

June 13, 2010    Japan’s Hayabusa spacecraft achieves the first asteroid sample return.

March 18, 2011    NASA’s MESSENGER spacecraft become the first to orbit Mercury.

July 11, 2011    Atlantis departs on STS-135, the final flight of the space shuttle.

August 6, 2012    The Curiosity rover lands on Mars, travels fifteen miles over the next decade.

December 14, 2013    China’s Chang’e 3 spacecraft makes the first soft landing on the moon since the Soviet Union’s Luna 24 in 1976.

November 12, 2014    The European Space Agency’s Rosetta mission makes the first soft landing on a comet.

March 6, 2015    NASA’s Dawn spacecraft become the first to orbit Ceres, the largest asteroid, having previously (July 16, 2011) entered orbit around Vesta, the fourth-largest asteroid.

July 14, 2015    NASA’s New Horizons spacecraft makes the first flyby of Pluto and its large moon Charon.

July 5, 2016    NASA’s Juno probe enters orbit around Jupiter.

October 19, 2017    Discovery of ‘Oumuamua, the first object in the solar system identified as originating outside it, apparently a chunk of frozen nitrogen from a Pluto-like object in another planetary system.

May 21, 2018    China sends the Queqiao spacecraft into orbit around the moon in order to relay data from the moon’s far side, which never faces the Earth.

January 3, 2019    China’s Chang’e 4 spacecraft makes the first landing on the moon’s far side, with signals relayed to Earth via the Queqiao spacecraft.

December 16, 2020    China’s Chang’e 5 spacecraft returns lunar sample material to Earth.

February 9, 2021    The United Arab Emirates Amal (Hope) spacecraft enters orbit around Mars.

February 10, 2021    China’s Tianwen-1 spacecraft enters orbit around Mars and prepares to send a rover to the Martian surface.

February 18, 2021    NASA’s Perseverance rover lands on Mars.

April 19, 2021    The Ingenuity helicopter makes the first aerial flight on another planet.

December 2021    NASA’s James Webb Space Telescope scheduled for launch from French Guiana.

Notes

Introduction

1. David Shayler and David Harland, The Hubble Space Telescope: From Concept to Success (New York: Springer Praxis Books, 2016) and Enhancing Hubble’s Vision: Service Missions That Expanded Our View of the Universe (New York: Springer Praxis Books, 2016).

2. Walter McDougall, The Heavens and the Earth: A Political History of the Space Age (New York: Basic Books, 1985).

3. John Noble Wilford, “A Salute to Long Neglected ‘Father of American Rocketry,’ ” New York Times, October 5, 1982, https://www.nytimes.com/1982/10/05/science/a-salute-to-long-neglected-father-of-american-rocketry.html.

4. An excellent history of the space program through history is Roger Launius, Space Exploration: From the Ancient World to the Extraterrestrial Future (Washington, DC: Smithsonian Books, 2018).

5. David Spergel telephone interview, December 25, 2021.

Chapter 1: Why Explore?

1. Megan Erickson, “Neil DeGrasse Tyson: Science Is in Our DNA,” Big Think, May 2, 2012, https://bigthink.com/humanizing-technology/neil-de-grasse-tyson.

2. “Should Humans Establish Colonies on Mars?,” discussion on Kialo, accessed August 15, 2021, https://www.kialo.com/colonizing-another-planet-is-in-line-with-the-human-spirit-of-exploration-2495.19?path=2495.0~2495.1_2495.19.

3. T. S. Eliot, quoted in Evelyn Lamb, “What T. S. Eliot Told Me about the Chain Rule,” Scientific American, March 21, 2014, https://blogs.scientificamerican.com/roots-of-unity/what-ts-eliot-told-me-about-the-chain-rule/.

4. Derrick Pitts, “The Future of Space Exploration,” Franklin Institute, July 17, 2019, https://www.fi.edu/blog/future-of-space-exploration.

5. “Read, Watch President Trump’s Full Republican Nomination Acceptance Speech,” WQAD, August 27, 2020, https://www.wqad.com/article/news/nation-world/president-donald-trump-rnc-speech-text/507-e8cd51c1-203a-488e-b782-4df532ab527e.

6. NASA’s Journey to Mars: Pioneering Next Steps in Space Exploration https://www.nasa.gov/sites/default/files/atoms/files/journey-to-mars-next-steps-20151008_508.pdf.

7. Kareem Shaheen, “First Mars Mission from UAE Aims to Inspire a New Generation of Space Scientists,” National Geographic, July 20, 2020, https://www.nationalgeographic.com/science/article/uae-mars-mission-hope-aims-inspire-new-generation-space-scientists.

8. “NASA’s Next Giant Leap,” NASA, July 18, 2014, https://mars.nasa.gov/news/1670/nasas-next-giant-leap/.

9. “Why Mars?,” Explore Mars, 2017, https://www.exploremars.org/wp-content/uploads/2017/05/EM-17-WHY-b-proof.pdf.

10. Clementine Poidatz, “My Personal Mission to (and for) Mars,” Huffington Post, November 15, 2016, https://www.huffpost.com/entry/my-personal-mission-to-and-for-mars_b_582b22d7e4b0c4b63b0e74bf.

11. John F. Kennedy speech at Rice University, September 12, 1962, https://er.jsc.nasa.gov/seh/ricetalk.htm.

12. James S. J. Schwartz, “Myth-Free Space Advocacy Part I—The Myth of Innate Exploratory and Migratory Urges,” Acta Astronautica 137 (2017): 450–460.

13. Oliver Morton, The Moon: A History for the Future (New York: Public Affairs, 2019), 199.

14. NASA’s discussion of “Why We Explore” and “Why Mars?” can be found at https://www.nasa.gov/exploration/whyweexplore/why_we_explore_main.html#.YN0nCBNKj4M.

15. David Shayler and David Harland, The Hubble Space Telescope: From Concept to Success (New York: Springer Praxis Books, 2016) and Enhancing Hubble’s Vision: Service Missions That Expanded Our View of the Universe (New York: Springer Praxis Books, 2016).

16. Hearing before the Subcommittee on Transportation, Aviation, and Materials of the Committee on Science and Technology, US House of Representatives, Ninety-eighth Congress, Second Session, Part 2 (Washington, DC: U.S. Government Printing Office, 1984). From p. 340: “Mr. NELSON. Do you think there is some truth to the practicality of Washington politics, that ‘no Buck Rogers, no bucks’?”

17. Wikipedia, “Budget of NASA,” https://en.wikipedia.org/wiki/Budget_of_NASA.

18. Patrick Chase, “NASA, Space Exploration, and American Public Opinion,” Medium, July 14, 2020, https://medium.com/westeastspace/nasa-space-exploration-and-american-public-opinion-139cbc1c6cce.

19. National Research Council, Pathways to Exploration: Rationales and Approaches for a U.S. Program of Human Space Exploration (Washington, DC: National Academies Press, 2014), 85.

20. National Research Council, Pathways to Exploration, 96.

21. Courtney Johnson, “How Americans See the Future of Space Exploration, 50 Years after the First Moon Landing,” Pew Research, July 17, 2019, https://www.pewresearch.org/fact-tank/2019/07/17/how-americans-see-the-future-of-space-exploration-50-years-after-the-first-moon-landing/.

22. National Research Council, Pathways to Exploration, 96.

23. National Research Council, Pathways to Exploration, 98.

24. National Research Council, Pathways to Exploration, 99.

25. National Research Council, Pathways to Exploration, 100.

26. National Research Council, Pathways to Exploration, 2.

27. National Research Council, Pathways to Exploration, 81.

Chapter 2: Organizing Space

1. “He that hath wife and children hath given hostages to fortune; for they are impediments to great enterprises, either of virtue or mischief.” Francis Bacon, “Of Marriage and the Single Life,” first published in 1625.

2. Roger Launius, Space Exploration: From the Ancient World to the Extraterrestrial Future. (Washington, DC: Smithsonian Books, 2018).

3. A useful reference can be found at “What Is a Lagrange Point?,” NASA, March 27, 2018, https://solarsystem.nasa.gov/resources/754/what-is-a-lagrange-point/.

4. See the discussion of this quotation at https://quoteinvestigator.com/2013/10/20/no-predict/.

5. For a map of the eclipse track, see “Total Solar Eclipse of 2027 Aug 02,” NASA, last updated March 14, 2014, https://eclipse.gsfc.nasa.gov/SEgoogle/SEgoogle2001/SE2027Aug02Tgoogle.html.

6. The escape velocity from an object equals the square root of the ratio (2GM / R), where G is Newton’s gravitational constant and M and R are the mass and radius of the object. Since an object’s mass varies in proportion to the cube of its radius times its average density, the ratio (M / R) varies in proportion to R², and its square root varies in direct proportion to R. Thus the escape velocity varies in proportion to the object’s radius times the square root of its average density. For example, Mars has a radius equal to 53 percent of Earth’s and an average density 71 percent of Earth’s, so its escape velocity equals 45 percent of Earth’s: 3.1 miles per second instead of 6.95.

7. This estimate is based on a total cost estimated at $150 billion, divided by 20,000 potential astronaut-days. If one assigns half of the total costs to the equipment, $150 billion would pay for 10,000 astronaut-days at $7.5 million each.

8. Jason Daley, “Secrets of Stonehenge Found in Quarries 180 Miles Away,” Smithsonian Magazine, February 25, 2019, https://www.smithsonianmag.com/smart-news/secrets-stonehenge-found-quarries-180-miles-away-180971562/.

9. Nick Woolf and Roger Angel, “Pantheon Habitat Made from Regolith, with a Focusing Solar Reflector,” Philosophical Transactions of the Royal Society A: Mathematical, Physical, and Engineering Sciences, published online November 23, 2020, https://royalsocietypublishing.org/doi/10.1098/rsta.2020.0142.

Chapter 3: Near-Earth Orbit

1. See “Your Guide to NASA’s Budget,” The Planetary Society, accessed August 15, 2021, https://www.planetary.org/space-policy/nasa-budget

2. Claus Jensen, No Downlink: A Dramatic Narrative about the Challenger Accident and Our Time (New York: Farrar, Straus, and Giroux, 1996).

3. “International Space Station,” Wikipedia, accessed August 15, 2021, https://en.wikipedia.org/wiki/International_Space_Station. Updates are available at NASA’s International Space Station website, https://www.nasa.gov/mission_pages/station/main/index.html.

4. “NASA Administrator Bill Nelson,” NASA, May 3, 2021, https://www.nasa.gov/feature/nasa-administrator-bill-nelson/.

5. Becky Ferreira, “Chris Hadfield’s Spirited Song in Space Was No ‘Oddity,’ ” New York Times, November 2, 2020, https://www.nytimes.com/2020/11/02/science/chris-hadfield-space-oddity.html.

6. “Forty Years of Living in Outer Space,” BBC, May 16, 2013, https://www.bbc.com/future/article/20130516-four-decades-of-living-in-space.

7. “How SpaceX Lowered Costs and Reduced Barriers to Space,” The Conversation, https://theconversation.com/how-spacex-lowered-costs-and-reduced-barriers-to-space-112586/

8. Emilee Speck, “NASA Might Not Repeat Test of Moon Rocket to Preserve It for Launch Later This Year,” https://www.clickorlando.com/news/local/2021/01/20/nasa-might-not-repeat-test-of-moon-rocket-to-preserve-it-for-launch-later-this-year/.

9. Francis Slakey and Paul D. Spudis, “Robots vs. Humans: Who Should Explore Space?,” Scientific American, February 1, 2008, https://www.scientificamerican.com/article/robots-vs-humans-who-should-explore/.

10. Haylie Kasap, “Exotic Glass Fibers from Space: The Race to Manufacture ZBLAN,” ISS National Laboratory, December 11, 2018, https://www.issnationallab.org/iss360/exotic-glass-fibers-from-space-the-race-to-manufacture-zblan/.

11. James Oberg, “Surviving the Isolation of Space,” NBC News, August 22, 2003, https://www.nbcnews.com/id/wbna3077943.

12. Mike Massimino, Spaceman: An Astronaut’s Unlikely Journey to Unlock the Secrets of the Universe (New York: Three Rivers Press, 2016), 176–177.

13. An excellent and detailed discussion of the hazards of radiation in space is “Space Radiation,” NASA Human Research Program Engagement and Communications, accessed August 15, 2021, https://www.nasa.gov/sites/default/files/atoms/files/space_radiation_ebook.pdf. Regarding other causes of death revealed by the data: for non-Russian astronauts, 38 percent of deaths resulted from accidents; the comparable figure among Russian cosmonauts was only 17 percent.

14. Adam Mann, “Starlink: SpaceX’s Satellite Internet Project,” Space.com, May 28, 2021, https://www.space.com/spacex-starlink-satellites.html.

15. Christian Davenport, “Thousands More Satellites Could Soon Be Launched into Space. Can the Federal Government Keep Up?,” Washington Post, July 23, 2020.

16. Louis de Gouyon Matignon, “The Kessler Syndrome,” Space Legal Issues, March 27, 2019, https://www.spacelegalissues.com/space-law-the-kessler-syndrome/.

17. L. Lebreton et al., “Evidence That the Great Pacific Garbage Patch is Rapidly Accumulating Plastic,” Nature Scientific Reports 8, no. 4666 (2018).

Chapter 4: The Moon

1. For a history of lunar orbiters, see “The Lunar Orbiter Program,” Lunar and Planetary Institute, accessed August 15, 2021, https://www.lpi.usra.edu/lunar/missions/orbiter/.

2. A history of lunar landers is at “Every Mission to the Moon, Ever,” The Planetary Society, accessed August 15, 2021, https://www.planetary.org/space-missions/every-moon-mission.

3. A. G. Brown, J. Holland, and A. Peckett, “Orange Soil from the Moon,” Nature 242 (1973): 515–516, https://doi.org/10.1038/242515a0.

4. A wide-ranging report and discussion of lunar water is “NASA Rover to Search for Water, Other Resources on Moon,” NASA, May 20, 2021, https://www.nasa.gov/feature/nasa-rover-to-search-for-water-other-resources-on-moon.

5. The NASA website for VIPER is at https://www.nasa.gov/viper.

6. Martin Elvis, Tony Milligan, and Alanna Krolikowski, “The Peaks of Eternal Light: a Near-Term Property Issue on the Moon,” accessed August 15, 2021, available at https://arxiv.org/pdf/1608.01989.pdf.

7. Saptarshi Bandyopadhyay, “Lunar Crater Radio Telescope (LCRT) on the Far-Side of the Moon,” NASA, April 7, 2020, https://www.nasa.gov/directorates/spacetech/niac/2020_Phase_I_Phase_II/lunar_crater_radio_telescope/.

8. “The World’s Largest Radio Telescope Should Open its Skies to All,” Nature 590 (2021): 527, https://doi.org/10.1038/d41586-021-00468-3.

9. “Helium-3 Mining on the Lunar Surface,” European Space Agency, accessed August 15, 2021, https://www.esa.int/Enabling_Support/Preparing_for_the_Future/Space_for_Earth/Energy/Helium-3_mining_on_the_lunar_surface.

10. Frank Close, “Fears over Factoids,” Physics World, August 2007, 16–17.

11. Information about the award is at https://www.aaai.org/Awards/squirrel-ai-award-call.php.

12. Ian Crawford, “Dispelling the Myth of Robotic Efficiency,” Astronomy and Geophysics 53, no. 2 (2012): 2.22–2.26.

13. Andrew Jones, “China, Russia Reveal Roadmap for International Moon Base,” SpaceNews, June 16, 2021, https://spacenews.com/china-russia-reveal-roadmap-for-international-moon-base/.

14. For a good summary of the Artemis program, SLS, the Orion spacecraft, and the Lunar Gateway, see “Artemis, NASA’s Moon Landing Program,” The Planetary Society, accessed August 15, 2021, https://www.planetary.org/space-missions/artemis.

15. “NASA’s Plan for Sustained Lunar Exploration and Development,” NASA, April 2020, https://www.nasa.gov/sites/default/files/atoms/files/a_sustained_lunar_presence_nspc_report4220final.pdf.

16. Karen Shahar and Dov Greenbaum, “Lessons in Space Regulations from the Lunar Tardigrades of the Beresheet Hard Landing,” Nature Astronomy 4 (February 13, 2020): 208–209.

17. Carl Sagan, Elliott C. Levinthal, and Joshua Lederberg, “Contamination of Mars,” Science 159 (March 15, 1968): 1191–1196.

Chapter 5: Mars

1. Karen Lee, “People Used to Believe Aliens Built Canals on Mars. Here’s Why You Should Care,” Fishwrap (blog), December 18, 2018, https://blog.newspapers.com/mars-canals/.

2. Camille Flammarion, La Planète Mars et ses conditions d’habitabilité (Paris: Gauthier-Villars et Fils, 1892). Available in English as Camille Flammarion’s The Planet Mars, as Translated by Patrick Moore (New York: Springer, 2014).

3. William Graves Hoyt, Lowell and Mars (Tucson: University of Arizona Press, 1976).

4. For Burroughs’s influence on Carl Sagan, see “Sagan’s Youth and the Progressive Promise of Space,” Library of Congress, accessed August 15, 2021, https://www.loc.gov/collections/finding-our-place-in-the-cosmos-with-carl-sagan/articles-and-essays/carl-sagan-and-the-tradition-of-science/sagans-youth-and-the-progressive-promise-of-space.

5. John McPhee’s simile appeared in his book Basin and Range (New York: Farrar, Straus & Giroux, 1982) and is quoted in Helen Thompson, “What Does ‘Deep Time’ Mean to You?,” Smithsonian Magazine, September 9, 2014, https://www.smithsonianmag.com/science-nature/what-does-deep-time-mean-to-you-180952603/.

6. Harry McSween quoted in “As Perseverance Approaches Mars, Scientists Debate Its Sampling Strategy,” All-News, February 16, 2021, https://all-news.co/as-perseverance-approaches-mars-scientists-debate-its-sampling-strategy/.

7. “Mars Sample Return,” European Space Agency, accessed August 15, 2021, https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/Exploration/Mars_sample_return.

8. Jeffrey Hoffman, telephone interview, December 21, 2020.

9. Steve Swanson, “Are Astronauts Worth Tens of Billions of Dollars in Extra Costs to Go to Mars?,” Associated Press, April 9, 2019, https://apnews.com/article/b76ff7b68cfb0c93919a62b3c7507912.

10. Steven Squyres, Roving Mars: Spirit, Opportunity, and the Exploration of the Red Planet (New York: Hyperion, 2005).

11. Chris McKay, email, April 17, 2021.

12. For Durante’s views, see European Space Agency, “The Radiation Showstopper for Mars Exploration,” June 3, 2019, https://phys.org/news/2019-06-showstopper-mars-exploration.html.

13. Meghan Bartels, “Astronauts Going to Mars Will Absorb Crazy Amounts of Radiation. Now We Know How Much,” Space.com, September 20, 2018.

14. Francis Cucinotta et al., “How Safe Is Safe Enough? Radiation Risk for a Human Mission to Mars,” PLOS One, October 16, 2013.

15. G. W. Wieger et al., “Can Plants Grow on Mars and the Moon: A Growth Experiment on Mars and Moon Soil Simulants,” PLOS One, August 27, 2014. See also Roberto Molar Candanosa, “Growing Green on the Red Planet,” ChemMatters, April–May 2017, https://www.acs.org/content/acs/en/education/resources/highschool/chemmatters/past-issues/2016-2017/april-2017/growing-green-on-the-red-planet.html.

16. For Laura Fackrell’s summary, see Maria Temming, “Farming on Mars Will Be a Lot Harder than ‘The Martian’ Made It Seem,” Washington Post, 28 November 28, 2020, https://www.washingtonpost.com/science/mars-growing-food/2020/11/27/cdc80e8a-2dc0-11eb-bae0-50bb17126614_story.html.

17. Ben Lindbergh, “Please Sterilize Your Spacecraft,” The Ringer, July 30, 2020. A description of the issues involved in the sterilization of spacecraft appears at https://www.theringer.com/2020/7/30/21347842/mars-2020-rover-launch-contamination-covid.

18. The European Space Agency’s JUICE (Jupiter Icy Moons Explorer) mission has its description at https://sci.esa.int/web/juice.

19. For a discussion of terraforming Mars, see Jatan Mehta, “Can We Make Mars Earth-Like Through Terraforming?,” The Planetary Society, April 19, 2021, https://www.planetary.org/articles/can-we-make-mars-earth-like-through-terraforming.

20. Carl Zimmer, “The Lost History of One of the World’s Strangest Science Experiments,” New York Times, (March 29, 2019), https://www.nytimes.com/2019/03/29/sunday-review/biosphere-2-climate-change.html.

21. John Grunsfeld, telephone interview, December 24, 2020.

22. Elton John and Bernie Taupin, “Rocket Man,” Honky Château (Uni, 1972), https://genius.com/Elton-john-rocket-man-i-think-its-going-to-be-a-long-long-time-lyrics.

Chapter 6: Asteroids

1. Ron Miller, Asteroids, Comets and Meteors, Worlds Beyond (New York: 21st Century, 2004).

2. For the spacecraft Hayabusa’s matching orbit with Itokawa, see Andrew Griffin, “Hayabusa 2: Japanese Spacecraft Returns to Earth Carrying Pieces of Distant Asteroid,” The Independent, December 6, 2020, https://www.independent.co.uk/life-style/gadgets-and-tech/space/hayabusa2 asteroid-japan-jaxa-spacecraft-b1766798.html.

3. The OSIRIS-REx mission is described at https://solarsystem.nasa.gov/missions/osiris-rex/in-depth/.

4. For a list of products requiring near-Earth elements, see Hobart M. King, “REE—Rare Earth Elements and Their Uses,” Geology.com, accessed August 15, 2021, https://geology.com/articles/rare-earth-elements/.

5. On the Timmins ore body, associated with the Kidd Creek mine, see “Kidd Creek Mine,” American Museum of Natural History, accessed August 15, 2021, https://www.amnh.org/exhibitions/permanent/planet-earth/why-is-the-earth-habitable/where-do-the-earth-s-riches-come-from/kidd-creek-mine.

6. Peter Diamandis quoted in Daniel Honan, “The First Trillionaires Will Make Their Fortunes in Space,” Big Think, May 2, 2011, https://bigthink.com/think-tank/the-first-trillionaires-will-make-their-fortunes-in-space.

7. Katie Kramer, “Neil deGrasse Tyson Says Space Ventures Will Spawn First Trillionaire,” NBC News, May 3, 2015, https://www.nbcnews.com/science/space/neil-degrasse-tyson-says-space-ventures-will-spawn-first-trillionaire-n352271.

8. Ted Cruz, quoted in Vishal Thakur, “Will Asteroid Mining Mint the First Trillionaire?,” Science ABC, last updated August 6, 2021, https://www.scienceabc.com/nature/universe/will-asteroid-mining-mint-the-first-trillionaire.html.

9. On ARM’s history, see “Asteroid Redirect Robotic Mission: ARRM,” Jet Propulsion Laboratory, accessed August 15, 2021, https://www.jpl.nasa.gov/missions/asteroid-redirect-robotic-mission-arrm.

10. “Deep Space Industries,” Wikipedia, accessed August 15, 2021, https://en.wikipedia.org/wiki/Deep_Space_Industries.

11. Alan Boyle, “After Buying Planetary Resources, ConsenSys Sets Its Space Ideas Free—but Will Sell Off the Hardware,” GeekWire, May 1, 2020, https://www.geekwire.com/2020/buying-planetary-resources-consensys-gives-away-science-asteroids-will-sell-rest/.

12. Sonnie Bailey, “ ‘The Dinosaurs Became Extinct Because They Didn’t Have a Space Program’: Redundancy Is an Important Risk Management Strategy,” NZ Wealth and Risk, August 28, 2015, https://wealthandrisk.nz/redundancy/.

Chapter 7: Space Colonization

1. An early reference to Gerard O’Neill’s concept can be found at “In His Own Words: Gerard O’Neill,” U.S. 1 Princeton Info, April 14, 2021, https://www.communitynews.org/princetoninfo/coverstories/in-his-own-words-gerard-o-neill/article_9c8ee03d-76ca-5d19-a680-42ce5dbbe0ca.html. His basic plan was presented in Gerard O’Neill, The High Frontier: Human Colonies in Space (New York: William Morrow, 1976).

2. For the language in the 1988 NASA authorization act, H.R. 4218, 100th Congress, 2nd Session, see https://space.nss.org/wp-content/uploads/Space-Settlement-Act-Of-1988.pdf, Section 3(a)(2)(d).

3. Michael Sainato, “Stephen Hawking, Elon Musk and Jeff Bezos Think the Earth Is Doomed,” Observer, June 30, 2017, https://observer.com/2017/06/colonizing-mars-elon-musk-stephen-hawking-jeff-bezos/.

4. Corey S. Powell, “Jeff Bezos Foresees a Trillion People Living in Millions of Space Colonies. Here’s What He’s Doing to Get the Ball Rolling,” NBC News, May 15, 2019, https://www.nbcnews.com/mach/science/jeff-bezos-foresees-trillion-people-living-millions-space-colonies-here-ncna1006036; Shawn Langlois, “Elon Musk Says Jeff Bezos’s Plan to Colonize Space ‘Makes No Sense,’ ” MarketWatch, May 23, 2019, https://www.marketwatch.com/story/elon-musk-jeff-bezos-space-colony-plan-makes-no-sense-2019-05-23; Sainato, “Stephen Hawking.”

5. Nicky Woolf, “SpaceX Founder Elon Musk Plans to Get Humans to Mars in Six Years,” The Guardian, September 27, 2016, https://www.theguardian.com/technology/2016/sep/27/elon-musk-spacex-mars-colony.

6. Daniel Deudney, Dark Skies: Space Expansionism, Planetary Geopolitics, and the Ends of Humanity (Oxford, UK: Oxford University Press, 2020), 210–211.

7. John Lewis, Mining the Sky: Untold Riches from the Asteroids, Comets, and Planets (Reading, MA: Helix Books, 1996), 256.

Chapter 8: The Global Costs of Space Exploration

1. The Planetary Society reports on the cost of Opportunity and Spirit at “Cost of the Mars Exploration Rovers,” accessed August 15, 2021, https://www.planetary.org/space-policy/cost-of-the-mars-exploration-rovers. For Perseverance, see Niall McCarthy, “Chart: This Is How Much Each of NASA’s Mars Missions Have Cost,” World Economic Forum, February 26, 2021, https://www.weforum.org/agenda/2021/02/mars-nasa-space-exploration-cost-perseverance-viking-curiosity/.

2. The Mars One website cites its budget: https://www.mars-one.com/faq/finance-and-feasibility/what-is-mars-ones-mission-budget.

3. O. Glenn Smith and Paul D. Spudis, “Mars for Only $1.5 Trillion,” SpaceNews, March 8, 2015, https://spacenews.com/op-ed-mars-for-only-1-5-trillion.

4. Philip Bump, “NASA’s Piece of the Budget Has Declined by Half Since the Pluto Mission Was Broached,” Washington Post, July 14, 2015, https://www.washingtonpost.com/news/the-fix/wp/2015/07/14/it-took-4-percent-of-the-federal-budget-to-get-to-the-moon-pluto-is-much-cheaper/.

5. “Department of Defense Releases 2021 Military Intelligence Program Budget Request,” press release, February 11, 2020, https://www.defense.gov/Newsroom/Releases/Release/Article/2080605/department-of-defense-releases-2021-military-intelligence-program-budget-request/.

6. For a good summary of the Artemis program, SLS, the Orion spacecraft, and the Lunar Gateway, see “Artemis, NASA’s Moon Landing Program,” The Planetary Society, accessed August 15, 2021, https://www.planetary.org/space-missions/artemis. More detailed information is available at “Artemis Program,” Wikipedia, accessed August 15, 2021, https://en.wikipedia.org/wiki/Artemis_program.

7. For the space shuttle launch costs per pound, see “Criticism of the Space Shuttle Program,” Wikipedia, accessed August 15, 2021, https://en.wikipedia.org/wiki/Criticism_of_the_Space_Shuttle_program#:~:text=Space%20Shuttle%20incremental%20per%2Dpound,low%20Earth%20orbit%20(LEO).

8. Martin Childs, “Qian Xuesen: Scientist and Pioneer of China’s Missile and Space Programmes,” The Independent, November 13, 2009, https://www.independent.co.uk/news/obituaries/qian-xuesen-scientist-and-pioneer-china-s-missile-and-space-programmes-1819724.html.

9. For China’s budget for space exploration, see Anthony Imperato, Peter Garretson, and Richard Harrison, “To Compete with China in Space, America Must Ramp Up Funding,” The National Interest, June 1, 2021, https://nationalinterest.org/blog/buzz/compete-china-space-america-must-ramp-funding-186383.

10. Ye Peijian’s statement appears in Alexander Bowe, “China’s Pursuit of Space Power Status and Implications for the United States,” U.S.-China Economic and Security Review Commission, Staff Report, April 11, 2019, https://www.uscc.gov/sites/default/files/Research/USCC_China’s%20Space%20Power%20Goals.pdf.

11. Pamela Melroy quoted in Jacqueline Feldscher, “Biden Space Advisers Urge Cooperation with China,” Politico, December 20, 2020, https://www.politico.com/news/2020/12/20/biden-china-space-448529.

12. “How Much Does It Cost?,” European Space Agency, accessed August 15, 2021, https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/International_Space_Station/How_much_does_it_cost.

13. “Exploring Together—ESA Space Exploration Strategy,” European Space Agency, September 10, 2016, http://youbenefit.spaceflight.esa.int/esa-space-exploration-strategy/.

14. “No. 6-2020: ExoMars to Take Off for the Red Planet in 2022,” European Space Agency, March 12, 2020, https://www.esa.int/Newsroom/Press_Releases/ExoMars_to_take_off_for_the_Red_Planet_in_2022.

15. Monica M. Grady, “Exploring Mars with Returned Samples,” Space Science Reviews 216, art. 51 (2020).

16. “Luna,” European Space Agency, accessed August 15, 2021, https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/Exploration/Luna.

17. Andrew Jones, “Russian Space Chief Discusses NASA’s Artemis Moon Landing Plans,” Space.com, November 4, 2020, https://www.space.com/russia-space-agency-chief-criticizes-nasa-moon-plans.

18. Dave Dooling, “Chandrayaan: Indian Lunar Space Probe Series,” Encylopaedia Britannica, last updated September 12, 2019, https://www.britannica.com/technology/Chandrayaan.

19. Park Si-soo, “Japan Budgets a Record $4.14 Billion for Space Activities,” SpaceNews, March 9, 2021, https://spacenews.com/japan-budgets-a-record-4-14-billion-for-space-activities/.

Chapter 9: Space Law

1. Glenn Reynolds and Robert Merger, Outer Space: Problems of Law and Policy, 2nd ed. (New York: Westview Press, 1997).

2. The International Seabed Authority is described at https://www.isa.org.jm/.

3. The Antarctic Treaty of 1959 is at https://2009-2017.state.gov/t/avc/trty/193967.htm.

4. “Committee on the Peaceful Uses of Outer Space,” United Nations Office for Outer Space Affairs, 2021, https://www.unoosa.org/oosa/en/ourwork/copuos/index.html.

5. The Outer Space Treaty is available at https://www.unoosa.org/oosa/en/ourwork/spacelaw/treaties/introouterspacetreaty.html.

6. The Moon Treaty can be seen at https://www.unoosa.org/oosa/en/ourwork/spacelaw/treaties/moon-agreement.html.

7. Art Dula, “Free Enterprise and the Proposed Moon Treaty,” Houston Journal of International Law 2, no. 3 (1979): 3–33.

8. The SPACE Act’s text is at https://www.congress.gov/bill/114th-congress/house-bill/2262/text.

9. The three Space Policy Directives are:

SPD-1, https://www.nasa.gov/press-release/new-space-policy-directive-calls-for-human-expansion-across-solar-system

SPD-2, https://spacepolicyonline.com/news/text-of-president-trumps-space-policy-directive-2-may-24-2018/

SPD-3, https://trumpwhitehouse.archives.gov/presidential-actions/space-policy-directive-3-national-space-traffic-management-policy/

10. Executive Order No. 13914, https://www.federalregister.gov/documents/2020/04/10/2020-07800/encouraging-international-support-for-the-recovery-and-use-of-space-resources.

11. The Artemis Accords are recorded at https://www.nasa.gov/specials/artemis-accords/img/Artemis-Accords-signed-13Oct2020.pdf.

12. “Keynote: NASA Administrator Jim Bridenstine,” 2nd Summit for Space Sustainability, September 9–11, 2020, https://swfound.org/media/207210/bridenstine-keynote.pdf.

13. Aaron Boley and Michael Byers, “U.S. Policy Puts the Safe Development of Space at Risk,” Science 370 (October 9, 2020): 174–175.

14. T. S. Eliot, “Little Gidding,” http://www.columbia.edu/itc/history/winter/w3206/edit/tseliotlittlegidding.html.

Epilogue

1. Mitch Daniels, “The U.S. Put a Man on the Moon. But It Might be Harder to Do the Same on Mars,” Washington Post, February 25, 2021, https://www.washingtonpost.com/opinions/the-us-put-a-man-on-the-moon-but-it-might-be-harder-to-do-the-same-on-mars/2021/02/25/5d85caba-76e3-11eb-9537-496158cc5fd9_story.html.

2. Pathways to Exploration: Rationales and Approaches for a U.S. Program of Human Space Exploration (Washington, DC: National Academy of Sciences, 2014), 10–11.

3. H. G. Wells, “The Discovery of the Future,” philosophical lecture presented to the Royal Institution, January 24, 1902.

Further Reading

Bergaust, Erik. Reaching for the Stars: A Biography of the Great Pioneer in Space Exploration, Wernher von Braun. New York: Doubleday, 1960.

Bradbury, Ray, Arthur C. Clarke, Bruce Murray, Carl Sagan, and Walter Sullivan. Mars and the Mind of Man. New York: Harper & Row, 1973.

Broad, William. Star Warriors. New York: Simon & Schuster, 1985.

Davenport, Christian. The Space Barons: Elon Musk, Jeff Bezos, and the Quest to Colonize the Cosmos. New York: Public Affairs, 2018.

Deudney, Daniel. Dark Skies: Space Expansionism, Planetary Geopolitics, and the Ends of Humanity. Oxford: Oxford University Press, 2020.

Elvis, Martin. Asteroids: How Love, Fear, and Greed Will Determine Our Future in Space. New Haven: Yale University Press, 2021.

Fishman, Charles. One Giant Leap: The Impossible Mission That Flew Us to the Moon. New York: Simon & Schuster, 2019.

Greene, Kate. Once upon a Time I Lived on Mars: Space, Exploration, and Life on Earth. New York: St. Martin’s Press, 2020.

Hand, Kevin Peter. Alien Oceans: The Search for Life in the Depths of Space. Princeton, NJ: Princeton University Press, 2021.

Hartmann, William. Mars: The Mysterious Landscapes of the Red Planet. New York: Workman Publishing, 2003.

Impey, Chris. Beyond: Our Future in Space. New York: W. W. Norton, 2015.

Jensen, Claus. No Downlink: A Dramatic Narrative about the Challenger Accident and Our Time. New York: Farrar, Straus, and Giroux, 1996.

Launius, Roger. Space Exploration: From the Ancient World to the Extraterrestrial Future. Washington, DC: Smithsonian Books, 2018.

Lewis, John. Mining the Sky: Untold Riches from the Asteroids, Comets, and Planets. Reading, MA: Helix Books, 1996.

Maher, Neil. Apollo in the Age of Aquarius. Cambridge, MA: Harvard University Press, 2017.

Massimino, Mike. Spaceman: An Astronaut’s Unlikely Journey to Unlock the Secrets of the Universe. New York: Three Rivers Press, 2016.

McCray, W. Patrick. The Visioneers: How a Group of Elite Scientists Pursued Space Colonies, Nanotechnologies, and a Limitless Future. Princeton, NJ: Princeton University Press, 2013.

McDougall, Walter. The Heavens and the Earth: A Political History of the Space Age. New York: Basic Books, 1985.

Morton, Oliver. The Moon: A History for the Future. New York: Public Affairs, 2019.

Murray, Bruce. Journey into Space: The First Thirty Years of Space Exploration. New York: W. W. Norton, 1989.

Needell, Alan, ed. The First 25 Years in Space: A Symposium. Washington, DC: Smithsonian Institution, 1983.

O’Neill, Gerard. The High Frontier: Human Colonies in Space. New York: William Morrow, 1976.

Ordway, Frederick, and Mitchell Sharpe. The Rocket Team: From the V-2 to the Saturn Moon Rocket—the Inside Story of How a Small Group of Engineers Changed World History. New York: Thomas Crowell, 1979.

Reynolds, Glenn, and Robert Merger. Outer Space: Problems of Law and Policy. 2nd ed. New York: Westview Press, 1997.

Sawyer, Kathy. The Rock from Mars: A Detective Story on Two Planets. New York: Random House, 2006.

Schmidle, Nicholas. Test Gods: Virgin Galactic and the Making of a Modern Astronaut. New York: Henry Holt, 2021.

Squyres, Steve. Roving Mars: Spirit, Opportunity, and the Exploration of the Red Planet. New York: Hyperion, 2005.

Trento, Joseph. Prescription for Disaster: From the Glory of Apollo to the Betrayal of the Shuttle. New York: Crown, 1987.

Wanjek, Christopher. Spacefarers: How Humans Will Settle the Moon, Mars, and Beyond. Cambridge, MA: Harvard University Press, 2020.

Westwick, Peter. Into the Black: JPL and the American Space Program 1976–2004. New Haven, CT: Yale University Press, 2007.

Wilford, John Noble. Mars Beckons: The Mysteries, the Challenges, the Expectations of Our Next Great Adventure in Space. New York: Vintage Books, 1990.

Zubrin, Robert, and Richard Wagner. The Case for Mars: The Plan to Settle the Red Planet and Why We Must. New York: Touchstone, 1997.

Acknowledgments

In writing The End of Astronauts, we have been fortunate to receive assistance from many people, including Charles Beichman, Konstantin Batygin, France Córdova, Mitch Daniels, Casey Dreier, Paul Goldsmith, John Grunsfeld, Jeffrey Hoffman, Jon Logsdon, Jonathan Lunine, Andrew McDowell, Chris McKay, Dirk Schulze-Makoch, David Spergel, Neil Tyson, and Joseph Wisnovsky. We thank Janice Audet, our editor at Harvard University Press, editorial assistant Emeralde Jensen-Roberts, Melody Negron, our editor at Westchester Publishing Services, and our agent, Michael Carlisle, for their efforts in bringing this book into existence.

Index

Aldrin, Buzz, 41

Angel, Roger, 30

Antarctic treaty, 134–136, 138, 139

Apollo program, 1, 5, 12, 14, 24, 32, 51–54, 65, 68, 82, 116, 119, 136

Arabidopsis thaliana, 86

Armstrong, Neil, 110

artificial intelligence, 8, 62–64, 81, 82, 110–112, 146

asteroids, 24, 25, 38, 46, 54, 88, 94–104, 109, 138, 148

astrobiologists, 68

astronauts: on asteroids, 94–104; compared to robots, 11, 64, 81–83, 92, 93, 103, 114, 146; construction by, 58; contamination by, 67, 68; costs of, 17, 22, 23, 30, 33, 34, 64, 115–123, 126; discoveries, 54, 55, 61; in Earth orbit, 31, 34, 35, 40, 42; hazards to, 14, 29, 42–45, 61, 83–85; as heroes, 1; inspiration from, 6–8, 10, 11, 13, 33; loss of, 18, 31; manufacturing by, 36, 37, 58; on Mars, 11, 13, 14, 24, 38, 78, 81, 114, 147, 149; on moon, 4, 5, 20, 24, 37, 50–55, 58, 65–68, 114, 119–121, 147, 148; in outer solar system, 149; requirements of, 26, 77, 78, 86, 115–118; worldwide funding, 123–129

Atlantic Monthly, 75

Bandyopadhyay, Saptoshi, 58

Bennu, 95, 97

Beresheet, 70

Berra, Yogi, 26

Bezos, Jeff, 38, 39, 90, 99, 108, 111, 113, 131, 148

Biosphere 2, 91

Biosphere 3, 91

Blue Origin, 39, 83, 120

Bohr, Niels, 26

Bradford Industries, 101

Branson, Richard, 38

Bridenstine, James, 142

Buck Rogers, 18

Burrough, Edgar Rice, 76

Byers, Michel, 143

cancer, 1, 44, 45, 63, 85, 110

carbonaceous chondrites, 96, 97

carbon dioxide: on Mars, 76, 78, 86, 90; on Venus, 92

Carter, Jimmy, 140

Cassini-Huygens, 24, 126

Ceres, 27, 94, 148, 149

Cernan, Eugene, 54, 61

Challenger, 31

Chandrayaan, 52, 55, 129

Chang’e 1, 52

Chang’e 3, 52

Chang’e 4, 52, 125

Chang’e 5, 53, 54, 125

China, 7, 19, 32, 37, 52, 53, 56, 65–67, 78, 99, 123–125, 129

Clark, Alvan, 75

Clementine, 51, 55

CMEs. See coronal mass ejections

colonies, 88; on Mars, 39, 75, 86, 88–92, 104; on moon, 39, 50, 55, 57, 72, 75, 88, 97; in space, 39, 90, 91, 104–113

Columbia, 31, 121

Comet Cheryumov-Gerasimov, 126

Commercial Lunar Payload Services, 67

Concorde, 14

Consensys, 101

contamination, 77, 88

coronal mass ejections, 43, 44, 84

cosmic rays, 43, 44, 84

COSPAR, 71

Crawford, Ian, 64

Cruz, Ted, 99

CSPAN, 20

Cupola observatory, 126

Curiosity rover, 18, 78, 79, 82, 116

Daniels, Mitch, 21, 149, 150

Dawn spacecraft, 149

Deimos, 27

deuterium, 59

dinosaurs, 95, 103

DNA, 68, 70, 73, 87, 88

Dragon, 37, 38, 120, 128

Dragonfly, 79

Dula, Art, 139, 140

Durante, Marco, 84

Eliot, T.S., 144

Enceladus, 24, 148, 149

escape velocity, 27, 28, 30

Europa, 24, 148, 149

European Space Agency (ESA), 5, 24, 32, 37, 51, 65, 81, 89, 121, 125–128, 149

Executive Order 13914, 141, 142

exploration, motivations, 2, 14, 88

Falcon, 34, 38, 120, 122

Flammarion, Camille, 57, 75

Franklin probe, 127

Gagarin, Yuri, 4, 33

gamma rays, 44

Gemini, 32

geostationary orbits, 25, 28

Glenn, John, 4

Goddard, Robert, 2, 3

Goddard Space Flight Center, 2

gold, 98, 99, 101–103

gravitational force, 29, 41, 60, 78, 94, 99

gravitational well, 26–29, 56, 94, 99, 102, 121

greenhouse effect, 92

Grunsfeld, John, 91, 92

habitats, 6, 23–25, 32, 35, 39; on Mars, 39, 75, 85, 86, 89, 92; on moon, 50, 55, 57, 72, 75, 97; in space, 32, 35, 105–109, 111

Hawking, Stephen, 108, 148

Hayabusa, 96

helium-3, 59–61; helium-4, 59–61

high-energy particles, 1, 28, 43, 44, 57, 60, 61, 69, 106

Hoffman, Jeffrey, 82

Hope spacecraft, 78

Hubble Space Telescope, 1, 17, 41, 82, 126

ice: on asteroids, 97; on Enceladus, 149; on Europa, 149; on Mars, 86, 92; on moon, 52, 55–57

India, 7, 37, 52, 55, 57, 129

Infrared Space Telescope, 126

Ingenuity, 78, 79

InSight, 78

Institute for Defense Analyses, 118

International Aeronautical Congress, 108

International Court of Justice, 135, 137

International Lunar Research Station, 65

International Seabed Authority, 133

International Space Station, 30–38, 42, 82, 84, 101, 117, 122–128

interstellar travel, 113

Italian Space Agency, 121

Itokawa, 96

Japanese Space Agency, 5, 37, 96, 121, 129, 130

JAXA, 5

Jezero crater, 79, 87

John, Elton, 93

Johnson, Lyndon, 45

JUICE mission, 89

Juno, 24

Jurvetson, Steve, 39

Kelly, Scott, 33

Kennedy, John, 4, 10, 13, 119

Kepler, Johannes, 49

Kessler, David, 47

Kessler effect, 47, 48

Kimball, Dan, 124

Korolev, Sergei, 4

Lagrange points, 108; L4 and L5, 25, 144

Law of the Sea Convention, 133

laws in space, 131–133, 136–139, 143

LCROSS, 55

Leary, Timothy, 106

Lederberg, Joshua, 71

Leonov, Alexei, 4

Levania, 49

Levinthal, Elliott, 71

Lewis, John, 110

low-Earth orbit (LEO), 6, 25, 28, 29, 31–37, 41–48, 84, 101, 103, 120–122, 125, 126, 129, 151

Lowell, Percival, 75, 76

Luna program, 51, 52

Lunar and Planetary Institute, 17

Lunar Prospector, 51

Lunar Reconnaissance Orbiter, 51

lunar rover, 62, 63, 129

Mangalyaan, 129

manufacturing in space, 35–37, 58

Mars, atmosphere, 78, 79, 86, 90; colonization, 88, 91, 104; humans on, 15, 81–85, 87–93; ice on, 86, 92; robots on, 17, 77, 82, 88, 116, 118, 127, 147, 149; water on, 75, 76, 86, 90, 93, 149

Marshall Space Flight Center, 37

Mars One, 117, 118

Martian, The, 86, 116

McAuliffe, Christa, 32

McKay, Chris, 83

McPhee, John, 77

Melroy, Pamela, 125

Mercury, 5, 74

Meteorites, 53, 80, 97

MeV, 44

microwaves, 46

mining: on asteroids, 23, 99–103, 107; on moon, 57, 61, 63, 110

Mir, 40

moon: colonies on, 39, 50, 55, 57, 72, 75, 88, 97; formation of, 50, 53; habitats on, 50, 55, 57, 72, 75, 97; humans on, 4, 12, 20, 51, 54–66; mining on, 57, 61, 63, 110; peaks of eternal light, 57, 147; robots on, 51–53, 59, 61–67

Moon Treaty, 137–140

Morton, Oliver, 13

Mount Everest, 12

Musk, Elon, 34, 38, 90, 99, 108, 120, 131, 148

Mutations, 44

National Academy of Sciences, 21, 150

National Aeronautics and Space: Administration (NASA), 2, 5, 15, 18–24, 31–39; limiting astronaut risks, 44, 47, 68; missions to Mars, 79–81, 85; to moon, 51, 52, 55, 65–68

Near-Earth orbit (NEO). See low-Earth orbit

Nelson, Bill, 31, 107, 121

Nereus, 98–100

neutrino, 59

neutron, 59, 60

Newton, Isaac, 49

Newton’s laws, 27

Niven, Larry, 103

Oberth, Hermann, 3

O. Henry, 40

Olympus Mons, 92

O’Neill, Gerard, 106–109, 111

Operation Paperclip, 3

Opportunity, 84, 114, 116

orange soil, 54

orbits, around Earth, 1–6, 15, 18, 23–25, 28–35, 37, 40–45, 50; geostationary, 25, 28; around Mars, 17, 37, 76–78, 81, 84, 86, 116; around moon, 51–53, 55, 59, 66, 67; around other stars, 73; overcrowding of, 45–48; around sun, 18, 26, 94–97, 100–103, 105, 108, 113

Orion spacecraft, 119

OSIRIS-Rex, 96, 97

Outer Space Treaty, 66, 71, 136–138, 140

Pantheon, 30

Peaks of Eternal Light, 57, 147

Peijian, Yi, 124, 126

Perseverance rover, 13, 18, 62, 78–81, 87, 116

Phobos, 27

Planetary Resources Corporation, 101

Plate tectonics, 56

polls, 19–21, 24

Polyakov, Valery, 33

Polynesians, 12

Psyche, 100

public attitudes toward space exploration, 2–4, 6, 8–13, 16–21, 30, 32, 76, 83, 92, 94, 102, 104, 106, 128, 147

Purdue University, 21

Quegiao, 125

radiation damage, 29, 43–46, 60, 69, 70, 84, 85, 118

Redstone Arsenal, 3

regolith, 61, 96, 143

robots, comparison with humans, 64, 65, 115, 146, 149; on Mars, 79, 81–83, 86, 93, 94, 102; on moon, 51–53, 59, 61–67; for space manufacturing, 6, 35–37

Roscosmos, 129

Ryumin, Valery, 40

Sagan, Carl, 71, 72

sample return, from asteroids, 24, 96, 97; from Mars, 14, 77, 80, 81, 127, 128, 147; from moon, 52–54, 56, 63, 125, 128, 139

Schmitt, Harrison, 54, 59, 61, 62

Schwartz, James, 11

Shackleton crater, 57, 129

Shorty crater, 54

Simonyi, Charles, 101

SKA (Square Kilometer Array), 59

SLS, 119, 120

Smart-1, 51

Smith, O. Glenn, 117

SOFIA, 55

Sojourner, 18

solar flares, 43, 84

solar wind, 43–45, 56, 84, 95

Somnium, 49

SPACE Act, 140–142

space colonies, 39, 91, 105–113

space elevator, 29

Space Force, 119

space law, 131–133, 136, 137, 139, 143

space manufacturing, 35–37

space shuttle, 20, 31–33, 82, 120–122, 125, 128

space travel: costs, 17, 22, 23, 30, 33, 34, 64, 115–123, 126; hazards, 1, 43–45, 56, 63, 85, 95, 110; public opinion, 2–4, 6, 8–13, 16–21, 30, 32, 76, 83, 92, 94, 102, 104, 106, 128, 147

SpaceX, 34, 37, 38, 45, 120, 122, 123, 128, 131

Spergel, David, 8, 103

Spirit rover, 18, 82, 116

Spudis, Paul, 117

Sputnik, 3

Starship, 39, 120

sterilization, 77, 88

Stonehenge, 30

Surveyor, 52

Swanson, Steve, 82

tardigrades, 70

telescope, 16, 17, 58, 74; on moon, 46, 73

Tereshkova, Valentina, 4

terraforming, 89–92

Tesla Motor Company, 38, 39

Tharsis Tholis, 92

Tianwen-1, 78, 125

Timmons ore body, 79

Titan, 24, 79, 126, 148, 149

tourism, 6, 13, 32

Trump, Donald, 10

Tsiolkovsky, Konstantin, 2, 105

Tyson, Neil, 99

UN Convention on Law of the Sea, 133

V-1, 3; V-2, 3

Venus, 24, 25, 50, 73, 74, 91, 92, 125, 129

Viking, 24, 80

VIPER, 56

Virgin Galactic, 39

volunteers, 12, 116

Von Braun, Wernher, 34, 124

Von Karmán, Theodor, 124

Voskhod, 32

Vostok, 32

War of the Worlds, 76

water: on asteroids, 96, 97, 149; for astrobiology, 79, 80; for astronauts, 26, 29, 41, 115, 117, 119; on Earth, 54, 56, 70; on Enceladus, 149; on Europa, 149; on Mars, 75, 76, 86, 90, 93, 149; on moon, 6, 50, 54–56, 67, 70, 72, 129; for space colonies, 108

weightlessness, 35, 40, 41

Wells, H. G., 2, 75, 150

Woolf, Neil, 30

X rays, 94

Xuesen, Qian, 124

Yutu-2, 52

ZBLAN, 36, 37

zero-g. See weightlessness