Pale Blue Dot: A Vision of the Human Future in Space - Carl Sagan, Ann Druyan (1997)


Who, my friend, can scale heaven?



What?, I sometimes ask myself in amazement: Our ancestors walked from East Africa to Novaya Zemlya and Ayers Rock and Patagonia, hunted elephants with stone spearpoints, traversed the polar seas in open boats 7,000 years ago, circumnavigated the Earth propelled by nothing but wind, walked the Moon a decade after entering space—and we’re daunted by a voyage to Mars? But then I remind myself of the avoidable human suffering on Earth, how a few dollars can save the life of a child dying of dehydration, how many children we could save for the cost of a trip to Mars—and for the moment I change my mind. Is it unworthy to stay home, or unworthy to go? Or have I posed a false dichotomy? Isn’t it possible to make a better life for everyone on Earth and to reach for the planets and the stars?

We had an expansive run in the ’60s and ’70s. You might have thought, as I did then, that our species would be on Mars before the century was over. But instead, we’ve pulled inward. Robots aside, we’ve backed off from the planets and the stars. I keep asking myself: Is it a failure of nerve or a sign of maturity?

Maybe it’s the most we could reasonably have expected. In a way it’s amazing that it was possible at all: We sent a dozen humans on week-long excursions to the Moon. And we were given the resources to make a preliminary reconnaissance of the whole Solar System, out to Neptune anyway—missions that returned a wealth of data, but nothing of short-term, everyday, bread-on-the-table practical value. They lifted the human spirit, though. They enlightened us about our place in the Universe. It’s easy to imagine skeins of historical causality in which there were no race to the Moon and no planetary program.

But it’s also possible to imagine a much more serious devotion to exploration, because of which we would today have robot vehicles probing the atmospheres of all the Jovian planets and dozens of moons, comets, and asteroids; a network of automatic scientific stations emplaced on Mars would daily be reporting their findings; and samples from many worlds would be under examination in the laboratories of Earth—revealing their geology, chemistry, and perhaps even their biology. Human outposts might be already established on the near-Earth asteroids, the Moon, and Mars.

There were many possible historical paths. Our particular causality skein has brought us to a modest and rudimentary, although in many respects heroic, series of explorations. But it is far inferior to what might have been—and what may one day be.

“TO CARRY THE GREEN Promethean spark of Life with us into the sterile void and ignite there a firestorm of animate matter is the very destiny of our race,” reads the brochure of something called the First Millennial Foundation. It promises, for $120 a year, “citizenship” in “space colonies—when the time comes.” “Benefactors” who contribute more also receive “the undying gratitude of a star-flung civilization, and their name carved on the monolith to be erected on the Moon.” This represents one extreme in the continuum of enthusiasm for a human presence in space. The other extreme—better represented in Congress—questions why we should be in space at all, especially people rather than robots. The Apollo program was a “moondoggle,” the social critic Amitai Etzioni once called it; with the Cold War over, there is no justification whatever, proponents of this orientation hold, for a manned space program. Where in this spectrum of policy options should we be?

Ever since the United States beat the Soviet Union to the Moon, a coherent, widely understood justification for humans in space seems to have vanished. Presidents and Congressional committees puzzle over what to do with the manned space program. What is it for? Why do we need it? But the exploits of the astronauts and the moon landings had elicited—and for good reason—the admiration of the world. It would be a rejection of that stunning American achievement, the political leaders tell themselves, to back off from manned spaceflight. Which President, which Congress wishes to be responsible for the end of the American space program? And in the former Soviet Union a similar argument is heard: Shall we abandon, they ask themselves, the one remaining high technology in which we are still world leaders? Shall we be faithless heirs of Konstantin Tsiolkovsky, Sergei Korolev, and Yuri Gagarin?

The first law of bureaucracy is to guarantee its own continuance. Left to its own devices, without clear instructions from above, NASA gradually devolved into a program that would maintain profits, jobs, and perquisites. Pork-barrel politics, with Congress playing a leading role, became an increasingly powerful force in the design and execution of missions and long-term goals. The bureaucracy ossified. NASA lost its way.

On July 20, 1989, the twentieth anniversary of the Apollo 11 landing on the Moon, President George Bush announced a long-term direction for the U.S. space program. Called the Space Exploration Initiative (SEI), it proposed a sequence of goals including a U.S. space station, a return of humans to the Moon, and the first landing of humans on Mars. In a later statement, Mr. Bush set 2019 as the target date for the first footfall on that planet.

And yet the Space Exploration Initiative, despite clear direction from the top, foundered. Four years after it was mandated, it did not even have a NASA office dedicated to it. Small and inexpensive lunar robotic missions—that otherwise might well have been approved—were canceled by Congress because of guilt by association with SEI. What went wrong?

One problem was the timescale. SEI extended five or so presidential terms of office into the future (taking the average presidency as one and a half terms). That makes it easy for a president to attempt to commit his successors, but leaves in considerable doubt how reliable such a commitment might be. SEI contrasted dramatically with the Apollo program—which, it might have been conjectured at the time it began, could have triumphed when President Kennedy or his immediate political heir was still in office.

Second, there was concern about whether NASA, which had recently experienced great difficulty in safely lifting a few astronauts 200 miles above the Earth, could send astronauts on an arcing year-long trajectory to a destination 100 million miles away and bring them back alive.

Third, the program was conceived exclusively in nationalist terms. Cooperation with other nations was not fundamental to either design or execution. Vice President Dan Quayle, who had nominal responsibility for space, justified the space station as a demonstration that the United States was “the world’s only superpower.” But since the Soviet Union had an operational space station that was a decade ahead of the United States, Mr. Quayle’s argument proved difficult to follow.

Finally, there was the question of where, in terms of practical politics, the money was supposed to come from. The costs of getting the first humans to Mars had been variously estimated, ranging as high as $500 billion.

Of course, it’s impossible to predict costs before you have a mission design. And the mission design depends on such matters as the size of the crew; the extent to which you take mitigating steps against solar and cosmic radiation hazards, or zero gravity; and what other risks you are willing to accept with the lives of the men and women on board. If every crew member has one essential specialty, what happens if one of them falls ill? The larger the crew, the more reliable the backups. You would almost certainly not send a full-time oral surgeon, but what happens if you need root canal work and you’re a hundred million miles from the nearest dentist? Or could it be done by an endodontist on Earth, using telepresence?

Wernher von Braun was the Nazi-American engineer who, more than anyone else, actually took us into space. His 1952 book Das Marsprojekt envisioned a first mission with 10 interplanetary spacecraft, 70 crew members, and 3 “landing boats.” Redundancy was uppermost in his mind. The logistical requirements, he wrote, “are no greater than those for a minor military operation extending over a limited theater of war.” He meant to “explode once and for all the theory of the solitary space rocket and its little band of bold interplanetary adventurers,” and appealed to Columbus’ three ships without which “history tends to prove that he might never have returned to Spanish shores.” Modern Mars mission designs have ignored this advice. They are much less ambitious than von Braun’s, typically calling for one or two spacecraft crewed by three to eight astronauts, with another robotic cargo ship or two. The solitary rocket and the little band of adventurers are still with us.

Other uncertainties affecting mission design and cost include whether you pre-emplace supplies from Earth and launch humans to Mars only after the supplies are safely landed; whether you can use Martian materials to generate oxygen to breathe, water to drink, and rocket propellants to get home; whether you land using the thin Martian atmosphere for aerobraking; the degree of redundancy in equipment thought prudent; the extent to which you use closed ecological systems or just depend on the food, water, and waste disposal facilities you’ve brought from Earth; the design of roving vehicles for the crew to explore the Martian landscape; and how much equipment you’re willing to carry to test our ability to live off the land in later voyages.

Until such questions are decided, it’s absurd to accept any figure for the cost of the program. On the other hand, it was equally clear that SEI would be extremely expensive. For all these reasons, the program was a nonstarter. It was stillborn. There was no effective attempt by the Bush Administration to spend political capital to get SEI going.

The lesson to me seems clear: There may be no way to send humans to Mars in the comparatively near future—despite the fact that it is entirely within our technological capability. Governments do not spend these vast sums just for science, or merely to explore. They need another purpose, and it must make real political sense.

It may be impossible to go just yet, but when it is possible, the mission, I think, must be international from the start, with costs and responsibilities equitably shared and the expertise of many nations tapped; the price must be reasonable; the time from approval to launch must fit within practical political timescales; and the space agencies concerned must demonstrate their ability to muster pioneering exploratory missions with human crews safely, on time, and on budget. If it were possible to imagine such a mission for less than $100 billion, and for a time from approval to launch less than 15 years, maybe it would be feasible. (In terms of cost, this would represent only a fraction of the annual civilian space budgets of the present spacefaring nations.) With aerobraking and manufacturing fuel and oxygen for the return trip out of Martian air, it’s now beginning to look as if such a budget and such a timescale might actually be realistic.

The cheaper and quicker the mission is, necessarily the more risk we must be willing to take with the lives of the astronauts and cosmonauts aboard. But as is illustrated, among countless examples, by the samurai of medieval Japan, there are always competent volunteers for highly dangerous missions in what is perceived as a great cause. No budget, no timeline can be really reliable when we attempt to do something on so grand a scale, something that has never been done before. The more leeway we ask, the greater is the cost and the longer it takes to get there. Finding the right compromise between political feasibility and mission success may be tricky.

IT’S NOT ENOUGH to go to Mars because some of us have dreamt of doing so since childhood, or because it seems to us the obvious long-term exploratory goal for the human species. If we’re talking about spending this much money, we must justify the expense.

There are now other matters—clear, crying national needs—that cannot be addressed without major expenditures; at the same time, the discretionary federal budget has become painfully constrained. Disposal of chemical and radioactive poisons, energy efficiency, alternatives to fossil fuels, declining rates of technological innovation, the collapsing urban infrastructure, the AIDS epidemic, a witches’ brew of cancers, homelessness, malnutrition, infant mortality, education, jobs, health care—there is a painfully long list. Ignoring them will endanger the well-being of the nation. A similar dilemma faces all the spacefaring nations.

Nearly every one of these matters could cost hundreds of billions of dollars or more to address. Fixing infrastructure will cost several trillion dollars. Alternatives to the fossil-fuel economy clearly represent a multitrillion-dollar investment worldwide, if we can do it. These projects, we are sometimes told, are beyond our ability to pay. How then can we afford to go to Mars?

If there were 20 percent more discretionary funds in the U.S. federal budget (or the budgets of the other spacefaring nations), I probably would not feel so conflicted about advocating sending humans to Mars. If there were 20 percent less, I don’t think the most diehard space enthusiast would be urging such a mission. Surely there is some point at which the national economy is in such dire straits that sending people to Mars is unconscionable. The question is where we draw the line. Plainly such a line exists, and every participant in these debates should stipulate where that line should be drawn, what fraction of the gross national product for space is too much. I’d like the same thing done for “defense.”

Public opinion polls show that many Americans think the NASA budget is about equal to the defense budget. In fact, the entire NASA budget, including human and robotic missions and aeronautics, is about 5 percent of the U.S. defense budget. How much spending for defense actually weakens the country? And even if NASA were cancelled altogether, would we free up what is needed to solve our national problems?

HUMAN SPACEFLIGHT in general—to say nothing of expeditions to Mars—would be much more readily supportable if, as in the fifteenth-century arguments of Columbus and Henry the Navigator, there were a profit lure.* Some arguments have been advanced. The high vacuum or low gravity or intense radiation environment of near-Earth space might be utilized, it is said, for commercial benefit. All such proposals must be challenged by this question: Could comparable or better products be manufactured down here on Earth if the development money made available were comparable to what is being poured into the space program? Judging by how little money corporations have been willing to invest in such technology—apart from the entities building the rockets and spacecraft themselves—the prospects, at least at present, seem to be not very high.

The notion that rare materials might be available elsewhere is tempered by the fact that freightage is high. There may, for all we know, be oceans of petroleum on Titan, but transporting it to Earth will be expensive. Platinum-group metals may be abundant in certain asteroids. If we could move these asteroids into orbit around the Earth, perhaps we could conveniently mine them. But at least for the foreseeable future this seems dangerously imprudent, as I describe later in this book.

In his classic science fiction novel The Man Who Sold the Moon, Robert Heinlein imagined the profit motive as the key to space travel. He hadn’t foreseen that the Cold War would sell the Moon. But he did recognize that an honest profit argument would be difficult to come by. Heinlein envisioned, therefore, a scam in which the lunar surface was salted with diamonds so later explorers could breathlessly discover them and initiate a diamond rush. We’ve since returned samples from the Moon, though, and there is not a hint of commercially interesting diamonds there.

However, Kiyoshi Kuramoto and Takafumi Matsui of the University of Tokyo have studied how the central iron cores of Earth, Venus, and Mars formed, and find that the Martian mantle (between crust and core) should be rich in carbon—richer than that of the Moon or Venus or Earth. Deeper than 300 kilometers, the pressures should transform carbon into diamond. We know that Mars has been geologically active over its history. Material from great depth will occasionally be extruded up to the surface, and not just in the great volcanos. So there does seem to be a case for diamonds on other worlds—on Mars, and not the Moon. In what quantities, of what quality and size, and in which locales we do not yet know.

The return to Earth of a spacecraft stuffed with gorgeous multicarat diamonds would doubtless depress prices (as well as the shareholders of the de Beers and General Electric corporations). But because of the ornamental and industrial applications of diamonds, perhaps there is a lower limit below which prices will not go. Conceivably, the affected industries might find cause to promote the early exploration of Mars.

The idea that Martian diamonds will pay for exploring Mars is at best a very long shot, but it’s an example of how rare and valuable substances may be discoverable on other worlds. It would be foolish, though, to count on such contingencies. If we seek to justify missions to other worlds, we’ll have to find other reasons.

BEYOND DISCUSSIONS OF PROFITS and costs, even reduced costs, we must also describe benefits, if they exist. Advocates of human missions to Mars must address whether, in the long term, missions up there are likely to mitigate any of the problems down here. Consider now the standard set of justifications and see if you find them valid, invalid, or indeterminate:

Human missions to Mars would spectacularly improve our knowledge of the planet, including the search for present and past life. The program is likely to clarify our understanding of the environment of our own planet, as robotic missions have already begun to do. The history of our civilization shows that the pursuit of basic knowledge is the way the most significant practical advances come about. Opinion polls suggest that the most popular reason for “exploring space” is “increased knowledge.” But are humans in space essential to achieve this goal? Robotic missions, given high national priority and equipped with improved machine intelligence, seem to me entirely capable of answering, as well as astronauts can, all the questions we need to ask—and at maybe 10 percent the cost.

It is alleged that “spinoff” will transpire—huge technological benefits that would otherwise fail to come about—thereby improving our international competitiveness and the domestic economy. But this is an old argument: Spend $80 billion (in contemporary money) to send Apollo astronauts to the Moon, and we’ll throw in a free stickless frying pan. Plainly, if we’re after frying pans, we can invest the money directly and save almost all of that $80 billion.

The argument is specious for other reasons as well, one of which is that DuPont’s Teflon technology long antedated Apollo. The same is true of cardiac pacemakers, ballpoint pens, Velcro, and other purported spinoffs of the Apollo program. (I once had the opportunity to talk with the inventor of the cardiac pacemaker, who himself nearly had a coronary accident describing the injustice of what he perceived as NASA taking credit for his device.) If there are technologies we urgently need, then spend the money and develop them. Why go to Mars to do it?

Of course it would be impossible for so much new technology as NASA requires to be developed and not have some spillover into the general economy, some inventions useful down here. For example, the powdered orange juice substitute Tang was a product of the manned space program, and spinoffs have occurred in cordless tools, implanted cardiac defibrillators, liquid-cooled garments, and digital imaging—to name a few. But they hardly justify human voyages to Mars or the existence of NASA.

We could see the old spinoff engine wheezing and puffing in the waning days of the Reagan-era Star Wars office. Hydrogen bomb-driven X-ray lasers on orbiting battle stations will help perfect laser surgery, they told us. But if we need laser surgery, if it’s a high national priority, by all means let’s allocate the funds to develop it. Just leave Star Wars out of it. Spinoff justifications constitute an admission that the program can’t stand on its own two feet, cannot be justified by the purpose for which it was originally sold.

Once upon a time it was thought, on the basis of econometric models, that for every dollar invested in NASA many dollars were pumped into the U.S. economy. If this multiplier effect applied more to NASA than to most government agencies, it would provide a potent fiscal and social justification for the space program. NASA supporters were not shy about appealing to this argument. But a 1994 Congressional Budget Office study found it to be a delusion. While NASA spending benefits some production segments of the U.S. economy—especially the aerospace industry—there is no preferential multiplier effect. Likewise, while NASA spending certainly creates or maintains jobs and profits, it does so no more efficiently than many other government agencies.

Then there’s education, an argument that has proved from time to time very attractive in the White House. Doctorates in science peaked somewhere around the time of Apollo 11, maybe even with the proper phase lag after the start of the Apollo program. The cause-and-effect relationship is perhaps undemonstrated, although not implausible. But so what? If we’re interested in improving education, is going to Mars the best route? Think of what we could do with $100 billion for teacher training and salaries, school laboratories and libraries, scholarships for disadvantaged students, research facilities, and graduate fellowships. Is it really true that the best way to promote science education is to go to Mars?

Another argument is that human missions to Mars will occupy the military-industrial complex, diffusing the temptation to use its considerable political muscle to exaggerate external threats and pump up defense funding. The other side of this particular coin is that by going to Mars we maintain a standby technological capacity that might be important for future military contingencies. Of course, we might simply ask those guys to do something directly useful for the civilian economy. But as we saw in the 1970s with Grumman buses and Boeing/Vertol commuter trains, the aerospace industry experiences real difficulty in producing competitively for the civilian economy. Certainly a tank may travel 1,000 miles a year and a bus 1,000 miles a week, so the basic designs must be different. But on matters of reliability at least, the Defense Department seems to be much less demanding.

Cooperation in space, as I’ve already mentioned, is becoming an instrument of international cooperation—for example, in slowing the proliferation of strategic weapons to new nations. Rockets decommissioned because of the end of the Cold War might be gainfully employed in missions to Earth orbit, the Moon, the planets, asteroids, and comets. But all this can be accomplished without human missions to Mars.

Other justifications are offered. It is argued that the ultimate solution to world energy problems is to strip-mine the Moon, return the solar-wind-implanted helium-3 back to Earth, and use it in fusion reactors. What fusion reactors? Even if this were possible, even if it were cost-effective, it is a technology 50 or 100 years away. Our energy problems need to be solved at a less leisurely pace.

Even stranger is the argument that we have to send human beings into space in order to solve the world population crisis. But some 250,000 more people are born than die every day—which means that we would have to launch 250,000 people per day into space to maintain world population at its present levels. This appears to be beyond our present capability.

I RUN THROUGH such a list and try to add up the pros and cons, bearing in mind the other urgent claims on the federal budget. To me, the argument so far comes down to this question: Can the sum of a large number of individually inadequate justifications add up to an adequate justification?

I don’t think any of the items on my list of purported justifications is demonstrably worth $500 billion or even $100 billion, certainly not in the short term. On the other hand, most of them are worth something, and if I have five items each worth $20 billion, maybe it adds up to $100 billion. If we can be clever about reducing costs and making true international partnerships, the justifications become more compelling.

Until a national debate on this topic has transpired, until we have a better idea of the rationale and the cost/benefit ratio of human missions to Mars, what should we do? My suggestion is that we pursue research and development projects that can be justified on their own merits or by their relevance to other goals, but that can also contribute to human missions to Mars should we later decide to go. Such an agenda would include:

·        U.S. astronauts on the Russian space station Mir for joint flights of gradually increasing duration, aiming at one to two years, the Mars flight time.

·        Configuration of the international space station so its principal function is to study the long-term effects of the space environment on humans.

·        Early implementation of a rotating or tethered “artificial gravity” module on the international space station, for other animals and then for humans.

·        Enhanced studies of the Sun, including a distributed set of robot probes in orbit about the Sun, to monitor solar activity and give the earliest possible warning to astronauts of hazardous “solar flares”—mass ejections of electrons and protons from the Sun’s corona.

·        U.S./Russian and multilateral development of Energiya and Proton rocket technology for the U.S. and international space programs. Although the United States is unlikely to depend primarily on a Soviet booster, Energiya has roughly the lift of the Saturn V that sent the Apollo astronauts to the Moon. The United States let the Saturn V assembly line die, and it cannot readily be resuscitated. Proton is the most reliable large booster now in service. Russia is eager to sell this technology for hard currency.

·        Joint projects with NASDA (the Japanese space agency) and Tokyo University, the European Space Agency, and the Russian Space Agency, along with Canada and other nations. In most cases these should be equal partnerships, not the United States insisting on calling the shots. For the robotic exploration of Mars, such programs are already under way. For human flight, the chief such activity is clearly the international space station. Eventually, we might muster joint simulated planetary missions in low Earth orbit. One of the principal objectives of these programs should be to build a tradition of cooperative technical excellence.

·        Technological development—using state-of-the-art robotics and artificial intelligence—of rovers, balloons, and aircraft for the exploration of Mars, and implementation of the first international return sample mission. Robotic spacecraft that can return samples from Mars can be tested on near-Earth asteroids and the Moon. Samples returned from carefully selected regions of the Moon can have their ages determined and contribute in a fundamental way to our understanding of the early history of the Earth.

·        Further development of technologies to manufacture fuel and oxidizer out of Martian materials. In one estimate, based on a prototype instrument designed by Robert Zubrin and colleagues at the Martin Marietta Corporation, several kilograms of Martian soil can be automatically returned to Earth using a modest and reliable Delta launch vehicle, all for no more than a song (comparatively speaking).

·        Simulations on Earth of long-duration trips to Mars, concentrating on potential social and psychological problems.

·        Vigorous pursuit of new technologies such as constant-thrust propulsion to get us to Mars quickly; this may be essential if the radiation or microgravity hazards make one-year (or longer) flight times too risky.

·        Intensive study of near-Earth asteroids, which may provide superior intermediate-timescale objectives for human exploration than does the Moon.

·        A greater emphasis on science—including the fundamental sciences behind space exploration, and the thorough analysis of data already obtained—by NASA and other space agencies.

These recommendations add up to a fraction of the full cost of a human mission to Mars and—spread out over a decade or so and done jointly with other nations—a fraction of current space budgets. But, if implemented, they would help us to make accurate cost estimates and better assessment of the dangers and benefits. They would permit us to maintain vigorous progress toward human expeditions to Mars without premature commitment to any specific mission hardware. Most, perhaps all, of these recommendations have other justifications, even if we were sure we’d be unable to send humans to any other world in the next few decades. And a steady drumbeat of accomplishments increasing the feasibility of human voyages to Mars would—in the minds of many at least—combat widespread pessimism about the future.

THERE’S SOMETHING MORE. There’s a set of less tangible arguments, many of which, I freely admit, I find attractive and resonant. Spaceflight speaks to something deep inside us—many of us, if not all. An emerging cosmic perspective, an improved understanding of our place in the Universe, a highly visible program affecting our view of ourselves might clarify the fragility of our planetary environment and the common peril and responsibility of all the nations and peoples of Earth. And human missions to Mars would provide hopeful prospects, rich in adventure, for the wanderers among us, especially the young. Even vicarious exploration has social utility.

I repeatedly find that when I give talks on the future of the space program—to universities, business and military groups, professional organizations—the audiences are much less patient with practical, real-world political and economic obstacles than I. They long to sweep away the impediments, to recapture the glory days of Vostok and Apollo, to get on with it and once more tread other worlds. We did it before; we can do it again, they say. But, I caution myself, those who attend such talks are self-selected space enthusiasts.

In 1969, less than half the American people thought the Apollo program was worth the cost. But on the twenty-fifth anniversary of the Moon landing, the number had risen to two thirds. Despite its problems, NASA was rated as doing a good-to-excellent job by 63 percent of Americans. With no reference to cost, 55 percent of Americans (according to a CBS News poll) favored “the United States sending astronauts to explore Mars.” For young adults, the figure was 68 percent. I think “explore” is the operative word.

It is no accident that, whatever their human flaws, and however moribund the human space program has become (a trend that the Hubble Space Telescope repair mission may have helped to reverse), astronauts and cosmonauts are still widely regarded as heroes of our species. A scientific colleague tells me about a recent trip to the New Guinea highlands where she visited a stone age culture hardly contacted by Western civilization. They were ignorant of wristwatches, soft drinks, and frozen food. But they knew about Apollo 11. They knew that humans had walked on the Moon. They knew the names of Armstrong and Aldrin and Collins. They wanted to know who was visiting the Moon these days.

Projects that are future-oriented, that, despite their political difficulties, can be completed only in some distant decade are continuing reminders that there will be a future. Winning a foothold on other worlds whispers in our ears that we’re more than Picts or Serbs or Tongans: We’re humans.

Exploratory spaceflight puts scientific ideas, scientific thinking, and scientific vocabulary in the public eye. It elevates the general level of intellectual inquiry. The idea that we’ve now understood something never grasped by anyone who ever lived before—that exhilaration, especially intense for the scientists involved, but perceptible to nearly everyone—propagates through the society, bounces off walls, and comes back at us. It encourages us to address problems in other fields that have also never before been solved. It increases the general sense of optimism in the society. It gives currency to critical thinking of the sort urgently needed if we are to solve hitherto intractable social issues. It helps stimulate a new generation of scientists. The more science in the media—especially if methods are described, as well as conclusions and implications—the healthier, I believe, the society is. People everywhere hunger to understand.

WHEN I WAS A CHILD, my most exultant dreams were about flying—not in some machine, but all by myself. I would be skipping or hopping, and slowly I could pull my trajectory higher. It would take longer to fall back to the ground. Soon I would be on such a high arc that I wouldn’t come down at all. I would alight like a gargoyle in a niche near the pinnacle of a skyscraper, or gently settle down on a cloud. In the dream—which I must have had in its many variations at least a hundred times—achieving flight required a certain cast of mind. It’s impossible to describe it in words, but I can remember what it was like to this day. You did something inside your head and at the pit of your stomach, and then you could lift yourself up by an effort of will alone, your limbs hanging limply. Off you’d soar.

I know many people have had similar dreams. Maybe most people. Maybe everyone. Perhaps it goes back 10 million years or more, when our ancestors were gracefully flinging themselves from branch to branch in the primeval forest. A wish to soar like the birds motivated many of the pioneers of flight, including Leonardo da Vinci and the Wright brothers. Maybe that’s part of the appeal of spaceflight, too.

In orbit about any world, or in interplanetary flight, you are literally weightless. You can propel yourself to the spacecraft ceiling with a slight push off the floor. You can go tumbling through the air down the long axis of the spacecraft. Humans experience weightlessness as joy; this has been reported by almost every astronaut and cosmonaut. But because spacecraft are still so small, and because space “walks” have been done with extreme caution, no human has yet enjoyed this wonder and glory: propelling yourself by an almost imperceptible push, with no machinery driving you, untethered, high up into the sky, into the blackness of interplanetary space. You become a living satellite of the Earth, or a human planet of the Sun.

Planetary exploration satisfies our inclination for great enterprises and wanderings and quests that has been with us since our days as hunters and gatherers on the East African savannahs a million years ago. By chance—it is possible, I say, to imagine many skeins of historical causality in which this would not have transpired—in our age we are able to begin again.

Exploring other worlds employs precisely the same qualities of daring, planning, cooperative enterprise, and valor that mark the finest in the military tradition. Never mind the night launch of an Apollospacecraft bound for another world. That makes the conclusion foregone. Witness mere F-14s taking off from adjacent flight decks, gracefully canting left and right, afterburners flaming, and there’s something that sweeps you away—or at least it does me. And no amount of knowledge of the potential abuses of carrier task forces can affect the depth of that feeling. It simply speaks to another part of me. It doesn’t want recriminations or politics. It just wants to fly.

“I … had ambition not only to go farther than anyone had done before,” wrote Captain James Cook, the eighteenth-century explorer of the Pacific, “but as far as it was possible for man to go.” Two centuries later, Yuri Romanenko, on returning to Earth after what was then the longest space flight in history, said “The Cosmos is a magnet … Once you’ve been there, all you can think of is how to get back.”

Even Jean-Jacques Rousseau, no enthusiast of technology, felt it:

The stars are far above us; we need preliminary instruction, instruments and machines, which are like so many immense ladders enabling us to approach them and bring them within our grasp.

“The future possibilities of space-travel,” wrote the philosopher Bertrand Russell in 1959,

which are now left mainly to unfounded fantasy, could be more soberly treated without ceasing to be interesting and could show to even the most adventurous of the young that a world without war need not be a world without adventurous and hazardous glory.* To this kind of contest there is no limit. Each victory is only a prelude to another, and no boundaries can be set to rational hope.

In the long run, these—more than any of the “practical” justifications considered earlier—may be the reasons we will go to Mars and other worlds. In the meantime, the most important step we can take toward Mars is to make significant progress on Earth. Even modest improvements in the social, economic, and political problems that our global civilization now faces could release enormous resources, both material and human, for other goals.

There’s plenty of housework to be done here on Earth, and our commitment to it must be steadfast. But we’re the kind of species that needs a frontier—for fundamental biological reasons. Every time humanity stretches itself and turns a new corner, it receives a jolt of productive vitality that can carry it for centuries.

There’s a new world next door. And we know how to get there.

*Even then it wasn’t easy. The Portuguese chronicler Gomes Eanes de Zurara reported this assessment by Prince Henry the Navigator: “It seemed to the Lord Infante that if he or some other lord did not endeavor to gain that knowledge, no mariners nor merchants would ever dare to attempt it, for it is clear that none of them ever trouble themselves to sail to a place where there is not a sure and certain hope of profit.”

*Russell’s phrase is noteworthy: “adventurous and hazardous glory.” Even if we could make human spaceflight risk-free—and of course we cannot—it might be counterproductive. The hazard is an inseparable component of the glory.