The Value of Human Exploration
Still, the proponents of manned exploration have a point – or rather, several. First, they might just as well acknowledge that the Shuttle has set space science back many years. Even the head of NASA thinks it was a mistake. But they might point out that the Shuttle is a very poorly designed system, not a good example of how manned exploration should be done. It is essentially a very large and heavy glider taken into low orbit by a partially reusable combination of solid and liquid fuel propulsion engines. It is at its worst when it ferries satellites into orbit, a task to which it was devoted through the 1980s, and for which it is still used. Suppose that I am eating dinner in Tokyo next to a sumo wrestler. Across the dining room a friend asks me for the small pitcher of warm saki. I could get up and take it to him. It would require me to spend a certain amount of energy, but not much, and to incur a certain amount of risk, but not much. Or I could hand the pitcher to the sumo wrestler and then carry him, saki in hand, across the room so he can give the saki to my friend. The energy required is far greater, as is the risk involved, both to the sumo wrestler and to me. Indeed, that is an extremely expensive and unsafe way to ferry satellites into orbit (or carry saki across a dining room). To make matters worse, the Shuttle is an extremely complicated machine, with more ways to fail than anything else that has flown before or since.
Was there a better way to fly people into space? Of course there was. Otherwise we would have never landed a man on the Moon and returned him safely to Earth “before the decade was out” as President Kennedy challenged us to do in the early 1960s. And when we went to the Moon, let us recall, there were also many complaints about the poor quality of the science that was expected to result. Those complaints were very misguided. The Apollo astronauts made great contributions to science, contributions, for example, to our understanding of the origin and evolution of our planet.
That Apollo era saw the flowering of unmanned exploration as well, a flowering that continued through the mid-1970s, until NASA put its rockets in mothballs and forced practically the entire U.S. space program into the coming “space bus” – the Shuttle. That era also gave us a reliable and relatively inexpensive space station, Skylab, which burnt in reentry when its orbit decayed and NASA no longer had rockets to move it into a higher orbit. The Russians, with a somewhat more modest program also based on rockets, had a very active exploration of the solar system and a station of their own: Mir.
So the important question is whether we should explore with people and with machines, as long as we have a sensible means again for ferrying astronauts into space. We could, for example, jettison the shuttle and continue using the Russian rockets until we have a good rocket program of our own again. We could also encourage private undertakings such as Spaceship1, which promise far cheaper access into space for astronauts.
In the meantime, though, we should realize that manned exploration is once again poised to help advance the cause of space science. I am referring to the search for life, or for fossils of life, in Mars. Rovers and other machines are already exploring the planet, finding evidence of water, laying the groundwork for when human geologists and paleontologist finally arrive, for practically all agree that their presence will be needed in this extraordinarily significant endeavor.
THE VALUE OF A PERMANENT HUMAN PRESENCE IN SPACE
The critics' fear is that the space station once again signals the commitment of the country to expensive manned exploration, with glamour winning over substance. I have already argued that there is more than glamour to the presence of humans in space. It is now time to take this argument further. Unless we had money to burn, it is difficult to justify a transcontinental journey to Paris for the sole purpose of sitting at a cafe to watch people go by as we sip a brandy or a cup of cafe au lait. But if we had to go to Paris for some other reason, it would make perfectly good sense to enjoy that aspect of Parisian life as well. Similarly a permanent manned presence in space – even if prompted by reasons of commerce or national prestige – would make feasible a multiplicity of scientific experiments that a society might not be willing to undertake otherwise. My suspicion is, then, that a permanent human presence in space would, if anything, help a new flowering of space science.
I am not here talking about the occasional grandiose project that becomes an end in itself and leaves more memories than it does future avenues of investigation. I am talking about a space station that marks the beginning of the sustained expansion of the human species into the solar system. Since that is the fear, that is the situation I would like to discuss. How can space science be well served by such an expansion during a period of fifty to a hundred years from today?
Since some branches of space science are obviously helped by a human presence, or so I hope to have shown, the issue is how space science as a whole is to be helped. We must consider, then, what effects that human presence will have on space astronomy, planetary exploration, and other areas where the human experimenter is either not wanted or has been traditionally absent. In space astronomy there is a clear initial benefit: the repair and regular maintenance of the large telescopic arrays in orbit. The role of servicing the Hubble visual telescope, for example, requires the ability of astronauts to fly to the telescope and work on it. (While the shuttle was out of commission, space scientists tried to design a robotic mission, but its future is uncertain; if it fails, the Hubble telescope will have its useful life cut short because astronauts could no longer reach it.) A space station would enhance significantly the capacity to support in space astronomical observatories of even larger magnitude (once we build spacecraft that station occupants can use for travel in orbit). This goal can be achieved in the next two or three decades, definitely a period in which humans are not likely to be replaced by their mechanical contraptions.
This role gives but a mere inkling of what humans in space can do for astronomy. As the expansion into space continues, it becomes possible to build even larger observatories that would be too difficult to take up in one piece. And it also becomes possible to place those observatories in many locations away from the Earth, either because of convenience – e.g., on the other side of the Moon, so as to shield them from the electromagnetic interference from the Earth – or simply to increase the baseline of the measurements. And these possibilities point to some aspects of a permanent human presence of potentially far greater significance.
Apart from producing goods that can be used on Earth, space labs and factories can build technology for space itself. There are several ways in which large space structures might be very advantageous, and some of them will merit discussion shortly. But my point goes further. A lot of the technology used in unmanned space flight today has to be built with the problems of lift-off, orbiting, and deployment in mind. It has to meet terrestrial conditions, withstand the accelerations and temperatures involved in the transportation from ground to orbit, its final stage must be fitted to the specifications of the boosters, and then it has to manage in space. But is all this necessary?
Having a technology that can meet all these challenges is no doubt beneficial. But imposing them on all technology and all experiments that go into space is not very reasonable unless there are no alternatives. It is not reasonable because it imposes greater difficulties and cost in design and production. Take the gravitational gyroscopes designed to test some extraordinary predictions of Einstein’s General Theory of Relativity (the Gravity Probe B experiment). To have the spheres suspended you must use thousands of volts on the Earth, and you must design and build the sphere so it can withstand that electrical potential, even though in space the amount of electricity used will be very small. If we could do the experimental development in space, many of these specification problems would be automatically solved. Not that it would pay now to send scientists to do that development in orbit. The point is rather that a massive, permanent human presence in space opens up a lot of possibilities for space science because it would be relatively feasible to undertake them under those conditions.
In this regard planetary exploration can be a clear beneficiary, since the requirements for an interplanetary probe to be launched from space may be far more relaxed. For example, rather flimsy structures may be perfectly adequate in propulsion modules. We could also employ vacuum tubes without going to the trouble of producing a vacuum artificially – indeed without a "tube" at all, just a cathode, anode, grids, and relevant circuitry. And of course the superior semi-conductors and crystals that can be produced in microgravity would be deployed in space technology without some of the costs of transportation up and down the gravity well of the Earth. The point is that once we make ourselves at home in space many possibilities for technological innovation in space will become readily apparent.
This point is made stronger when we realize that it is possible to avail ourselves of the resources of space in the development of such technologies, as well as in the development of products for the Earth. Once in place, a vigorous exploitation of the minerals and energy of the solar system can make important contributions to an infrastructure that may support the routine exploration of the planets. This is not to say that we should commit ourselves to such exploitation at this time. Indeed one of the present tasks of solar system exploration is to determine the availability and distribution of such resources. Nor can we expect to have the complete means for taking advantage of those resources immediately, even if we wanted to. But as our presence in space becomes wider and better established it is reasonable to expect that we will begin to use the native materials. Plans are already being prepared for that eventuality, and so the promise of space may be more fully realized once we make it our environment.
The ability to create very large structures in space, which for at least many decades is likely to require astronauts, will make possible to assemble very large solar sails and other forms of propulsion that will considerably shorten the travel times and increase the distances our spacecraft can travel. That is also going to have a beneficial effect on all of space science.
The urge to explore the solar system must of necessity go hand in hand with scientific exploration. A survey of what Mars has to offer to potential colonists, for example, would require first an extensive scientific survey of Mars. And any plans for setting up such a colony, as well as for the extraction and processing of materials would at the very least challenge our talents in several branches of space science. Eventually advanced science would no longer be necessary for the technology of prospecting and colonization, since a very well tried science will become routine. This is not to suggest that science is always a prerequisite for technology. The industrial revolution was spurred as much by the development of craft as by the great intellectual feats of science. The relationship between science and technology is clearly dialectical – changes in science affect areas of technology, which in turn make scientific change possible, and so on – although just as clearly at any one time there is also a good deal of independence between them. In this case, however, the nature of the exploring to be done has a major scientific component, in that the questions that we need to ask are not different from the kinds of questions that many planetary scientists would like to ask. Thus the technology to be developed would not only depend on the scientific answers to these questions but would also to a large extent be guided by them. Even at the level of building a colony, we need to progress trough a series of experiments on ecological loops if we have any hope of designing human outposts that approach self-sufficiency.
A significant human presence throughout the solar system would not only enhance by orders of magnitude the amount and quality of space science, but also would change drastically the very conception of what may be done in and with space science. Once we are in space permanently the range of possibilities is also altered permanently, not only because humans are around to lend a helping hand, but because they are there under conditions that permit them to move with far greater ease. There are simply far more starting points for space science research, a radically different interplay with a different technology, and a qualitative difference in what may be undertaken. In areas where success turns exploration into routine colonization, the frontiers of science will move further outward, and those that remain may not be so closely connected anymore with the day-to- day activities of the ordinary humans in space. But that turning of the extraordinary into the commonplace will not happen overnight. And when it does, it may simply point to a new horizon of opportunity for science and technology beyond what has just been reached.
The first colonies on the Moon, on Mars, and on the moons of the outer planets would be dedicated mainly to the scientific exploration of those worlds, but also to determining the feasibility of even bigger settlements. As our presence increases so will the opportunities for space science (although I am sure there will be drawbacks on occasion. Once we are up there in force, the panorama of scientific, technological, industrial, and social opportunities may seem vastly different from what we may imagine today.
As those colonies grow, they will transform their extraterrestrial environments. The point may come when we engage in the science, or art, of "terraforming," which at its most grandiose envisions transforming entire planets and giant moons into habitable worlds. If a world does not have enough water, for example, we bring to it one of the thousands of small asteroids from the Kuiper belt composed mainly of water. Crashing the asteroid into that world would also help to increase the density and raise the temperature of the atmosphere. In another world, Venus for instance, we could place a cloud of dust around it to reduce the amount of light it receives from the sun, and then manipulate its atmosphere to reduce its greenhouse effect considerably. We might thus achieve a range of temperatures amenable to life.
Decades, probably centuries, will pass before we understand planet dynamics well enough to attempt to transform any world into a second Earth, a task that should not begin until we have learned the scientific lessons those worlds have to teach us. But eventually, it may open up new niches to our species. In the truly long run, but long before the sun becomes a red giant, the Earth’s “thermostat” is likely to malfunction. James Lovelock, of Gaia fame, and M. Whitfield argued in a 1982 article that life was steadily removing CO2 from the atmosphere – it actually has been doing so for the last 400 million years, since plants conquered the land – and in about 100 million years the level of CO2 will go below 150 parts per million (ppm) of air. This level is important because most plants require at least as much atmospheric CO2 to survive. Newer forms of plants – grass, palm trees – use slightly different mechanisms for photosynthesis and can go well below the 150 ppm. The flora of the future, then, will have a very different view: gone will be the apple orchards and the rose gardens, replaced by new and exotic varieties of plants. Inexorably, unless we intervene, the level of atmospheric CO2 will go below 10 ppm and photosynthesis will come to an end altogether. More recent studies following on Lovelock and Whitfield’s footsteps have revised their estimate to between 500 million and a billion years.
The loss of plants will be a catastrophe for animals, obviously, but also for marine life, since it depends so much on the run-off of the soil nutrients that result from the presence of plants. Those few animals that can manage to survive will be done in a few million years by the rising temperatures, for eventually geological processes will bring again significant levels of atmospheric CO2 , which will no longer be kept in check by photosynthetic organisms. Several scenarios have been proposed to explain what will happen after that point. Likely, the expected increasing level of solar energy, coupled with high levels of atmospheric CO2, will quickly lead to the sort of runaway greenhouse effect that vaporized Venus’ oceans. Thus life will come to an end billions of years before the sun’s transition to a red giant obliterates the atmosphere and the oceans altogether.
In those perilous days the full development of space exploration will come to humankind’s rescue. It could, for example, “terrraform” its own home planet so it will adjust to the new conditions. When that is no longer feasible because the sun’s sphere will expand beyond Venus, we might be able to change the Earth’s orbit. And on failing that, humankind will hang on, on terraformed Mars and Titan, as well perhaps on artificial worlds along the lines of Gerard O’Neill’s space colonies. As humanity expands in search of resources in the solar system, the size and complexity of its space habitats is likely to increase. Eventually our species may move into the Oort Cloud. We will then have followed in space the example of expansion set by our ancestors in our own planet. To accomplish that will require many but plausible advances in propulsion systems, with concomitant increases in the speed of travel. Under those conditions, migration from the Oort Cloud to the stars may well be possible. Humankind will then be able to survive in the truly long run.
Eons before then, a large human presence will make it easier to track, and then to deflect asteroids and comets most in danger of colliding with the Earth, thus saving millions of human lives, and even preventing a repeat of the global catastrophe that wiped out the dinosaurs and most other life 65 million years ago.
It all begins with astronauts.
 Tracy Watson, “NASA Chief: Shuttles were a Mistake,” reprinted from USA Today in Detroit Free Press, September 28, 2005, p. 13A.
 See S.G. Brush, "Harold Urey and the Origin of the Moon: The Interaction of Science and the Apollo Program," in the Proceedings of the Twentieth Goddard Memorial Symposium, 1982, published by the American Astronautical Society; and "From Bump to Clump: Theories of the Origin of the Solar System 1900-1960," in P.A. Hanle and V.D. Chamberlain, eds. Space Science Comes of Age: Perspectives in the History of the Space Sciences, Smithsonian Institution Press, 1981, pp.78-100.
 The Constellation program, which NASA has proposed for returning to the Moon is a high-tech update of the Apollo program.
 See, for example, James E. Oberg, New Earths, Stackpole Books, 1981.
 J.E. Lovelock and M. Whitfield. 1982. “Life Span of the Biosphere.” Nature 296, pp. 561-563.
 This account is borrowed from Peter D. Ward and Donald Brownlee, The Life and Death of Planet Earth, Times Books, 2002, pp. 101-116.
 See Gerard O'Neill's The High Frontier, Anchor Press/Doubleday, 1982 (2nd edition). See also T. Heppenheimer, Colonies in Space, Stackpole Books, 1977.
 The probability of such collisions can be found Dana Desoinie’s Cosmic Collisions, a Scientific American Focus Book, Henry Holt & Co., 1996, pp. 100-101. Thermonuclear weapons are the first choice, although O’Neill’s mass drivers might also do the job. He envisioned using such drivers to transport asteroids rich in valuable minerals to a lunar orbit, op.cit.