Ever since NASA was founded, the greater part of its resources have gone into putting men and women into space. On January 14 of this year, President Bush announced a "New Vision for Space Exploration" that would further intensify NASA's concentration on manned space flight. The International Space Station, which has been under construction since 1998, would be completed by 2010; it would be kept in service until around 2016, with American activities on the station from now on focused on studies of the long-term effects of space travel on astronauts. The manned spacecraft called the space shuttle would continue flying until 2010, and be used chiefly to service the space station. The shuttle would then be replaced by a new manned spacecraft, to be developed and tested by 2008. Between 2015 and 2020 the new spacecraft would be used to send astronauts back to the moon, where they would live and work for increasing periods. We would then be ready for the next step—a human mission to Mars.
This would be expensive. The President gave no cost estimates, but John McCain, chairman of the Senate Commerce, Science, and Transportation Committee, has cited reports that the new initiative would cost between $170 billion and $600 billion. According to NASA briefing documents, the figure of $170 billion is intended to take NASA only up to 2020, and does not include the cost of the Mars mission itself. After the former President Bush announced a similar initiative in 1989, NASA estimated that the cost of sending astronauts to the moon and Mars would be either $471 billion or $541 billion in 1991 dollars, depending on the method of calculation. This is roughly $900 billion in today's dollars. Whatever cost may be estimated by NASA for the new initiative, we can expect cost overruns like those that have often accompanied big NASA programs. (In 1984 NASA estimated that it would cost $8 billion to put the International Space Station in place, not counting the cost of using it. I have seen figures for its cost so far ranging from $25 billion to $60 billion, and the station is far from finished.) Let's not haggle over a hundred billion dollars more or less—I'll estimate that the President's new initiative will cost nearly a trillion dollars.
Compare this with the $820 million cost of recently sending the robots Spirit and Opportunity to Mars, roughly one thousandth the cost of the President's initiative. The inclusion of people inevitably makes any space mission vastly more expensive. People need air and water and food. They have to be protected against cosmic rays, from which we on the ground are shielded by the Earth's atmosphere. On a voyage to Mars astronauts would be beyond the protective reach of the Earth's magnetic field, so they would also have to be shielded from the charged particles that are sent out by the sun during solar flares. Unlike robots, astronauts will want to return to Earth. Above all, the tragic loss of astronauts cannot be shrugged off like the loss of robots, so any casualties in the use of the new spacecraft would cause costly delays and alterations in the program, as happened after the disastrous accidents to the Challenger shuttle in 1986 and to the Columbia shuttle in February 2003.
The President's new initiative thus makes it necessary once more to take up a question that has been with us since the first space ventures: What is the value of sending human beings into space? There is a serious conflict here. Astronomers and other scientists are generally skeptical of the value of manned space flight, and often resent the way it interferes with scientific research. NASA administrators, astronauts, aerospace contractors, and politicians typically find manned space flight just wonderful. NASA's Office of Space Science has explained that "the fundamental goal of the President's Vision is to advance US scientific, security, and economic interests through a robust space exploration program." So let's look at how manned space flight advances these interests.
Many Americans remember the fears for US national security that were widely felt when the Soviets launched the unmanned Sputnik satellite in October 1957. These fears were raised to new heights in 1961, when the Soviet cosmonauts Yuri Gagarin and then Gherman Titov went into space. Titov's spacecraft made seventeen orbits around the Earth, three of them passing for the first time over the United States. The American reaction is described by Tom Wolfe in The Right Stuff:
Once again, all over the country, politicians and the press seemed profoundly alarmed, and the awful vision was presented; suppose the cosmonaut were armed with hydrogen bombs and flung them as he came over, like Thor flinging thunderbolts.... Toledo disappears off the face of the earth ...Kansas City...Lubbock....
As it turned out, the ability to send rockets into space did have tremendous military importance. Ballistic missiles that travel above the Earth's atmosphere all but replaced bombers as the vehicle of choice for carrying Soviet or American nuclear weapons to an adversary's territory. Even in the nonnuclear wars of today, artificial satellites in orbit around the Earth play an essential part in surveillance, communications, and navigation. But these missiles and satellites are all unmanned. One can't just drop bombs from satellites to the Earth's surface—once something is put in orbit above the Earth's atmosphere, it stays in orbit unless a rocket brings it down. As far as I know there never has been a moment from Titov's flight to the present when the ability to put people into space gave any country the slightest military advantage.
I say this despite the fact that some military satellites have been put into orbit by the space shuttle. This could be done just as well and much more cheaply by unmanned rockets. It had been hoped that the shuttle, because reusable, would reduce the cost of putting satellites in orbit. Instead, while it costs about $3,000 a pound to use unmanned rockets to put satellites in orbit, the cost of doing this with the shuttle is about $10,000 a pound. The physicist Robert Park has pointed out that at this rate, even if lead could be turned into gold in orbit, it would not pay to send it up on the shuttle. Park could have added that in this case NASA would probably send lead bricks up on the shuttle anyway, and cite the gold in press releases as proof of the shuttle's value. There doesn't seem to have been any reason for the use of the shuttle to take some military satellites into orbit other than that NASA has needed some way to justify the shuttle's existence. During the Carter administration, NASA explained to the deputy national security adviser that unless President Carter forced military satellite missions onto the space shuttle it would be the President who would be responsible for the end of the shuttle program, since the shuttle could never survive if it had to charge commercial users the real cost of space launches.
Similar remarks apply to the direct economic benefits of space travel. There is no doubt about the great value of artificial satellites in orbit around the Earth. Those that survey the Earth's surface give us information about weather, climate, and environmental change of all sorts, as well as warnings of military buildups and rocket launches. Satellites relay television programs and telephone conversations beyond the horizon. The Global Positioning System, which calculates the location of automobiles, ships, and planes, as well as missiles, relies on the timing of signals from satellites. But again, these are all unmanned satellites, and can be put into orbit most cheaply by unmanned rockets.
It is difficult to think of any direct economic benefit that can be gained by putting people into space. There has been a continuing effort to grow certain crystals in the nearly zero gravity on an orbiting satellite such as the International Space Station, or to make ultra-pure semiconductor films in the nearly perfect vacuum in the wake of the space station. Originally President Reagan approved the space station in the expectation that eventually it could be run at a profit. Nothing of economic value has come of this, and these programs have now apparently been wisely abandoned in the President's new plans for the space station.
Lately there has been some talk of sending astronauts to mine the light isotope helium three on the moon, where it has been deposited through billions of years of exposure of the moon's surface to the solar wind. The point is that the more familiar thermonuclear reactions that use hydrogen isotopes as fuel produce large numbers of neutrons, which could damage surrounding materials and make them radioactive, while thermonuclear reactions involving helium three produce far fewer neutrons, and hence less radioactive waste. A thermonuclear reactor using helium three might also allow a more efficient conversion of nuclear energy to electricity, if it could be made to work.
Unfortunately, that is a big "if." One of the things that makes the development of thermonuclear power so difficult is the necessity of heating the fuel to a very high temperature so that atomic nuclei can collide with each other with enough velocity to overcome the repulsive forces between the electric charges carried by the nuclei. Helium nuclei have twice the electric charge of hydrogen nuclei, so the temperature needed to produce thermonuclear reactions involving helium three and hydrogen isotopes is much higher than the temperature needed for reactions involving hydrogen isotopes alone. So far, no one has been able to produce a useful, self-sustaining thermonuclear reaction using hydrogen isotopes. Until that is done, there seems little point in going to great expense on the moon to mine a fuel whose use would make it even more difficult to generate thermonuclear power.
In his speech on January 14 President Bush emphasized that the space program produces "technological advances that have benefited all humanity." It is true that pursuing a demanding task like putting men on Mars can yield indirect benefits in the form of new technologies, but here too I think that unmanned missions are likely to be more productive. Trying to think of some future spinoff from space missions that would really benefit humanity, I find it hard to come up with anything more promising than the experience of designing robots that are needed for unmanned space missions. This experience can help us in building robots that can spare humans from dangerous or tedious jobs here on Earth. Surprises are always possible, but I don't see how anything of comparable value could come out of developing the specialized techniques needed to keep people alive on space missions.
President Bush's presentation of his space initiative emphasized the scientific knowledge to be gained. Some readers of his speech may imagine astronauts on the shuttle or the space station peering through telescopes at planets or stars, or wandering about on the moon or Mars making discoveries about the history of the solar system. It doesn't work that way.
There is no question that observatories in space have led to a tremendous increase in astronomical knowledge. To take just one example, in the early 1990s instruments on the Cosmic Background Explorer satellite made measurements of a faint background of microwave radio static that had been discovered in 1965. This radiation is left over from a time when the universe was only about four hundred thousand years old. The new data showed that the intensity of this radiation at various wavelengths was just what would be emitted by opaque matter at a temperature of 2.725 degrees Celsius above absolute zero. It was the first time in the history of cosmology that anything had been measured to four significant figures. More important, the intensity of this radiation was found to be not perfectly uniform, but slightly lumpy. The observed intensity differs from one part of the sky to another by roughly one part in a hundred thousand for directions separated by a few degrees of arc. This amount of lumpiness is just what was expected, on the assumption that these variations in the cosmic microwave background arose from quantum fluctuations in the spatial distribution of energy in the very early universe, fluctuations that also eventually gave rise to the concentrations of matter—galaxies and clusters of galaxies—that astronomers see throughout the universe.
There followed a decade of increasingly refined observations of the cosmic microwave background from mountaintops, balloons, and the South Pole, but the distorting effect of the Earth's atmosphere sets a limit to the precision that can be obtained with measurements from even the highest altitudes accessible to balloons. Finally these studies were dramatically advanced in 2002 by a remarkable new space mission, the Wilkinson Microwave Anisotropy Probe. After making repeated loops around the Earth to build up speed, this probe traveled out to a point in space known as L2, about a million miles from the Earth (four times farther than the moon), in the direction opposite from the Sun. Anything placed at L2 orbits the Sun at just the speed needed to keep it at L2. There, in the cold quiet of interplanetary space, it was possible to map out the lumpiness of the cosmic microwave radiation background to an unprecedented level of accuracy. The comparison of these measurements with theory has confirmed our general ideas about the emergence of fluctuations in the very early universe; it has shown that the universe now consists of about 4 percent ordinary atoms, about 23 percent dark matter of some exotic type that does not interact with radiation, and the rest some sort of mysterious "dark energy" having negative pressure; and it has given the age of the universe as between 13.5 billion and 13.9 billion years.
Exciting research, of which NASA may justly feel proud. Research of this sort has made this a golden age for cosmology. But neither the Cosmic Microwave Background Explorer nor the Wilkinson Microwave Anisotropy Probe had any astronauts aboard. People were not needed. On the contrary, through their movements and body heat they would have fouled up these measurements, as well as greatly increasing the cost of these missions. The same is true of every one of the space observatories that have expanded our knowledge of the universe through observations of ultraviolet light, infrared light, X-rays, or gamma rays from above the Earth's atmosphere. Some of these observatories were taken into orbit by the shuttle, while others (including the Cosmic Microwave Background Explorer and the Wilkinson Microwave Anisotropy Probe) were carried up by unmanned rockets, as all of them could have been.
The Hubble Space Telescope is a special case. Like the other orbiting observatories, the Hubble operates under remote control, with no people traveling with it. But unlike these other observatories, the Hubble was not only launched by the shuttle, but has also been serviced several times by astronauts brought up to its orbit by the shuttle. The Hubble has made a great contribution to astronomy, one that goes way beyond taking gorgeous color photos of planets and nebulae. Most dramatically, teaming up with observatories on the ground, the Hubble carried out a program of measuring the distances and velocities of far-away galaxies. In 1998 these measure- ments revealed that the expansion of the universe is not being slowed down by the mutual gravitational attraction of its matter, as had been thought, but is rather speeding up, presumably in response to the gravitational repulsion of the dark energy I mentioned earlier. The Hubble may have given NASA its best argument for the scientific value of manned space flight.
But like the other space observatories, the Hubble Space Telescope could have been carried into orbit by unmanned rockets. This would have spared astronauts the danger of shuttle flights, and it would have been much cheaper. Riccardo Giacconi, the former director of the Space Telescope Science Institute, has estimated that by using unmanned rockets instead of the space shuttle, we could have sent up seven Hubbles without increasing the total mission cost. It would then not have been necessary to service the Hubble; when design flaws were discovered or parts wore out, we could just have sent up another Hubble.
What about the scientific experiments done by astronauts on the space shuttle or the space station? Recently I asked to see the list of experiments that NASA assigned to the astronauts aboard the Columbia space shuttle on its last flight, which ended tragically when the shuttle exploded during re-entry. It is sad to report that it is not an impressive list of experiments. Roughly half had to do with the effect of the space environment on the astronauts. This at least is a kind of science that cannot be done without the presence of astronauts, but it has no point unless one plans to put people into space for long periods for some other reason.
Of the other half of the Columbia's experiments, a large fraction dealt with the growth of crystals and the flow of fluids in nearly zero gravity, old standbys of NASA that have neither illuminated any fundamental issues of science nor led to any practical applications. It is always dangerous for a scientist in one field to try to judge the value of work done by specialists in other fields, but I think I would have heard about it if anything really exciting was coming out of any of these experiments, and I haven't. Much of the "scientific" program assigned to astronauts on the space shuttle and the space station has the flavor of projects done for a high school science talent contest. Some of the work looks interesting, but it is hard to see why it has to be done by people. For instance, there was just one experiment on Columbia devoted to astronomy, a useful measurement of variations in the energy being emitted from the sun. The principal investigator tells me that the only intervention of the astronauts consisted of turning the apparatus on and then turning it off.
Looking into the future, we need to ask, what scientific work can be done by astronauts on Mars? They can walk around and look at the terrain, and carry out tests on rocks, looking for signs of water or life, but all that can be done by robots. They can bring back rock samples, as the Apollo astronauts did from the moon, but that too can be done by robots. Samples of rocks from the moon were also brought back to Earth by unmanned Soviet lunar missions. It is sometimes said that the great disadvantage of using robots in a mission to Mars is that they can only be controlled by people on Earth with a long wait (at least four minutes) for radio signals to travel each way between the Earth and Mars. That would indeed be a severe problem if the robots were being sent to Mars to play tennis with Martians, but not much is happening there now, and I don't see why robots can't be left to operate with only occasional intervention from Earth. Any marginal advantage that astronauts may have over robots in exploring Mars would be more than canceled by the great cost of manned missions. For the cost of putting a few people in a single location on Mars, we could have robots studying many different landscapes all over the planet.
Many scientists and some NASA administrators understand all this very well. I have frequently been told that it is necessary publicly to defend programs of manned space flight anyway, because the voters and their elected representatives only care about the drama of people in space. (Richard Garwin has reminded me of the old astronauts' proverb "No bucks without Buck Rogers.") It is hoped that while vast sums are being spent on manned space flight missions, a little money will be diverted to real science. I think that this attitude is self-defeating. Whenever NASA runs into trouble, it is science that is likely to be sacrificed first. After NASA had pushed the Apollo program to the point where people stopped watching lunar landings on television, it canceled Apollo 18 and 19, the missions that were to be specifically devoted to scientific research.
It is true that the administration now projects a 5 percent increase per year in NASA's funding for the next three years. So far, funding is being maintained for the next large space telescope, and is being increased for some other scientific programs, including robotic missions to the planets and their moons. But we can already see damage to programs that are not related to exploration of the solar system, and especially to research in cosmology. Studying the origin of the planets is interesting, but certainly not more so than studying the origin of the universe.
Two days after President Bush presented his new space initiative, NASA announced that the planned shuttle mission to service Hubble in 2006 would be canceled. This mission would have replaced gyroscopes and batteries that are needed to extend Hubble's life into the next decade, and it would have installed two new instruments (which have already been built, at a cost of $167 million) to extend Hubble's capacities. One of these instruments would have allowed Hubble to survey the sky in infrared and ultraviolet light, revealing much about the formation of the earliest stars and galaxies. The other was an ultraviolet spectrograph, which would have explored intergalactic matter in the early universe. Using older instruments, Hubble would also have pushed the program of measuring distances and velocities of galaxies to greater distances, mapping out the dark energy that is accelerating the expansion of the universe. Instead, in about three years, when the Hubble gyroscopes can no longer point the telescope accurately, it will cease operation. This will leave us with no large space telescope until 2011 at the earliest. Eventually, before the slight drag of the Earth's atmosphere at its altitude can bring the Hubble down, an unmanned rocket will be sent up to the Hubble to take it out of orbit and deposit it harmlessly into the ocean. Part of the increase in NASA's spending for science will be about $300 million for destroying Hubble.
NASA's stated reason for terminating the Hubble while continuing work on the space station is that it is more dangerous for the shuttle to go up to Hubble than to the space station. Supposedly, if the astronauts on the shuttle find that damage has been done to the shuttle's protective tiles during launch, they could wait in the space station for a rescue, while this would not be possible during a mission to the Hubble. But there are many other dangers to astronauts that are the same whether the shuttle is going to the space station or the Hubble Space Telescope. Among these is an explosion during launch, like the one that destroyed the Challenger shuttle in 1986. The New York Times Web site has carried a report from an anonymous NASA engineer who challenges NASA's statement that a shuttle flight to Hubble would be more risky than a flight to the space station. He or she points out that the shuttle would be less exposed to micrometeoroids and orbital debris at the altitude of Hubble than at the lower altitude of the space station.
Even if one considers only the possibility of damage to the shuttle's protective tiles, there may not be much difference in the risks of going to Hubble or the space station. The Columbia Accident Investigation Board discussed this safety problem, but it recommended that NASA develop the ability to repair the shuttle's tiles in space, whether or not it is docked to the space station, and it did not conclude that the Hubble had to be abandoned. To be reasonably sure of rescuing the astronauts even if it turns out that damage to the shuttle can't be repaired in space, it could be arranged at some extra cost that when one shuttle goes up to service Hubble, the other shuttle will be kept ready on the ground. For instance, the Hubble servicing mission could be scheduled just before one of the planned missions to the space station. In response to pressure from Congress and the scientific community, NASA has agreed to re-consider this decision. I don't know enough about questions of safety to judge this issue myself, but I share the widespread suspicion that Hubble is being sacrificed to save funds for the President's initiative, and in particular in order to reserve all flights on the shuttle's limited schedule for the one purpose of taking astronauts to and from the space station.
Perhaps because of its timing, the Hubble decision attracted great public attention, but there are other recent NASA decisions that have nothing to do with safety, and that therefore give clearer evidence of the willingness of NASA and the administration to sacrifice science to save money for manned space flight. In January 2003, after several years of scientists' making difficult decisions about their priorities, NASA announced a new initiative, called Beyond Einstein, to explore some of the more exotic phenomena predicted by Einstein's General Theory of Relativity. This includes a satellite (to be developed jointly with the Department of Energy) that would look at many more galaxies at great distances, in order to uncover the nature of the dark energy by finding whether its density has been changing as the universe expands. Equally important for cosmology, there would be another probe that would study the polarization of the cosmic microwave background to find indirect effects of gravitational waves from the early universe. (Gravitational waves bear the same relation to ordinary gravity that light waves bear to electric and magnetic fields—they are self-sustaining oscillations in the gravitational field, which propagate through empty space at the speed of light.)
Beyond Einstein also includes another satellite dedicated to searching for black holes, and two larger facilities. One is an array of X-ray telescopes called Constellation-X, which would observe matter falling into black holes. The other is called LISA, the Laser Interferometer Space Antenna. This "antenna" would consist of three unmanned spacecraft in orbit around the sun, separated from each other by about three million miles. Changes in the distances between the three spacecraft would be continually measured with a precision better than a millionth of an inch by combining laser beams passing between them. These exquisite measurements would be able to reveal the presence of gravitational waves passing through the solar system. LISA would have enough sensitivity to detect gravitational waves produced by stars being torn apart as they fall into black holes or by black holes merging with each other, events we can't see with ordinary telescopes. NASA has another particularly cost-effective program called Explorer, which has supported small and mid-sized observatories like the Cosmic Background Explorer and Wilkinson Microwave Anisotropy Probe.
Alas, NASA's Office of Space Science has now announced that the Beyond Einstein and Explorer programs "do not clearly support the goals of the President's Vision for space exploration," so their funding has been severely reduced. Funding for the three smaller Einstein missions has been put off for five years; LISA will be deferred for a year or more; Explorer will be reduced in scope for the next five years; and no proposals for new Explorer missions will be considered for one or two years. None of this damage is irreparable, but spending on the President's "New Vision" has barely begun. These deferrals, along with the end of Hubble servicing, are warnings that as the moon and Mars missions absorb more and more money, the golden age of cosmology is going to be terminated, in order to provide us with the spectacle of people going into space for no particular reason.
When advocates of manned space flight run out of arguments for its contribution to "scientific, security, and economic interests," they invoke the spirit of exploration, and talk of the Oregon Trail (Bush I) or Lewis and Clark (Bush II). Like many others, I am not immune to the excitement of seeing astronauts walking on Mars or the moon. We have walked on Mars so often in our reading—with Dante and Beatrice, visiting the planet of martyrs and heroes; with Ray Bradbury's earthmen, finding ruins and revenants of a vanished Martian civilization; and more recently with Kim Stanley Robinson's pioneers, transforming Mars into a new home for humans. I hope that someday men and women will walk on the surface of Mars. But before then, there are two conditions that will need to be satisfied.
One condition is that there will have to be something for people to do on Mars which cannot be done by robots. If a few astronauts travel to Mars, plant a flag, look at some rocks, hit a few golf balls, and then come back, it will at first be a thrilling moment, but then, when nothing much comes of it, we will be left with a sour sense of disillusion, much as happened after the end of the Apollo missions. Perhaps after sending more robots to various sites on Mars something will be encountered that calls for direct study by humans. Until then, there is no point in people going there.
The other necessary condition is a reorientation of American thinking about government spending. There seems to be a general impression that government spending harms the economy by taking funds from the private sector, and therefore must always be kept to a minimum. Unlike what is usually called "big science"—orbiting telescopes, particle accelerators, genome projects—sending humans to the moon and Mars is so expensive that, as long as the public thinks of government spending as parasitic on the private economy, this program would interfere with adequate support for health care, homeland security, education, and other public goods, as it has already begun to interfere with spending on science.
My training is in physics, so I hesitate to make pronouncements about economics; but it seems obvious to me that for the government to spend a dollar on public goods affects total economic activity and employment in just about the same way as for government to cut taxes by a dollar that will then be spent on private goods. The chief difference is in the kind of goods produced by the economy—public or private. The question of what kind of goods we most need is not one of economic science but of value judgments, which anyone is competent to make. In my view the worst problem facing our society is not that there is a scarcity of private goods—food or clothing or SUVs or consumer electronics—but rather that there are sick people who cannot get health care, drug addicts who cannot get into rehabilitation programs, ports vulnerable to terrorist attack, insufficient resources to deal with Afghanistan and Iraq, and American children who are being left behind. As Justice Holmes said, "Taxes are what we pay for civilized society." But as long as the public is so averse to being taxed, there will be even less money either to ameliorate these societal problems or to do real scientific research if we spend hundreds of billions of dollars on sending people into space.
In the foregoing, I have taken the President's space initiative seriously. That may be a mistake. Before the "New Vision" was announced, the administration was faced with the risk of political damage from a possible new fatal shuttle accident like the Columbia disaster less than a year earlier. That problem could be eased by canceling all shuttle flights before the 2004 presidential election, and allowing only enough flights after that to keep building the space station. The space station posed another problem: no one was excited any more by what had become the Great Orbital Turkey. While commitments to domestic contractors and international partners protected it from being immediately scrapped, its runaway costs needed to be cut. But just cutting back on the shuttle and the space station would be too negative, not at all in keeping with what might be expected from a President of Vision. So, back to the moon, and on to Mars! Most of the huge bills for these manned missions would come due after the President leaves office in 2005 or 2009, and the extra costs before then could be covered in part by cutting other things that no one in the White House is interested in anyway, like research on black holes and cosmology. After the end of the President's time in office, who cares? If future presidents are not willing to fund this initiative then it is they who will have to bear the stigma of limited vision. So, looking on the bright side, instead of spending nearly a trillion dollars on manned missions to the moon and Mars we may wind up spending only a fraction of that on nothing at all.