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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.

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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.

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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.

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