NASA robots chase tumbling asteroids and speeding comets. They take snapshots on Mars and soar out of the solar system as ambassadors to the stars. They monitor the health of Earth and probe the deepest mysteries of the universe.
All without risking a life.
So the death of seven astronauts on the shuttle Columbia a week ago has renewed an old debate about the value and purpose of sending humans into the hostile environs of space.
Critics say that the costs are hideously high - 14 lives lost in two shuttle accidents since 1981, a rate of one death for every eight flights. As a financial proposition, the shuttle has been a nightmare, too. Taxpayers spent $96,000 per pound to orbit Columbia's research cargo - and critics say the scientific return on investment on research by men and women in space is embarrassingly small.
"There is a NASA that does science, and they are terrific, and we rewrite the textbooks every year," said Robert L. Park, a University of Maryland physicist, of the agency's $4 billion unmanned flight program.
"And then there is the NASA that puts men in space, and that has had no discernible impact on any field of science."
Yet man-in-space boosters insist that the price - $7.8 billion, $28 a year per American - is a small one for a noble extension of U.S. "Manifest Destiny."
"This cause of exploration and discovery is not an option we choose; it is a desire written in the human heart," President Bush said at a memorial service for Columbia's crew.
The debate mixes science, patriotism, adventurism, economics and more than a dash of old-fashioned pork-barrel politics: Crew support alone for the agency's International Space Station provides jobs for 100,000 workers in 37 states.
There's little doubt that Americans stand by the manned space program.
Eighty-two percent in a USA Today poll last week said flights should continue despite the Columbia accident.
And about 75 percent of people surveyed by the Orlando Sentinel after the disaster ranked space exploration as "very important" or "somewhat important," a number virtually unchanged from that of the poll it conducted a year ago.
NASA's position is certainly clear.
"We're taking the risk to go into space for valid reasons, and that's to conduct research for science," said shuttle program manager Ron Dittemore, even as his engineers groped to find the cause of the Columbia disaster. "That's the return on the investment. It's the research, the exploration."
Science, however, has never been the sole reason for sending humans into space - not even for the president who launched the race to the moon.
"President Kennedy was not too interested in space exploration," said space historian Howard E. McCurdy, a professor at American University's School of Public Affairs. Instead, Kennedy was looking for a way to impress and win over governments that had not aligned themselves with either side in the Cold War.
It didn't necessarily have to be a race to the moon, McCurdy said: "It could have been building a city underneath the sea."
But flying to the moon had been the stuff of dreams for hundreds of years, and a moon flight "was a sure way to impress the other peoples of the world," McCurdy said. "The science was an afterthought."
After the moon race was won, the justification for sending people into space changed to research and defense. NASA promoted the shuttle as a reusable spaceship that could lift people and cargo into orbit and do it at a low cost - a hope that proved forlorn.
For a time, the military wanted shuttle crews to refuel spy satellites and retrieve film. They also wanted a reconnaissance space station with a crew of 50, McCurdy said.
But the military found cheaper ways to perform those chores with unmanned rockets, electronics and robots.
The only satellite getting shuttle service now is the Hubble Space Telescope. But all sides agree that the Hubble launch and repair missions have provided some of NASA's shining moments.
"If there weren't a servicing capability, almost none of the important science with Hubble would have been possible," said Steven Beckwith, director of the Space Telescope Science Institute in Baltimore, which manages Hubble's work.
Astronauts fixed the mirror flaw discovered after Hubble's launch in 1990. Their subsequent visits have kept the observatory alive, and new instruments they installed have improved its performance 100-fold, Beckwith said.
But Hubble is in a category by itself. No one is designing more satellites that require shuttle servicing because it's just too costly, Beckwith said.
Today the shuttle's main function is to help build and supply the International Space Station, which occupied 13 of the last 16 flights.
NASA promoted the station as a world-class scientific laboratory dedicated to microgravity research. But billions of dollars in cost overruns led the Clinton administration, and now the Bush administration, to crack down and demand redesigns and cutbacks.
In 2001 a new, less ambitious station configuration called "Core Complete" replaced the original, expansive plan. Development of a new transport capable of evacuating all seven crew members was canceled, limiting the station's crew to three - the capacity of a Russian Soyuz capsule. And that, in turn, limits the station's capacity to conduct experiments.
"According to NASA, you need 2 1/2 crew members just to maintain the space station," said Sandra J. Graham, who directed a National Research Council review for Congress. "That leaves only half a person" for science.
As a result, crew time on U.S. experiments has been cut back to 7.5 hours a week, "not sufficient to take advantage of even the reduced scientific capabilities of the Core Complete ISS," the research council found.
Cuts to the $6 billion annual space station budget also eliminated or delayed a large portion of the science facilities and equipment planned for the station.
"Serious questions have been raised about whether international partners will continue to support [the space station] at originally planned levels," the report said.
"Loss of the Japanese experiment module ... . for example, would all but eliminate research in fundamental physics."
But scientists have long wondered whether research aboard manned spacecraft is worth doing at all.
Experiments on the early space capsules, Skylab and the shuttles "don't stand up well to scrutiny - the type of scrutiny you would get in peer-reviewed journals," said John H. McElroy, chairman of the National Research Council's Space Studies Board.
The Columbia astronauts, for example, spent part of their 16 days in space gathering aromatic samples from roses and rice flowers sent into orbit by the New York-based International Flavors & Fragrances Inc. The scents - or at least their links to outer space - were to be used to concoct and market new perfumes.
The only science on manned space flights that has had any impact is the study of the effect of microgravity on humans, said Maryland's Robert Park, who is also a spokesman for the American Physical Society.
"And then you have to ask, 'What is the goal if you're only putting men in space to find out if you can put men in space?' There's not much sense in it."
Not so fast, says NASA.
"Historically, the science alone has not justified the cost of space research in the minds of a lot of the science community," concedes Roger K. Crouch, a former Columbia astronaut and now senior scientist for the International Space Station.
"And yet historically ... the basic research has been worth much more than foresight would have allowed you to guess."
The National Research Council agrees that NASA's manned space flight science is improving. Although it doesn't get as much press as colorful student experiments with spider webs and ant farms, the NRC applauded shuttle and space station research in fluid physics, combustion, materials research and fundamental physics.
Metallurgists, for example, find it almost impossible to study fluid flow in liquid metals on Earth because gravity interferes. In space, that interference disappears, and scientists gain clearer understanding of the phenomenon, one that can lead to manufacturing improvements on the ground, said NRC study director Sandra Graham.
Manned space science has made significant theoretical advances and forced changes in the content of standard textbooks. It is also attracting first-rate scientists, including six Nobel Prize winners and dozens of members of respected professional societies.
"You're beginning to see a very respectable, very sound group of investigators who wish to conduct work on the space station," McElroy said. "We see a much greater respect for that work in the last five years."
But can't such experiments be done remotely by robots, critics ask.
Some can, and robotic capabilities are improving, Graham said. But "it's generally acknowledged there are many types of experiments that would be very difficult to do without human intervention because of their technical difficulty."
For example, she said, "if you had mice or rats on board and needed to collect blood samples, it would be difficult to do in an automated way."
An astronaut can also observe and tweak an experiment, responding to unforeseen developments in ways machines could not.
And "if we do eventually plan to send humans out beyond Earth orbit - say back to the moon or to Mars for extended periods," she said, "we really need to understand how our bodies are affected by low gravity."
But scientists agree that there must be other justifications for the costs and risks of space travel, such as jobs - here and overseas.
The United States secured Russian participation in the International Space Station in part to keep former Soviet scientists from selling their skills elsewhere. The European Space Agency, Canada and Japan are contributing to the station, and scientific cooperation now extends to 16 nations.
"We spend hundreds of billions of dollars on defense and social spending," said former astronaut Jeff Wisoff. "I look at it [manned space flight] as seed money for bettering things here."
NASA's $7.8 billion annual manned space flight budget also funds hundreds of thousands of jobs. That gives it plenty of influence in Washington, but it also puts a drag on innovation, McCurdy said.
It's one reason Congress decided to upgrade the shuttle fleet rather than replace it with a cheaper craft, as urged by the commission that investigated the Challenger accident.
NASA also argues for the power of astronauts to inspire what Crouch calls "a new generation of explorers" of all kinds.
"We need psychologists, sociologists, writers; we need people who are artists," he said.
There are romantic arguments for manned space flight - the notion that astronauts represent a perceived American, or even universal, drive to explore and expand, a "Manifest Destiny" that extends beyond Earth's boundaries.
"To leave behind Earth and air and gravity is an ancient dream of humanity," said President Bush.
Many space boosters argue for even more aggressive missions, manned voyages truly worth the expense and risk - the moon and Mars.
"We are for a human spaceflight program that is leading someplace, for noble exploratory purposes," says Louis Friedman, executive director of the Planetary Society, which claims more than 100,000 space enthusiasts.
Tommy Holloway, a former manager of the space shuttle program, said, "I have no illusions about going to the moon or Mars anytime soon. But I believe man one day will leave the planet again and go forth to establish other civilizations on other planets in this solar system."
Humbug, says Maryland's Robert Park.
"Whatever they say, we're not going to be colonizing space, and we're not going to be traveling to other planets or dealing with aliens," he declared.
"There's one great reason to go to Mars, and that's the possibility of finding life on Mars to which we're not related. That is one of the great questions of science."
But sending people, with their baggage of bacteria and other organisms, would risk contaminating the planet.
"Human beings would be forbidden to ever set foot near there. We should do it robotically," Park said.
But the romance of space travel seems inescapable, even for some scientists.
"There's nothing to be ashamed of there," said the space telescope's Steven Beckwith. He compared the Columbia mission to the Lewis and Clark expedition 200 years ago.
"It was science and it was dangerous, and they knew they could die," he said. But "we're all going to die; the question is whether we use our lives for noble purposes."
"They [Lewis and Clark] believed they did, and the astronauts believe they are," he said. "I believe we will continue to send people into space because it's part of our pioneering spirit."
Sun staff writers Alec MacGillis, Michael Stroh and Dennis O'Brien contributed to this article.