Every generation of Americans since the opening of the Space Age has seen astronauts don spacesuits only to pay the ultimate price in the risky enterprise of human spaceflight.
Each time the space program picks itself up from a disaster, each generation has had to answer for itself the fundamental questions: Why are we doing this? What justifies spending billions of dollars on space travel when more pressing issues demand money and attention?
The importance of answering those questions has seldom been higher.
Next Wednesday, a world that witnessed tragedy in the skies over the southwestern United States in early 2003 will watch with anticipation as the National Aeronautics and Space Administration launches the first space shuttle since the orbiter Columbia disintegrated on reentry, killing its seven-member crew.
Despite the safety changes the space agency has made to the orbiters since that disaster, shuttle missions remain anything but routine. "These next two flights are test flights" to gauge the effectiveness of those changes, NASA administrator Michael Griffin warned lawmakers last week. "It must be fully understood that these carry the risks of test flights."
And their objective - to finish building a scaled-down international space station whose utility will fall far short of the original vision - is not as awe-inspiring as the rovers now charting Mars or images of "the pillars of creation" - star nurseries - from the Hubble Space Telescope. So as President Bush pushes his blueprint to return humans to the moon no later than 2020 and eventually send them to Mars, even space enthusiasts are asking anew why the US should pursue manned spaceflight when machines can so far do more for far fewer dollars.
"We are at a crossroads," says former NASA historian Roger Launius, now the curator of the Smithsonian Air and Space Museum in Washington. "The decisions reached in the next two to three years will drive what happens in the next 30 to 40 years."
The administration's program will require support that far outlasts Mr. Bush's presidency, which ends seven years before the earliest date for a moon landing. This makes long-term public support for manned spaceflight vital, specialists say.
Over the long haul, that support must be grounded in a "convincing argument of why it is in the nation's interest to make and sustain such an expensive commitment," according to John Logsdon, director of George Washington University's Space Policy Institute in Washington.
When US astronauts return to space next week, they will also launch into a geopolitical atmosphere far different than the one Columbia left. Since the accident on Feb. 1, 2003, China has orbited its first astronaut. The first American to reach space after the Columbia disaster was a hard-scrabble test pilot who guided aircraft designer Burt Rutan's Spaceship One on two suborbital flights last fall. Virgin Atlantic chairman Sir Richard Branson has licensed the technology behind Spaceship One, creating Virgin Galactic. He plans to begin flying tourists to space - or at least the edge of it - in 2007. Another space entrepreneur, Robert Bigelow, who heads Bigelow Aerospace in Las Vegas, is offering a $50 million prize to the first group to build a vehicle able to loft seven astronauts to a destination in low Earth orbit by 2010.
Meanwhile, Europe's Aurora program is slowly moving ahead. It envisions a set of unmanned and manned missions aimed at putting humans on Mars by 2030. The European Space Agency initiated its program two years before Bush unveiled his plan.
Other countries are pursuing manned spaceflight today for many of the same reasons the US and the Soviet Union did during the cold war, explains Joan Johnson-Freese, who heads the department of national-security studies at the US Naval War College in Newport, R.I. Manned spaceflight carries the image of technological sophistication and advanced industrial and economic development. "It's an indicator of power," she says. Today, "other countries see their technology gap with the United States grow, and they don't want the gap to become insurmountable. For China, a manned-spaceflight program does all of these things. It leapfrogs China into a position of technological leadership in Asia, of being a global player technologically - one capable of more than making shoes."
Yet at least for the US, the geopolitical reasons for putting humans in space that held sway during the cold war have lost their punch since the fall of the Berlin Wall, some analysts say. The old enemy is gone. And more avenues have opened for exhibiting economic and technological prowess in areas such as biotechnology and information science. There, Asia in general and China in particular are striving to position themselves among the global leaders.
As if to warn that congressional support can't be taken for granted, the US House of Representatives fired a legislative warning shot in 1993. House lawmakers, angered by space-station cost overruns, approved funding for the project by one vote. Twelve years later, that warning still reverberates. During last week's hearings with Dr. Griffin, lawmakers on the House Science Committee welcomed him warmly, then politely expressed frustration at what they saw as continued reshuffling of key pieces of the president's agenda. One message lawmakers were trying to make: We need a clear, consistent, timely, and fiscally credible story if we are to help fend off members of Congress critical of the manned spaceflight program.
Outside Congress, many scientists see NASA's reinvigorated push coming at the expense of research programs that in some cases have the potential to bear more immediately on human well-being. In a position statement released early last month, for example, the American Geophysical Union criticized cuts in the White House budget for space and earth sciences, which feed activities as diverse as weather forecasting, earthquake research, and unmanned space exploration. The organization argued that NASA was being asked to do more than the White House and Congress were willing to fund.
"I'm one of the most durable advocates for space exploration around," says James Van Allen, one of the deans of US space science and a professor emeritus at the University of Iowa. But beyond Apollo's moon landings and missions to service the Hubble Space Telescope, he adds, human spaceflight hasn't contributed as much to humanity's understanding of the cosmos as increasingly sophisticated unmanned probes.
"It's the cost," he says. "If it was easy to do, I'd be all for it." But with record federal deficits, an increasingly expensive war in Iraq, problems with Social Security, and other demands on the federal purse, the benefits to science from human spaceflight over the past 10 to 15 years have not justified the cost, he adds.
Public support for the space program varies. Surveys indicate that Americans will rally around the program in times of crisis. But between disasters, backing is fairly stable, though less robust.
"Human spaceflight in a democracy is hard," Dr. Johnson-Freese acknowledges. "If you ask people in a democracy if they support space, the majority answer is, 99 times out of 100, yes.... If you then ask the same group to rank priorities for funding, space comes in pretty much dead last. That's been consistent since Apollo."
Moreover, surveys that ask about funding levels for the space program typically show a plurality, if not a slight majority, agreeing that funding levels are about right - regardless of the state of the budget at the time the question is asked.
As time passes and more global players emerge on the wings of technologies that don't require putting humans in orbit, "the rationales that have traditionally been invoked are dwindling," notes Alex Roland, a former NASA historian, currently a history professor at Duke University.
The Smithsonian's Dr. Launius breaks these rationales down into five broad themes: geopolitics, human destiny, national security, economic competitiveness, and scientific discovery.
Yet for many spaceflight supporters, what appears to be a shrinking list of reasons to put humans in space may instead reflect a shift in emphasis as global conditions change.
George Washington University's Dr. Logsdon has argued that national prestige can still be harnessed as a powerful motivator for pushing humanity's presence farther into space. Indeed, the shuttle program itself owes its existence in large part to President Nixon's desire to avoid going down in history as the president who pulled the plug on the manned spaceflight program after he canceled Apollo, historians say.
For Lori Garver - a former NASA associate administrator and someone who nearly landed a slot on one of Russia's tourist trips to the space station - it's important to take a long-term view.
"We have to learn to be a multi-planet species to survive," she says. "It could be centuries before we have a requirement like an incoming asteroid" or some other disaster. "But we have to get started."
As if to punctuate her point, astronomers have been tracking asteroid 2004 MN4, which will pass within 22,600 miles of Earth in 2029 - just inside the orbits of geostationary satellites. Approaches by an asteroid this large - roughly 1,000 feet across - are rare, occurring about once every 1,300 years, astronomers say.
Even without the cold war, the ideological symbolism of manned spaceflight cannot be ignored, adds Robert Zubrin, president of the Mars Society. He holds that an ideological battle is still being fought between the West and its remaining "totalitarian enemies" and "radical fundamentalists." Human space exploration, particularly sending humans to Mars, would represent a declaration of "the power of reason, courage, and freedom ... in handwriting large enough that no one will need spectacles to read it," he writes in The New Atlantis, a science and technology policy journal.
Over the long term, he says in an interview, humans will naturally move into space, just as early humans left Kenya's rift valley to populate the planet.
"We'll break out of the 'valley' when we build our first Jamestown on Mars," he says. "If we break out of the valley, 500 years from now we'll occupy many worlds. When humanity looks back 500 years from now, no one will care who rules Iraq." They will, however, celebrate their Jamestown.
April 12, 1961
Yuri Gagarin (right), first human in space, Vostok 1 Program.
May 5, 1961
Alan Shepard, first American in space, Mercury 1.
February 20, 1962
John Glenn, first American to orbit Earth.
June 16, 1963
USSR's Valentina Tereshkova, first woman in space.
January 27, 1967
Americans Virgil Grissom, Edward White, and Roger Chaffee die in preflight test, Apollo 1.
July 16, 1969
First humans to land on the Moon:AmericansNeil Armstrong and Buzz Aldrin, Apollo 11.
April 11, 1970
Service-module explosion causes deep space abort. Crew returns safely (right), Apollo 13.
December 19, 1972
Final Apollo lunar mission returns, Apollo 17.
April 12, 1981
First piloted orbital test flight of US space shuttle.
June 18, 1983
First flight of US female astronaut, Sally Ride.
August 30, 1983
First flight of African-American astronaut, Guion "Guy" Bluford.
January 28, 1986
Challenger shuttle explodes moments after takeoff, killing the entire crew, including the first civilian on a NASA mission, schoolteacher Christa McAuliffe.
September 12, 1992
Mae Jemison, first African-American woman in space (right).
March 22, 1995
Russsian Valeriy Polyakov sets space endurance record: 438 days aboard Mir space station.
October 29, 1998
At age 77, US Sen. John Glenn (left) becomes oldest person to travel into space.
August 28, 1999
Sergei Avdeyev sets record for total time spent in space: 747 days in three missions.
April 30, 2001
Dennis Tito serves as the first "space tourist" after paying $20 million to accompany Russian space officials as a guest.
February 1, 2003
Columbia explodes during reentry. US grounds shuttle.
October 15, 2003
China becomes third nation capable of manned spaceflight, launching Lt. Col. Yang Liwei (above) into orbit.
Sources: Spaceflight: A Smithsonian Guide; CBSNews.com