Forty years ago Monday, Neil Armstrong made his "giant leap for mankind." Since that triumphant moment, astronauts in the U.S. space program have gone no farther.
The first footsteps on the moon — made by Armstrong on July 20, 1969, on the mission known as Apollo 11— came 3½ years before the last ones. Since then, astronauts have been stuck close to the Earth, mostly circling a few hundred miles overhead in a spacecraft that's little more than a glorified cargo truck.
So now what?
That question preoccupies NASA and worries the Obama administration. The president said in March that NASA is beset by "a sense of drift." Even some of the men who once walked on the moon are divided on how to proceed. Options could include going back to the moon, landing on an asteroid, shooting for Mars or even ending human exploration of space altogether.
Former president George W. Bush tried to give NASA a sense of purpose, ordering the agency in 2004 to retire the space shuttle and return humans to the moon. The public yawned. Bush never publicly mentioned the plan again and didn't add much to NASA's budget for it.
NASA is still trying to carry out Bush's goals, but the effort is in doubt. At the White House's request, a panel of independent space experts is giving NASA's human spaceflight program a top-to-bottom review. The panel, which will make recommendations at the end of the summer, could tell Obama that NASA is on track. Or, it could send the agency back to the drawing board.
No matter what the panel decides, the federal deficit and competition from programs such as health care mean that NASA is unlikely to get enough money to do anything truly ambitious. Already Obama's proposed budget for 2010 shows that the administration plans to slash funding later this decade for the rocket and spacecraft needed to take astronauts back to the moon.
If that stands, it's a "an absolutely going-out-of-business budget," says former NASA official Scott Pace, now at George Washington University.
Many space historians and even NASA veterans agree that the glory days of Apollo — which spawned countless songs, movies and books — can't be recaptured. Gone is the vast budget for building spaceships. Gone is the Cold War with the Soviet Union, which unified the nation and lent urgency to the effort to put an American on the moon.
"The Apollo program was such a success because it did have complete support," Aaron Cohen, a top Apollo official, said last month at an MIT symposium on the 40th anniversary of man's first step on the moon. "This may be very difficult to achieve in the near future."
America "is a different place" now than during Apollo, says Rep. Bart Gordon, D-Tenn., head of the House Science and Technology Committee. "We were in a space race with the Soviet Union. (Apollo) was about geopolitics, not space exploration."
All the same, polls regularly show that Americans have a warm feeling for the human spaceflight program and don't want it to end. That means figuring out what astronauts should do next. Should they forge outward into the solar system, despite the huge cost and a soaring deficit? And if so, where?
The decision is not just technical, says David Mindell, who directs MIT's Department of Science, Technology and Society.
"It's emotional and it's political, because human spaceflight is primarily a symbolic activity," he says. "If you really are looking strictly (at the) technical, you wouldn't be sending people."