The final space shuttle mission means the 30-year-old shuttle program is about to enter the history books alongside the famous Mercury, Gemini and Apollo programs.
And as the end of the shuttle era looms, NASA leaders say they're about to build a new vehicle, one that will let astronauts go exploring deep into space. But some experts doubt that plan will ever get off the ground.
To understand the big question mark hanging over NASA's future, it helps to first turn the clock back to 2004 — the year after the space shuttle Columbia disaster.
President George W. Bush declared that NASA would finish building the International Space Station, then retire its aging shuttles. "It is time for America to take the next steps," he said in a speech at the space agency's headquarters in Washington, D.C. "Today I announce a new plan to explore space and extend a human presence across our solar system."
NASA would build a new capsule and a pair of rockets. First, a rocket to take astronauts up to low Earth orbit, where the station is. And then a bigger rocket, to support a return to the moon by 2020.
The new program was called Constellation, and for years, that was the post-shuttle plan. But after President Obama took office, he ordered a review. A panel of experts said despite the billions already spent, Constellation had been underfunded, was behind schedule and couldn't reach its goals without a lot more money.
Last year, the administration decided to kill Constellation, and Obama traveled to Kennedy Space Center in Florida to make the case.
"The bottom line is, nobody is more committed to manned space flight, to human exploration of space, than I am," he said. "But we've got to do it in a smart way."
He said a smarter plan was to forget about a rocket for routine flights to the station — NASA should turn that work over to commercial companies. They'd develop space taxis, and NASA would just buy rides.
This would let the agency focus on designing a big new rocket for deep space missions, although it wouldn't be the rocket planned under Constellation, and it wouldn't first aim for the lunar surface. Instead, the president set his sights on an asteroid.
A State Of Uncertainty?
The loss of Constellation was a shock for many NASA workers. Shuttle launch director Mike Leinbach recently expressed those feelings when he made some personal remarks to his launch team after they finished a practice countdown for the final shuttle mission.
"Throughout the history of the manned space flight program, we've always had another program to transition into — from Mercury to Gemini, and to Apollo to the Apollo-Soyuz test program, to Skylab and then to the shuttle — we've always had something to transition into," Leinbach said. "And we had that, and it got canceled, and now we don't have anything, and I'm embarrassed that we don't."
As a senior NASA manager, he'd like to apologize for this state of uncertainty, Leinbach said. "The end of the shuttle program is a tough thing to swallow," he said, "and we're all victims of poor policy out of Washington, D.C., both at the NASA level and the executive branch of the government."
These blunt words got applause, and the audio was posted on websites. But not surprisingly, leaders in Washington don't share those views.
"Mike is an incredibly talented person, and I think he is to be touted for the job that he has done as the launch director down there," says former astronaut Charles Bolden, the head of NASA. "I would disagree with him, you know, in terms of 'there is no program going forward.' "
Bolden says NASA does have a program, and the future is robust.
"We will begin to fly commercial spacecraft taking cargo to the International Space Station as early as hopefully the first quarter of 2012, next year," Bolden says. And until those commercial providers can carry people as well as cargo, astronauts will ride on Russia's rockets.
"American astronauts will continue to be going to the International Space Station. We just named a new crew about two weeks ago, and we will continue to name crews until 2020," Bolden says.
Plus, he says, NASA is designing the big new rocket — the one that will carry a crew capsule out beyond the station, to go exploring new places in deep space.
"It'll be a system that the nation will be proud of, that will enable us to get humans beyond low Earth orbit and eventually on to Mars," Bolden says.
'A Frontier For Humanity'
Congress recently told NASA to build that system by 2016, and to use existing industry contracts as much as possible. Sen. Bill Nelson, a Florida Democrat who flew on space shuttle Columbia, thinks building the big new rocket is what NASA needs to do, no matter where it's going next.
"Maybe it's going to be an asteroid, as the president suggested, for 2025," Nelson says. "It's possible we may go back to the moon. There may be other destinations. All of these are going to develop as we develop technology. But the first thing we have to have is a big rocket that can get all of these different components and refueling up into Earth orbit."
But given that NASA just canceled its first post-shuttle rocket program, this latest one is being greeted with skepticism.
"I think the most likely outcome is that the big rocket will be canceled, and the only uncertainty is will it be canceled shortly before or shortly after it starts flying," says Jeff Greason, head of a rocket company called XCOR Aerospace, who served on the committee that reviewed NASA's options for the president.
Greason thinks NASA's new rocket plan is too expensive in an era of shrinking budgets. He says the space program needs to totally rethink what the goals of exploration are and how to realistically accomplish them.
"The ultimate purpose of space, in my mind, is to open a frontier for humanity," Greason says. "Many people, even going back to the Apollo era, supported the space program because they thought that's what it was about."
The End of NASA Rockets
These days, he says, the space program has a lot of activity without any purpose. "I don't think it's about anything right now," Greason says. He thinks decision-makers should consider the lessons of the soon-to-be-retired space shuttle.
"It was a very impressive machine. And the people who built it, you know, should be proud of it," Greason says. "But I also think that in some ways it warns us of the trap that we can get into when we get carried away by the desire to build something, as a nation, without stopping to ask the question of what's the purpose of it."
He says maybe NASA doesn't need to build its own rocket for exploring deep space. It could find ways of using commercially available rockets, just like it's doing closer to home for getting to the space station. Private companies are seizing the opportunities that NASA has opened up, and commercial capsules could be taking people to the station in just a few years.
Astronaut Chris Ferguson, the commander of the final shuttle mission, says that once the shuttle lands for the last time, "the next person that flies a U.S. rocket to low Earth orbit probably will not have a NASA badge on."
Instead, that person's spacesuit will probably have the name of a company like SpaceX or Boeing or Sierra Nevada — "which is kind of an interesting concept, if you think about it," Ferguson notes.
It's a completely new concept for a government agency that has long had human spaceflight all to itself — and it's a concept that is supposed to free up NASA for exciting new missions. But after 30 years of flying the shuttle, it's not clear what those missions should be.