By John D. Sutter                                      , says NASA, but maybe not in a government-built spaceship -- and maybe not any time soon.The future of American space exploration came into question on Monday as President Obama released his 2011 budget. If passed by Congress, the budget would eliminate Constellation -- NASA's project to send humans back to the moon by 2020.

Constellation was to follow NASA's space shuttle program, which, after about 30 years of taking astronauts to space, is scheduled to end later this year, following five more flights.

Instead of building new spacecraft of its own, NASA, under the proposal, would invest in space technology research and spend $6 billion to pay private space groups to develop and build new rockets to take astronauts into orbit.

The plan leaves many open questions about the future of U.S. space travel, including if and when NASA will ever build rockets of its own again, when astronauts will return to space and in what kind of spacecraft.

"It's almost like a reboot of NASA's human space flight program," said Tariq Malik, managing editor of

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images: Space technology, including this crew module, is already in development for NASA's moon-exploration program. (By Getty Images/AFP)