The White House has redlined the agency's flagship Constellation program, which includes building a replacement for the space shuttle to allow astronauts to reach low-earth orbit, a second more-powerful rocket, and modules for a moon base.
Instead, NASA would rely on private-financed rockets built by commercial launch companies, to ferry astronauts and cargo to and from the International Space Station.
The administration is asking for $19 billion for NASA for fiscal 2011, which is a 1.5 percent increase over the budget request in 2010. By 2015, the administration anticipates a NASA budget of $20.99 billion.
The budget proposal would extend US involvement with the space station by some five years to 2020, and perhaps beyond. It seeks billions for research and development aimed at new types of rocket motors and other elements needed to build larger, more powerful rockets than the US currently lofts, as well as capabilities for storing and transferring rocket fuel on orbit.
The goal is to develop what NASA official call "transformative" technologies for human exploration beyond low-Earth orbit.
The budget plan will allow the US to "pursue a more sustainable and affordable approach to spaceflight," said NASA administrator Charles Bolden Jr., during a briefing Monday.
The alternative was financially unappealing, according to James Kohlenberger, chief of staff at the president's Office of Science and Technology Policy.
The Constellation program emerged at part of former President George W. Bush's Vision for Space Exploration, announced in January 2004. But it failed to receive budgets to match the vision.
"The fact that we've poured $9 billion into an unexecutable program really isn't an excuse to pour another $50 billion and still not have an executable program," Mr. Kohlenberger says.
Lawmakers slam shift
Reaction from some lawmakers has been swift and pointed.
"The president's proposed NASA budget begins the death march for the future of US human spaceflight," said Sen. Richard Shelby (R) of Alabama, who counts employees at NASA's Marshall Spaceflight Center in Huntsville, Ala., among his constituents.
Sen. Bill Nelson (D) of Florida argued in a statement Monday that the budget proposal for NASA would replace lost space-shuttle jobs "too slowly, risking US leadership in space to China and Russia, and relying too heavily on unproven commercial companies."
Others say the shift is long overdue.
But that effort has faced "a lot of push-back from the centers," he says, referring to major NASA facilities such as the Johnson Space Center in Houston, the Marshall center, and the Kennedy Space Center in Florida.
The budget plan faces several significant challenges. Key lawmakers signaled their displeasure at notion of using more private companies as early as last summer. At a House hearing on the Augustine Committee's report last September, Rep. Gabrielle Giffords (D) of Arizona and chairwoman of the House's space and aeronautics subcommittee, expressed skepticism that private companies could step in to replace the Ares 1 and its Orion crew capsule.
Riding on space entrepreneurs
One of NASA's biggest hurdles, analyst Mr. Williamson says, will be "sorting the folks with real promise from the ones who do mostly view-graph engineering."
Much, he continues, will be riding on the shoulders of space entrepreneurs such as Elon Musk, who heads the Space Exploration Technologies Corporation in Hawthorne, Calif.. His company has conducted successful launches with its Falcon 1 rocket, and is building a more powerful sibling, the Falcon 9, as well as a capsule for carrying cargo and crew.
If he and others can be successful in demonstrating human spaceflight capabilities, "then that will make the biggest difference" in building traction for the administration's proposed direction for spaceflight.
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