But with the collapse of the Constellation program to put humans back on the moon, the U.S. is on the brink of a "space gap"—perhaps five years during which the nation will have no craft of its own capable of sending humans into space. (See "Obama Scrubs Manned Moon Missions.")
During this gap, U.S. astronauts will be able to reach the International Space Station (ISS) only by buying seats on Russian Soyuz spacecraft at U.S. $51 to $63 million each, round trip.
NASA's looming spaceflight lapse isn't unprecedented. For instance, the 1981 space shuttle launch was the first U.S. space flight since the 1975 Apollo-Soyuz joint mission.
And NASA Administrator Charlie Bolden has already outlined a two-tiered plan for closing the gap in a "Future of NASA" Web chat: Private aerospace companies and "American ingenuity" will drive efforts for getting astronauts into low-Earth orbit, while NASA shifts its focus to longer-term exploration of deep space.
"Immediately following the successful flight of STS-135 and closeout of the shuttle era, attention will turn to facilitating the success of U.S. commercial spacecraft for cargo and crew transportation to low-Earth orbit," Bolden said in the chat.
"As we have always done, NASA is partnering with the aerospace industry to produce vehicles to provide safe, reliable access to low-Earth orbit for astronauts and cargo. Our role now, compared to the shuttle era, is to be a purchaser of service as opposed to the owner and operator."
Private Space Race Nothing New
Of course, this arrangement isn't entirely new, noted Frank Slazer, head of the space-systems division at the Aerospace Industries Association (AIA). The situation is somewhat analogous to what happened with space cargo after the 1986 Challenger disaster put a temporary hold on shuttle flights.
"The Reagan Administration changed things, and government agencies were told to go out and buy commercial launch services," Slazer said.
"That's basically how we've operated with cargo since 1987, so if the U.S. Air Force wants to launch a military satellite, they are basically going to a private company and having that company build the rocket and launch vehicle for them."
NASA's new support for commercial spaceflight "is really just using a similar approach to launch crew to a place that we've already been many times before, which is lower Earth orbit."
The firms in this private space race are already getting some significant financial boosts from Uncle Sam.
Aerospace firm Blue Origin, for example, scored $22 million for development of its New Shepard spacecraft, which is meant to take off and land vertically.
Sierra Nevada Corporation was awarded $80 million to develop the Dream Chaser space plane, while SpaceX was granted some $75 million for work on a crewed version of its existing Dragon capsule.
And Boeing has so far received $92.3 million for development of its CST-100 crew capsule.
NASA hopes that private contractors might be able to keep costs low for government flights by creating a boom in space-based enterprises, such as space tourism or commercial product and technology development in microgravity.
"Every extra use is going to help chip into the fixed costs, and that will help reduce the cost of NASA's launches to the International Space Station," Slazer said.
Deep Space—What's the Point?
Thanks to the shuttle program and the ISS, humans have learned to live and work in low-Earth orbit and to integrate the contributions of many different nations to run such a facility.
NASA hopes to build on that knowledge to design longer-term missions that will send astronauts to asteroids and maybe even Mars.
According to NASA's Bolden, the agency will focus "on the design and development of a heavy-lift rocket with a multipurpose crew vehicle, to enable us to at long last embark on deep-space exploration with humans." The new crew vehicle will be based on the Orion capsule from the defunct Constellation program.
But any deep-space mission would put astronauts far beyond the reach of earthly aid, and some experts wonder whether humanity really has a future in the far reaches of space.
"You need to know if humans can live without resupply from Earth, live off the land, and also if there is anything commercially useful to do up there to pay the way," said Scott Pace, director of George Washington University's Space Policy Institute.
"If the answer to both of those questions is yes, you get space colonies. If the answer to both those questions is no, then it's more like Mount Everest, where a few people might visit or make a living [off it], but nobody really lives there.
"If you can live off the land but there is nothing commercially justifiable to do, then it's like Antarctica—a scientific outpost and maybe even a place for a few tourists to visit, but not something that really entails a human future."
Alternatively, viable commercial operations in space that require constant resupply from Earth, such as mining, might function like offshore oil platforms, he added.
"We really don't know which of these answers is correct," Pace said, "and in my view the purpose of exploration is to find out if humanity really does have a future beyond the Earth."
NASA's Next Step: Moon vs. Asteroid
NASA's main thrust for deep space under the Obama Administration is a human mission to a near-Earth asteroid, which supporters say would be a bridge to a Mars mission. (Related: "Astronauts Could Ride Asteroids to Mars, Study Says.")
In April, President Obama explained to a crowd at Kennedy Space Center why he was abandoning a return to the moon.
"We've been there before," he said. "There's a lot more of space to explore, and a lot more to learn when we do. So I believe it's more important to ramp up our capabilities to reach and operate at a series of increasingly demanding targets while advancing our technological capabilities with each step forward."
But George Washington University's Pace says there's a lack of big enough asteroids that could be reached in a six-month mission—a round-trip spaceflight limit set by environmental factors such as radiation damage to the crew.
What's more, astronauts might not be able to do much once they've reached an asteroid other than study its geology and collect samples.
"I think walking away from the lunar program was a mistake," Pace said. In his view, the moon is a better training ground for learning about human limits and capabilities during extended stays on another world.
A moon base would allow humans to stay longer and develop more self-reliant skills and technologies, such as extracting oxygen or even water from local resources.
"In my mind," Pace said, "the administration needs to make a course correction."