The teams, led by Orbital Sciences Corp. and Sierra Nevada Corp., both propose flying passengers on reusable winged spaceships that launch on expendable rockets and land on runways like NASA's space shuttles.
These designs "could revolutionize orbital space flight in much the same way that SpaceShipTwo has revolutionized suborbital space flight," Virgin said in a statement, referring to the first of a fleet of suborbital commercial spaceships being developed by Scaled Composites.
Scaled built the prototype SpaceShipOne, which won a $10 million prize in 2004 for making the first privately funded human spaceflights.
Virgin is selling tickets to ride the six-passenger, two-pilot SpaceShipTwo, named Enterprise, for $200,000, and plans to begin flight services in about a year.
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The company has collected more than $54 million in deposits from 400 customers, Virgin Galactic said.
Orbital and Sierra Nevada are among at least four firms competing for the next round of funding in NASA's Commercial Crew Development program.
The program would provide a U.S. alternative to flying astronauts to the International Space Station besides Russian Soyuz capsules after the space shuttles are retired in 2011.
The other bidders include Space Exploration Technologies, or SpaceX, and Boeing. Privately owned SpaceX on December 8 successfully flew the cargo version of its Dragon capsule, which NASA is supporting under a separate development effort.
Orbital has a similar arrangement with NASA for a cargo-carrying Cygnus capsule, expected to debut next year.
SpaceX plans to upgrade Dragon for passengers with the addition of a launch escape system and other enhancements. Orbital plans a completely different spacecraft, not yet named, and launcher.
NASA plans to select two or more projects for funding by March. The agency, which is retiring its three space shuttles next year due to high operating costs and ongoing safety concerns, started its commercial crew development effort with $50 million in stimulus funds that went to five firms, including Sierra Nevada and Boeing.
The deadline for submitting proposals was Monday. NASA has not said how many proposals it received.
(Editing by Jane Sutton and Xavier Briand)
