Nasa plans to spend $1.6 billion over the next two years bolstering industry efforts to develop space taxis, officials said on Monday.
The US space agency will be looking for complete systems -- launchers, spaceships, mission operations and ground support -- to ferry astronauts to the International Space Station by the middle of the decade, a draft solicitation released on Monday shows.
The money will supplement investments that private companies are making to develop commercial space transportation services.
President Barack Obama has requested $850 million for Nasa's so-called Commercial Crew initiative for the year beginning Oct. 1. The Senate Appropriations Committee last week offered $500 million.
With the US space shuttles retired, the United States is dependent on Russia to fly its astronauts to the space station, a $100 billion project of 16 nations that orbits about 225 miles (360 km) above Earth. Russia charges more than $50 million a person, including training and support services.
A Russian cargo ship failed last month to reach orbit after a launch accident, exposing the vulnerability of having only one way for crew to fly to the space station. The Progress rocket, which was carrying a cargo capsule of food and fuel, and the Soyuz booster that carries crew use nearly identical upper-stage motors.
China, the only other country that has flown people in orbit, is not a member of the space station program.
"Right now, we have a single-string failure for a $100 billion national lab," Nasa's commercial spaceflight development director, Phil McAlister, said at an industry briefing in Florida on Friday, referring to the reliance on one option to transport crew to the space station.
"Every year we do not have a commercial crew capability, the station is at risk," he said.
Nasa expects to award multiple contracts for the third phase of its commercial crew development work next year. The contracts would begin in July 2012 and conclude in April 2014.
The solicitation is due to be released before the end of the year.
Nasa is now supporting spaceship development by four firms -- Boeing, Space Exploration Technologies, Sierra Nevada Corp and Blue Origin, a privately funded aerospace company set up by Amazon's Jeff Bezos. The contracts are worth a combined $269 million.
Also on Monday, Nasa added $46 million to its current commercial crew program, allotting an extra $25.6 million for Sierra Nevada and $20.6 million for Boeing for additional work on their spaceships.