WASHINGTON - The US National Aeronautics and Space Administration (NASA) announced Monday it has handed more than $269 million to four companies vying to develop a commercial spacecraft that could replace its aging space shuttle fleet.

Among the total, Boeing received $92.3 million and Sierra Nevada Corp got $80 million, as part of the second round of NASA's commercial crew development program, or CCDev2, the space agency said.

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Space Exploration Technology, alias SpaceX, was awarded $75 million while Blue Origin received a contract worth $22 million.

"We're committed to safely transporting US astronauts on American-made spacecraft and ending the outsourcing of this work to foreign governments," NASA Administrator Charles Bolden said in a statement.

"These agreements are significant milestones in NASA's plans to take advantage of American ingenuity to get to low-Earth orbit, so we can concentrate our resources on deep space exploration."

The goal of CCDev2 is to accelerate the availability of US commercial crew transportation capabilities and reduce the gap in American human spaceflight capability.

NASA's 30-year-old shuttle program is ending due to high operating costs. The Obama administration wants to attract private companies into the space taxi business, freeing NASA to focus on deep space exploration and new technology development.

Once the US space shuttle program officially ends later this year, the Russian space program's Soyuz capsule will be the only method for transporting astronauts to and from the station.