The Government Accountability Office on Monday denied Sierra Nevada Corp.s challenge to a major NASA contract to ferry astronauts to the International Space Station, saying the agency acted properly in issuing the $6.8 billion award last year.

Last fall, NASA awarded contracts to Boeing and SpaceX to launch a series of missions that would allow the United States, for the first time since the space shuttle was retired three years ago, to launch astronauts into space from U.S. soil.

The so-called commercial crew contract would end U.S. reliance on Russia, which has been taking American astronauts to the space station at a cost of more than $70million a trip.

Boeings contract is worth as much as $4.2 billion; SpaceX, which said it could perform the work for far less, was awarded a contract valued at $2.6 billion.

In its filed protest, Sierra Nevada said that there had been serious questions and inconsistencies in the source selection process. Its own proposal was the second-lowest-priced, it argued, while it achieved mission suitability scores comparable to the other two proposals.

The company argued that by using its own special vehicle, the government could have saved up to $900 million.

Unlike SpaceX and Boeing, which would use capsules to dock to the space station, Sierra Nevada proposed using a reusable miniature shuttle, or space plane, called the Dream Chaser. The craft provides a wider range of capabilities and value, Sierra Nevada had said.

In announcing the GAO decision, Ralph White, the agencys managing associate general counsel, said that NASA recognized Boeings higher price but also considered Boeings proposal to be the strongest of all three proposals in terms of technical approach, management approach and past performance, and to offer the crew transportation system with most utility and highest value to the government.

The agency also found several favorable features in Sierra Nevadas proposal, but ultimately concluded that SpaceXs lower price made it a better value.

Sierra Nevada is still evaluating the decision, the company said in a statement Monday. While the outcome was not what SNC expected we maintain our belief that the Dream Chaser spacecraft is technically very capable, reliable and was qualified to win based on NASAs high ratings of the space system.

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GAO denies Sierra Nevadas legal challenge to NASA space contract