Sierra Nevada Corp., maker of the Dream Chaser spacecraft, has lost its challenge over NASA’s decision to award Boeing and SpaceX a new contract to launch astronauts into space. (Carla Thomas/NASA via AP)

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 $70 million a trip.

Boeing’s 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 agency’s managing associate general counsel, said that NASA “recognized Boeing’s higher price but also considered Boeing’s 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 Nevada’s proposal, “but ultimately concluded that SpaceX’s 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 NASA’s high ratings of the space system.”

The company said that it “firmly believes that the Dream Chaser will play a central role in shaping the future of space transportation.” Sierra Nevada is also bidding on a NASA contract to deliver cargo to the space station and developing new partnerships with customersacross the world who will “benefit from multiple commercial space transportation providers for commercial space access, research and operations.”

NASA said it was “pleased” with the GAO decision, and that it allows the agency to move forward. If all goes according to plan, NASA expects to launch from U.S. soil with American rockets as early as 2017.