Sierra Nevada Corp. (SNC) has filed a formal protest with the U.S. Government Accountability Office (GAO) asking the congressional watchdog agency to reevaluate NASA’s decision to select two rival space-capsule designs instead of the company’s lifting-body Dream Chaser as a candidate to deliver U.S. crews to the International Space Station (ISS).

The company said late Friday that its bid in the NASA Commercial Crew Transportation Capability (CCTCap) was $900 million less than the bid submitted by Boeing, which won a contract worth as much as $4.2 billion to complete development, test fly and operate its CST-100 crew capsule. At the same time, SNC said, its proposal was "near equivalent [in] technical and past performance" source-selection scoring.

"[T]he official NASA solicitation for the CCtCap contract prioritized price as the primary evaluation criteria for the proposals, setting it equal to the combined value of the other two primary evaluation criteria: mission suitability and past performance," the company stated. "SNC’s Dream Chaser proposal was the second lowest priced proposal in the CCtCap competition."

NASA also awarded SpaceX a contract worth as much as $2.6 billion to finish developing the crew version of its Dragon commercial cargo capsule, test fly it to the ISS and use it for 2-6 crew-transportation missions. Both Boeing and Sierra Nevada plan to launch their vehicles on variants of the United Launch Alliance Atlas V, while SpaceX will use its Falcon 9 to lift the crewed Dragon.

A GAO attorney said his agency will have 100 days to make a ruling, which would place a question mark over the NASA commercial crew contract awards to Boeing and SpaceX until Jan. 5, 2015. On Sept. 17 NASA announced its selection of the two capsules for development and crew-transportation work over the next five years. That started a 10-day clock that expired Sept. 26 for a protest from Sierra Nevada, which had received funding in earlier NASA commercial crew competitions.

"The company believes that, in this time of critical budget limits, it is more important than ever to deliver the best value to the American public," SNC stated in a press release. " … Given [the] facts, we believe that a thorough review must be conducted of the award decision."

Even before filing the protest, SNC had said it intended to continue developing the Dream Chaser with its own resources, and to enter it in the competition for the second phase of NASA’s Commercial Resupply Services (CRS-2) commercial cargo competition. As it happened, the U.S. space agency issued its CRS-2 request for proposals on Friday.

NASA plans to spend between $1-1.4 billion per year on the CRS-2 cargo-delivery buy, which will cover delivery of 14,250-16,750 lb. of pressurized cargo per year, and another 1,500-4,000 kg of unpressurized gear. The agency expects to need four to five cargo missions a year under the contract, which will run 2017-2024 under present plans.

The Dream Chaser is a composite lifting body design based on the HL-20 NASA testbed of the early 1990s. During the NASA commercial crew competition, SNC has touted its vehicle as a flexible spacecraft able to handle a variety of human missions, and to glide to a low-g, horizontal landing on aircraft runways worldwide.