Boeing and SpaceX beat out Sierra Nevada for the contracts, which are worth up to $6.8 billion and cover development, testing and operational flights through 2019 if NASA exercises all options in both deals. NASA announced the winners of the Commercial Crew Transportation Capability, or CCtCap, contracts Sept. 16, and Sierra Nevada filed a protest to the GAO on Sept. 26, seeking "a further detailed review and evaluation of the submitted proposals and capabilities," the company said in a statement. The legal challenge stops any work to be executed under the Boeing and SpaceX contracts, according to Stephanie Schierholz, a NASA spokesperson. "Pursuant to the GAO protest, NASA has instructed Boeing and SpaceX to stop performance of the CCtCap contract," Schierholz said. Officials did not say if the work stoppage prevents activities using internal funds. The GAO has until Jan. 5 to recommend a response to Sierra Nevada's challenge, but the congressional watchdog agency could release a ruling within weeks.