Sierra Nevada Corp. says it's challenging NASA's $6.8 billion award to Boeing and SpaceX for the development of space taxis that would transport astronauts to and from the International Space Station. Sierra Nevada had received more than $300 million from NASA for development of its Dream Chaser space plane, but lost out on further funding. In a news release, the company said there were "serious questions and inconsistencies in the source selection process." Friday was the deadline for appealing the CCtCap (Commercial Crew Transportation Capability) award, and Sierra Nevada's challenge means the Government Accountability Office will review the process. That generally takes 100 days.

Also on Friday, NASA sent out a request for proposals for the next phase in its Commercial Resupply Services program (CRS-2). In Phase 1, SpaceX and Orbital Sciences Corp. were granted a total of $3.5 billion for 20 robotic cargo flights to the space station through 2016. Phase 2 would extend the program through 2020, with an optional extension to 2024. SpaceX and Orbital are expected to put in proposals, and Boeing and Sierra Nevada might do so as well.

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Our updated @SpaceNews_Inc article about SNC's protest of the commercial crew contracts, and their earlier layoffs: http://t.co/HKapC7qmBs — Jeff Foust (@jeff_foust) September 27, 2014

I don't blame SNC for protesting the commercial crew decision; especially if their bid came in under Boeing's. — Lars (@LarsTheWanderer) September 26, 2014

A little #DreamChaser porn for those of you standing in solidarity with #SNC. https://t.co/kDOYA6OFV4 — Stephen C. Smith (@SpaceKSCBlog) September 27, 2014

— Alan Boyle