Last month, NASA announced the decision to transport U.S. crews to and from the International Space Station (ISS) through spacecrafts built by Boeing and SpaceX. In a move that aims to end reliance on Russia, NASA hailed the prospect of sourcing the transportation to American companies as a means of allowing NASA to focus on more ambitious missions – like sending mankind to Mars.

The Commercial Crew Transportation Capability (CCtCap) contracts will require NASA certification for human space transportation systems, with at least one crewed flight test for the Boeing CST-100 and SpaceX Dragon V2 spacecrafts with at least one NASA astronaut aboard to verify system performance. Following approval, each contractor will conduct two to six missions to the ISS. NASA will be working with both of the contractors to ensure the safety and reliability of the vehicles. The vehicles will be owned by the contractors, who will also be able to sell human space transportation services to others.

The decision has been challenged by Sierra Nevada, so all projects have been put on hold while the Government Accountability Office (GAO) deals with the protest. Sierra Nevada’s Dream Chaser was the third spacecraft in the running for the contracts, and the company is seeking a detailed review and evaluation of the submitted proposals and capabilities, claiming that the current contracts will cost $900 million more than what one of their proposals would cost. Boeing’s contract amounts to $4.2 billion, while SpaceX has been awarded $2.6 billion. While both Boeing and SpaceX proposed capsule designs, Sierra Nevada’s proposal entailed a space plane design that is arguably more refined. Despite this, after 30 years of shuttle flights, NASA’s decision to use capsules seems to be a reflection on the simplicity and economy of capsule-based design.

NASA has ordered Boeing and SpaceX to stop work on the spacecraft while the protest is being investigated. The GAO will reach a decision on the appeal in 100 days, no later than Jan 5, 2015.