New York (CNN) Government oversight officials issued a scathing report about delays in NASA's commercial crew program, warning that Boeing and SpaceX are facing "significant safety and technical challenges" with their spacecraft — which could leave NASA astronauts stranded on the ground next year.

The report, published Thursday by NASA's Office of Inspector General, also said that the space agency unnecessarily allocated $187 million to Boeing. As a result, the OIG estimates that NASA will pay roughly $90 million per seat to fly its astronauts on Boeing's Starliner spacecraft.

That's more than the space agency has paid Russia for use of its Soyuz capsule, which the United States has relied on to ferry people to and from the International Space Station since 2011. Soyuz seats have cost NASA up to $86 million, according to OIG, and $55.4 million on average.

OIG estimates SpaceX's Crew Dragon will cost NASA about $55 million per seat for the first six missions.

NASA and Boeing both pushed back on the assertion that Boeing was awarded additional money unnecessarily. NASA said it's currently working to purchase more seats from Russia to ensure its astronauts won't be left without a ride to space next year if the commercial crew program encounters more delays.

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