It has generally been assumed that NASA will save money by spurring the development of services by US companies to supply the International Space Station, but such conclusions have largely been based on estimates.

According to the new research paper by Edgar Zapata, who works at Kennedy Space Center, the supply services offered by SpaceX and Orbital ATK have cost NASA two to three times less than if the space agency had continued to fly the space shuttle.

Specifically, the analysis of development and operational expenses, as well as vehicle failures, found that SpaceX had cost NASA about $89,000 per kg of cargo delivered to the space station.

By the same methodology, he found Orbital ATK had cost $135,000 per kg.

The analysis extended to the commercial crew program, in which SpaceX and Boeing are providing transportation services for astronauts to the space station.

Based upon publicly available data, the study estimates the cost of a crew rotation (four astronauts) for SpaceX at $405 million and for Boeing at $654 million.

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