An internal NASA study found the fuel depot option to be $79 billion cheaper ($64 billion versus $143 billion) than a Space Launch System option and the fuel depot option would be 5 years faster for Near earth Asteroid mission.
Rohrabacher noted "When NASA proposed on-orbit fuel depots in this Administration's original plan for human space exploration, they said this game-changing technology could make the difference between exploring space and falling short. Then the depots dropped out of the conversation, and NASA has yet to provide any supporting documents explaining the change," says Rohrabacher."
NASA had actually been rather busy studying those very topics. The conclusions that NASA arrived at during these studies are in direct contrast to what the agency had been telling Congress, the media, and anyone else who would listen.
This presentation "Propellant Depot Requirements Study - Status Report - HAT Technical Interchange Meeting - July 21, 2011" (69 pages) is a distilled version of a study buried deep inside of NASA. The study compared and contrasted an SLS/SEP architecture with one based on propellant depots for human lunar and asteroid missions. Not only was the fuel depot mission architecture shown to be less expensive, fitting within expected budgets, it also gets humans beyond low Earth orbit a decade before the SLS architecture could.
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