Feasibility of Propellant Depots
Studies have shown that a depot centric architecture with smaller launch vehicles could be 57 billion dollars cheaper than a heavy lift architecture over a 20 year time frame. The cost of large launch vehicles is so high that a depot able to hold the propellant lifted by two or more medium sized launch vehicles may be profitable.
An additional flight of the Ares V heavy launch vehicle was required to stage a Mars mission due to 70 tons of boiloff, assuming 0.1% boiloff/day. This study clearly identifies the need to decrease the boiloff rate by an order or magnitude or more.
Approaches to the design of low-earth orbit (LEO) propellant depots are discussed in the 2009 Augustine report to NASA, which "examined the current concepts for in-space refueling." The report determined there are essentially two approaches to refueling a spacecraft in LEO,
- "a single tanker performs a rendezvous and docking with on orbit, transfers fuel and separates, much like an airborne tanker refuels an aircraft."
- "many tankers rendezvous and transfer fuel to an in-space depot. Then at a later time, a spacecraft docks with the depot, fuels, and departs Earth orbit."
"The found both of these concepts feasible with current technology, but in need of significant further engineering development and in-space demonstration." The report concluded that, with "some development investment, long-term life-cycle savings may be obtained."
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