Propellant Depot - LEO Depot Fuels

LEO Depot Fuels

For rockets and space vehicles, propellants usually take up 2/3 or more of their total mass.

Large upper stage rocket engines generally use cryogenic fuels like liquid hydrogen and liquid oxygen (LOX) because of the large specific impulse possible, but must carefully consider a problem called "boil off". The boil off from only a few days of delay may not allow sufficient fuel for higher orbit injection, potentially resulting in a mission abort. Lunar or Mars missions will require require weeks to months to accumulate 10,000s to 100,000s kgs of propellant, so additional equipment may be required on the transfer stage or the depot to mitigate boiloff.

Non-cryogenic, earth-storable liquid rocket propellants including RP-1 (kerosene), hydrazine and nitrogen tetroxide (NTO), and mildly cryogenic, space-storable propellants like liquid methane, can be kept in liquid form with less boiloff than the cryogenic fuels, but also have lower specific impulse. Additionally, gaseous or supercritical propellants such as those used by ion thrusters include xenon, argon, and bismuth.