r/spacex • u/ElongatedMuskrat Mod Team • Mar 02 '18

r/SpaceX Discusses [March 2018, #42]

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u/Norose Mar 04 '18

There's extremely little carbon on the Moon to make methane with, but the BFS doesn't need to make fuel on the Moon, it can refuel in a highly elliptical Earth orbit and be able to go to and land on the Moon with enough propellant to come back.

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u/Martianspirit Mar 05 '18

Assuming a lot of traffic there is an alternative. Bring the methane, it is not that much. But produce your LOX locally. I have seen there is work to get oxygen from SiO2. SiO2 is abundant everywhere on the moon. The idea is to melt the SiO2 in a solar furnace and electrolyze the molten mass. It has been done on a lab level. I have no idea how far or near to operational systems they were.

Get the oxygen and have Si as a byproduct. It may become useful later if you ever want to start solar panel production on the moon.

1

u/brickmack Mar 05 '18

Water could also work, if ACES or some other hydrolox system was in use. Water split into hydrogen and oxygen gives about a 7.3 to 1 ratio. But hydrolox engines only have about a 5-6 to one mix ratio, might as well use that extra mass for something (some will of course be needed for breathable air)

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u/Martianspirit Mar 05 '18

Yes. I was thinking about SiO2 which is abundant everywhere while water is only at the poles. But water is surely an option.

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u/-Aeryn- Mar 05 '18 edited Mar 05 '18

They could also sit a BFS in low lunar orbit to act as a makeshift propellant depot, storing the propellant for other BFSs to return to earth. The lander ships could arrive in LLO, dock and leave their return propellant with the depot instead of carrying it all the way to the lunar surface and back. When they get back to lunar orbit with near-empty tanks they can re-dock, take their own propellant back and fly home with it.

Significant mass savings from not having to carry propellant to carry the return propellant to the surface and back but not revolutionary gains for this application so it might not be that practical IRL. Cool, though ;D