Lunar Methalox

We see craters on the moon, so we know where the asteroid impact ore bodies will be found. If we ball park a 100 meter asteroid at half a megatonne of carbon and we can recover one or more percent of that inside the one km crater, that's about 5 kilonnes of carbon, which is three quarters of the mass of the methane we can make from it. We need more than thirteen tonnes of oxygen to oxidize or burn it out of the ore, although it may exist as carbonates, where impactor carbon chemically bound itself to oxides in the local regolith, in which case we refine the ore and capture the oxygen, carbon dioxide and monoxide. Either way we make carbon dioxide to transport carbon to the South Pole where the hydrogen is, unless there's minable water in the ore body, or permafrost in nearby lava tubes.

Making some wild-ass guesses, we need twelve tonnes of carbon and thirty-eight tonnes of oxygen for forty-four tonnes of CO2, then thirty-six tonnes of water for four tonnes of hydrogen to make sixteen tonnes of methane and sixty-four tonnes of oxygen. If we assume we need forty-four tonnes of mining equipment to gather ore for forty-four tonnes of CO2 which would be some multiple of that (tailings could easily be nearly an order of magnitude, ~400 tonnes, although some of it will be iron, aluminum and silicate slag which might be useful feedstocks to add value and utility to the enterprise), and perhaps another forty-four tonnes of refining and processing equipment, so a moonships’ worth of cargo, producing forty-four tonnes of CO2 per hour, which needs to be transported to wherever the source of hydrogen is.

If I’m under estimating the ore body, or the amount which might be bound to local regolith in the form of carbonates, so be it. What I see here is probably the smallest example that might be profitable to recover, although I imagine the equipment will be easy to relocate, as it arrived by rocket after all. A larger carbonaceous asteroid impactor, one kilometer across might be half a gigatonne of carbon and one percent would be five megatonnes, which would take a rather longer time to mine out, if we can source fifteen megatonnes of water ice for the hydrogen!Not to be too obtuse, but the power to do all this is produced by the eighty-eight tonnes of mining and refining equipment; it’s a black box and has absolutely no real-world figures behind it. Anyway, same situation with the polar or lava tube ice mines, seventy-two tonnes plus eighty tonnes to process eight tonnes of water and carbon dioxide, rounded up to a double cargo load for moonships. Some of the power will be electricity, but a lot will be process heat from concentrated solar or from a small fission reactor or large RTG.