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In addition to being full-flow, Raptor runs on methane (CH4, the simplest hydrocarbon), which already exists many places in the solar system (including Mars), a

• apendleton 6y ago
  Slight clarification: while there have been traces of methane detected on Mars, there's probably not enough to be able to easily use it as fuel. Methane is still beneficial for refueling on Mars, though, because you can make it in place out of water (which is plentiful on Mars as water ice) and CO2 (also plentiful, in the atmosphere) using the Sabatier process. So it remains the case that methane as fuel lets you avoid needing to bring enough fuel for a round trip.
  • SEJeff 6y ago
    Exactly. Elon has explicitly mentioned manufacturing metholox (the raptor engine fuel) using a really beefy ISRU factory. It would be feasible, but is still a lot of work required.
• ba2plus 6y ago
  Mars could be the key to opening up the entire solar system. It's close enough to the sun for solar power to be practical, it's proven to have the mass amounts of subsurface ice and atmospheric CO2 needed for Sabatier-process methane/oxygen production, and it has a very shallow gravity well that would make it easy to lift huge propellant loads into orbit. I don't think it's a stretch to imagine that Mars-based tankers supplying propellants and breathing oxygen would be commonplace through the solar system by the end of the century.