Assuming you're hitting on carbon stuff. There are simple solutions even with rockets. For instance liquid H2 / liquid O2 rocket engines are a thing - this is w

Assuming you're hitting on carbon stuff. There are simple solutions even with rockets. For instance liquid H2 / liquid O2 rocket engines are a thing - this is what the Space Shuttle Main Engine used. [1] Reacting hydrogen with oxygen is, counter-intuitively, an extremely effective propellant! And the exhaust is literally water vapor. Some reason SpaceX decided on methane based propulsion are because it's more safe/stable than liquid hydrogen, because Mars is the goal, and the Sabatier reaction! [2] You can create methane + water from reacting CO2 + hydrogen. And Mars has practically infinite CO2 + hydrogen, which translates to practically infinite fuel + water. Add in fully reusable rockets and you have one heck of a nice starting framework for colonization, that in some ways almost feels too convenient. [1] - https://en.wikipedia.org/wiki/RS-25 https://en.wikipedia.org/wiki/RS-25 [2] - https://en.wikipedia.org/wiki/Sabatier_reaction https://en.wikipedia.org/wiki/Sabatier_reaction