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From what I've read from NASA's Mars Design Reference Architecture (DRA) 5.0 and other articles, the use of ISRU for the ascent vehicle propellant is usually considered (be it atmospheric based, surface based or both). However, I haven't seen any mention as to producing fuel for the return trip.

Is there any major setback that doesn't allow for this? For instance, not having enough time to produce the amount of fuel needed or not enough resources. Sources are appreciated, if available.

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In the case of the Sabatier process (making oxygen and methane which are then super-chilled to cryogenic liquids), you need to bring a smaller quantity of liquid hydrogen to "fuel" the process and collecting sufficient quantities of Carbon Dioxide requires digging into a martian ice cap. So this process is complicated, takes a lot of infrastructure, requires significant Martian travel, requires time, and requires bringing lh2 with you. So bringing all of the infrastructure and setting it up will require a lot of launches, money, Martian travel, and time on the surface.

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  • $\begingroup$ I agree but, as far as I know, these all apply to just producing ascent propellant as well. I want to know if there is something that favours only producing ascent propellant (which seems to be the only studied case in the articles I've found) over producing return propellant as well. I've seen both atmospheric and surface based ISRU systems being considered, so operational complexity (e.g. mining regolith) shouldn't be the reason for not assessing production of return propellant. $\endgroup$ – Jak Apr 24 at 17:51
  • $\begingroup$ The Sabatier_reaction proper on Mars' atmospheric CO2 requires you to bring all of the hydrogen that ends up in the methane from Earth. Yes it's light in mass but a real pain to package and transport. If however gaseous hydrogen could come from electrolysis of water also found on Mars, you wouldn't have to bring all your hydrogen from home. $\endgroup$ – uhoh Apr 25 at 1:00

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