[m4rtink]

Well, the ideal chemical rocket fuel is hydrogen + oxygen - eq. the two things that make up water. Thats perfectly renewable once you pump some energy into it to split water into the two.

Methane + oxygen popular in the new generation of rockets is not much different, you basically add some carbon to the process & Methane can be made on Mars from local resources.

Best fuel for nuclear thermal rockets is again hydrogen, abundant everywhere.

Current Ion Engines run on noble gases, but supply does not seem to be a problem so far.

Sure, the uranium needed for Orion and Nuclear Salt Water rocket indeed is not really renewable but given the performance &opening the way to grab more of it from space make it a non-issue as well.