Basically, how to make modern weapon systems, specifically, tanks and planes, work in all environments.
I'm currently putting together a role-play setting, which is fair high tech. The setting is limited to all planets in the solar system. Anything that can be terraformed, has had chunks of it terraformed. Jupiter houses multiple 'Gas Cities.'
The setting takes place on the moon. Using purchased military hardware, which is meant to be all purpose.
The moon is being fought over by private military contractors, funded by two brothers, each of whom wants the other's inheritance. Both sides have access to the same suppliers, and gear. Both sides have fortunes to spend.
The problem, in hindsight, was obvious.
Tanks don't work on the moon. Nor would a jet fighter, at least not how it was designed to.
What, exactly, would they need to have to operate in various space environments? What kind of traits, and difficulties would they face?
Edit: The answers so far have said something I overlooked. An one for all system, is useless. To make it more practical, what about a modular system. Specifically, a mass produced skeleton, with multiple modular parts for varying environments.
To limit the environments, only the Moon, Venus, Mars, Jupiter.
What would those modules be?