Autogenously Cycling Methane power generator & ECLESS feedback system

Formula; Large SpaceX spaceship slightly used.

ICE engine burns some CH4 produce power, crew if any also produce CO2 and reverse gas shift back to Methane.This proposal is a fuel depot out in the outer planets and beyond waiting for future human or robotic missions.The spacecraft pressurized spaces are a sink to the ICE exhaust.

Is this a perpetual motion machine? yes, so I propose that a Nuclear Electric (RTG)source keeps the margin going on the methane CO2 back to Methane cycle.In deep space however out among the ice giants and beyond its cold enough to rid our selfs of perpetual motion machine charges and make the claim the RTG NE source is a Methane propellant heat source along with the ICE engine for additional heat and power and our Methane propellant depot is a Battery.

If this depot is using a retired spaceship then if no crew we want some plant and mice experiments running in the pressurized volume as a far outer solar system ECLESS test.These retired spaceships are also more then depots.they have earth derived methane but they are docked at an ice giant satellite or scattered object with machines to attempt ISRU.The Earth Methane is our insurance in case of IRSU challenges.

So we turn Elon Musks outer planet spaceships into a serious  prepositioned depots for future explorers  or to refuel interplanetary probes

These things deserve new names

“Distributed planetary probe tugs and fuel depot”

In the Giant planets and ice giants and satellites, ACES and ARRM derived SEP could perform this commercial type mission on a much smaller scale from the ITS spaceship.