Change from uranium fuel cell to spent uranium fuel cell.
Reasoning- most spaceborne RTGs use plutonium-238 as the radioisotope due to high power density, long half-life and low shielding requirements. Plutonium must be synthesized from uranium in a reactor.

This is an interesting idea and I have considered it, but I think for gameplay reasons it might be better to use a Uranium Fuel Cell since those are more expensive to make and use than a used up fuel cell. I'll still think about it however. The opportunity cost of a used up fuel cell is very low compared to a normal fuel cell, and I'd like to make the satellite more expensive.