Fission is not a good energy solution for the outer solar system (except maybe on Titan) because of the need for a detour through a clunky heat engine. Likewise

Fission is not a good energy solution for the outer solar system (except maybe on Titan) because of the need for a detour through a clunky heat engine. Likewise, hot-neutron fusion. Layered mirrors concentrating monochromatic solar irradiation into laser cavities, and beaming power to where needed, is the fallback until aneutronic fusion works.