For anyone wanting to play with fictional starships and radiators, I'd like to suggest Kerbal Space Program with the Interstellar Mod. It adds fission, fusion and antimatter reactors with all their drawbacks(), generators (even gives the carnot efficiency), and of course radiators, with the generator efficiency depending on how hot the reactor is vs how cold the radiators are.

() fission produces waste subproducts, have to be shutdown for maintenance and cool down, fusion requires an electrical generator to sustain the fusion (also fuel, have to centrifuge deuterium etc) and of course antimatter have to be collected and stored in magnetic containment devices which require power to maintain. etc.