Radiators scale at best linearly, so once they are dominant you don't get any improvement with power. A mylar mirror is extremely cheap and light (kW or tens o

Radiators scale at best linearly, so once they are dominant you don't get any improvement with power. A mylar mirror is extremely cheap and light (kW or tens of kW of heat can be trivially concentrated per kg), so the fact that there are no even semi-serious proposals for space based CSP should be fairly telling as to the viabity. At 200W/kg, a hypothetical fission generator is strictly worse than a current generation solar array in the inner planets for space based acceleration. Seems useful outside mars though.