Abstract: A variable, thermal control system (10) for regulating the temperature of an exothermic process plant carried aboard an earth orbiting spacecraft is made with a plurality of curved radiator panels (14) arcuately positioned in a circular arrangement to form an open receptacle. A module (12) containing the process is insertable into the receptacle. Heat exchangers (42) having broad exterior surfaces (43) extending axially above the circumference of the module (12) fit within arcuate spacings (18) between adjacent radiator panels (14). Banks of variable conductance heat pipes (24) partially embedded within and thermally coupled to the radiator panels (14) extend across the arcuate spacings (18) and are thermally coupled to broad exterior surfaces (43) of the heat exchangers by flanges (26). Temperature sensors (86) monitor the temperature of process fluid flowing from the module through the heat exchanges.