Thermal considerations of space solar power concepts with 3.5 GW RF output

This paper presents the thermal challenge of the space solar power (SSP) design concepts with a 3.5 GW radio-frequency (RF) output. High efficiency klystrons are thermally more favored than solid state (butterstick) to convert direct current (DC) electricity to radio-frequency (RF) energy at the transmitters in these concepts. Using klystrons, the heat dissipation is 0.72 GW. Using solid state, the heat dissipation is 2.33 GW. The heat dissipation of the kystrons is 85% at 500°C, 10% at 300°C, and 5% at 125°C. All the heat dissipation of the solid state is at 100°C. Using klystrons, the radiator area is 74470 m². Using solid state, the radiator area is 2362160 m². Space constructable heat pipe radiators are assumed in the thermal analysis. Also, to make the SSP concepts feasible, the mass of the heat transport system must be minimized. Thus, the heat transport distance from the transmitters to the radiators must be minimized. It can be accomplished by dividing the radiator into a cluster of small radiators. The area of each small radiator is of the order of 1 m². Two concepts for accommodating a cluster of small radiators are presented, If the distance between the transmitters and radiators is 1.5 m or less, constant conductance heat pipes (CCHPs) are acceptable for heat transport. If the distance exceeds 1.5 m, loop heat pipes (LHPs) are needed