Technical Paper
Design Considerations for Lightweight Space Radiators Based on Fabrication and Test Experience With a Carbon-Carbon Composite Prototype Heat Pipe
1999-07-12
1999-01-2094
This report discusses the design implications for spacecraft radiators made possible by the successful fabrication and proof-of-concept testing of a graphite-fiber-carbon-matrix composite (i.e., carbon-carbon (CC)) heat pipe. The prototype heat pipe, or space radiator element, consists of a C-C composite shell with integrally woven fins. It has a thin-walled furnace-brazed metallic (Nb-1%Zr) liner with end caps for containment of the potassium working fluid. A short extension of this liner, at increased wall thickness beyond the C-C shell, forms the heat pipe evaporator section which is in thermal contact with the radiator fluid that needs to be cooled. During the fabrication process the C-C shell condenser section was exposed to an atomic oxygen (AO) ion source for a total AO fluence of 4x1020 atoms/cm2, thereby raising its surface emissivity for heat radiation to a value of 0.85 to 0.90 at design operating temperatures of 700 to 800 K.