SP‐100 high‐temperautre advanced radiator development

Abstract

Under contract to NASA‐Lewis Research Center, an advanced radiator concept design has been developed meeting SP‐100 thermoelectric requirements. Carbon‐carbon heat pipes are utilized to produce this lightweight, high performance radiator. Two fundamental feasibility issues had to be solved to enable the design: first, to produce a carbon‐carbon heat pipe tube with integral fins, meeting both thermal and mechanical requirements; and second, to develop a coating that protects the carbon‐carbon substrate from 875 K potassium working fluid.Carbon‐carbon tubes with integral fins were successfully produced using a T‐300 fiber, an angle interlocking weave architecture, and pitch densification. A barrier coating to protect the inside diameter of these tubes was developed which utilized the chemical vapor deposition (CVD) of niobium over a thin rhenium interlayer. The rhenium interlayer proved to be critical to the success of this coating technique by providing a gradation in coefficient of thermal expansion (CTE), carrying a portion of the induced stress load, improving coating adhesion, and providing a partial carbon diffusion barrier. Coatings with good adhesion to the interlayer and to the carbon‐carbon substrate have been produced.