A Ceramic Coated Thermal Radiation Heat Shield in the Near Solar Environment: Testing Methods and Performance Prediction

(Abstract) Applying white ceramic optical surfaces to the carbon-carbon (C-C) heat shield for a near solar exploration spacecraft significantly reduced its temperature. The coatings are designed to be highly reflective in the visible band (thus reflecting the majority of the visible solar irradiance) yet highly emitting in the infrared band. Optical property testing was performed on C-C coupons coated with either alumina (Al2O3) or pyrolitic boron nitride (PBN). Testing was conducted using lasers at discrete wavelengths (spanning the visible to near-IR (NIR) bands) and at temperatures up to 1773 K (in an inert gas). While uncoated C-C surfaces had solar absorptance to IR emittance ratios ( α α α αS/eIR ) approaching 1, the α α α αS/eIR of C-C coated with the white ceramic coatings was 0.6 or less. At a distance of 4 solar radii from the Sun, the resulting predicted temperature of an uncoated C-C heat shield is ~2100 K, while that of an ceramic coated heat shields is more than 250 K lower. Such a temperature reduction lowers the potential for mass loss from the C-C substrate, reduces spacecraft weight, and decreases mission risk.