Alumina Optical Surface Heat Shield for Use in Near-Solar Environment

Experiments indicate that coating a heat shield with alumina can significantly reduce spacecraft temperature during operation near the sun. A thin alumina (Al2O3) coating applied to carbon–carbon (C–C) reflects the majority of the visible solar irradiance while reemitting absorbed energy in the infrared. Testing on Al2O3-coated C–C coupons using visible and NIR lasers (from ambient to 1773 K) show that the solar-absorptance-to-IR emittance ratio (αS/ɛIR) of the Al2O3-coated heat shield was 0.6 or less. Compared with an uncoated carbon–carbon heat shield, the coated version is at least 12% cooler, enabling thermal insulation mass reductions, improved scientific measurements, and the use of less exotic thermal protection materials.