Development of a High-Temperature Optical Coating for Thermal Management on Solar Probe Plus

NASA’s Solar Probe Plus (SPP) is approaching within 9.5 solar radii from the center of the sun. The SPP thermal protection system (TPS) is a 2.7 meter heat shield. The heat shield reaches temperatures of 1400uC on its front surface, its worst thermal case, and is subjected to launch loads, its worst mechanical case. The front surface of the thermal protection system is coated with an optically white coating in order to reduce the front surface temperature of the TPS and reduce the resulting heat flow into the spacecraft. At the temperatures experienced by the TPS, the optical properties are influenced by temperature more than in standard thermal control surfaces. Being able to accurate predict the optical performance of the coating at the temperature extremes of the mission is critical to understanding the thermal capabilities of the spacecraft and thermal protection system. A coating has been developed that can meet the requirements of the SPP TPS and it has been engineered to improve its optical properties at high temperature.