Variable Emissivity Thermal Control Capability Development for Space based Applications

Keeping an orbital asset at an optimal operating temperature is extremely challenging as orbiting spacecraft experience large temperature swings, the difficulty in getting hardware into space, the limited amount of volume and power available on spacecraft, and the restriction that any heat that is released from a spacecraft must leave radiatively. Radiative cooling using a high-emissivity coating proves to be a very effective way to reduce high surface temperature in orbital conditions where atmosphere is absent. However, the coating would continue to undesirably cool the surface at low temperatures, worsening the temperature swing. To address this challenge, various smart radiation devices are under development to realize variable emissivity based on the temperature of radiating surfaces. However, these devices require temperature sensors, control circuits, and additional electrical power input. In this STTR Phase II program, ACT and the UC Berkeley propose to develop a space temperature-adaptive radiative coating (STARC) that automatically senses the temperature and switches emissivity from a high value at high temperatures to a low value at low temperatures. The proposed technology allows us to achieve large difference between low and high emissivity states (differs by at least 0.5) and provide excellent thermal control for both high and low temperature extremes. The mass production capability to be developed in Phase II will allow us fabrication STARC in meters length scale in an economical approach.  The STARC will be highly reliable and can stand the harsh space environment for at least thousands of operation cycles.