Variable Emittance Coatings for Satellite Thermal Control

The development of thin-film electrochromic coatings for emittance control in the 5-25 um range is proposed. The coatings would be used on satellites and other space structures for modulating radiant heat transfer. They are intended to replace conventional mechanical louvers and provide a new capability to integrate thermal control functions onto a variety of external and internal spacecraft surfaces. The emittance switching is based on electrochromic reactions in thin-films of crystalline WO3 which undergo an infrared transmitting to reflecting modulation when electrochemically reduced to LixWO3. An all-thin-film electrochromic structure is proposed to provide a high degree of space environment stability. The objective of the Phase I program is to demonstrate the fabrication and performance of a thin-film variable emittance tile that would be used as a building block for integration into spacecraft hardware in a Phase Ii effort. The tiles developed in Phase I would have a total emittance modulation of >0.4 and an optically static solar absorptance of <0.18.