Electrochromic Variable Emissivity Devices for Thermal Control

Small light-weight satellites and space vehicles under development for future NASA missions have reduced thermal mass and are rapidly affected by changes in orbital conditions, resulting in large temperature variations. Restrictions on payload weight and volume limit the usefulness of many thermal control system technologies. To address this problem, Eclipse Energy Systems, Inc. (EES) has suggested the application of electrochromic variable emittance devices (VEDs) to control the rate of energy dissipation by thermal emission from the satellite surface. During Phase I EES has demonstrated the feasibility of fabricating all-solid-state inorganic electrochromic VEDs built on high resistance silicon wafers. This VED is advantageous, because the silicon serves as a thermal shock resistant infrared window that can protect the electrochromic layers against the harsh space environment. The Phase II program will be directed toward the development of VEDs with 44cm2 active area that can achieve a tunable emittance modulation range from 0.2 to 0.6. VEDs will be subjected to different reliability tests to demonstrate feasibility of use in low, middle-earth, and geosynchronous orbit environments. The electrochromic technology under development by EES holds promise as an alternate for the ST5 mission should any of the scheduled participants fail in the preliminary test protocols.