Thermal Control Coatings for Satellites

The development of coatings with electrically tunable infrared emittance for controlling radiant heat transfer in the space environment is proposed. The emittance modulation is achieved using electrochromic materials whose infrared reflectance can be continuously and reversibly modulated. The coatings have a multilayer, thin film structure that allows emittance to be switched in response to a low voltage DC signal. Innovations in electrochromic materials, infrared transparent electrical contacts, and vacuum deposition processes which allow fabrication of the coatings with a large emittance modulation are proposed. The objective of the Phase I program is the fabrication and characterization of variable emittance coatings employing crystalline LixWO3 as the variable reflectance component. Emittance switching between ~0.2-0.8 in the 3-14 um wavelength range is sought for Phase I coatings. The coatings may be attached to external surfaces of spacecraft, individual instrument packages, or on radiator surfaces. They will allow a non-mechanical means of temperature control and heat distribution through radiant transfer between exterior and interior surfaces. These capabilities should greatly enhance the performance and flexibility of thermal management systems without adding significant weight or complexity.