Radiative Thermal Control of Spacecraft using Thermochromic Infrared Materials

Thermochromic infrared surfaces have temperature-dependent emissivity spectra that enable radiators to respond to changes in the thermal environment. Spacecraft can leverage this unique behavior for autoregulating thermal control, where thermochromic surfaces are designed to passively transition between a high thermal emissivity (to radiate heat when hot) and a low thermal emissivity (to retain heat when cold). The “thermal emissivity” is defined as a total, hemispherical emissivity integrated across the entire hemisphere and a sufficiently wide infrared band to capture the majority of the emitted energy. This intrinsically broadband, omnidirectional characteristic presents a unique set of challenges for engineering variable emissivity materials (VEMs) for thermal control applications. In this talk, we introduce the materials, methods, and analyses of VEMs using thermal objectives, where spectral and directional infrared engineering is used to achieve passive control over temperature and heat flux. We show how the models and materials are validated calorimetrically and describe a novel set of thermo-optic characteristics used in both the design and system modeling of VEMs. Finally, we present a design space and optimization perspective for further development of VEMs for thermal control.