Solid-State Phase-Change Heterostructures for Radiative Heating and Cooling in Space

High-power satellites offer promising new imaging and communications capabilities, yet there exist significant thermal management challenges for satellites with a limited radiating surface area. Conventional approaches for mitigating overheating use deployable radiators to increase total heat rejection and louvers to switch between heating and cooling states. These components are often mechanical and can exhibit high broadband emissivity, such as for radiators comprising composite graphite coatings. As a result, these radiators can absorb unwanted solar irradiation, which reduces their cooling potential. We present an approach for radiative thermal management using few-layer optical heterostructures comprising solid-state phase-change materials that exhibit a tunable refractive index, enabling dynamic control of emissivity. The thickness and material composition of these layered structures may be optimized to switch between reflecting solar radiation and emitting long-wavelength radiation in a cooling state and absorbing solar radiation while reflecting long-wavelength radiation in a heating state. We describe the design and optimization procedure for these structures and show that radiators that incorporate phase-change materials could reach temperatures below a blackbody emitter through selective reflection of solar radiation. We initially evaluate thermochromic and electrochromic materials and then analyze the use of chalcogenide glasses as an active variable emissivity thermal management solution. In addition to having a highly reversible solid-state phase transition, chalcogenide glasses remove the need for mechanical actuation of louvers and thermal switches when alternating between heating and cooling. Furthermore, they require no net electrical power to maintain either state.