Smart and Flexible Optical Solar Reflectors for Passive Radiative Cooling Regulation in Space Using a W:VO ₂ Metasurface

Smart optical solar reflectors (OSRs) with temperature-adaptive radiative emission around room temperature are highly desirable for passive thermal management in spacecraft. This work demonstrates a smart and flexible metasurface-based OSR, or meta-OSR, consisting of an optimized W:VO₂-based metasurface and a low emissivity solar reflector. The fabricated smart meta-OSR overcomes long-standing challenges by combining a solar absorption (<i>α</i>) of 0.22, high-temperature emissivity (<i>ε</i> _hot) of 0.8, infrared emissivity contrast (Δ<i>ε</i>) of 0.33 and a transition temperature (<i>T</i> _MIT) of 30°C. In addition, through the use of nanoimprint lithography and a low-temperature W:VO₂ process, the smart meta-OSR is demonstrated over an area of 10 × 10 cm² on space-grade polyimide, achieving significant weight reduction and easy integration on satellite surfaces. The fabricated devices successfully passed various space qualification tests, including thermal cycling, proton and electron radiation, adhesion, bending and humidity resistance, showing negligible performance degradation. The smart meta-OSRs in this work are production-ready and hold promise as next-generation thermal control solution for ultralight spacecraft and small satellites.