# Smart and Flexible Optical Solar Reflectors for Passive Radiative Cooling Regulation in Space Using a W:VO2 Metasurface

## TL;DR

A smart, flexible thermal coating for spacecraft adjusts its heat emission based on temperature, surviving harsh space conditions and offering lightweight thermal management.

## Contribution

A production-ready smart metasurface-based optical solar reflector with temperature-adaptive emissivity for passive thermal control in space.

## Key findings

- The smart meta-OSR achieves a solar absorption of 0.22 and high-temperature emissivity of 0.8.
- The device passed space qualification tests including thermal cycling and radiation resistance with minimal performance degradation.
- The meta-OSR is fabricated on space-grade polyimide with a 10 × 10 cm² area using low-temperature processes.

## Abstract

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 (α) of 0.22, high‐temperature emissivity (ε
hot) of 0.8, infrared emissivity contrast (Δε) of 0.33 and a transition temperature (T
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.

Passive regulation of thermal management in space relies on engineered radiative coatings that can vary their emissivity with temperature. Here a smart and flexible solution is presented combining a W:VO2 metasurface with a low‐emissivity solar reflector. This highly durable first‐surface coating survives space qualification tests and offers attractive performance metrics as light‐weight and flexible solution for space‐based and terrestrial applications.