Scalable flexible membranes with photonic structures for aerospace radiative cooling in stratospheric environment

Currently, radiative cooling technologies are widely applied in traditional ground-based applications such as buildings, clothing, and solar cells, but research on stratospheric applications remains limited. Compared to ground-based applications, stratospheric conditions are more extreme, and the radiative cooling effect is influenced by factors such as solar radiation, wind speed, humidity, and orientation. In this study, we designed multilayer nanoparticle-polymer metamaterials (MNPM) and silica/Ag specimens suitable for stratospheric environments, which were deployed on the top, side, and bottom of a high-altitude balloon platform with a propulsion system for flight tests. Under natural convection conditions, which do not consume propulsion power, the side-mounted MNPM achieved a maximum cooling of 21.2°C at noon compared to the silica/Ag. Under forced convection conditions, the side-mounted MNPM achieved a maximum cooling of 15.6°C at noon. When there were no cold clouds in the surrounding area at night, the bottom-mounted MNPM achieved a maximum cooling of 7°C. When influenced by radiation from cold clouds below at night, the top-mounted MNPM achieved a maximum cooling of 2.4°C. These results provide valuable insights into the feasibility of radiative cooling technology for stratospheric applications and lay the foundation for thermal management systems for future stratospheric vehicles that do not rely on external energy sources.