Development of Spectral Selective Multilayer Film for a Variable Emittance Device and Its Radiation Properties Measurements

A smart radiation device (SRD) that is a variable emittance radiator has been developed as a thermal control material for spacecraft. The SRD has the unique feature of large variation of the total hemispherical emittance eH near room temperature. The eH of the SRD changes depending on its temperature. However, there is a drawback of a large solar absorptance αS. It is too large to use as a thermal control material for spacecraft. In order to reduce the large αS, spectral selective multilayer film was developed. This multilayer film reflects solar radiation and transmits far-infrared radiation to maintain the variation in the eH of the SRD. This paper presents thermal radiative properties of the SRD with spectral selective multilayer film. The multilayer film was designed by using a genetic algorithm (GA). The designed multilayer film was evaporated on the surface of the SRD by the electron beam evaporation method. The experimental results of αS and eH of the SRD with the multilayer film agreed well with calculated results.