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 ε_H near room temperature. The ε_H of the SRD changes depending on its temperature. However, there is a drawback of a large solar absorptance α_S. It is too large to use as a thermal control material for spacecraft. In order to reduce the large α _S, spectral selective multilayer film was developed. This multilayer film reflects solar radiation and transmits far-infrared radiation to maintain the variation in the ε_H 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 α_S and ε_H of the SRD with the multilayer film agreed well with calculated results.