Evaluation of IR emitter with periodic array for spacecraft radiator

A radiator is a thermal control device which radiates waste heat from the spacecraft to space and cools equipment. Since an infrared space telescope observes weak infrared signals, it is important to shift thermal radiation wavelength to longer values than the observation signals and to reduce the radiation intensity by cooling the equipment. Especially, the next generation infrared space telescope will be cooled at cryogenic temperatures so as to enhance the observation performance. However, a conventional radiator material, such as black paint, shows lower emissivity at cryogenic temperatures. That is why a new radiator with high emissivity at cryogenic temperatures is required. Therefore, we focused on a structure consisting of periodic array of metallic elements separated from a ground plane by a dielectric spacer layer in order to realize a high emittance radiator at cryogenic temperatures. In this work, we reported the performance of the IR emitter with periodic array. It was designed by the FDTD method. The periodic structure is a circle. The metal layer was made by aluminum and the dielectric layer was made by SiO2. The prototype IR emitters were fabricated. Spectral reflectance of the prototype emitter was measured by FT-IR. Moreover, spectral emittance was measured by the blackbody comparison method, and it was compared with spectral absorptance calculated by spectral reflectance.