Excess heat can only be rejected from spacecraft by radiation and a reliable method to control radiation is desired. Agiltron proposes to design, fabricate, and test a self-adjusting, unpowered, easily scalable variable emissivity radiator that has no moving parts for the temperature control of satellites. The design is based upon an innovative metamaterial that has low emissivity in the near infrared band (IR) and shorter wavelengths, and temperature-dependent high emissivity in the long wavelength IR band. The variation is controlled by incorporating a thermochromic element into the metamaterial that will turn the emitting layer on when the temperature is above a preset value, and turn emission off when the temperature falls below this value. Published results show that the ratio of maximum absorption to minimum absorption for the metamaterial is much greater than a factor of ten. In Phase 1 we will demonstrate broad emission in the 8 to 12 um band in a variable emissivity radiator suitable for satellite applications.
Benefit: The proposed technology provides another tool for the thermal management of satellites, one easily integrated in the temperature control system and customizable (as to transition temperature) by mission designers. It is passive, inherently low-weight, reliable, and can significantly lower the weight dedicated to thermal control of the spacecraft. It is most effective in those missions where the expected temperature variations are the greatest, such as low earth orbit. In addition to NASA spacecraft applications, the metamaterial coating developed by this project has application for helping to cool aircraft when on the ground. The outer covering of aircraft is mostly highly reflecting to avoid absorbing sunlight and further cooling problems. Radiation cooling is negligible. A metamaterial that reflects most of the suns energy but emits long wave infrared radiation such as proposed herein would increase radiation cooling
Keywords: Thermal Management And Control, Passive Systems, Metamaterials, Photonics
