Molecular contamination effects on the thermal emittance of highly reflective surfaces at cryogenic temperatures

Abstract

For contamination effects on thermal control surfaces, changes in solar absorptance are the effect noted. Emittance of the surface is not normally affected. The SIRTF (Space InfraRed Telescope Facility) and NGST (Next Generation Space Telescope) spacecraft will fly large low emissivity surfaces (e.g. aluminized Kapton shields and gold mirrors). During the orbital missions, these surfaces will not be exposed to the sun and will be at temperatures less than 150 K. Concern is that a thick molecular film, even water, will cause a change in emittance and results in affecting the thermal performance primarily controlled by emittance alone. Although an emphasis will be placed upon examining the effects on thermal performance for low emissivity surfaces, the effects on optical performance will also be examined because changes of the optical characteristics such as reflectance and scattering are of greater concern for the NGST mission.