Effects of thin cryo-contaminant films on Midcourse Space Experiment (MSX) satellite cryo-optics

Abstract

The Midcourse Space Experiment (MSX) satellite program is scheduled for launch in 1996. The SPIRIT 3 telescope will be a major part of the spacecraft and will have sensor system components cooled to temperatures varying between 10 and 65 K. Contamination of the mirrors, windows, and detectors is of concern since the operational lifetime in space is projected to be approximately 15 months. Real-time monitoring of contaminant mass deposition will be provided through the use of a cryogenic quartz crystal microbalance which will be located adjacent to the telescope primary mirror. Operation of the sensor optical surfaces can be impaired by contamination deposition. The deposition of contaminant films on critical surfaces can affect optical element performance primarily by changing the reflectance/transmittance and by increasing scatter of the optical element. In the infrared wavelength region, the effects of condensed films on sensor surfaces can be particularly detrimental. This presentation will describe effects of condensed gas films on optical surfaces from a transmittance/reflectance/absorptance standpoint, and the effects of condensed films on the optical scatter. Scattering effects of contaminant films that were condensed at 20 K (from the vapor state) will be discussed and will be correlated with quartz crystal microbalance results for contaminant mass deposition. Effects of outgassing products from spacecraft materials will also be described. Both experimental and analytical results will be discussed.