Flight measurement of contamination effects on fused silica mirrors

David F. Hall

doi:10.1117/12.258313

11 November 1996 Flight measurement of contamination effects on fused silica mirrors

David F. Hall

Proceedings Volume 2864, Optical System Contamination V, and Stray Light and System Optimization; (1996) https://doi.org/10.1117/12.258313
Event: SPIE's 1996 International Symposium on Optical Science, Engineering, and Instrumentation, 1996, Denver, CO, United States

Abstract

A spacecraft was instrumented with five calorimeters and four temperature controlled quartz crystal microbalances. The calorimeters which are fitted with identical second surface silvered fused silica mirrors of the type frequently used for sun-illuminated spacecraft radiators, serve as contamination effects detectors. Two of the minus 50 degree Celsius TQCMs are located near four of the calorimeters. Over a four year period, the five calorimeter temperatures have increased because accumulated deposit of molecular contamination (from the outgassing spacecraft) has increased the solar absorptance of the mirrors. One, with a significant field of view of the spacecraft, has increased far more than the others which have either little or no spacecraft surfaces in their fields of view. The increases in calorimeter temperatures have been converted into increases in solar absorption. The ratios of these quantities range between 8 multiplied by 10^-3 and 1.4 multiplied by 10^-2 solar absorptance units per (mu) g/cm² deposit. These values are consistent with industry practice of designing thermal systems with the expectation that sunlit surface solar absorptance will increase about 0.01 for every 100 angstroms of molecular contamination accumulated. Since the calorimeters were significantly warmer than the TQCMs, an even larger value of this ratio can be supported for conservative design of critical thermal systems.

Citation Download Citation

David F. Hall "Flight measurement of contamination effects on fused silica mirrors", Proc. SPIE 2864, Optical System Contamination V, and Stray Light and System Optimization, (11 November 1996); https://doi.org/10.1117/12.258313

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