Wavelength and coverage dependence of spacecraft contaminant photodeposition

Details Wavelength and coverage dependence of spacecraft contaminant photodeposition Wavelength and coverage dependence of spacecraft contaminant photodeposition

Nov 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996spie.2864..258s&link_type=abstract

Proc. SPIE Vol. 2864, p. 258-268, Optical System Contamination V, and Stray Light and System Optimization, A. Peter M. Glassford

Physics

Scientific paper

The physical processes involved in the permanent deposition of contaminant molecules on sunlit spacecraft surfaces have been explored in greater depth by a series of measurements in a ground test facility. Solar simulation was provided at narrow line wavelengths of 0.12, 0.18, and 0.25 (mu) by the use of low-pressure hydrogen and mercury lamps instead of the broader-spectrum krypton and xenon lamps used in previous studies. Surface coverage was varied from sub- monolayer to bulk both by surface temperature change and by changes in the incident molecular flux. Photofixing of contaminants deposited on cooler surfaces in the dark was measured by warming the surfaces after periods of ultraviolet irradiation. For the model contaminant DC-704, photodeposition rates at 0.12 (mu) were about 6 times larger than 0.18 (mu) . This calls into question the practice of comparing ultraviolet simulators to the solar ultraviolet in terms of total photon incidence below 0.2 (mu) . Proper ground simulation of contaminant photodeposition may require the use of Lyman-alpha lamps for certain materials. The results of this work also indicate that even at constant surface coverage of unreacted contaminants, the photodeposition rate is strongly dependent on surface temperature.

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