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1 January 1987 Prevention Of Primary Mirror Contamination By Helium Purging
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Telescopes mounted on space platforms may be subject to performance degradation by the condensation of gaseous species on cryogenically cooled optical surfaces. Attenuations of the flux of impinging contaminants by a purging counterflow of helium (He) gas at the telescope entrance aperture have been calculated by a Monte Carlo procedure that follows individual trajectories selected at random. The calculations involve no significant approximations and should be quite accurate. In particular, multiple-collision trajectories are treated, employing the best available information on the atomic and molecular collision cross sections. Extensive calculations on protection of the Shuttle-mounted CIRRIS I and CIRRIS IA telescopes are presented which illustrate the extent of protection afforded.
© (1987) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
R. R. Herm, B. R. Johnson, and S. J. Young "Prevention Of Primary Mirror Contamination By Helium Purging", Proc. SPIE 0777, Optical Systems Contamination: Effects, Measurement, Control, (1 January 1987);


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