11 November 1996 Contamination-induced degradation of optics exposed to the Hubble Space Telescope interior
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Abstract
After the first Hubble Space Telescope (HST) servicing mission, the WFPC-1 and HSP instruments were returned to earth. Three optical surfaces from these instruments were analyzed in detail. They were the WFPC-1 pickoff mirror, the WFPC-1 aperture window, and the HSP filter assembly, all of which faced the central hub area of the HST. Hub-facing optics were of particular interest because any degradation in their performance might indicate a changed environment within the telescope itself. The pickoff mirror reflectance and aperture window transmittance were both found to be severely degraded in the far UV. The cause of the reflectance loss was contamination; the pickoff mirror was covered with a contaminant film about 450 angstrom thick, and the aperture window and HSP filters each had about 150 angstrom. The contamination contained multiple chemical species, some of which had been photopolymerized by exposure to earth-albedo UV. A UV-stimulated deposition and polymerization mechanism was posited. This contamination process is not expected to happen, however, for current and future instruments in HST. The HST components outgassed for 3.5 years before the first servicing mission, so the contaminants are no longer present in any appreciable quantity. Steps are being taken to ensure that any new equipment installed in the HST will not outgas. Over 2.5 years of operation, neither the WFPC-2 instrument nor the corrective optics module (COSTAR) has shown performance degradation in the UV There is also no evidence that the primary or the secondary mirror of the HST has changed.
© (1996) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
June L. Tveekrem, Douglas B. Leviton, Charles M. Fleetwood, Lee D. Feinberg, "Contamination-induced degradation of optics exposed to the Hubble Space Telescope interior", Proc. SPIE 2864, Optical System Contamination V, and Stray Light and System Optimization, (11 November 1996); doi: 10.1117/12.258316; https://doi.org/10.1117/12.258316
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KEYWORDS
Mirrors

Contamination

Ultraviolet radiation

Reflectivity

Chemical analysis

Polymers

Space telescopes

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