Cleaning the Southern African Large Telescope's M5 mirror

Lisa A. Crause; Hitesh Gajjar; Jonathan Love; Francois Strümpfer; James E. O'Connor; Darragh E. O'Donoghue; Ockert J. Strydom; David A. H. Buckley; Peter Gillingham

doi:10.1117/12.856795

20 July 2010 Cleaning the Southern African Large Telescope's M5 mirror

Lisa A. Crause, Hitesh Gajjar, Jonathan Love, Francois Strümpfer, James E. O'Connor, Darragh E. O'Donoghue, Ockert J. Strydom, David A. H. Buckley, Peter Gillingham

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Proceedings Volume 7739, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation; 77393Z (2010) https://doi.org/10.1117/12.856795
Event: SPIE Astronomical Telescopes + Instrumentation, 2010, San Diego, California, United States

Abstract

This paper describes the cleaning of M5, one of the four mirrors that make up the Southern African Large Telescope's Spherical Aberration Corrector. As the top upward-facing mirror in a relatively exposed environment, M5 had accumulated a considerable amount of dust and dirt during the six years it had been on the telescope. With the corrector on the ground for re-alignment and testing, we had the opportunity to remove, wash and replace the mirror. Various cleaning techniques were investigated, including an unsuccessful trial application of First Contact surface cleaning polymer film - fortunately only to a small region outside the mirror's clear aperture. Ultimately, "drag-wiping" with wads of cotton wool soaked in a 10g/l sodium lauryl sulphate solution proved highly effective in restoring the reflectivity of M5's optical surface. Following this success, we repeated the procedure for M3, the other upward-facing mirror in the corrector. The results for M3 were equally spectacular.

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Lisa A. Crause, Hitesh Gajjar, Jonathan Love, Francois Strümpfer, James E. O'Connor, Darragh E. O'Donoghue, Ockert J. Strydom, David A. H. Buckley, and Peter Gillingham "Cleaning the Southern African Large Telescope's M5 mirror", Proc. SPIE 7739, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation, 77393Z (20 July 2010); https://doi.org/10.1117/12.856795

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KEYWORDS

Mirrors

Laser sintering

Telescopes

Reflectivity

Optical coatings

Sodium

Inspection

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