Cleaning the Southern African Large Telescope's M5 mirror
2010
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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