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Cryogenic Testing Of A Beryllium Mirror

This paper describes the vacuum cryogenic test program conducted on a 32-inch by 34-inch elliptical, flat, beryllium mirror over a temperature range of 300°K to 150°K. It discusses the arrangement of optical test equipment for in-situ measurements of mirror optical quality, describes the thermal environmental control and data system, and covers the test setup and operational activity. The optical measurements were made using a scat-ter plate interferometer in conjunction with a 36-inch diameter parabolic mirror and appropriate transfer optics arranged to work over a 65-foot optical path length. The main-tenance of optical alignment and the real-time adjustments of the interferometer were carried out remotely under the test environment using a TV display of the test interferogram.