20 August 1986 Planning The National New Technology Telescope (NNTT): III. Primary Optics - Tests On A 1.8-M Borosilicate Glass Honeycomb Mirror
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Abstract
Materials for large primary mirrors should have low density, high elastic modulus, low coefficient of thermal expansion, dimensional stability over time, favorable polishing characteristics and affordable cost. The mirror's structural shape can contribute to high stiffness, low weight and a short thermal time constant. These characteristics can be provided by cast honeycomb borosilicate glass mirrors, but the coefficient of thermal expansion is high enough to require thermal control to achieve images at the 1/4-arcsecond level. This paper describes a series of tests performed on a 1.8-meter cast honeycomb mirror with an integral ventilation system for temperature control. Surface distortions have been related to the pattern of temperatures present, and the effect of ventilation on the thermal time constant has been explored. The results are extrapolated to larger size mirrors using finite-element analysis.
© (1986) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
E. Pearson, E. Pearson, L. Stepp, L. Stepp, W-Y . Wong, W-Y . Wong, J. Fox, J. Fox, D. Morse, D. Morse, J. Richardson, J. Richardson, S. Eisenberg, S. Eisenberg, } "Planning The National New Technology Telescope (NNTT): III. Primary Optics - Tests On A 1.8-M Borosilicate Glass Honeycomb Mirror", Proc. SPIE 0628, Advanced Technology Optical Telescopes III, (20 August 1986); doi: 10.1117/12.963515; https://doi.org/10.1117/12.963515
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