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Proceedings Paper

Response Of Large Optical Mirrors To Thermal Distributions
Author(s): E. Pearson; L. Stepp
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Paper Abstract

The National New Technology Telescope program at NOAO is developing technology to be used in the design of a 15-meter multiple-mirror telescope. One configuration being considered for the primary mirrors is a lightweight honeycomb sandwich structure cast from borosilicate glass. This material has a relatively large coefficient of thermal expansion (about 3 parts per million per degree C) which can produce optically-significant distortions when the mirror is exposed to a typical observatory thermal environment. To study this problem we have tested a prototype borosilicate glass mirror, 1.8 meters in diameter, in various thermal environments. Finite-element modeling was used to predict the thermal distortions of the optical surface. This led to an analysis in which temperature patterns were described by a least-squares fit to a polynomial expression, and the polynomial was then used to predict nodal temperatures of the model. The individual terms of the polynomial describe patterns of temperature such as linear-diametral gradients, radial gradients, etc. The optical distortions resulting from these cases are described in this paper. An analytical solution for a 3-dimensional linear temperature gradient was developed to check the finite-element results, and is also presented.

Paper Details

Date Published: 3 June 1987
PDF: 14 pages
Proc. SPIE 0748, Structural Mechanics of Optical Systems II, (3 June 1987); doi: 10.1117/12.939833
Show Author Affiliations
E. Pearson, National Optical Astronomy Observatories (United States)
L. Stepp, National Optical Astronomy Observatories (United States)

Published in SPIE Proceedings Vol. 0748:
Structural Mechanics of Optical Systems II
Alson E. Hatheway, Editor(s)

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