Telescope mirror substrate trades: is the landscape between low- and high-thermal expansion substrates changed by the entry of Kyocera Cordierite CO720?

Tony B. Hull; Antoine Carre; Günter Weidmann; Janina Krieg; Thomas Westerhoff

doi:10.1117/12.2594852

24 August 2021 Telescope mirror substrate trades: is the landscape between low- and high-thermal expansion substrates changed by the entry of Kyocera Cordierite CO720?

Tony B. Hull, Antoine Carre, Günter Weidmann, Janina Krieg, Thomas Westerhoff

Author Affiliations +

Proceedings Volume 11820, Astronomical Optics: Design, Manufacture, and Test of Space and Ground Systems III; 1182007 (2021) https://doi.org/10.1117/12.2594852
Event: SPIE Optical Engineering + Applications, 2021, San Diego, California, United States

Abstract

The dominant selection characteristic between candidate mirror materials with acceptable strength and “polishability” is dimensional stability. 250K to 290K represents the temperature of many spaceborne telescopes. Furthermore, pointing and orbital motion, changing solar view factors create thermal transients. Traditionally, stability has been passively managed either with high thermal diffusivity materials (e.g. Al, Be, SiC) or low thermal expansion materials (e.g. ZERODUR®, ULE, ClearCeram and Carbon Fibers). Recently Kyocera introduced a high thermal diffusivity material, Cordierite CO720, with its Coefficient of Thermal Expansion (CTE) passing from negative to positive near 23C, postulating this would provide simultaneous low expansion and high diffusivity. We examine this postulate, noting both CO720’s CTE(T)’s high slope and Zero CTE at a warmer temperature than typical for space telescopes. Our conclusion from FEM simulations is that CO720 does not change the trade space

Conference Presentation

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Tony B. Hull, Antoine Carre, Günter Weidmann, Janina Krieg, and Thomas Westerhoff "Telescope mirror substrate trades: is the landscape between low- and high-thermal expansion substrates changed by the entry of Kyocera Cordierite CO720?", Proc. SPIE 11820, Astronomical Optics: Design, Manufacture, and Test of Space and Ground Systems III, 1182007 (24 August 2021); https://doi.org/10.1117/12.2594852

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