LSST primary/tertiary mirror thermal control system

Douglas R. Neill

doi:10.1117/12.857438

28 July 2010 LSST primary/tertiary mirror thermal control system

Douglas R. Neill

Proceedings Volume 7733, Ground-based and Airborne Telescopes III; 77331E (2010) https://doi.org/10.1117/12.857438
Event: SPIE Astronomical Telescopes + Instrumentation, 2010, San Diego, California, United States

Abstract

The Large Synoptic Survey Telescope (LSST) primary/tertiary monolithic mirror will be fabricated as a single cast borosilicate substrate that requires an extensive thermal control system. The relatively large coefficient of thermal expansion (CTE) of borosilicate glass requires the thermal system maintain differences throughout the mirror to below 0.1C. The thermal control system is also required to take full advantage of the relatively thin glass sections for good tracking of ambient temperatures. A modified version of the thermal control system utilized on the Magellan telescope primary mirror will provide adequate cooling. This type of system supplies coolant to multiple on-board blowers in the mirror cell. Each blower contains a fan and a heat exchanger supplying conditioned and mildly pressurized air to the mirror cell. The mirror cell then acts as an air plenum which distributes the air through individual nozzles to each honeycomb cell of the mirror. Unlike previous systems, each LSST blower assembly will incorporate individual air temperature and air flow control systems. Since air can be more accurately heated than cooled, the air will be initially slightly overcooled and then reheated electrically to match the ambient air temperature. Based on thermal sensors in the mirror, the optimum cooling air flow rate to balance mirror thermal distortion and mirror seeing will be determined and enforced by the variable speed fans on the blower assemblies. To further equalize the cooling throughout the mirror, the coolant flow system has also been designed to provide inherently equal coolant flow to each blower assembly.

Citation Download Citation

Douglas R. Neill "LSST primary/tertiary mirror thermal control system", Proc. SPIE 7733, Ground-based and Airborne Telescopes III, 77331E (28 July 2010); https://doi.org/10.1117/12.857438

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