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Proceedings Paper

Advances in thermal control and performance of the MMT M1 mirror
Author(s): J. D. Gibson; G. G. Williams; S. Callahan; B. Comisso; R. Ortiz; J. T. Williams
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Paper Abstract

Strategies for thermal control of the 6.5-meter diameter borosilicate honeycomb primary (M1) mirror at the MMT Observatory have included: 1) direct control of ventilation system chiller setpoints by the telescope operator, 2) semiautomated control of chiller setpoints, using a fixed offset from the ambient temperature, and 3) most recently, an automated temperature controller for conditioned air. Details of this automated controller, including the integration of multiple chillers, heat exchangers, and temperature/dew point sensors, are presented here. Constraints and sanity checks for thermal control are also discussed, including: 1) mirror and hardware safety, 2) aluminum coating preservation, and 3) optimization of M1 thermal conditions for science acquisition by minimizing both air-to-glass temperature differences, which cause mirror seeing, and internal glass temperature gradients, which cause wavefront errors. Consideration is given to special operating conditions, such as high dew and frost points. Precise temperature control of conditioned ventilation air as delivered to the M1 mirror cell is also discussed. The performance of the new automated controller is assessed and compared to previous control strategies. Finally, suggestions are made for further refinement of the M1 mirror thermal control system and related algorithms.

Paper Details

Date Published: 6 August 2010
PDF: 12 pages
Proc. SPIE 7733, Ground-based and Airborne Telescopes III, 77333Y (6 August 2010);
Show Author Affiliations
J. D. Gibson, MMT Observatory, Univ. of Arizona (United States)
G. G. Williams, MMT Observatory, Univ. of Arizona (United States)
S. Callahan, MMT Observatory, Univ. of Arizona (United States)
B. Comisso, MMT Observatory, Univ. of Arizona (United States)
R. Ortiz, MMT Observatory, Univ. of Arizona (United States)
J. T. Williams, MMT Observatory, Univ. of Arizona (United States)

Published in SPIE Proceedings Vol. 7733:
Ground-based and Airborne Telescopes III
Larry M. Stepp; Roberto Gilmozzi; Helen J. Hall, Editor(s)

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