Advances in thermal control and performance of the MMT M1 mirror

J. D. Gibson, G. G. Williams, S. Callahan, B. Comisso, R. Ortiz, J. T. Williams

Research output: Chapter in Book/Report/Conference proceedingConference contribution

5 Scopus citations


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) semi-automated 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.

Original languageEnglish (US)
Title of host publicationGround-Based and Airborne Telescopes III
EditionPART 1
StatePublished - 2010
EventGround-Based and Airborne Telescopes III - San Diego, CA, United States
Duration: Jun 27 2010Jul 2 2010

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
NumberPART 1
ISSN (Print)0277-786X


OtherGround-Based and Airborne Telescopes III
Country/TerritoryUnited States
CitySan Diego, CA


  • MMT
  • Telescope primary mirror
  • Thermal ventilation control

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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