STEPS TOWARD 8M HONEYCOMB MIRRORS VIII: DESIGN AND DEMONSTRATION OF A SYSTEM OF THERMAL CONTROL.

A. Y.S. Cheng, J. R.P. Angel

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

10 Scopus citations

Abstract

If they are to achieve the best possible images, honeycomb borosilicate telescope mirrors must follow ambient temperature changes while maintaining low internal temperature gradients. This is best done by cooling or heating the internal, edge and back mirror surfaces at the same rate established by convection on the front surface. We propose to use directed jets of air at ambient temperature, arranged with more air flow on thicker sections so as to match cooling rates. A full scale glass thermal model of one honeycomb cell of an 8m mirror was built, along with a system to flow in air at controlled temperature. We find that the air jets realize high thermal coupling efficiency, and allow good control of internal gradients. With the air cooling steadily at 0. 25 degree C/hour, typical of nighttime cooling at good sites, internal gradients were less than 0. 1 degree C and the overall lag between air and glass temperature was 0. 25 degree C. This performance, achieved with a flow rate of 6-10 litres/sec per cell, will ensure negligible image degradation from convection at the mirror surface (mirror seeing) or from thermal distortion of the mirror substrate.

Original languageEnglish (US)
Title of host publicationProceedings of SPIE - The International Society for Optical Engineering
PublisherSPIE
Pages536-544
Number of pages9
ISBN (Print)0892526637
StatePublished - Dec 1 1986

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
Volume628
ISSN (Print)0277-786X

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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  • Cite this

    Cheng, A. Y. S., & Angel, J. R. P. (1986). STEPS TOWARD 8M HONEYCOMB MIRRORS VIII: DESIGN AND DEMONSTRATION OF A SYSTEM OF THERMAL CONTROL. In Proceedings of SPIE - The International Society for Optical Engineering (pp. 536-544). (Proceedings of SPIE - The International Society for Optical Engineering; Vol. 628). SPIE.