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

A. Y S Cheng, J Roger P Angel

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

7 Citations (Scopus)

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
Volume628
ISBN (Print)0892526637
StatePublished - 1986

Fingerprint

honeycomb mirrors
Demonstrations
mirrors
Mirrors
Air
Cooling
cooling
ambient temperature
air
convection
air cooling
air jets
Glass
gradients
Temperature
glass
air flow
cells
Telescopes
Thermal gradients

ASJC Scopus subject areas

  • Electrical and Electronic Engineering
  • Condensed Matter Physics

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 (Vol. 628, pp. 536-544). SPIE.

STEPS TOWARD 8M HONEYCOMB MIRRORS VIII : DESIGN AND DEMONSTRATION OF A SYSTEM OF THERMAL CONTROL. / Cheng, A. Y S; Angel, J Roger P.

Proceedings of SPIE - The International Society for Optical Engineering. Vol. 628 SPIE, 1986. p. 536-544.

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

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