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Proceedings Paper

Development and performance of Hobby-Eberly Telescope 11-m segmented mirror
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Paper Abstract

The Hobby Eberly Telescope features a unique eleven-meter spherical primary mirror consisting of a single steel truss populated with 91 ZerodurTM mirror segments. The 1 meter hexagonal segments are fabricated to 0.033 micron RMS spherical surfaces with matched radii to 0.5 mm. Silver coatings are applied to meet reflectance criteria for wavelengths from 0.35 to 2.5 micron. To support the primary spectroscopic uses of the telescope the mirror must provide a 0.52 arc sec FWHM point spread function. Mirror segments are co-aligned to within 0.0625 ar sec and held to 25 microns of piston envelope using a segment positioning system that consists of 273 actuators (3 per mirror), a distributed population of controllers, and custom developed software. A common path polarization shearing interferometer was developed to provide alignment sensing of the entire array from the primary mirror's center of curvature. Performance of the array is being tested with an emphasis on alignment stability. Distributed temperature measurements throughout the truss are correlated to pointing variances of the individual mirror segments over extended periods of time. Results are very encouraging and indicate that this mirror system approach will prove to be a cost-effective solution for large optical collecting apertures.

Paper Details

Date Published: 25 August 1998
PDF: 10 pages
Proc. SPIE 3352, Advanced Technology Optical/IR Telescopes VI, (25 August 1998); doi: 10.1117/12.319265
Show Author Affiliations
Victor L. Krabbendam, Univ. of Texas McDonald Observatory (Chile)
Thomas A. Sebring, National Optical Astronomy Observatories (United States)
Frank B. Ray, Univ. of Texas McDonald Observatory (United States)
James R. Fowler, Univ. of Texas McDonald Observatory (United States)


Published in SPIE Proceedings Vol. 3352:
Advanced Technology Optical/IR Telescopes VI
Larry M. Stepp, Editor(s)

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