Fabrication and testing of the first 8.4 m off-axis segment for the Giant Magellan Telescope

H. M. Martin, R. G. Allen, J. H. Burge, D. W. Kim, J. S. Kingsley, M. T. Tuell, S. C. West, C. Zhao, T. Zobrist

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

32 Scopus citations

Abstract

The primary mirror of the Giant Magellan Telescope consists of seven 8.4 m segments which are borosilicate honeycomb sandwich mirrors. Fabrication and testing of the off-axis segments is challenging and has led to a number of innovations in manufacturing technology. The polishing system includes an actively stressed lap that follows the shape of the aspheric surface, used for large-scale figuring and smoothing, and a passive "rigid conformal lap" for small-scale figuring and smoothing. Four independent measurement systems support all stages of fabrication and provide redundant measurements of all critical parameters including mirror figure, radius of curvature, off-axis distance and clocking. The first measurement uses a laser tracker to scan the surface, with external references to compensate for rigid body displacements and refractive index variations. The main optical test is a full-aperture interferometric measurement, but it requires an asymmetric null corrector with three elements, including a 3.75 m mirror and a computer-generated hologram, to compensate for the surface's 14 mm departure from the best-fit sphere. Two additional optical tests measure large-scale and small-scale structure, with some overlap. Together these measurements provide high confidence that the segments meet all requirements.

Original languageEnglish (US)
Title of host publicationModern Technologies in Space- and Ground-Based Telescopes and Instrumentation
DOIs
StatePublished - Sep 23 2010
EventModern Technologies in Space- and Ground-Based Telescopes and Instrumentation - San Diego, CA, United States
Duration: Jun 27 2010Jul 2 2010

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
Volume7739
ISSN (Print)0277-786X

Other

OtherModern Technologies in Space- and Ground-Based Telescopes and Instrumentation
CountryUnited States
CitySan Diego, CA
Period6/27/107/2/10

Keywords

  • Active optics
  • Aspheres
  • Off-axis
  • Optical fabrication
  • Optical testing
  • Telescopes

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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    Martin, H. M., Allen, R. G., Burge, J. H., Kim, D. W., Kingsley, J. S., Tuell, M. T., West, S. C., Zhao, C., & Zobrist, T. (2010). Fabrication and testing of the first 8.4 m off-axis segment for the Giant Magellan Telescope. In Modern Technologies in Space- and Ground-Based Telescopes and Instrumentation [77390A] (Proceedings of SPIE - The International Society for Optical Engineering; Vol. 7739). https://doi.org/10.1117/12.857494