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Proceedings Paper

Production of primary mirror segments for the Giant Magellan Telescope
Author(s): H. M. Martin; R. G. Allen; J. H. Burge; J. M. Davis; W. B. Davison; M. Johns; D. W. Kim; J. S. Kingsley; K. Law; R. D. Lutz; P. A. Strittmatter; P. Su; M. T. Tuell; S. C. West; P. Zhou
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Paper Abstract

Segment production for the Giant Magellan Telescope is well underway, with the off-axis Segment 1 completed, off-axis Segments 2 and 3 already cast, and mold construction in progress for the casting of Segment 4, the center segment. All equipment and techniques required for segment fabrication and testing have been demonstrated in the manufacture of Segment 1. The equipment includes a 28 m test tower that incorporates four independent measurements of the segment's figure and geometry. The interferometric test uses a large asymmetric null corrector with three elements including a 3.75 m spherical mirror and a computer-generated hologram. For independent verification of the large-scale segment shape, we use a scanning pentaprism test that exploits the natural geometry of the telescope to focus collimated light to a point. The Software Configurable Optical Test System, loosely based on the Hartmann test, measures slope errors to submicroradian accuracy at high resolution over the full aperture. An enhanced laser tracker system guides the figuring through grinding and initial polishing. All measurements agree within the expected uncertainties, including three independent measurements of radius of curvature that agree within 0.3 mm. Segment 1 was polished using a 1.2 m stressed lap for smoothing and large-scale figuring, and a set of smaller passive rigid-conformal laps on an orbital polisher for deterministic small-scale figuring. For the remaining segments, the Mirror Lab is building a smaller, orbital stressed lap to combine the smoothing capability with deterministic figuring.

Paper Details

Date Published: 7 August 2014
PDF: 14 pages
Proc. SPIE 9151, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation, 91510J (7 August 2014); doi: 10.1117/12.2057012
Show Author Affiliations
H. M. Martin, Steward Observatory, The Univ. of Arizona (United States)
R. G. Allen, Steward Observatory, The Univ. of Arizona (United States)
J. H. Burge, College of Optical Sciences, The Univ. of Arizona (United States)
College of Optical Sciences, The Univ. of Arizona (United States)
J. M. Davis, Steward Observatory, The Univ. of Arizona (United States)
W. B. Davison, Steward Observatory, The Univ. of Arizona (United States)
M. Johns, GMTO Corp. (United States)
D. W. Kim, College of Optical Sciences, The Univ. of Arizona (United States)
J. S. Kingsley, Steward Observatory, The Univ. of Arizona (United States)
K. Law, Steward Observatory, The Univ. of Arizona (United States)
R. D. Lutz, Steward Observatory, The Univ. of Arizona (United States)
P. A. Strittmatter, Steward Observatory, The Univ. of Arizona (United States)
P. Su, College of Optical Sciences, The Univ. of Arizona (United States)
M. T. Tuell, Steward Observatory, The Univ. of Arizona (United States)
S. C. West, Steward Observatory, The Univ. of Arizona (United States)
P. Zhou, College of Optical Sciences, The Univ. of Arizona (United States)


Published in SPIE Proceedings Vol. 9151:
Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation
Ramón Navarro; Colin R. Cunningham; Allison A. Barto, Editor(s)

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