Production of primary mirror segments for the Giant Magellan Telescope

Martin, Hubert M.; Allen, R. G.; Burge, James H.; Davis, Jeffrey; Davison, Warren B.; Johns, Matt; Kim, D. W.; Kingsley, J. S.; Law, K.; Lutz, R. D.; Strittmatter, P. A.; Su, Peng; Tuell, Michael T.; West, S. C.; Zhou, Ping

doi:10.1117/12.2057012

Cited by 12 publications

(10 citation statements)

References 11 publications

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“…This prototype is the first of the six, identical off-axis segments and one spare that will be produced. The fabrication process and final figure of GMT1 are discussed in detail in Martin et al 11 and Tuell et al 12 . Briefly, the GMT1 surface is accurate to 19 nm RMS after a simulated active-optics correction using 27 bending modes, with more bending modes providing even greater accuracy.…”

Section: Telescope Opticsmentioning

confidence: 99%

Overview and status of the Giant Magellan Telescope project

Bernstein

McCarthy

Raybould³

et al. 2014

SPIE Proceedings

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The Giant Magellan Telescope (GMT) is a 25.4-m diameter, optical/infrared telescope that is being built by an international consortium of universities and research institutions as one of the next generation of Extremely Large Telescopes. The primary mirror of GMT consists of seven 8.4 m borosilicate honeycomb mirror segments that are optically conjugate to seven corresponding segments in the Gregorian secondary mirror. Fabrication is complete for one primary mirror segment and is underway for the next two. The final focal ratio of the telescope is f/8.2, so that the focal plane has an image scale of 1.0 arcsec/mm. GMT will be commissioned using a fast-steering secondary mirror assembly comprised of conventional, rigid segments to provide seeing-limited observations. A secondary mirror with fully adaptive segments will be used in standard operation to additionally enable ground-layer and diffraction-limited adaptive optics. In the seeing limited mode, GMT will provide a 10 arcmin field of view without field correction. A 20 arcmin field of view will be obtained using a wide-field corrector and atmospheric dispersion compensator. The project has recently completed a series of sub-system and system-level preliminary design reviews and is currently preparing to move into the construction phase. This paper summarizes the technical development of the GMT sub-systems and the current status of the GMT project.

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Section: Telescope Opticsmentioning

confidence: 99%

Overview and status of the Giant Magellan Telescope project

Bernstein

McCarthy

Raybould³

et al. 2014

SPIE Proceedings

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“…GMT Segment 1, the first off-axis segment, was completed in August 2012. [7], [8] The surface is accurate to 18 nm rms after a simulated active-optics correction using 27 bending modes with 21 N rms correction force. The off-axis geometry meets its tolerances, with the error in off-axis distance = 0.2 ± 1.2 mm and the clocking error = 0 ± 13 arcseconds.…”

Section: Status Of Segment Productionmentioning

confidence: 99%

“…The final measurements of Segment 1 in 2012 showed agreement among the tests, within the expected uncertainties, for radius of curvature, off-axis distance, clocking, and low-order aberrations through spherical. [7] These are the parameters that are sensitive to alignment errors in the tests and, therefore, the parameters most vulnerable to a mistake in any one test. The agreement among the tests guarantees that the mirror surface can be corrected with active optics in the telescope to eliminate low-order errors and leave only mid-scale and small-scale errors of about 20 nm rms.…”

Section: Validatiomentioning

confidence: 99%

Manufacture of primary mirror segments for the Giant Magellan Telescope

Martin

Allen

Gasho

et al. 2018

Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation III

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The Richard F. Caris Mirror Lab at the University of Arizona continues the production of 8.4 m lightweight honeycomb segments for the primary mirror of the Giant Magellan Telescope. GMT will have a center segment surrounded by six identical off-axis segments, plus an additional off-axis segment to allow continuous operation as segments are removed for coating. Production highlights of the last two years include the spin-casting of Segment 5, preliminary polishing of Segment 2, and completion of the rear surface processing for Segments 3 and 4. We completed a preliminary design of the significant modifications of the test systems required for Segment 4, the center segment. We finished an upgrade of the 8.4 m polishing machine; both the upgrade and experience gained with Segment 1 have contributed to much faster polishing convergence for Segment 2. Prior to polishing Segment 2, we verified the stability and accuracy of the measurement systems by re-measuring Segment 1, achieving good agreement among multiple independent tests as well as good agreement with the original acceptance tests of Segment 1.

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“…When we polished Segment 1 we found that our 1.2 m stressed lap polishing system was not as effective for the off-axis mirror as it had been for symmetric mirrors. [5] The removal rate varied across the surface, probably because of inconsistent fit between the lap and the aspheric surface. We implemented an orbital polisher with passive tools up to 35 cm diameter and gradually built up its capabilities during the polishing of Segment 1.…”

Section: Improved Orbital Polishingmentioning

confidence: 99%

“…[5], [6] The surface is accurate to 18 nm rms after a simulated active-optics correction using 27 bending modes with 21 N rms correction force. The off-axis geometry meets its tolerances with the error in off-axis distance = +0.2 ± 1.2 mm and the clocking error = 0 ± 13 arcseconds.…”

Section: Status Of Segment Productionmentioning

confidence: 99%

Status of mirror segment production for the Giant Magellan Telescope

et al. 2016

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The Richard F. Caris Mirror Lab at the University of Arizona is responsible for production of the eight 8.4 m segments for the primary mirror of the Giant Magellan Telescope, including one spare off-axis segment. We report on the successful casting of Segment 4, the center segment. Prior to generating the optical surface of Segment 2, we carried out a major upgrade of our 8.4 m Large Optical Generator. The upgrade includes new hardware and software to improve accuracy, safety, reliability and ease of use. We are currently carrying out an upgrade of our 8.4 m polishing machine that includes improved orbital polishing capabilities. We added and modified several components of the optical tests during the manufacture of Segment 1, and we have continued to improve the systems in preparation for Segments 2-8. We completed two projects that were prior commitments before GMT Segment 2: casting and polishing the combined primary and tertiary mirrors for the LSST, and casting and generating a 6.5 m mirror for the Tokyo Atacama Observatory.

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Production of primary mirror segments for the Giant Magellan Telescope

Cited by 12 publications

References 11 publications

Overview and status of the Giant Magellan Telescope project

Overview and status of the Giant Magellan Telescope project

Manufacture of primary mirror segments for the Giant Magellan Telescope

Status of mirror segment production for the Giant Magellan Telescope

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