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Proceedings Paper

Development of the fast steering secondary mirror for the Giant Magellan Telescope
Author(s): Myung Cho; Andrew Corredor; Christoph Dribusch; Won-Hyun Park; Gary Muller; Matt Johns; Charlie Hull; Michael Sheehan; Jonathan Kern; Young Soo Kim; Eric Hansen; Seongdo Kim
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Paper Abstract

The Giant Magellan Telescope (GMT) Fast Steering Secondary Mirror (FSM) is one of the GMT two Gregorian secondary mirrors. The FSM is 3.2 m in diameter and built as seven 1.06 m diameter circular segments. The conceiving philosophy used on the design of the FSM segment mirror is to minimize development and fabrication risks ensuring a set of secondary mirrors are available on schedule for telescope commissioning and early operations in a seeing limited mode, thereby mitigating risks associated with fabrication of the Adaptive Secondary Mirrors (ASM). This approach uses legacy design features from the Magellan Telescope secondary mirrors to reduce such risks. The final design of the substrate and support system configuration was optimized using finite element analyses and optical performance analyses. The optical performance predictions of the FSM are based on a substrate with a diameter of 1.058m (on-axis), 1.048m (off-axis), a depth of 120mm, and a face plate thickness of 20mm leading to a mass of approximately 90kg. The optical surface deformations, image qualities, and structure functions for the axial and lateral gravity print-through cases, thermal gradient effects, and dynamic performances were evaluated. The results indicated that the GMT FSM mirror and its support system will favorably meet the optical performance goals for residual surface error and the FSM surface figure accuracy requirement defined by encircled energy in the focal plane. The mirror cell assembly analysis indicated an excellent dynamic stiffness which will support the goal of 20 Hz tip-tilt motion.

Paper Details

Date Published: 18 September 2013
PDF: 12 pages
Proc. SPIE 8836, Optomechanical Engineering 2013, 88360V (18 September 2013); doi: 10.1117/12.2024164
Show Author Affiliations
Myung Cho, National Optical Astronomy Observatory (United States)
Andrew Corredor, The Univ. of Arizona (United States)
Christoph Dribusch, The Univ. of Arizona (United States)
Won-Hyun Park, College of Optical Sciences, The Univ. of Arizona (United States)
Gary Muller, Giant Magellan Telescope Project (United States)
Matt Johns, Giant Magellan Telescope Project (United States)
Charlie Hull, Giant Magellan Telescope Project (United States)
Michael Sheehan, Giant Magellan Telescope Project (United States)
Jonathan Kern, Giant Magellan Telescope Project (United States)
Young Soo Kim, Korea Astronomy and Space Science Institute (Korea, Republic of)
Eric Hansen, National Solar Observatory (United States)
Seongdo Kim, Kyungsung Univ. (Korea, Republic of)

Published in SPIE Proceedings Vol. 8836:
Optomechanical Engineering 2013
Alson E. Hatheway, Editor(s)

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