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Proceedings Paper

Development of GMT fast steering secondary mirror assembly
Author(s): Myung Cho; Andrew Corredor; Christoph Dribusch; Won Hyun Park; Gary Muller; Matt Johns; Charlie Hull; Jonathan Kern; Young-Soo Kim
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Paper Abstract

The Giant Magellan Telescope (GMT) is one of Extremely large telescopes, which is 25m in diameter featured with two Gregorian secondary mirrors, an adaptive secondary mirror (ASM) and a fast-steering secondary mirror (FSM). The FSM is 3.2 m in diameter and built as seven 1.1 m diameter circular segments conjugated 1:1 to the seven 8.4m segments of the primary. The guiding philosophy in 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. Each FSM segment contains a tip-tilt capability for fine co-alignment of the telescope subapertures and fast guiding to attenuate telescope wind shake and mount control jitter, thus optimizing the seeing limited performance of the telescope. The final design of the FSM mirror and support system configuration was optimized using finite element analyses and optical performance analyses. The optical surface deformations, image qualities, and structure functions for the 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 (EE80) in the focal plane. The mirror cell assembly analysis indicated an excellent dynamic stiffness which will support the goal of tip-tilt operation.

Paper Details

Date Published: 22 July 2014
PDF: 14 pages
Proc. SPIE 9145, Ground-based and Airborne Telescopes V, 91451M (22 July 2014); doi: 10.1117/12.2056533
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, 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)
Jonathan Kern, Giant Magellan Telescope Project (United States)
Young-Soo Kim, Giant Magellan Telescope Project (United States)
Korea Astronomy and Space Science Institute (Korea, Republic of)

Published in SPIE Proceedings Vol. 9145:
Ground-based and Airborne Telescopes V
Larry M. Stepp; Roberto Gilmozzi; Helen J. Hall, Editor(s)

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