Development of the fast steering secondary mirror for the Giant Magellan Telescope

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

doi:10.1117/12.2024164

18 September 2013 Development of the fast steering secondary mirror for the Giant Magellan Telescope

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

Author Affiliations +

Proceedings Volume 8836, Optomechanical Engineering 2013; 88360V (2013) https://doi.org/10.1117/12.2024164
Event: SPIE Optical Engineering + Applications, 2013, San Diego, California, United States

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.

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Myung Cho, Andrew Corredor, Christoph Dribusch, Won-Hyun Park, Gary Muller, Matt Johns, Charlie Hull, Michael Sheehan, Jonathan Kern, Young Soo Kim, Eric Hansen, and Seongdo Kim "Development of the fast steering secondary mirror for the Giant Magellan Telescope", Proc. SPIE 8836, Optomechanical Engineering 2013, 88360V (18 September 2013); https://doi.org/10.1117/12.2024164

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