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Proceedings Paper

Discovery Channel Telescope active optics system early integration and test
Author(s): Alexander J. Venetiou; Thomas A. Bida
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Paper Abstract

The Discovery Channel Telescope (DCT) is a 4.3-meter telescope with a thin meniscus primary mirror (M1) and a honeycomb secondary mirror (M2). The optical design is an f/6.1 Ritchey-Chrétien (RC) with an unvignetted 0.5° Field of View (FoV) at the Cassegrain focus. We describe the design, implementation and performance of the DCT active optics system (AOS). The DCT AOS maintains collimation and controls the figure of the mirror to provide seeing-limited images across the focal plane. To minimize observing overhead, rapid settling times are achieved using a combination of feed-forward and low-bandwidth feedback control using a wavefront sensing system. In 2011, we mounted a Shack-Hartmann wavefront sensor at the prime focus of M1, the Prime Focus Test Assembly (PFTA), to test the AOS with the wavefront sensor, and the feedback loop. The incoming wavefront is decomposed using Zernike polynomials, and the mirror figure is corrected with a set of bending modes. Components of the system that we tested and tuned included the Zernike to Bending Mode transformations. We also started open-loop feed-forward coefficients determination. In early 2012, the PFTA was replaced by M2, and the wavefront sensor moved to its normal location on the Cassegrain instrument assembly. We present early open loop wavefront test results with the full optical system and instrument cube, along with refinements to the overall control loop operating at RC Cassegrain focus.

Paper Details

Date Published: 17 September 2012
PDF: 11 pages
Proc. SPIE 8444, Ground-based and Airborne Telescopes IV, 84441E (17 September 2012); doi: 10.1117/12.925439
Show Author Affiliations
Alexander J. Venetiou, Lowell Observatory (United States)
Thomas A. Bida, Lowell Observatory (United States)


Published in SPIE Proceedings Vol. 8444:
Ground-based and Airborne Telescopes IV
Larry M. Stepp; Roberto Gilmozzi; Helen J. Hall, Editor(s)

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