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Proceedings Paper

Cornell Caltech Atacama Telescope primary mirror surface sensing and controllability
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Paper Abstract

To meet the 10 µm RMS half wavefront error requirement for the 25 m diameter Cornell Caltech Atacama Telescope (CCAT), active control of the approximately 200 primary mirror panels is required. The CCAT baseline design includes carbon fiber aluminum honeycomb sandwich mirror panels. Distortions of the panels due to thermal gradients, gravity and the mounting scheme need to be taken into consideration in the control system design. We have modeled the primary mirror surface as both flat and curved surfaces and have investigated mirror controllability with a variety of sensor types and positions. To study different mirror segmentation schemes and find acceptable sensor configurations, we have created a software package that supports multiple segment shapes and reconfigurable panel sizing and orientation. It includes extensible sensor types and flexible positioning. Inclusion of panel and truss deformations allows modeling the effects of thermal and gravity distortions on mirror controllability. Flat mirrors and curved mirrors with the correct prescription give similar results for controlled modes, but show significant differences in the unsensed flat mirror modes. Both flat and curved mirror models show that sensing schemes that work well with rigid, thermally stable panels will not control a mirror with deformable panels. Sensors external to the mirror surface such as absolute distance measurement systems or Shack-Hartmann type sensors are required to deal with panel deformations. Using a combination of segment based sensors and external sensors we have created a promising prototype control system for the CCAT telescope.

Paper Details

Date Published: 17 July 2008
PDF: 9 pages
Proc. SPIE 7012, Ground-based and Airborne Telescopes II, 701211 (17 July 2008); doi: 10.1117/12.790528
Show Author Affiliations
Daniel MacDonald, Jet Propulsion Lab. (United States)
David Woody, California Institute of Technology (United States)
C. Matt Bradford, Jet Propulsion Lab. (United States)
Richard Chamberlin, California Institute of Technology (United States)
Mark Dragovan, Jet Propulsion Lab. (United States)
Paul Goldsmith, Jet Propulsion Lab. (United States)
Simon Radford, California Institute of Technology (United States)
Thomas Sebring, Cornell Univ. (United States)
Jonas Zmuidzinas, Jet Propulsion Lab. (United States)

Published in SPIE Proceedings Vol. 7012:
Ground-based and Airborne Telescopes II
Larry M. Stepp; Roberto Gilmozzi, Editor(s)

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