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Proceedings Paper

Mirror alignment recovery system (MARS) on the Hobby-Eberly Telescope
Author(s): Marsha J. Wolf; Povilas Palunas; John A. Booth; Michael H. Ward; Allan Wirth; Gordon L. Wesley; Darragh O'Donoghue; Lawrence W. Ramsey
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Paper Abstract

The Mirror Alignment Recovery System (MARS) is a Shack-Hartmann based sensor at the center of curvature (CoC) of the Hobby-Eberly Telescope (HET) spherical primary mirror used to align the 91 mirror segments. The instrument resides in a CoC tower next to the HET dome, a location which provides a challenging set of problems including wind shake and seeing from two different domes. The system utilizes an internal light source to illuminate the HET and a reference mirror to provide focused spot locations from a spherical surface. A custom lenslet array is sized to the HET pupil image, matching a single hexagonal lenslet to each mirror segment. Centroids of the HET mirror segment spots are compared to the reference spot locations to measure tip/tilt misalignments of each segment. A MARS proof-of-concept (POC) instrument, tested on the telescope in 2001, utilized a commercial wavefront sensor from Adaptive Optics Associates. The final system uses the same concept, but is customized for optimal performance on the HET. MARS replaces previous burst-antiburst alignment techniques and provides a more intuitive method of aligning the primary mirror for telescope operators. The POC instrument has improved median HET stack sizes by 0.3" EE50, measured at the CoC tower. The current alignment accuracy is 0.14" rms (0.28" rms on the sky), resolution is 0.014", measurement precision is 0.027" rms, and segment capture range is ± 5". With continuing improvements in HET dome ventilation and the addition of software customized for removal of tower motion during measurement, the alignment accuracy is expected to reach approximately 0.04" rms in the final MARS, to be installed in late 2002.

Paper Details

Date Published: 4 February 2003
PDF: 12 pages
Proc. SPIE 4837, Large Ground-based Telescopes, (4 February 2003); doi: 10.1117/12.458034
Show Author Affiliations
Marsha J. Wolf, Univ. of Texas at Austin (United States)
Povilas Palunas, McDonald Observatory/Univ. of Texas at Austin (United States)
John A. Booth, McDonald Observatory/Univ. of Texas at Austin (United States)
Michael H. Ward, McDonald Observatory/Univ. of Texas at Austin (United States)
Allan Wirth, Adaptive Optics Associates, Inc. (United States)
Gordon L. Wesley, McDonald Observatory/Univ. of Texas at Austin (United States)
Darragh O'Donoghue, South African Astronomical Observatory (South Africa)
Lawrence W. Ramsey, The Pennsylvania State Univ. (United States)

Published in SPIE Proceedings Vol. 4837:
Large Ground-based Telescopes
Jacobus M. Oschmann; Larry M. Stepp, Editor(s)

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