27 July 2016 W. M. Keck Observatory primary mirror segment repair project: overview and status
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Abstract
The W. M. Keck Observatory Segment Repair Project is repairing stress-induced fractures near the support points in the primary mirror segments. The cracks are believed to result from deficiencies in the original design and implementation of the adhesive joints connecting the Invar support components to the ZERODUR mirror. Stresses caused by temperature cycling over 20 years of service drove cracks that developed at the glass-metal interfaces. Over the last few years the extent and cause of the cracks have been studied, and new supports have been designed. Repair of the damaged glass required development of specialized tools and procedures for: (1) transport of the segments; (2) pre-repair metrology to establish the initial condition; (3) removal of support hardware assemblies; (4) removal of the original supports; (5) grinding and re-surfacing the damaged glass areas; (6) etching to remove sub-surface damage; (7) bonding new supports; (8) re-installation of support assemblies; and (9) post-repair metrology. Repair of the first segment demonstrated the new tools and processes. On-sky measurements before and after repair verified compliance with the requirements. This paper summarizes the repair process, on-sky results, and transportation system, and also provides an update on the project status and schedule for repairing all 84 mirror segments. Strategies for maintaining quality and ensuring that repairs are done consistently are also presented.
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Robert L. Meeks, Robert L. Meeks, Steve Doyle, Steve Doyle, Jamie Higginson, Jamie Higginson, John S. Hudek, John S. Hudek, William Irace, William Irace, Dennis McBride, Dennis McBride, Mike Pollard, Mike Pollard, Kuochou Tai, Kuochou Tai, Tod Von Boeckmann, Tod Von Boeckmann, Leslie Wold, Leslie Wold, Truman Wold, Truman Wold, } "W. M. Keck Observatory primary mirror segment repair project: overview and status", Proc. SPIE 9906, Ground-based and Airborne Telescopes VI, 990603 (27 July 2016); doi: 10.1117/12.2233693; https://doi.org/10.1117/12.2233693
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