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An overview of optical fabrication of the JWST mirror segments at Tinsley

The context, preparation, and facilitization of Tinsley to produce the 18 JWST primary mirror segments are described, and an overview of the Project at Tinsley is presented. The mirror segments are aggressively lightweighted, approximately hexagonal, and approximately 1.32m flat-to-flat. While the optical finishing approach is strongly seated in Tinsley's Computer Controlled Optical Surfacing (CCOSTM) technology, extensions have been implemented to address safe and efficient nearly simultaneous flow of the high value mirror segments through numerous cycles of optical finishing, processing and metrology steps. JWST will operate at cryogenic temperatures, and Tinsley will do final figuring from a "hit map" made during cryogenic testing at the NASA MSFC X-Ray Calibration Facility (XRCF). A formal beryllium safety protocol has been established throughout. Extensive handling fixtures assure that the mirrors are moved from station to station experiencing low accelerations. A rigorous qualification process is applied to each new fixture, machine and instrument. Special problems of cryo figuring, and co-finishing the segments to stringent specifications are described.