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Proceedings Paper

Cryogenic radius of curvature matching for the JWST primary mirror segments
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Paper Abstract

The JWST (James Webb Space Telescope) primary mirror consists of 18 hexagonal mirror segments. Each segment is approximately 1.5 meters point to point and is constructed from a lightweight beryllium substrate. In order for the 18 segments to act as a single 6.5 meter diameter mirror each one must be capable of 6 degrees of freedom motion relative to the mirror backplane and be able to change its radius of curvature to closely match those of the other segments. As it would be nearly impossible to manufacture the 18 individual segments with the same radius, a RoC (radius of curvature) actuation mechanism is attached to each mirror allowing RoC fine tuning post manufacturing. The RoC actuation system consists of a single actuator and six struts attached to the back of the mirror. The radius of curvature is matched by closely manufacturing the radius of each segment relative to the nominal value and then, during cryogenic testing, actuating the RoC of each mirror. This cryogenic actuation reduces polishing times and allows for compensation of radius changes measured during other manufacturing steps. Presented here is a high-level overview of the method used to set the mirror's radius of curvature at cryogenic temperature, disassemble the mirror system for additional polishing and processing, and perform final cryogenic verification.

Paper Details

Date Published: 17 September 2009
PDF: 9 pages
Proc. SPIE 7439, Astronomical and Space Optical Systems, 743916 (17 September 2009); doi: 10.1117/12.845115
Show Author Affiliations
David M Chaney, Ball Aerospace & Technologies Corp. (United States)
James B. Hadaway, The Univ. of Alabama in Huntsville (United States)
Jackson A. Lewis, Ball Aerospace & Technologies Corp. (United States)

Published in SPIE Proceedings Vol. 7439:
Astronomical and Space Optical Systems
Penny G. Warren; James B. Heaney; Robert K. Tyson; Michael Hart; E. Todd Kvamme; Cheryl J. Marshall, Editor(s)

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