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JWST mirror and actuator performance at cryo-vacuum

Wolf, Erin M. and Gallagher, Ben B. and Knight, J. Scott and Chonis, Taylor S. and Sullivan, Joseph F. and Smith, Koby Z. and Rudeen, Andrew and Babcock, Kevin and Hardy, Bruce and Barto, Allison and Coppock, Eric and Davis, Clinton R. (2018) JWST mirror and actuator performance at cryo-vacuum. In: Space Telescopes and Instrumentation 2018: Optical, Infrared, and Millimeter Wave. Proceedings of SPIE. No.10698. Society of Photo-optical Instrumentation Engineers (SPIE) , Bellingham, WA, Art. No. 1069808. ISBN 9781510619494.

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The James Webb Space Telescope (JWST) telescope’s Secondary Mirror Assembly (SMA) and eighteen Primary Mirror Segment Assemblies (PMSAs) are each actively controlled in rigid body position via six hexapod actuators. Each of the PMSAs additionally has a radius of curvature actuator. The mirrors are stowed to the mirror support structure to survive the launch environment and then must be deployed 12.5 mm to reach the nominally deployed position before the Wavefront Sensing & Control (WFSC) alignment and phasing process begins. JWST requires testing of the full optical system in a Cryogenic Vacuum (CV) environment before launch. The cryo vacuum test campaign was executed in Chamber A at the Johnson Space Center (JSC) in Houston Texas. The test campaign consisted of an ambient vacuum test, a cooldown test, a cryo stable test at 65 Kelvin, a warmup test, and finally a second ambient vacuum test. Part of that test campaign was the functional and performance testing of the hexapod actuators on the flight mirrors. This paper will describe the testing that was performed on all 132 hexapod and radius of curvature actuators. The test campaign first tests actuators individually then tested how the actuators perform in the hexapod system. Telemetry from flight sensors on the actuators and measurements from external metrology devices such as interferometers, photogrammetry systems and image analysis was used to demonstrate the performance of the JWST actuators. The mirror move commanding process was exercised extensively during the JSC CV test and many examples of accurately commanded moves occurred. The PMSA and SMA actuators performed extremely well during the JSC CV test, and we have demonstrated that the actuators are fully functional both at ambient and cryo temperatures and that the mirrors will go to their commanded positions with the accuracy needed to phase and align the telescope.

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Additional Information:© 2018 Society of Photo-optical Instrumentation Engineers (SPIE). The James Webb Space Telescope project is an international collaboration led by NASA’s Goddard Space Flight Center in Greenbelt, MD. Ball Aerospace would like to acknowledge and thank NASA for their leadership, funding, and support during the testing and analysis of the OTIS cryogenic testing campaign. We would also like to thank the many individuals, companies, and government institutions not previously identified who supported the integration and testing effort of the OTIS at both Goddard Space Flight Center and Johnson Space Center.
Group:Thirty Meter Telescope
Funding AgencyGrant Number
Subject Keywords:James Webb Space Telescope, segmented mirror, mirror actuators, hexapod, radius of curvature
Series Name:Proceedings of SPIE
Issue or Number:10698
Record Number:CaltechAUTHORS:20181207-092321264
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Official Citation:Erin M. Wolf, Benjamin B. Gallagher, J. Scott Knight, Taylor S Chonis, Joseph F. Sullivan, Koby Z. Smith, Andrew Rudeen, Kevin Babcock, Bruce Hardy, Allison Barto, Eric Coppock, Clinton R. Davis, "JWST mirror and actuator performance at cryo-vacuum", Proc. SPIE 10698, Space Telescopes and Instrumentation 2018: Optical, Infrared, and Millimeter Wave, 1069808 (6 July 2018); doi: 10.1117/12.2312872
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:91565
Deposited By: Tony Diaz
Deposited On:07 Dec 2018 17:38
Last Modified:03 Oct 2019 20:36

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