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JWST mirror and actuator performance at cryo-vacuum
Author(s): 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
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Paper Abstract

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.

Paper Details

Date Published: 6 July 2018
PDF: 14 pages
Proc. SPIE 10698, Space Telescopes and Instrumentation 2018: Optical, Infrared, and Millimeter Wave, 1069808 (6 July 2018); doi: 10.1117/12.2312872
Show Author Affiliations
Erin M. Wolf, Ball Aerospace (United States)
Benjamin B. Gallagher, Thirty Meter Telescope (United States)
J. Scott Knight, Ball Aerospace (United States)
Taylor S Chonis, Ball Aerospace (United States)
Joseph F. Sullivan, Ball Aerospace (United States)
Koby Z. Smith, Ball Aerospace (United States)
Andrew Rudeen, Ball Aerospace (United States)
Kevin Babcock, Ball Aerospace (United States)
Bruce Hardy, Ball Aerospace (United States)
Allison Barto, Ball Aerospace (United States)
Eric Coppock, Ball Aerospace (United States)
Clinton R. Davis, Genesis Engineering Solutions (United States)

Published in SPIE Proceedings Vol. 10698:
Space Telescopes and Instrumentation 2018: Optical, Infrared, and Millimeter Wave
Makenzie Lystrup; Howard A. MacEwen; Giovanni G. Fazio; Natalie Batalha; Nicholas Siegler; Edward C. Tong, Editor(s)

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