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Proceedings Paper

Alignment test results of the JWST Pathfinder Telescope mirrors in the cryogenic environment
Author(s): Tony L. Whitman; Conrad Wells; James B. Hadaway; J. Scott Knight; Sharon Lunt
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Paper Abstract

After integration of the Optical Telescope Element (OTE) to the Integrated Science Instrument Module (ISIM) to become the OTIS, the James Webb Space Telescope OTIS is tested at NASA’s Johnson Space Center (JSC) in the cryogenic vacuum Chamber A for alignment and optical performance. The alignment of the mirrors comprises a sequence of steps as follows: The mirrors are coarsely aligned using photogrammetry cameras with reflective targets attached to the sides of the mirrors. Then a multi-wavelength interferometer is aligned to the 18-segment primary mirror using cameras at the center of curvature to align reflected light from the segments and using fiducials at the edge of the primary mirror. Once the interferometer is aligned, the 18 primary mirror segments are then adjusted to optimize wavefront error of the aggregate mirror. This process phases the piston and tilt positions of all the mirror segments. An optical fiber placed at the Cassegrain focus of the telescope then emits light towards the secondary mirror to create a collimated beam emitting from the primary mirror. Portions of the collimated beam are retro-reflected from flat mirrors at the top of the chamber to pass through the telescope to the Science Instrument (SI) detector. The image on the detector is used for fine alignment of the secondary mirror and a check of the primary mirror alignment using many of the same analysis techniques used in the on-orbit alignment. The entire process was practiced and evaluated in 2015 at cryogenic temperature with the Pathfinder telescope.

Paper Details

Date Published: 29 July 2016
PDF: 8 pages
Proc. SPIE 9904, Space Telescopes and Instrumentation 2016: Optical, Infrared, and Millimeter Wave, 990449 (29 July 2016); doi: 10.1117/12.2233421
Show Author Affiliations
Tony L. Whitman, Harris Corp. (United States)
Conrad Wells, Harris Corp. (United States)
James B. Hadaway, The Univ. of Alabama in Huntsville (United States)
J. Scott Knight, Ball Aerospace & Technologies Corp. (United States)
Sharon Lunt, Harris Corp. (United States)

Published in SPIE Proceedings Vol. 9904:
Space Telescopes and Instrumentation 2016: Optical, Infrared, and Millimeter Wave
Howard A. MacEwen; Giovanni G. Fazio; Makenzie Lystrup; Natalie Batalha; Nicholas Siegler; Edward C. Tong, Editor(s)

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