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Alignment Test Results of the JWST Pathfinder Telescope Mirrors in the Cryogenic EnvironmentAfter 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 NASAs 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 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.
Document ID
20160007972
Acquisition Source
Goddard Space Flight Center
Document Type
Conference Paper
Authors
Whitman, Tony L.
(Northrop Grumman Space and Mission Systems Corp. Fairfax, VA, United States)
Wells, Conrad
(Exelis, Inc. Greenbelt, MD, United States)
Hadaway, James
(Alabama Univ. Huntsville, AL, United States)
Knight, J. Scott
(Ball Aerospace and Technologies Corp. Boulder, CO, United States)
Lunt, Sharon
(Exelis, Inc. Greenbelt, MD, United States)
Date Acquired
June 28, 2016
Publication Date
June 26, 2016
Subject Category
Instrumentation And Photography
Optics
Report/Patent Number
GSFC-E-DAA-TN32747
Meeting Information
Meeting: SPIE Astronomical Telescopes & Instrumentation 2016
Location: Edinburgh, Scotland
Country: United Kingdom
Start Date: June 26, 2016
End Date: July 12, 2016
Sponsors: International Society for Optical Engineering
Funding Number(s)
CONTRACT_GRANT: NNG11FD64C
CONTRACT_GRANT: NAS5-02200
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
Interferometer
Optical Alignment
OTIS
Photogrammetry
Multi-wavelength
JWST
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