NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
Performance of the Center-Of-Curvature Optical Assembly During Cryogenic Testing of the James Webb Space TelescopeThe James Webb Space Telescope (JWST) primary mirror (PM) is 6.6 meters in diameter and consists of 18 hexagonal segments, each 1.5 meters point-to-point. Each segment has a 6 degree-of-freedom hexapod actuation system and a radius-of-curvature (ROC) actuation system. The full telescope was tested at its cryogenic operating temperature at Johnson Space Center (JSC) in 2017. This testing included center-of-curvature measurements of the PM wavefront error using the Center-of-Curvature Optical Assembly (COCOA), along with the Absolute Distance Meter Assembly (ADMA). The COCOA included an interferometer, a reflective null, an interferometer-null calibration system, coarse and fine alignment systems, and two displacement measuring interferometer systems. A multiple-wavelength interferometer was used to enable alignment and phasing of the PM segments. By combining measurements at two laser wavelengths, synthetic wavelengths up to 15 millimeters could be achieved, allowing mirror segments with millimeter-level piston errors to be phased to the nanometer level. The ADMA was used to measure and set the spacing between the PM and the focus of the COCOA null (i.e., the PM center-of-curvature) for determination of the ROC. This paper describes the COCOA, the PM test setup, the testing performed, the test results, and the performance of the COCOA in aligning & phasing the PM segments and measuring the final PM wavefront error.
Document ID
20180004017
Acquisition Source
Goddard Space Flight Center
Document Type
Conference Paper
Authors
Hadaway, James B.
(Alabama Univ. Huntsville, AL, United States)
Wells, Conrad
(Harris Corp. Rochester, NY, United States)
Olczak, Gene A.
(Harris Corp. Rochester, NY, United States)
Waldman, Mark
(Sigma Space Corp. Lanham, MD, United States)
Whitman, Tony L.
(Harris Corp. Rochester, NY, United States)
Cosentino, Joseph
(Harris Corp. Rochester, NY, United States)
Zarella, Michael
(Harris Corp. Rochester, NY, United States)
Connelly, Mark
(Harris Corp. Rochester, NY, United States)
Chaney, David M.
(Ball Aerospace and Technologies Corp. Boulder, CO, United States)
Telfer, Randal
(Space Telescope Science Inst. Baltimore, MD, United States)
Date Acquired
July 25, 2018
Publication Date
June 10, 2018
Subject Category
Optics
Report/Patent Number
GSFC-E-DAA-TN57655
Report Number: GSFC-E-DAA-TN57655
Meeting Information
Meeting: SPIE Astronomical Telescopes + Instrumentation
Location: Austin, TX
Country: United States
Start Date: June 10, 2018
End Date: June 15, 2018
Sponsors: International Society for Optical Engineering
Funding Number(s)
CONTRACT_GRANT: NAS5-03127
CONTRACT_GRANT: NAS5-02200
CONTRACT_GRANT: NNG11FD64C
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
JWST
optical testing
interferometry
multiple-wavelength interferometer
primary mirror
cryogenic
James Webb Space Telescope
optical metrology.
No Preview Available