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  • 1
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    Performance of the Center-Of-Curvature Optical Assembly During Cryogenic Testing of the James Webb Space Telescope (2018)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The 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.
    Keywords: Optics
    Type: GSFC-E-DAA-TN57655 , SPIE Astronomical Telescopes + Instrumentation; Jun 10, 2018 - Jun 15, 2018; Austin, TX; United States
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  • 2
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    Measuring Segmented Primary Mirror WFE in the Presence of Vibration and Thermal Drift on the Light-Weighted JWST (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The light-weighted design of the Optical Telescope Element (OTE) of the James Webb Telescope (JWST) leads to additional sensitivity to vibration from the ground - an important consideration to the measurement uncertainty of the wavefront error (WFE) in the primary mirror. Furthermore, segmentation of the primary mirror leads to rigid-body movements of segment areas in the WFE. The ground vibrations are minimized with modifications to the test facility, and by the architecture of the equipment supporting the load. Additional special test equipment (including strategically placed isolators, tunable mass dampers, and cryogenic magnetic dampers) mitigates the vibration and the response sensitivity before reaching the telescope. A multi-wavelength interferometer is designed and operated to accommodate the predicted residual vibration. Thermal drift also adds to the measurement variation. Test results of test equipment components, measurement theory, and finite element analysis combine to predict the test uncertainty in the future measurement of the primary mirror. The vibration input to the finite element model comes from accelerometer measurements of the facility with the environmental control pumps operating. One of the isolators have been built and tested to validate the dynamic performance. A preliminary model of the load support equipment and the OTE with the Integrated Science Instrument Module (ISIM) is complete. The performance of the add-on dampers have been established in previous applications. And operation of the multi-wavelength interferometer was demonstrated on a scaled hardware version of the JWST in an environment with vibration and thermal drift.
    Keywords: Instrumentation and Photography
    Type: GSFC.CP.6555.2012 , SPIE Astronomical Telescopes and Instrumentation Conference 2012; Jul 01, 2012; Amsterdam; Netherlands
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  • 3
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    JWST's Cryogenic Position Metrology System (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The James Webb Space Telescope will undergo a full system test in the cryogenic vacuum chamber A at the Johnson Spaceflight Center in order to verify the overall performance of the combined telescope and instrument suite. This will be the largest and most extensive cryogenic test ever undertaken. Early in the test system development, it was determined that precise position measurements of the overall hardware would enhance the test results. Various concepts were considered before selecting photogrammetry for this metrology. Photogrammetry has been used in space systems for decades, however cryogenic use combined with the size and the optical/thermal sensitivity of JWST creates a unique set of implementation challenges. This paper provides an overview of the JWST photogrammetric system and mitigation strategies for three key engineering design challenges: 1) the thermal design of the viewing windows to prevent excessive heat leak and stray light to the test article 2) cost effective motors and mechanisms to provide the angle diversity required, and 3) camera-flash life and reliability sufficient for inaccessible use during the number and duration of the cryogenic tests.
    Keywords: Spacecraft Design, Testing and Performance
    Type: GSFC.CPR.6481.2012 , SPIE Astronomical Telescopes and Instrumentation Conference 2012; Jul 06, 2012; Amsterdam; Netherlands
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  • 4
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    JWST Pathfinder Telescope Risk Reduction Cryo Test Program (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: In 2014, the Optical Ground Support Equipment was integrated into the large cryo vacuum chamber at Johnson Space Center (JSC) and an initial Chamber Commissioning Test was completed. This insured that the support equipment was ready for the three Pathfinder telescope cryo tests. The Pathfinder telescope which consists of two primary mirror segment assemblies and the secondary mirror was delivered to JSC in February 2015 in support of this critical risk reduction test program prior to the flight hardware. This paper will detail the Chamber Commissioning and first optical test of the JWST Pathfinder telescope.
    Keywords: Optics; Astronomy; Ground Support Systems and Facilities (Space)
    Type: GSFC-E-DAA-TN25498 , SPIE Optics and Photonics; Aug 09, 2015 - Aug 13, 2015; San Diego, CA; United States
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  • 5
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    JWST Telescope Integration and Test Progress (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The James Webb Space Telescope (JWST) is a 6.5m, segmented, IR telescope that will explore the first light of the universe after the big bang. The JWST Optical Telescope Element (Telescope) integration and test program is well underway. The telescope was completed in the spring of 2016 and the cryogenic test equipment has been through two optical test programs leading up to the final flight verification program. The details of the telescope mirror integration will be provided along with the current status of the flight observatory. In addition, the results of the two optical ground support equipment cryo tests will be shown and how these plans fold into the flight verification program.
    Keywords: Astronomy
    Type: GSFC-E-DAA-TN32784-2 , International Conference on Environmental Systems (ICES 2016); Jul 10, 2016 - Jul 14, 2016; Vienna; Austria
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  • 6
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    JWST Telescope Integration and Test Progress (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Astronomy; Spacecraft Design, Testing and Performance
    Type: GSFC-E-DAA-TN32784-1 , International Conference on Environmental Systems (ICES 2016); Jul 10, 2016 - Jul 14, 2016; Vienna; Austria
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  • 7
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    Alignment Test Results of the JWST Pathfinder Telescope Mirrors in the Cryogenic Environment (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: 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 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.
    Keywords: Instrumentation and Photography; Optics
    Type: GSFC-E-DAA-TN32747 , SPIE Astronomical Telescopes & Instrumentation 2016; Jun 26, 2016 - Jul 12, 2016; Edinburgh, Scotland; United Kingdom
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  • 8
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    Wide-Field Infrared Survey Telescope (WFIRST) - Optical Telescope Assembly (OTA) Status (2018)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The WFIRST Mission is the next large astrophysical observatory for NASA after the James Webb Space Telescope and is the top priority mission from the 2010 National Academy of Sciences' decadal survey. The WFIRST OTA includes the inherited primary and secondary mirrors with precision metering structures that are to be integrated to new mirror assemblies to provide optical feeds to the two WFIRST science instruments. We present here: (1) the results for the review of the inherited hardware for WFIRST through a thorough technical pedigree process, (2) the status of the effort to establish the capability of the telescope to perform at a cooler operational temperature of 265K, and (3) the status of the work in requirement development for OTA to incorporate the inherited hardware, and (4) the path forward.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN57338 , SPIE Astronomical Telescopes + Instrumentation; Jun 10, 2018 - Jun 15, 2018; Austin, TX; United States
    Format: application/pdf
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