Aligning and maintaining the optics for the James Webb Space Telescope (JWST) on-orbit: the wavefront sensing and control concept of operations

Contos, Adam R.; Acton, D. Scott; Atcheson, Paul D.; Barto, Allison; Lightsey, Paul A.; Shields, Duncan M.

doi:10.1117/12.669067

Cited by 20 publications

(18 citation statements)

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“…6 The WFE is measured every 2 days, and the measurements taken during the last 2-week period are used to determine if a correction is needed. For the baseline algorithm, only the most recent measurement W m7 is used.…”

Section: Baseline and Averaging Algorithmsmentioning

confidence: 99%

“…The baseline control scheme for the first large active optical/infrared space telescope, the James Webb Space Telescope (JWST), is conceptually simple, consisting of measuring the wavefront error (WFE) every 2 days and using these measurements to apply corrections every 2 weeks as needed. 6 This scheme satisfies the observatory's requirements; however, alternative control algorithms may further improve the performance, providing lower and/or more stable WFEs and enhancing science capabilities.…”

Section: Introductionmentioning

confidence: 99%

“…We do not discuss the details of how the wavefront measurements are to be obtained nor how the desired controls are applied via spacecraft actuators; these topics have been discussed at length in other papers. 6,7,11 Our focus here is on the question of how often sensing and control should take place and how multiple sensing measurements may be combined in order to optimize performance. Although our analysis is based on JWST specifically, the general approach taken is also applicable to other missions, such as the proposed Astrophysics Focused Telescope Assets (AFTA) and Advanced Technology Large-Aperture Space Telescope (ATLAST) mission concepts.…”

Section: Introductionmentioning

confidence: 99%

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Improving active space telescope wavefront control using predictive thermal modeling

Gersh-Range

Perrin

2014

J. Astron. Telesc. Instrum. Syst

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Abstract. Active control algorithms for space telescopes are less mature than those for large ground telescopes due to differences in the wavefront control problems. Active wavefront control for space telescopes at L2, such as the James Webb Space Telescope (JWST), requires weighing control costs against the benefits of correcting wavefront perturbations that are a predictable byproduct of the observing schedule, which is known and determined in advance. To improve the control algorithms for these telescopes, we have developed a model that calculates the temperature and wavefront evolution during a hypothetical mission, assuming the dominant wavefront perturbations are due to changes in the spacecraft attitude with respect to the sun. Using this model, we show that the wavefront can be controlled passively by introducing scheduling constraints that limit the allowable attitudes for an observation based on the observation duration and the mean telescope temperature. We also describe the implementation of a predictive controller designed to prevent the wavefront error (WFE) from exceeding a desired threshold. This controller outperforms simpler algorithms even with substantial model error, achieving a lower WFE without requiring significantly more corrections. Consequently, predictive wavefront control based on known spacecraft attitude plans is a promising approach for JWST and other future active space observatories. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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Section: Baseline and Averaging Algorithmsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Improving active space telescope wavefront control using predictive thermal modeling

Gersh-Range

Perrin

2014

J. Astron. Telesc. Instrum. Syst

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“…17 The WFSC process uses imagery taken with the science instruments to sense the state of telescope and provide feedback information on performance. The fine phasing will be done using imagery from the NIRCam, and field-dependent alignment of the PM/SM to the aft optics and instruments uses imagery from all instruments.…”

Section: Wavefront Sensing and Controlmentioning

confidence: 99%

James Webb Space Telescope: large deployable cryogenic telescope in space

Lightsey¹,

et al. 2012

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Abstract. The James Webb Space Telescope (JWST) is an infrared space telescope designed to explore four major science themes: first light and reionization, the assembly of galaxies, the birth of stars and protoplanetary systems, and planetary systems and origins of life. JWST is a segmented architecture telescope with an aperture of 6.6 m. It will operate at cryogenic temperature (40 K), achieved via passive cooling, in an orbit about the Earth-Sun second Lagrange point (L2). Passive cooling is facilitated by means of a large sunshield that provides thermal isolation and protection from direct illumination from the Sun. The large size of the telescope and spacecraft systems require that they are stowed for launch in a configuration that fits the Ariane 5 fairing, and then deployed after launch. Routine wavefront sensing and control measurements are used to achieve phasing of the segmented primary mirror and initial alignment of the telescope. A suite of instruments will provide the capability to observe over a spectral range from 0.6-to 27-μm wavelengths with imaging and spectroscopic configurations. An overview is presented of the architecture and selected optical design features of JWST are described.

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“…2,3 NIRCam also has unique design and materials features, including two completely redundant optics modules, a Be optical bench, and 10 2048 × 2048 pixel HgCdTe HAWAII-2RG detector arrays. It also uses refractive collimator / camera optics with dichroic beasmsplitters to allow simultaneous imaging of 0.6 -2.3 μm and 2.4 -5.0 μm wavelengths over a 2.2 × 4.4 arc-minute field of view (using both the A and B optics modules).…”

Section: Introductionmentioning

confidence: 99%

NIRCam: development and testing of the JWST near-infrared camera

et al. 2010

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The Near Infrared Camera (NIRCam) is one of the four science instruments of the James Webb Space Telescope (JWST). Its high sensitivity, high spatial resolution images over the 0.6 − 5 μm wavelength region will be essential for making significant findings in many science areas as well as for aligning the JWST primary mirror segments and telescope. The NIRCam engineering test unit was recently assembled and has undergone successful cryogenic testing. The NIRCam collimator and camera optics and their mountings are also progressing, with a brass-board system demonstrating relatively low wavefront error across a wide field of view. The flight model's long-wavelength Si grisms have been fabricated, and its coronagraph masks are now being made. Both the short (0.6 − 2.3 μm) and long (2.4 − 5.0 μm) wavelength flight detectors show good performance and are undergoing final assembly and testing. The flight model subsystems should all be completed later this year through early 2011, and NIRCam will be cryogenically tested in the first half of 2011 before delivery to the JWST integrated science instrument module (ISIM).

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Aligning and maintaining the optics for the James Webb Space Telescope (JWST) on-orbit: the wavefront sensing and control concept of operations

Cited by 20 publications

References 0 publications

Improving active space telescope wavefront control using predictive thermal modeling

Improving active space telescope wavefront control using predictive thermal modeling

James Webb Space Telescope: large deployable cryogenic telescope in space

NIRCam: development and testing of the JWST near-infrared camera

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