Multi-field alignment of the James Webb Space Telescope

Acton, D. Scott; Knight, J. Scott

doi:10.1117/12.925004

Cited by 13 publications

(9 citation statements)

References 6 publications

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“…The JWST creates a unique alignment challenge since the primary mirror is segmented but the secondary must still be aligned to the parent primary independent of any of the segment misalignments. Using multiple field point wavefront measurements, an alignment plan for the secondary mirror of the JWST has been developed and shown in simulations to be able to account for field-dependent astigmatism and focal plane tilt due to the secondary mirror misalignments [197]. A set of linear equations describe the multifield wavefront errors that result from a misaligned secondary, which can be inverted to provide a correction for the secondary mirror position.…”

Section: Optical System Alignmentmentioning

confidence: 99%

Optics technology for large-aperture space telescopes: from fabrication to final acceptance tests

et al. 2018

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This review paper addresses topics of fabrication, testing, alignment, and as-built performance of reflective space optics for the next generation of telescopes across the x-ray to far-infrared spectrum. The technology presented in the manuscript represents the most promising methods to enable a next level of astronomical observation capabilities for space-based telescopes as motivated by the science community. While the technology to produce the proposed telescopes does not exist in its final form, the optics industry is making steady and impressive progress toward these goals across all disciplines. We hope that through sharing these developments in context of the science objectives, further connections and improvements are enabled to push the envelope of the technology.

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Section: Optical System Alignmentmentioning

confidence: 99%

Optics technology for large-aperture space telescopes: from fabrication to final acceptance tests

et al. 2018

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“…Wavefront-error 3rd-order aberrations: The last step of the 9-step commissioning procedure for the JWST OTE on orbit is called Multi-Instrument, Multi-Field (MIMF) alignment [5][6] ; see Figure 1. The purpose of MIMF alignment is to make sure that we are correctly separating system wavefront error between the OTE and NIRCam (the primary wavefront sensor for the Observatory), so that the OTE mirror segments are not aligned so as to imprint the NIRCam wavefront error on the other SIs.…”

Section: Isim Element-level Requirements and Goals For Wavefront Error Performance Characterizationmentioning

confidence: 99%

Wavefront-error performance characterization for the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) science instruments

et al. 2016

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The science instruments (SIs) comprising the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) were tested in three cryogenic-vacuum test campaigns in the NASA Goddard Space Flight Center (GSFC)'s Space Environment Simulator (SES) test chamber.In this paper, we describe the results of optical wavefront-error performance characterization of the SIs. The wavefront error is determined using image-based wavefront sensing, and the primary data used by this process are focus sweeps, a series of images recorded by the instrument under test in its as-used configuration, in which the focal plane is systematically changed from one image to the next. High-precision determination of the wavefront error also requires several sources of secondary data, including 1) spectrum, apodization, and wavefront-error characterization of the optical ground-support equipment (OGSE) illumination module, called the OTE Simulator (OSIM), 2) f/# and pupil-distortion measurements made using a pseudo-nonredundant mask (PNRM), and 3) pupil geometry predictions as a function of SI and field point, which are complicated because of a tricontagon-shaped outer perimeter and small holes that appear in the exit pupil due to the way that different light sources are injected into the optical path by the OGSE. One set of wavefront-error tests, for the coronagraphic channel of the Near-Infrared Camera (NIRCam) Longwave instruments, was performed using data from transverse translation diversity sweeps instead of focus sweeps, in which a sub-aperture is translated and/or rotated across the exit pupil of the system.Several optical-performance requirements that were verified during this ISIM-level testing are levied on the uncertainties of various wavefront-error-related quantities rather than on the wavefront errors themselves. This paper also describes the methodology, based on Monte Carlo simulations of the wavefront-sensing analysis of focus-sweep data, used to establish the uncertainties of the wavefront-error maps.

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“…This is the approach adopted for JWST to sense and control the position of the secondary mirror in the Multi-Instrument Multi-Field (MIMF) stage of commissioning. 14 Since we have derived an optical design that is very similar to the TMA but in transmission, we analyzed if this property holds true for the JOST design. Independently from the segment cophasing errors and assuming that the segmented mirror is perfectly flat, we therefore need to check that we have:…”

Section: Optical Properties Of Jost Three-lens Anastigmatmentioning

confidence: 99%

James Webb Space Telescope Optical Simulation Testbed II: design of a three-lens anastigmat telescope simulator

Choquet¹,

Levecq²,

N’Diaye³

et al. 2014

SPIE Proceedings

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The James Webb Space Telescope (JWST) Optical Simulation Testbed (JOST) is a tabletop experiment designed to reproduce the main aspects of wavefront sensing and control (WFS&C) for JWST. To replicate the key optical physics of JWST's three-mirror anastigmat (TMA) design at optical wavelengths we have developed a three-lens anastigmat optical system. This design uses custom lenses (plano-convex, plano-concave, and bi-convex) with fourth-order aspheric terms on powered surfaces to deliver the equivalent image quality and sampling of JWST NIRCam at the WFS&C wavelength (633 nm, versus JWST's 2.12 µm). For active control, in addition to the segmented primary mirror simulator, JOST reproduces the secondary mirror alignment modes with five degrees of freedom. We present the testbed requirements and its optical and optomechanical design. We study the linearity of the main aberration modes (focus, astigmatism, coma) both as a function of field point and level of misalignments of the secondary mirror. We find that the linearity with the transmissive design is similar to what is observed with a traditional TMA design, and will allow us to develop a linear-control alignment strategy based on the multi-field methods planned for JWST.

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Multi-field alignment of the James Webb Space Telescope

Cited by 13 publications

References 6 publications

Optics technology for large-aperture space telescopes: from fabrication to final acceptance tests

Optics technology for large-aperture space telescopes: from fabrication to final acceptance tests

Wavefront-error performance characterization for the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) science instruments

James Webb Space Telescope Optical Simulation Testbed II: design of a three-lens anastigmat telescope simulator

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