Using multifield measurements to eliminate alignment degeneracies in the JWST testbed telescope

Sabatke, Erin; Acton, Scott T.; Schwenker, John P.; Towell, Tim; Carey, Larkin; Shields, Duncan M.; Contos, Adam R.; Leviton, Doug

doi:10.1117/12.736309

Cited by 3 publications

(2 citation statements)

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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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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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“…In this example, the extreme points of the JWST science field show more than 1 micron PTV. The field-dependent wavefront is well represented by a linear combination of power and astigmatism, which varies linearly with field [2]. If a relationship between the MF errors and the SM position could be established, it should be possible to generate SM corrections based on the observed field dependent errors.…”

Section: Introductionmentioning

confidence: 99%

Multi-field alignment of the James Webb Space Telescope

Acton¹,

Knight²

2012

Space Telescopes and Instrumentation 2012: Optical, Infrared, and Millimeter Wave

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When the secondary mirror (SM) of a Three-Mirror Anastigmat (TMA) telescope is misaligned with respect to the primary mirror (PM), optical wavefront errors are created. In general, the errors take the form of a dominant coma term, common to all field points, in addition to astigmatism and power terms which vary with field position. The magnitude of the field dependent wavefront is usually only a few percent of that of the common coma term, depending on the size of the field of view being considered. The architecture of the James Webb Space Telescope (JWST), however, presents a unique optical problem in that the common term created by misplacement of the SM is compensated by adjustment of the PM segments. As such, the residual field dependent terms become dominant and can be sensed at multiple field points using phase retrieval techniques. In this paper, we present a linear set of equations that describe the multi-field (MF) wavefront errors resulting from a misaligned SM. It is shown that inverting these equations yields corrections for the SM alignment that can independently control the field-dependent astigmatism and the focal-plane tilt. Computer simulations illustrating the correction are presented.

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Phase retrieval on broadband and under-sampled images for the JWST testbed telescope

et al. 2009

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Using multifield measurements to eliminate alignment degeneracies in the JWST testbed telescope

Cited by 3 publications

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

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

Multi-field alignment of the James Webb Space Telescope

Phase retrieval on broadband and under-sampled images for the JWST testbed telescope

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