The James Webb Space Telescope (JWST) telescope’s Secondary Mirror Assembly (SMA) and eighteen Primary Mirror Segment Assemblies (PMSAs) are each actively controlled in rigid body position via six hexapod actuators. Each of the PMSAs additionally has a radius of curvature actuator. The mirrors are stowed to the mirror support structure to survive the launch environment and then must be deployed 12.5 mm to reach the nominally deployed position before the Wavefront Sensing & Control (WFSC) alignment and phasing process begins. JWST requires testing of the full optical system in a Cryogenic Vacuum (CV) environment before launch. The cryo vacuum test campaign was executed in Chamber A at the Johnson Space Center (JSC) in Houston Texas. The test campaign consisted of an ambient vacuum test, a cooldown test, a cryo stable test at 65 Kelvin, a warmup test, and finally a second ambient vacuum test. Part of that test campaign was the functional and performance testing of the hexapod actuators on the flight mirrors. This paper will describe the testing that was performed on all 132 hexapod and radius of curvature actuators. The test campaign first tests actuators individually then tested how the actuators perform in the hexapod system. Telemetry from flight sensors on the actuators and measurements from external metrology devices such as interferometers, photogrammetry systems and image analysis was used to demonstrate the performance of the JWST actuators. The mirror move commanding process was exercised extensively during the JSC CV test and many examples of accurately commanded moves occurred. The PMSA and SMA actuators performed extremely well during the JSC CV test, and we have demonstrated that the actuators are fully functional both at ambient and cryo temperatures and that the mirrors will go to their commanded positions with the accuracy needed to phase and align the telescope.
NASA’s James Webb Space Telescope (JWST) is a 6.6m diameter, segmented, deployable telescope for cryogenic IR space astronomy. The JWST Observatory architecture includes the Optical Telescope Element (OTE) and the Integrated Science Instrument Module (ISIM) element which contains four science instruments (SIs). Prior to integration with the spacecraft, the JWST optical assembly is put through rigorous launch condition environmental testing. This work reports on the metrology operations conducted to measure changes in subassembly alignment, including the primary mirror segments, the secondary mirror to its support structure, the tertiary mirror assembly to the backplane of the telescope and ISIM.
NASA’s James Webb Space Telescope (JWST) is a 6.6m diameter, segmented, deployable telescope for cryogenic IR space astronomy. The JWST Observatory architecture includes the Optical Telescope Element (OTE) and the Integrated Science Instrument Module (ISIM) element which contains four science instruments (SI), including a guider. The SIs and guider are mounted to a composite metering structure with outer envelope approximate measurements of 2.2x2.2x1.7m. These SI units are integrated to the ISIM structure and optically tested at NASA Goddard Space Flight Center as an instrument suite using an Optical telescope element SIMulator (OSIM). OSIM is a high-fidelity, cryogenic JWST simulator that features a ~1.5m diameter powered mirror. The SIs are aligned to the flight structure’s coordinate system under ambient, clean room conditions using opto-mechanical metrology and customized interfaces. OSIM is aligned to the ISIM mechanical coordinate system at the cryogenic operating temperature via internal mechanisms and feedback from alignment sensors and metrology in six degrees of freedom. SI performance, including focus, pupil shear, pupil roll, boresight, wavefront error, and image quality, is evaluated at the operating temperature using OSIM. This work reports on the as-run ambient assembly and ambient alignment steps for the flight ISIM, including SI interface fixtures and customization and kinematic mount adjustment. The ISIM alignment plan consists of multiple steps to meet the “absolute” alignment requirements of the SIs and OSIM to the flight coordinate system. In this paper, we focus on key aspects of absolute, optical-mechanical alignment. We discuss various metrology and alignment techniques. In addition, we summarize our approach for dealing with and the results of ground-test factors, such as gravity.
KEYWORDS: James Webb Space Telescope, Cryogenics, Space telescopes, Optical testing, Optical components, Sensors, Signal attenuation, Lamps, Tungsten, Calibration
NASA’s James Webb Space Telescope (JWST) is a 6.5 m diameter, segmented, deployable telescope for cryogenic infrared space astronomy (~40 K). The JWST Observatory architecture includes the Optical Telescope Element (OTE) and the Integrated Science Instrument Module (ISIM) element that contains four science instruments (SIs), including a guider. The SI and guider units are integrated to the ISIM structure and optically tested at NASA Goddard Space Flight Center as an instrument suite using a telescope simulator (Optical Telescope Element SIMulator; OSIM). OSIM is a high-fidelity, cryogenic JWST telescope simulator that features a ~1.5m diameter powered mirror. The SIs are aligned to the flight structure’s coordinate system under ambient, clean room conditions using optomechanical metrology and customized interfaces. OSIM is aligned to the ISIM mechanical coordinate system at the cryogenic operating temperature via internal mechanisms and feedback from alignment sensors and metrology in six degrees of freedom. SI performance, including focus, pupil shear, pupil roll, boresight, wavefront error, and image quality, is evaluated at the operating temperature using OSIM. The comprehensive optical test plans include drafting OSIM source configurations for thousands of exposures ahead of the start of a cryogenic test campaign. We describe how we predicted the performance of OSIM light sources illuminating the ISIM detectors to aide in drafting these optical tests before a test campaign began. We also discuss the actual challenges and successes of those exposure predictions encountered during a test campaign to fulfill the demands of the ISIM optical performance verification.
KEYWORDS: James Webb Space Telescope, Optical components, Space telescopes, Optical testing, Sensors, Calibration, Data modeling, Human-machine interfaces, Error analysis, Analytical research
NASA’s James Webb Space Telescope (JWST) is a 6.5m diameter, segmented, deployable telescope for cryogenic IR space astronomy. The JWST Observatory includes the Optical Telescope Element (OTE) and the Integrated Science Instrument Module (ISIM), that contains four science instruments (SI) and the Fine Guidance Sensor (FGS). The SIs are mounted to a composite metering structure. The SIs and FGS were integrated to the ISIM structure and optically tested at NASA's Goddard Space Flight Center using the Optical Telescope Element SIMulator (OSIM). OSIM is a full-field, cryogenic JWST telescope simulator. SI performance, including alignment and wavefront error, was evaluated using OSIM. We describe test and analysis methods for optical performance verification of the ISIM Element, with an emphasis on the processes used to plan and execute the test. The complexity of ISIM and OSIM drove us to develop a software tool for test planning that allows for configuration control of observations, implementation of associated scripts, and management of hardware and software limits and constraints, as well as tools for rapid data evaluation, and flexible re-planning in response to the unexpected. As examples of our test and analysis approach, we discuss how factors such as the ground test thermal environment are compensated in alignment. We describe how these innovative methods for test planning and execution and post-test analysis were instrumental in the verification program for the ISIM element, with enough information to allow the reader to consider these innovations and lessons learned in this successful effort in their future testing for other programs.
NASA’s James Webb Space Telescope (JWST) is a 6.5m diameter, segmented, deployable telescope for cryogenic IR space astronomy (~40K). The JWST Observatory architecture includes the Optical Telescope Element (OTE) and the Integrated Science Instrument Module (ISIM) element that contains four science instruments (SI), including a guider. OSIM is a full field, cryogenic, optical simulator of the JWST OTE. It is the “Master Tool” for verifying the cryogenic alignment and optical performance of ISIM by providing simulated point source/star images to each of the four Science Instruments in ISIM. Included in OSIM is a Pupil Imaging Module (PIM) - a large format CCD used for measuring pupil alignment. Located at a virtual stop location within OSIM, the PIM records superimposed shadow images of pupil alignment reference (PAR) targets located in the OSIM and SI pupils. The OSIM Pupil Imaging Module was described by Brent Bos, et al, at SPIE in 2011 prior to ISIM testing. We have recently completed the third and final ISIM cryogenic performance verification test before ISIM was integrated with the OTE. In this paper, we describe PIM implementation, performance, and measurement results.
OSIM is a full field, cryogenic, optical simulator of the James Webb Space Telescope (JWST) Optical Telescope Element (OTE). It is the “Master Tool” for verifying the cryogenic alignment and optical performance of the JWST Integrated Science Instrument Module (ISIM) by providing simulated point source/star images individually or simultaneously to each of the four Science Instruments in ISIM. Additionally, each star image can be scanned in focus to support the evaluation of both image quality and best focus for each Science Instrument. OSIM has recently completed supporting the ISIM performance verification test campaign which spanned three separate cryogenic test campaigns over 3 years. In this paper, we describe the alignment to the JWST coordinate system at cryogenic temperatures, OSIM optical performance, repeatability, and its role in testing the cryogenic optical performance of the individual Science Instruments in addition to providing calibration data needed for flight operations.
In late 2015/early 2016, a major cryo-vacuum test was carried out for the Integrated Science Instrument Module (ISIM) of the James Webb Space Telescope (JWST). This test comprised the final cryo-certification and calibration test of the ISIM, after its ambient environmental test program (vibration, acoustics, EMI/EMC), and before its delivery for integration with the rest of the JWST observatory. Over the 108-day period of the round-the-clock test program, the full complement of ISIM flight instruments, structure, harness radiator, and electronics were put through a comprehensive program of thermal, optical, electrical, and operational tests. The test verified the health and excellent performance of the instruments and ISIM systems, proving the ISIM element’s readiness for integration with the telescope. We report here on the context, goals, setup, execution, and key results for this critical JWST milestone.
This will address Lessons Learned on the approaches that worked or did not work over various programs when integrating and aligning elements into fairly complex optical systems. The appropriate planning can prevent many unnecessary headaches and achieve the desired optical performance while optimizing integration efficiency.
Optical alignment and testing of the Integrated Science Instrument Module of the James Webb Space Telescope is underway. We describe the Optical Telescope Element Simulator used to feed the science instruments with point images of precisely known location and chief ray pointing, at appropriate wavelengths and flux levels, in vacuum and at operating temperature. The simulator's capabilities include a number of devices for in situ monitoring of source flux, wavefront error, pupil illumination, image position and chief ray angle. Taken together, these functions become a fascinating example of how the first order properties and constructs of an optical design (coordinate systems, image surface and pupil location) acquire measurable meaning in a real system. We illustrate these functions with experimental data, and describe the ray tracing system used to provide both pointing control during operation and analysis support subsequently. Prescription management takes the form of optimization and fitting. Our core tools employ a matrix/vector ray tracing model which proves broadly useful in optical engineering problems. We spell out its mathematical basis, and illustrate its use in ray tracing plane mirror systems relevant to optical metrology such as a pentaprism and corner cube.
Douglas Leviton, Thomas Anderjaska, James Badger, Tom Capon, Clinton Davis, Brent Dicks, William Eichhorn, Mario Garza, Corina Guishard, Shadan Haghani, Claef Hakun, Paul Haney, David Happs, Lars Hovmand, Madhu Kadari, Jeffrey Kirk, Richard Nyquist, F. David Robinson, Joseph Sullivan, Erin Wilson
The JWST Optical Telescope Element Simulator (OSIM) is a configurable, cryogenic, optical stimulus for high fidelity
ground characterization and calibration of JWST’s flight instruments. OSIM and its associated Beam Image Analyzer
(BIA) contain several ultra-precise, cryogenic mechanisms that enable OSIM to project point sources into the
instruments according to the same optical prescription as the flight telescope will image stars – correct in focal surface
position and chief ray angle. OSIM’s and BIA’s fifteen axes of mechanisms navigate according to redundant, cryogenic,
absolute, optical encoders – 32 in all operating at or below 100 K. OSIM’s encoder subsystem, the engineering
challenges met in its development, and the encoders’ sub-micron and sub-arcsecond performance are discussed.
Joe Sullivan, Bill Eichhorn, Rob von Handorf, Derek Sabatke, Nick Barr, Rich Nyquist, Bob Pederson, Rick Bennnett, Paul Volmer, Dave Happs, Adrian Nagle, Rick Ortiz, Tony Kouri, Paul Hauser, Jon Seerveld, Dave Kubalak, Brad Greeley, Claef Hakun, Doug Leviton, Qian Gong, Pam Davila, Ray Ohl, Jeff Kirk, Clint Davis, Jenny Chu, Erin Wilson, Bill Chang, Steve Mann, Robert Rashford, Corbett Smith
OSIM is a full field, cryogenic, optical simulator of the James Webb Space Telescope (JWST) Optical Telescope
Element (OTE). It provides simulated point source/star images for optical performance testing of the JWST Integrated
Science Instrument Module (ISIM). OSIM is currently being assembled at the Goddard Space Flight Center (GSFC).
In this paper, we describe the capabilities, design, manufacturing and integration status, and uses of the OSIM during the
optical test program of ISIM and the Science Instruments. Where applicable, the ISIM tests are also described.
The polarization behavior of the Leica Geosystems absolute distance meter is investigated in order to understand
measurement noise and dropouts sometimes observed when the instrument is used with fold mirrors. A Stokes-
Mueller calculus analysis suggests retardance in the fold elements is a likely culprit. We establish the heuristic
that for folds in a single plane, successful operation is obtained when the sum of the ellipsometric angle ▵ for
each element in single pass is an integer multiple of 180°. The heuristic is validated experimentally, and found
to have a tolerance in the range of ±12° to hold distance standard deviations to 10μm. Strategies to achieve this
condition include keeping angles of incidence near 90°, tuning with angle of incidence, and judicious selection of
mirror coatings.
The James Webb Space Telescope (JWST) is an infrared space telescope scheduled for launch in 2013. JWST has a 6.5 meter diameter deployable and segmented primary mirror, a deployable secondary mirror, and a deployable sun-shade. The optical train of JWST consists of the Optical Telescope Element (OTE), and the Integrated Science Instrument Module (ISIM), which contains four science instruments. When the four science instruments are integrated to ISIM at NASA Goddard Space Flight Center, the structure becomes the ISIM Element. The ISIM Element is assembled at ambient cleanroom conditions using theodolite, photogrammetry, and laser tracker metrology, but it operates at cryogenic temperature, and temperature-induced mechanical and alignment changes are measured using photogrammetry. The OTE simulator (OSIM) is a high-fidelity, cryogenic, telescope simulator that features a ~1.5 meter diameter powered mirror. OSIM is used to test the optical performance of the science instruments in the ISIM Element, including focus, pupil shear, and wavefront error. OSIM is aligned to the flight coordinate system in six degrees of freedom via OSIM-internal cryogenic mechanisms and feedback from alignment sensors. We highlight optical metrology methods, introduce the ISIM and the Science Instruments, describe the ambient alignment and test plan, the cryogenic test plan, and verification of optical performance of the ISIM Element in cryo-vacuum environment.
From its orbit around the Earth-Sun second Lagrange point some million miles from Earth, the James Webb Space Telescope
(JWST) will be uniquely suited to study early galaxy and star formation with its suite of infrared instruments.[1]
To maintain exceptional image quality using its 6.6 meter segmented primary mirror, wavefront sensing and control
(WFS&C) is vital to ensure the optical alignment of the telescope throughout the mission. After deployment of the observatory
structure and mirrors from the "folded" launch configuration, WFS&C is used to align the telescope[2], as well
as maintain that alignment. WFS&C verification includes the verification of the software and its incorporated algorithms,
along with the supporting aspects of the integrated ground segment, instrumentation, and telescope through increasing
levels of assembly. The software and process are verified with the Integrated Telescope Model (ITM), which is
a Matlab/Simulink integrated observatory model which interfaces to CodeV/OSLO/IDL. In addition to lower level testing,
the Near-Infrared Camera[3] (NIRCam) with its wavefront sensing optical components is verified with the other instruments
with a cryogenic optical telescope simulator (OSIM) before moving on to the final WFS&C testing in Chamber
A at the Johnson Space Center (JSC) where additional observatory verification occurs.
The James Webb Space Telescope (JWST) is a space-based, infrared observatory designed to study the early stages of
galaxy formation in the Universe. It is currently scheduled to be launched in 2013 and will go into orbit about the
second Lagrange point of the Sun-Earth system and passively cooled to 30-50 K to enable astronomical observations
from 0.6 to 28 μm. The JWST observatory consists of three primary elements: the spacecraft, the optical telescope
element (OTE) and the integrated science instrument module (ISIM). The ISIM Element primarily consists of a
mechanical metering structure, three science instruments and a fine guidance sensor with significant scientific capability.
One of the critical opto-mechanical alignments for mission success is the co-registration of the OTE exit pupil with the
entrance pupils of the ISIM instruments. To verify that the ISIM Element will be properly aligned with the nominal
OTE exit pupil when the two elements come together, we have developed a cryogenic pupil measurement test
architecture to measure three of the most critical pupil degrees-of-freedom during optical testing of the ISIM Element.
The pupil measurement scheme makes use of: specularly reflective pupil alignment references located inside of the
JWST instruments; ground support equipment that contains a pupil imaging module; an OTE simulator; and pupil
viewing channels in two of the JWST flight instruments. Current modeling and analysis activities indicate this
measurement approach will be able to verify pupil shear to an accuracy of 0.5-1%.
The James Webb Space Telescope Observatory will consist of three flight elements: (1) the Optical Telescope Element
(OTE), (2) the Integrated Science Instrument Module Element (ISIM), and (3) the Spacecraft Element. The ISIM
element consists of a composite bench structure that uses kinematic mounts to interface to each of the optical benches of
the three science instruments and the guider. The ISIM is also kinematically mounted to the telescope primary mirror
structure. An enclosure surrounds the ISIM structure, isolates the ISIM region thermally from the other thermal regions
of the Observatory, and serves as a radiator for the science instruments and guider. Cryogenic optical testing of the ISIM
Structure and the Science Instruments will be conducted at Goddard Space Flight Center using an optical telescope
simulator that is being developed by a team from Ball Aerospace and Goddard Space Flight Center, and other local
contractors. This simulator will be used to verify the performance of the ISIM element before delivery to the Northup
Grumman team for integration with the OTE. In this paper, we describe the O
OTE Sim TE Simulator (OSIM) and provide a brief
overview of the optical test program.
ulator
With a planned launch of 2013, NASA's James Webb Space Telescope (JWST) will be the premier space observatory
for astronomers worldwide. This infrared space telescope will be passively cooled to cryogenic temperatures in its solar
L2 orbit. The JWST Optical Telescope Element (OTE) features a 6.5 meter, segmented Primary Mirror, which focuses
light onto a Secondary Mirror and finally redirected into and through the Aft Optics Subsystem (AOS). The AOS
consists of an optical bench which aligns and supports the telescope's Tertiary Mirror and Fine Steering Mirror
Assemblies. This paper describes the unique cryogenic requirements and design of the JWST Beryllium AOS optical
bench. Key performance requirements are reviewed including: launch environment, the cryogenic operating environment
(nominally 39K), and optical alignment stability at cryogenic temperatures. The mechanical design approach utilizing
Beryllium as the structural material for the AOS Bench is described relative to meeting the driving requirements.
Material property verification, low and predictable material variability, and low thermal gradients across the structure are
also discussed.
The Wide Field Camera 3 (WFC3) instrument was designed and built to replace the Hubble Space Telescope (HST) instrument Wide Field and Planetary Camera 2 (WFPC2) and to provide improved ultra-violet through near infra-red imaging capability during the extended HST mission. The WFC3 instrument consists of a two-channel instrument providing diffraction-limited imaging across an average 160 arc second square field of view over 200 to 1000 nm on a 4k x 4k Si detector and an average 135 arc second square field of view over 850 to 1700 nm on a 1k x 1k HgCdTe detector. We describe the optical design and predicted performance of WFC3.
The Wide Field Camera 3 (WFC3) instrument was designed and built to replace the Hubble Space Telescope (HST) instrument Wide Field and Planetary Camera 2 (WF/PC2) and to provide improved ultra-violet through near infrared imaging capability over the extended HST mission. We describe the optical component integration, alignment, and performance testing of the optical bench assembly.
The James Webb Space Telescope (JWST) Secondary Mirror (SM) is a 738 mm edge-diameter convex hyperbola that will be operating at 30K. Due to JWST’s science and technical requirements, the requirements on the SM are relatively tight. Therefore highly accurate, rigorous cryogenic testing of the surface figure as well as the prescription is required. The optical testing of a convex mirror of this size has not been performed before at cryogenic temperatures. This paper discusses the testing approaches and configurations that are under consideration at Ball Aerospace & Technologies Corp. (BATC) for testing the JWST SM at cryogenic temperatures.
The Space Telescope Imaging Spectrograph (STIS) operates from the UV to near IR providing a general purpose, imaging spectroscopic capability. An internal, two mirror relay system corrects the spherical aberration and astigmatism present at the STIS field position. Low and medium resolution imaging spectroscopy is possible throughout the spectral range and over the 25 arcsecond UV and 52 arcsecond visible fields. High resolution echelle spectroscopy capability is also provided in the UV. Target acquisition is accomplished using the STIS cameras, either UV or visible; these cameras may also be used to provide broad band imaging over the complete spectral range or with the small selection of available bandpass filters. A wide selection of slits and apertures permit various combinations of spectral resolution and field size in all modes. On board calibration lamps provide wavelength calibration and flat fielding capability. We report here on the optical performance of STIS as determined during orbital verification.
The advanced camera for surveys (ACS), scheduled for installation on the HST observatory in December 1999, is nearing completion at Ball Aerospace. This versatile camera, comprising 3 detector systems covering the wavelength range from the far UV through 1.1 micron, a large complement of filters, polarizers, prism and grism dispersers and a coronagraph, must be fully characterized before launch. We present plans for the instrument-level optical performance verification and calibration which will be performed later this year. Our intent is to perform a comprehensive characterization of the ACS to facilitate plans for its use aborad HST and to optimize the scientific usefulness of the immense data volume that ACS will provide. In order to comply with the aggressive delivery schedule and relatively restrictive budget, the calibration program will make use of much of the tools and apparatus developed at Ball for previous HST instruments and the data acquisition process will be improved, applying the lessons learned from those earlier programs.
The STIS instrument was installed into HST in February 1997 during the Servicing Mission 2. It has almost completed checkout and is beginning its science program, and is working well. Several scientific demonstration observations were taken to illustrate some of the range of scientific uses and modes of observation of STIS.
The Refractive Aberration Simulator (RAS) produces an image field which matches the as- built Hubble Space Telescope (HST) image field to a very high degree at 632.8 nm. The instrument is used to provide HST-like aberrated image plane illumination to the COSTAR and FOC-STM instruments during the final performance verification operations. It is capable of providing up to 15 simultaneous inputs to the instruments or metrology equipment located at its image plane. It consists of 6 anti-reflection coated glass lenses, each requiring lateral positioning accuracy as fine as +/- 10 microns, axial positioning accuracy of +/- 140 microns, and angular positioning of +/- 12.7 arcseconds, a fiber coupled laser source system, removable aperture stops for providing obscured or unobscured wavefronts, and a three-axis positionable source plate with removable fiber couplers for measurement or alignment operations.
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