The James Webb Space Telescope (JWST) project has entered into a comprehensive integration and test (I and T) program that over the coming years will assemble and test the various elements of the observatory and verify the readiness of the integrated system for launch. Highlights of the I and T program include a sequence of cryo-vacuum tests of the Integrated Science Instrument Module (ISHvf), to be carried out at NASA's Goddard Space Flight Center (GSFC) and an end-to- end cryo-vacuum optical and thermal test - of unprecedented scale - of the telescope plus instruments at NASA's Johnson Space Center (JSC). The I and T program, as replanned for a 2018 launch readiness date, contains a number of risk-reduction features intended to maximize the prospects for success of the critical tests, leading to reduced cost and schedule risk for those activities. For the JSC test, these include enhancement of the precursor Pathfinder program, the addition of a second cryo-vacuum thermal test of the observatory's Core region, and enhancement of the subsystem level testing program for the cryo-cooler for the Mid-InfraRed Instrument (MlRl). We report here on the I and T program for JWST, focusing on the I and T path for the instruments and telescope, and on the status of the hardware and plans that support it.
The Integrated Science Instrument Module (ISIM) of the James Webb Space Telescope (JWST) is discussed from a
systems perspective with emphasis on development status and advanced technology aspects. The ISIM is one of
three elements that comprise the JWST space vehicle and is the science instrument payload of the JWST. The major
subsystems of this flight element and their build status are described.
KEYWORDS: Cryogenics, Interfaces, James Webb Space Telescope, Space telescopes, Sensors, Data acquisition, Telescopes, Composites, Space operations, Image processing
The Integrated Science Instrument Module (ISIM) of the James Webb Space Telescope (JWST) is discussed from a
systems perspective with emphasis on development status and advanced technology aspects. The ISIM is one of three
elements that comprise the JWST space vehicle and is the science instrument payload of the JWST. The major
subsystems of this flight element and their build status are described.
The James Webb Space Telescope Integrated Science Instrument Module utilizes two fixtures to
align the Optical Telescope Element Simulator (OSIM) to the coordinate systems established on the
ISIM and the ISIM Test Platform (ITP). These fixtures contain targets which are visible to the OSIM
Alignment Diagnostics Module (ADM). Requirements on these fixtures must be met under ambient and
cryogenic conditions. This paper discusses the cryogenic metrology involving Laser Radar
measurements through a chamber window that will be used to link photogrammetry target measurements
used during ISIM structure cryogenic verification and the ADM targets, including evaluation of
distortion introduced from the window.
The James Webb Space Telescope (JWST) is a general astrophysics mission which consists of a 6.6m diameter,
segmented, deployable telescope for cryogenic IR space astronomy (~35K). The JWST Observatory architecture
includes the Optical Telescope Element and the Integrated Science Instrument Module (ISIM) element that contains four
science instruments (SI) including a Guider.
The alignment philosophy of ISIM is such that the cryogenic changes in the alignment of the SI interfaces are captured in
the ISIM alignment error budget. The SIs are aligned to the structure's coordinate system under ambient, clean room
conditions using laser tracker and theodolite metrology. The ISIM structure is thermally cycled and temperature-induced
structural changes are concurrently measured with a photogrammetry metrology system to ensure they are within
requirements.
We compare the ISIM photogrammetry system performance to the ISIM metrology requirements and describe the
cryogenic data acquired to verify photogrammetry system level requirements, including measurement uncertainty. The
ISIM photogrammetry system is the baseline concept for future tests involving the Optical Telescope Element (OTE) and
Observatory level testing at Johnson Space Flight Center.
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.
KEYWORDS: Phase retrieval, Wavefronts, Sensors, James Webb Space Telescope, Wavefront sensors, Cryogenics, Monochromatic aberrations, Monte Carlo methods, Data modeling, Error analysis
Phase retrieval results are presented for the James Webb Space Telescope (JWST) Near InfraRed Spectrograph
(NIRSpec) demonstration model (DM). NIRSpec is one of five science instruments (SIs) comprising the Integrated
Science Instrument Module (ISIM); the NIRSpec is being built for the European Space Agency by a consortium led
by EADS Astrium GmbH. During this initial DM test campaign, focal-sweep images were collected over the
science field of view (FOV) for determining best focus at both ambient and cryogenic (cryo) temperature
environments, and these images were then used as input to the Hybrid Diversity Algorithm (HDA) for phase
retrieval, using Variable Sampling Mapping (VSM). Wavefront estimates from phase retrieval, an error budget, and
diagnostics used to assess phase retrieval stability and convergence are discussed. The ambient phase retrieval
results were compared against wavefront measurements taken with a Shack-Hartmann wavefront sensor.
The Mid Infrared Instrument (MIRI), one of the four instruments on the Integrated Science Instrument Module (ISIM) of
the James Webb Space Telescope (JWST), supports all of the science objectives of the observatory. MIRI optical
alignment is an important step in the verification process, directly affecting mission success. The MIRI optical alignment
is verified on the ground at the integrated ISIM level using an element in the MIRI Filter Wheel, the pupil alignment
reference (PAR), developed by NASA GSFC and provided to MIRI. It is a ~2.3g aluminum piece that has a flat,
specularly reflective, 3mm diameter surface in its center, with laser-etched fiducials within its aperture. The PAR is
illuminated via an optical stimulus (ground support equipment) and imaged using a pupil imaging camera, during the
ISIM test program in order to determine absolute and relative changes in the alignment that impact pupil shear and roll.
Here we describe the MIRI PAR; its physical properties and challenges during its design, manufacturing, and testing.
KEYWORDS: Cameras, Cryogenics, Photogrammetry, James Webb Space Telescope, Distortion, Error analysis, Metrology, Calibration, Received signal strength, Optical alignment
The alignment philosophy of the James Webb Space Telescope (JWST) Integrated Science Instrument
Module (ISIM) is such that the cryogenic changes in the alignment of the science instruments (SIs) and
telescope-related interfaces are captured in an alignment error budget. The SIs are aligned to the structure's
coordinate system under ambient, clean room conditions using laser tracker and theodolite metrology. The
ISIM structure is thermally cycled and temperature-induced mechanical and structural changes are
concurrently measured to ensure they are within the predicted boundaries.
We report on the ISIM photogrammetry system and its role in the cryogenic verification of the ISIM
structure. We describe the cryogenic metrology error budget and the analysis and testing that was
performed on the ISIM mockup, a full scale aluminum model of the ISIM structure, to ensure that the
system design allows the metrology goals to be met, including measurement repeatability and distortion
introduced from the camera canister windows.
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.
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
KEYWORDS: Photogrammetry, Nondestructive evaluation, Cameras, Metrology, James Webb Space Telescope, Cryogenics, Temperature metrology, Optical alignment, Space telescopes, Interfaces
The James Webb Space Telescope (JWST) is a 6.6m diameter, segmented, deployable telescope for cryogenic IR space
astronomy (~40K). The JWST Observatory architecture includes the Optical Telescope Element and the Integrated Science
Instrument Module (ISIM) element that contains four science instruments (SI) including a Guider. The ISIM structure must meet
its requirements at the ~40K cryogenic operating temperature.
The SIs are aligned to the structure's coordinate system under ambient, clean room conditions using laser tracker and theodolite
metrology. The ISIM structure is thermally cycled for stress relief and in order to measure temperature-induced mechanical,
structural changes. These ambient-to-cryogenic changes in the alignment of SI and OTE-related interfaces are an important
component in the JWST Observatory alignment plan and must be verified.
We report on the planning for and preliminary testing of a cryogenic metrology system for ISIM based on photogrammetry.
Photogrammetry is the measurement of the location of custom targets via triangulation using images obtained at a suite of digital
camera locations and orientations. We describe metrology system requirements, plans, and ambient photogrammetric
measurements of a mock-up of the ISIM structure to design targeting and obtain resolution estimates. We compare these
measurements with those taken from a well known ambient metrology system, namely, the Leica laser tracker system.
The James Webb Space Telescope's (JWST) Integrated Science Instrument Module (ISIM) contains the observatory's four science instruments and their support subsystems. During alignment and test of the integrated ISIM at NASA's Goddard Space Flight Center (GSFC), the Optical telescope element SIMulator (OSIM) will be used to optically stimulate the science instruments to verify their operation and performance. In this paper we present the design of two cryogenic alignment fixtures that will be used to align the OSIM to the ISIM during testing at GSFC. These fixtures, the Master Alignment Target Fixture (MATF) and the ISIM Alignment Target Fixture (IATF), will provide continuous, six degree of freedom feedback to OSIM during initial ambient alignment as well as during cryogenic vacuum testing. These fixtures will allow us to position the OSIM and detect OSIM-ISIM absolute alignment to better than 180 microns in translation and 540 micro-radians in rotation. We will provide a brief overview of the OSIM system and we will also discuss the relevance of these fixtures in the context of the overall ISIM alignment and test plan.
KEYWORDS: James Webb Space Telescope, Point spread functions, Space telescopes, Telescopes, Sensors, Code v, Linear filtering, Mirrors, Cameras, Wavefronts
The James Webb Space Telescope (JWST) is a segmented deployable telescope that will require on-orbit alignment
using the Near Infrared Camera as a wavefront sensor. The telescope will be aligned by adjusting seven degrees of
freedom on each of 18 primary mirror segments and five degrees of freedom on the secondary mirror to optimize the
performance of the telescope and camera at a wavelength of 2 microns. With the completion of these adjustments, the
telescope focus is set and the optical performance of each of the other science instruments should then be optimal
without making further telescope focus adjustments for each individual instrument. This alignment approach requires
confocality of the instruments after integration and alignment to the composite metering structure, which will be verified
during instrument level testing at Goddard Space Flight Center with a telescope optical simulator. In this paper, we
present the results from a study of several analytical approaches to determine the focus for each instrument. The goal of
the study is to compare the accuracies obtained for each method, and to select the most feasible for use during optical
testing.
This report describes the facility and experimental methods at the Goddard Space Flight Center Optics Branch for the measurement of the surface figure of cryogenically-cooled spherical mirrors using standard phase-shifting interferometry, with a standard uncertainty below 2nm rms. Two developmental silicon carbide mirrors were tested: both were spheres with radius of curvature of 600 mm, and clear apertures of 150 mm. The mirrors were cooled within a cryostat, and the surface figure error measured through a fused-silica window. The GSFC team developed methods to measure the change in surface figure with temperature (the cryo-change) with a combined standard uncertainty below 1 nm rms. This paper will present the measurement facility, methods, and uncertainty analysis.
The James Webb Space Telescope (JWST) Observatory, the follow-on mission to the Hubble Space Telescope and to the Spitzer Space Facility, will yield astounding breakthroughs in the realms of infrared space science. The science instrument suite for this Observatory will consist of a Near-Infrared Camera, a Near-Infrared Spectrograph, a Mid-Infrared Instrument with imager, coronagraph and integral field spectroscopy modes, and a Fine Guider System Instrument with both a Guider module and a Tunable Filter Module. In this paper we present an overview of the optical designs of the telescope and instruments.
The James Webb Space Telescope (JWST) is a space-based, infrared observatory designed to study the early stages of galaxy formation in the Universe. The telescope will be launched into orbit about the second Lagrange point and passively cooled to 30-50 K to enable astronomical observations from 0.6 to 28 μm. A group from the NASA Goddard Space Flight Center and the Northrop Grumman Space Technology prime contractor team has developed an optical and mechanical layout for the science instruments within the JWST field of view that satisfies the mission requirements. Four instruments required accommodation within the telescope’s field of view: a Near-Infrared Camera (NIRCam), a Near-Infrared Spectrometer (NIRSpec), a Mid-Infrared Instrument (MIRI) and a Fine Guidance Sensor (FGS) with a tunable filter module. The size and position of each instrument’s field of view allocation were developed through an iterative, concurrent engineering process involving key observatory stakeholders. While some of the system design considerations were those typically encountered during the development of an infrared observatory, others were unique to the deployable and controllable nature of JWST. This paper describes the optical and mechanical issues considered during the field of view layout development, as well as the supporting modeling and analysis activities.
This report describes the equipment, experimental methods, and first results at a new facility at the Goddard Space Flight Center Optics Branch for interferometric measurement of cryogenically-cooled spherical mirrors. A mirror is cooled to 80 K and 20 K within a cryostat; and its surface figure error is measured through a fused-silica window using standard phase-shifting interferometry. The first mirror tested was a concave spherical silicon foam-core mirror with a clear aperture of 120 mm. The optic surface was measured at room temperature outside the dewar using standard "absolute" techniques; and then the change in surface figure error within the dewar from room temperature to 80 K was measured, and the two measurements added to create a representation of the two-dimensional surface figure error at 80 K, with a combined standard uncertainty of 3.4 nm rms. The facility and techniques will be used to measure the surface figure error at 20K of prototype lightweight silicon carbide and Cesic mirrors developed by Galileo Avionica (Italy) for the European Space Agency (ESA).
This report describes the facility and experimental methods at the Goddard Space Flight Center Optics Branch for the measurement of the surface figure of cryogenically-cooled spherical mirrors using standard phase-shifting interferometry, with an uncertainty goal of 6 nm rms. The mirrors to be tested will be spheres with radius of curvature of 600 mm, and clear apertures of 120 - 150 mm. The optic surface will first be measured at room temperature using standard "absolute" techniques with an uncertainty of 2.6 nm rms; and then the change in surface figure error between room temperature and 20 K will be measured with an uncertainty goal of 5.4 nm rms. The mirror will be cooled within a cryostat, and its surface figure error measured through a fused-silica window. The facility and techniques are being developed to measure the cryogenic surface figure error of prototype lightweight mirrors being developed by the European Space Agency (ESA) and by US companies in SBIR's for NASA. This paper will present the measurement facility, methods and uncertainty analysis.
The NGST Wavefront Control Testbed (WCT) is a joint technology program managed by the Goddard Space Flight Center (GSFC) and the Jet Propulsion Laboratory (JPL) for the purpose of developing technologies relevant to the NGST optical system. The WCT provides a flexible testing environment that supports the development of wavefront sensing and control algorithms that may be used to align and control a segmented optical system. WCT is a modular system consisting of a Source Module (SM), Telescope Simulator Module (TSM) and an Aft-Optics (AO) bench. The SM incorporates multiple sources, neutral density filters and bandpass filters to provide a customized point source for the TSM. The telescope simulator module contains a flip-in mirror that selects between a small deformable mirror and three actively controlled spherical mirror segments. The TSM is capable of delivering a wide range of aberrated, unaberrated, continuous and segmented wavefronts to the AO optical bench for analysis. The AO bench consists of a series of reflective and transmissive optics that images the exit pupil of the TSM onto a 349 actuator deformable mirror that is used for wavefront correction. A Fast Steering Mirror (FSM) may be inserted into the system (AO bench) to investigate image stability and to compensate for systematic jitter when operated in a closed loop mode. We will describe the optical design and performance of the WCT hardware and discuss the impact of environmental factors on system performance.
A telescope simulator was built as part of the Nexus wavefront control testbed, an NGST technology experiment at NASA's Goddard Space Flight Center. This testbed was designed to demonstrate complete control of a segmented telescope, from initial capture of light, through coarse alignment and phasing, to fine phasing and wavefront control. The existing telescope simulator allows testing of the fine phasing and wavefront control steps. A small deformable mirror in the simulator allows generation of an unobscured aberrated wavefront, for use in exploring the range of measurement and correction using the testbed's image-based wavefront sensor and larger deformable mirror. An alternate path under development for the simulator will create a segmented wavefront using three spherical mirrors; three-degree-of-freedom mounts under each mirror enable alignment and phasing experiments that will cover most of the operation sequence. Details of the hardware design and performance will be presented.
By segmenting and folding the primary mirror, quite large telescopes can be packed into the nose cone of a rocket. Deployed after launch, initial optical performance can be quite poor, due to deployment errors, thermal deformation, fabrication errors and other causes. We describe an automatic control system for capturing, aligning, phasing, and deforming the optics of such a telescope, going from initial cm-level wavefront errors to diffraction-limited observatory operations. This system was developed for the Next Generation Space Telescope and is being tested on the NGST Wavefront Control Testbed.
This paper describes the results of a few of the initial series of tests being conducted with the first configuration of the Next Generation Space Telescope Wavefront sensing and Control Testbed (WCT1). WCT1 is a 1:1, f/16.6 re-imaging system, incorporating two deformable mirrors located at pupil conjugate positions with 6 actuators/diameter (SM/DM) and 20 actuators/diameter (AO/DM). A CCD on a precision stage is used for obtaining defocused images providing phase diversity for wavefront determination using phase retrieval. In a typical experiment, wavefront error is injected into the optical path with the SM/DM and then corrected using the more densely actuated AO/DM. Wavefront analysis is provided via a phase retrieval algorithm, and control software is used to reshape the AO/DM and correct the wavefront. A summary of the results of some initial tests are presented.
Control algorithms developed for coarse phasing the segmented mirrors of the Next Generation Space Telescope (NGST) are being tested in realistic modeling and on the NGST wavefront control testbed, also known as DCATT. A dispersed fringe sensor (DFS) is used to detect piston errors between mirror segments during the initial coarse phasing. Both experiments and modeling have shown that the DFS provides an accurate measurement of piston errors over a range from just under a millimeter to well under a micron.
An Integrated Product Team was formed to develop a detailed concept for optical test methodology for testing of the NGST individual primary, secondary and tertiary mirrors and the full telescope system on the ground. The large, lightweight, deployable primary mirror, and the cryogenic operating environment make optical testing of NGST OTA (Optical Testing Assembly) extremely challenging. A telescope of the complexity of NGST has never been built and tested on the ground in 1-g environment. A brief summary of the preliminary metrology test plan at the mirror component and telescope system level is presented.
Various efforts are underway to demonstrate hardware for the NGST. One such effort is the development of the DCATT testbed. This testbed is an NGST effort geared to demonstrating in hardware the end-to-end system functionality. The system includes a segmented telescope, active optics subsystem with a deformable mirror (DM), and a wavefront sensor. The degree to which the DCATT can demonstrate this functionality depends crucially on its performance. A system performance analysis of this testbed is presented. The analysis is based on the design of the DCATT developed by Goddard and JPL. In the analysis, the performance of the system as a function of key system factors is calculated. These factors include the following: control, environmental, fabrication, alignment, and design. The performance after correction by the DM is required to be diffraction-limited at a wavelength of 2.0 microns. The flowdown of this performance is called the corrected error budget. To fully characterize the testbed performance as a system, one must develop a budget for the performance of the system before action of the DM. The flowdown of this performance is called the uncorrected error budget. The top line of this budget is related to the correction capability of the DM.
In the summer of 1996, three study teams developed conceptual designs and mission architectures for the NGST. All three conceptual designs provided scientific capabilities that met or surpassed those envisioned by the Hubble Space Telescope and Beyond Committee. Each group highlighted areas of technology study included: deployable structures, lightweight optics, cryogenic optics and mechanisms, passive cooling, a non-orbit closed loop wavefront sensing and control. NASA and industry are currently planning to develop a series of ground testbeds and validation flights to demonstrate many of these technologies. The developmental cryogenic active telescope testbed (DCATT) is a system level testbed to be developed at Goddard Space Flight Center in three phases over an extended period of time. This testbed will combine an actively controlled telescope with the hardware and software elements of a closed loop wavefront sensing and control system to achieve diffraction limited imaging at 2 microns. We will present an overview of the system level requirements, a discussion of the optical design, and results of performance analyses for the Phase 1 ambient concept for DCATT.
As part of the technology validation strategy of the next generation space telescope (NGST), a system testbed is being developed at GSFC, in partnership with JPL and Marshall Space Flight Center, which will include al of the component functions envisioned in an NGST active optical system. The system will include an actively controlled, segmented primary mirror, actively controlled secondary, deformable, and fast steering mirrors, wavefront sensing optics, wavefront control algorithms, a telescope simulator module, and an interferometric wavefront sensor for use in comparing final obtained wavefronts from different tests. The developmental cryogenic active telescope testbed will be implemented in three phase. Phase 1 will focus on operating the testbed at ambient temperature. During Phase 2, a cryocapable segmented telescope will be developed and cooled to cryogenic temperature to investigate the impact on the ability to correct the wavefront and stabilize the image. In Phase 3, it is planned to incorporate industry developed flight-like components, such as figure controlled mirror segments, cryogenic, low hold power actuators, or different wavefront sensing and control hardware or software. A very important element of the program is the development and subsequent validation of the integrated multidisciplinary models. The phase 1 testbed objectives, plans, configuration, and design will be discussed.
There is no doubt that astronomy with the `new, improved' Hubble Space Telescope will significantly advance our knowledge and understanding of the universe for years to come. The Corrective Optics Space Telescope Axial Replacement (COSTAR) was designed to restore the image quality to nearly diffraction limited performance for three of the first generation instruments; the faint object camera, the faint object spectrograph, and the Goddard high resolution spectrograph. Spectacular images have been obtained from the faint object camera after the installation of the corrective optics during the first servicing mission in December of 1993. About 85% of the light in the central core of the corrected image is contained within a circle with a diameter of 0.2 arcsec. This is a vast improvement over the previous 15 to 17% encircled energies obtained before COSTAR. Clearly COSTAR is a success. One reason for the overwhelming success of COSTAR was the ambitious and comprehensive test program conducted by various groups throughout the program. For optical testing of COSTAR on the ground, engineers at Ball Aerospace designed and built the refractive Hubble simulator to produce known amounts of spherical aberration and astigmatism at specific points in the field of view. The design goal for this refractive aberrated simulator (RAS) was to match the aberrations of the Hubble Space Telescope to within (lambda) /20 rms over the field at a wavelength of 632.8 nm. When the COSTAR optics were combined with the RAS optics, the corrected COSTAR output images were produced. These COSTAR images were recorded with a high resolution 1024 by 1024 array CCD camera, the Ball image analyzer (BIA). The image quality criteria used for assessment of COSTAR performance was encircled energy in the COSTAR focal plane. This test with the BIA was very important because it was a direct measurement of the point spread function. But it was difficult with this test to say anything quantitative about the aberration content of the corrected images. Also, from only this test it was difficult to measure important pupil parameters, such as pupil intensity profiles and pupil sizes and location. To measure the COSTAR wavefront accurately and to determine pupil parameters, another very important test was performed on the COSTAR optics. A Hartmann test of the optical system consisting of the RAS and COSTAR was conducted by the Goddard Independent Verification Team (IVT). In this paper, we first describe the unique Hartmann sensor that was developed by the IVT. Then we briefly describe the RAS and COSTAR optical systems and the test setup. Finally, we present the results of the test and compare our results with results obtained from optical analysis and from image tests with the BIA.
Several wavefront sensing techniques were tested against a common aberrated beam. The error on the beam was predominantly spherical aberration. The techniques included Shack- Hartmann Test, Lateral Shear interferometry, Point Diffraction Interferometry, and a Knife Edge Test. Beam calibration was accomplished using Fizeau Interferometry.
Optical instruments designed for use with large telescopes need to be tested before being installed at their work site. This is especially true for space-based instruments. To perform these tests, an auxiliary optical system is required which simulates the telescope exit pupil. Two-mirror projection systems can be used for this purpose. In this paper the first-order geometric properties and third-order aberrations of the general two-mirror system used at finite conjugates are examined. Relations are given in terms of five design parameters: object distance, image distance, exit pupil size, and the two mirror magnifications. A particular application of these relations is presented for a system designed to simulate the HST, for ground testing of the next generation of scientific instruments to be installed in the observatory. We show that a sufficient number of degrees of freedom are available to meet requirements when both mirrors are conics.
Lyman/FUSE, the Far Ultraviolet Spectroscopic Explorer, is a proposed low earth orbit mission to explore the
1OO-16OGi spectra of diverse astronomical sources. The simultaneous design goals of high spectral resolution, high
sensitivity, high signal to noise ratio, limited slit imaging capability, wide spectral coverage, compactness, and high
stability were a formidable challenge. In the design, a Wolter type II glancing incidence telescope (70 cm aperture,
f/1O) feeds two spectroscopic channels. A boresighted fme error sensor is used to point the instrument. In the
4oo-16oc1i range, a 1.84m Rowland circle spectrograph uses five near normal incidence gratings with a common
MAMA detector. To achieve acceptable resolving power and limited imaging with a fast telescope, the grating
aberrations must be significantly reduced below those obtained with toroidal or ellipsoidal gratings. A modified
ellipsoidal grating is used to achieve resolving powers of 30000 in the three high resolution bands covering 91O-125Q.
A separate EUV channel will explore the 1OO-35O range with lower spectral and spatial resolution. The throughput
in this range is improved by more than an order of magnitude over the Extreme Ultraviolet Explorer (EUVE), when
EUVE is operating in its spectroscopic mode. The optical design and results of ray tracing studies are presented, as
well as the expected effective area in each channel.
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