Proceedings Volume 6265

Space Telescopes and Instrumentation I: Optical, Infrared, and Millimeter

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Proceedings Volume 6265

Space Telescopes and Instrumentation I: Optical, Infrared, and Millimeter

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Volume Details

Date Published: 20 July 2006
Contents: 31 Sessions, 135 Papers, 0 Presentations
Conference: SPIE Astronomical Telescopes + Instrumentation 2006
Volume Number: 6265

Table of Contents

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Table of Contents

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  • Plenary Session on the Search for Extra-Solar Planets
  • Roadmap Overviews
  • Current and Planned Missions: SPITZER
  • Current and Planned Missions: HERSCHEL
  • Current and Planned Missions: PLANCK
  • Current and Planned Missions: HUBBLE
  • Current and Planned Missions: SPICA
  • James Webb Space Telescope: Science and General Overview
  • James Webb Space Telescope: Testing
  • James Webb Space Telescope: Optical Telescope Element (OTE)
  • James Webb Space Telescope: Wavefront Sensing and Control
  • James Webb Space Telescope: Instruments
  • Terrestrial Planet Finder: Coronagraphy I
  • Terrestrial Planet Finder: Coronagraphy II
  • Terrestrial Planet Finder: Interferometry
  • Terrestrial Planet Finder: Other Concepts
  • Future Missions: Mission and Telescope Concepts I
  • Future Missions: Mission and Telescope Concepts II
  • Future Missions: Solar System Telescopes
  • Future Missions: Joint Dark Energy Mission
  • Future Missions: Infrastructure
  • Advanced Technologies: Instruments
  • Advanced Technologies: Materials
  • Advanced Technologies: Modeling
  • Advanced Technologies: Other
  • Poster Session: Current and Planned Missions
  • Poster Session: JWST
  • Poster Session: TPF
  • Poster Session: Future Mission Concepts
  • Poster Session: Future Telescope Concepts
  • Poster Session: Advanced Technologies
Plenary Session on the Search for Extra-Solar Planets
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Learning about other planetary systems from space
We only began to detect other planetary systems with the discovery of debris disks in 1983 with IRAS, followed by the great success of gravitational recoil measurements starting in 1995. We now know of many hundreds of them. Despite the phenomenal growth of this new field of study, our knowledge of each system is meager, strongly conditioned by observational limitations. In addition, our grasp of the ensemble properties is weak because of strong selection effects in the known samples. A series of new capabilities - Herschel, Kepler, WISE, SIM Planetquest, and JWST - will provide a systematic understanding by 2018, marking the 35th anniversary of the first IRAS detections. Specifically, we should have a good census of solar-type stars in habitable zones, a far better understanding of the evolution of terrestrial planets, and direct detections of a number of gas giants as well as new insights to their frequent migration into orbits very close to their stars and the consequences of this process for planetary systems in general.
Direct imaging of Earth-like planets from space (TPF-C)
Wesley A. Traub, Lisa Kaltenegger, Kenneth W. Jucks, et al.
The "big question" that the average person will ask an astronomer today is, "Are there Earth-like planets?" followed immediately by "Is there life on those planets?" We live in an age when we are privileged to be able to ask such a question, and have a reasonable expectation of receiving an answer, at least within the coming decade. As astronomers and physicists we are even more privileged to be the people who can provide those answers. This paper discusses the roles of four space missions that are planned by NASA to search for and characterize extrasolar planets: Kepler, Space Interferometer Mission (SIM-PlanetQuest), Terrestrial Planet Finder Coronagraph (TPF-C), and Terrestrial Planet finder Interferometer (TPF-I). The Kepler and SIM-PlanetQuest missions will search for and discover planets down to the few-Earth size and mass, around distant and nearby stars respectively. In favorable cases they will even be able to find Earth-size or mass planets. But to answer the questions "is a given planet habitable?" and "does it show signs of life?" we will need the TPF-C and TPF-I missions. Only these missions can isolate the light of the planet from the confusion of otherwise blinding starlight, and only these missions can perform spectroscopy on the planets. Visible and thermal infrared spectroscopy together will tell us if a planet is habitable and shows signs of life. TPF-C and TPF-I will build on the legacy of Kepler and SIM-PlanetQuest, and together these four missions will provide complete and unambiguous answers to our "big questions." This paper concentrates on the TPF-C mission.
Roadmap Overviews
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Mirror technology roadmap for optical/IR/FIR space telescopes
The NASA Advanced Telescope and Observatory (ATO) Capability Roadmap addresses technologies necessary for NASA to enable future space telescopes and observatories operating in all electromagnetic bands, from x-rays to millimeter waves, and including gravity-waves. It lists capability priorities derived from current and developing Space Missions Directorate (SMD) strategic roadmaps. Technology topics include optics; wavefront sensing and control and interferometry; distributed and advanced spacecraft systems; cryogenic and thermal control systems; large precision structure for observatories; and the infrastructure essential to future space telescopes and observatories. This paper summarizes optic technology capability requirements necessary to enable space telescopes from the UV to Far-Infared.
The technology roadmap for future ESA science missions
Marcos Bavdaz, David Lumb, Tone Peacock
The Science Programme of the European Space Agency (ESA) for the next decade is currently being defined, and it is expected that the first steps in its implementation will be taken in the coming year. The technology developments required will necessarily depend on this Program: Cosmic Visions 2015-2025 [1]. However for any suite of potential missions, the timely and systematic development of key technologies will be crucial for its success. While the details of the technologies required will mature as the programme and mission characteristics become clearer, it is still possible to identify at an early stage many of the key developments. In addition it is also possible to identify those technologies, which may be common to a number of potential future science missions. For example; large aperture deployable mirror systems are a common requirement for astrophysics-type missions although the design details differ significantly depending on wavelength. Another example is European-based near infrared sensor array technology, which embraces many areas of space science.
Current and Planned Missions: SPITZER
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The Spitzer Space Telescope: the first 30 months
We provide an overview of the design of the Spitzer Space Telescope and review scientific highlights from the first 30 months of on-orbit operations.
Spitzer space telescope: dark current and total noise prediction for InSb detector arrays in the infrared array camera (IRAC) for the post-cryogen era
Craig W. McMurtry, Judith L. Pipher, William J. Forrest
During the expected 5+ years of operation, the Spitzer Space Telescope is and will continue to produce outstanding infrared images and spectra, and greatly further scientific understanding of our universe. The Spitzer Space Telescope's instruments are cryogenically cooled to achieve low dark current and low noise. After the cryogens are exhausted, the Spitzer Space Telescope will only be cooled by passively radiating into space. The detector arrays in the IRAC instrument are expected to equilibrate at approximately 30K. The two shortest wavelength channels (3.6 and 4.5 micron) employ InSb detector arrays and are expected to function and perform with only a modest degradation in sensitivity. Thus, an extended mission is possible for Spitzer. We present the predicted dark current, noise, quantum efficiency and image residuals for the 3.6 and 4.5 micron IRAC channels in the post-cryogen era.
Current and Planned Missions: HERSCHEL
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Herschel-SPIRE: design, performance, and scientific capabilities
Matthew Griffin, Alain Abergel, Peter Ade, et al.
SPIRE, the Spectral and Photometric Imaging Receiver, is a submillimetre camera and spectrometer for the European Space Agency's Herschel Space Observatory. It comprises a three-band imaging photometer operating at 250, 360 and 520 μm, and an imaging Fourier Transform Spectrometer (FTS) covering 200-670 μm. The detectors are arrays of feedhorn-coupled NTD spider-web bolometers cooled to 0.3 K. The photometer field of view of is 4 x 8 arcmin., observed simultaneously in the three spectral bands. The FTS has an approximately circular field of view with a diameter of 2.6 arcmin., and employs a dual-beam configuration with broad-band intensity beam dividers to provide high efficiency and separated output and input ports. The spectral resolution can be adjusted between 0.04 and 2 cm-1 (resolving power of 20-1000 at 250 μm). The flight instrument is currently undergoing integration and test. The design of SPIRE is described, and the expected scientific performance is summarised, based on modelling and flight instrument test results.
The photodetector array camera and spectrometer (PACS) for the Herschel Space Observatory
Albrecht Poglitsch, Christoffel Waelkens, Otto H. Bauer, et al.
The Photodetector Array Camera and Spectrometer (PACS) is one of the three science instruments for ESA's far infrared and submillimeter observatory Herschel. It employs two Ge:Ga photoconductor arrays (stressed and unstressed) with 16 × 25 pixels, each, and two filled silicon bolometer arrays with 16 × 32 and 32 × 64 pixels, respectively, to perform imaging line spectroscopy and imaging photometry in the 60-210μm wavelength band. In photometry mode, it will simultaneously image two bands, 60-85μm or 85-130μm and 130-210μm, over a field of view of ~ 1.75' × 3.5', with full beam sampling in each band. In spectroscopy mode, it will image a field of ~50"×50", resolved into 5×5 pixels, with an instantaneous spectral coverage of ~1500 km/s and a spectral resolution of ~ 175 km/s. In both modes the performance is expected to be not far from background-noise limited, with sensitivities (5σ in 1h) of ~ 4 mJy or 3 - 20 ×10-18W/m2, respectively. We summarize the design of the instrument and its subunits, describe the observing modes in combination with the telescope pointing modes, report results from instrument level performance tests of the Qualification Model, and present our current prediction of the in-orbit performance of the instrument based on tests done at subunit level.
The Herschel/PACS 2560 bolometers imaging camera
Nicolas Billot, Patrick Agnèse, Jean-Louis Auguères, et al.
The development program of the flight model imaging camera for the PACS instrument on-board the Herschel spacecraft is nearing completion. This camera has two channels covering the 60 to 210 microns wavelength range. The focal plane of the short wavelength channel is made of a mosaic of 2×4 3-sides buttable bolometer arrays (16×16 pixels each) for a total of 2048 pixels, while the long wavelength channel has a mosaic of 2 of the same bolometer arrays for a total of 512 pixels. The 10 arrays have been fabricated, individually tested and integrated in the photometer. They represent the first filled arrays of fully collectively built bolometers with a cold multiplexed readout, allowing for a properly sampled coverage of the full instrument field of view. The camera has been fully characterized and the ground calibration campaign will take place after its delivery to the PACS consortium in mid 2006. The bolometers, working at a temperature of 300 mK, have a NEP close to the BLIP limit and an optical bandwidth of 4 to 5 Hz that will permit the mapping of large sky areas. This paper briefly presents the concept and technology of the detectors as well as the cryocooler and the warm electronics. Then we focus on the performances of the integrated focal planes (responsivity, NEP, low frequency noise, bandwidth).
Optical performance characterisation of HERSCHEL/SPIRE
Bruce Swinyard, Marc Ferlet, Kjetil Dohlen, et al.
The Spectral and Photometric Imaging Receiver (SPIRE) is one of three scientific instruments on ESA's Herschel Space Observatory. The instrument covers 200 to 670 μm with a three band photometric camera and a two band imaging Fourier Transform Spectrometer (IFTS). In this paper we discuss the performance of the optics of the instrument as determined during the pre-flight instrument testing to date. In particular we concentrate on the response of the instrument to a point source, the comparison between the visible light alignment and the infrared alignment and the effect of the optical performance on the overall instrument sensitivity. We compare the empirical performance of the instrument optics to that expected from elementary diffraction theory.
Preliminary results from Herschel-SPIRE flight instrument testing
Tanya Lim, Bruce Swinyard, Matthew Griffin, et al.
The Spectral and Photometric Imaging REceiver (SPIRE) is one of the three scientific instruments to fly on the European Space Agency's Herschel Space Observatory, and contains a three-band imaging submillimetre photometer and an imaging Fourier transform spectrometer. The flight model of the SPIRE cold focal plane unit has been built up in stages with a cold test campaign associated with each stage. The first campaign focusing on the spectrometer took place in early 2005 and the second campaign focusing on the photometer was in Autumn 2005. SPIRE is currently undergoing its third cold test campaign following cryogenic vibration testing. Test results to date show that the instrument is performing very well and in general meets not only its requirements but also most of its performance goals. We present an overview of the instrument tests performed to date, and the preliminary results.
Current and Planned Missions: PLANCK
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Calibration and testing of the Planck-LFI QM instrument
A. Mennella, B. Aja, E. Artal, et al.
In this paper we present the test results of the qualification model (QM) of the LFI instrument, which is being developed as part of the ESA Planck satellite. In particular we discuss the calibration plan which has defined the main requirements of the radiometric tests and of the experimental setups. Then we describe how these requirements have been implemented in the custom-developed cryo-facilities and present the main results. We conclude with a discussion of the lessons learned for the testing of the LFI Flight Model (FM).
Performances of the Planck-HFI cryogenic thermal control system
Christophe Leroy, Antoine Arondel, Jean-Philippe Bernard, et al.
The core of the High Frequency Instrument (HFI) on-board the Planck satellite consists of 52 bolometric detectors cooled at 0.1 Kelvin. In order to achieve such a low temperature, the HFI cryogenic architecture consists in several stages cooled using different active coolers. These generate weak thermal fluctuations on the HFI thermal stages. Without a dedicated thermal control system these fluctuations could produce unwanted systematic effects, altering the scientific data. The HFI thermal architecture allows to minimise these systematic effects, thanks to passive and active control systems described in this paper. The passive and active systems are used to damp the high and low frequency fluctuations respectively. The last results regarding the tests of the HFI passive and active thermal control systems are presented here. The thermal transfer functions measurement between active coolers and HFI cryogenic stages will be presented first. Then the stability of the temperatures obtained on the various cryogenic stages with PID regulations systems will be checked through analysis of their power spectrum density.
Current and Planned Missions: HUBBLE
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Status and performance of HST/wide field camera 3
Randy A. Kimble, John W. MacKenty, Robert W. O'Connell
Wide Field Camera 3 (WFC3) is a powerful UV/visible/near-infrared camera currently in development for installation into the Hubble Space Telescope. WFC3 provides two imaging channels. The UVIS channel features a 4096 x 4096 pixel CCD focal plane covering 200 to 1000 nm wavelengths with a 160 x 160 arcsec field of view. The UVIS channel provides unprecedented sensitivity and field of view in the near ultraviolet for HST. It is particularly well suited for studies of the star formation history of local galaxies and clusters, searches for Lyman alpha dropouts at moderate redshift, and searches for low surface brightness structures against the dark UV sky background. The IR channel features a 1024 x 1024 pixel HgCdTe focal plane covering 800 to 1700 nm with a 139 x 123 arcsec field of view, providing a major advance in IR survey efficiency for HST. IR channel science goals include studies of dark energy, galaxy formation at high redshift, and star formation. The instrument is being prepared for launch as part of HST Servicing Mission 4, tentatively scheduled for late 2007, contingent upon formal approval of shuttle-based servicing after successful shuttle return-to-flight. We report here on the status and performance of WFC3.
Wide-field camera 3 ground testing and calibration
H. Bushouse, S. Baggett, T. Brown, et al.
Wide Field Camera 3 (WFC3), a panchromatic imager being developed for the Hubble Space Telescope (HST), is now fully integrated and has undergone extensive ground testing at Goddard Space Flight Center, in both ambient and thermal-vacuum test environments. The thermal-vacuum testing marks the first time that both of the WFC3 UV/Visible and IR channels have been operated and characterized in flight-like conditions. The testing processes are completely automated, with WFC3 and the optical stimulus that is used to provide external targets and sources being commanded by coordinated computer scripts. All test data are captured and stored in the long-term Hubble Data Archive. A full suite of instrument calibration tests have been performed, including measurements of detector properties such as dark current, read noise, flat field response, gain, linearity, and persistence, as well as total system throughput, encircled energy, grism dispersions, IR thermal background, and image stability tests. Nearly all instrument characteristics have been shown to meet or exceed expectations and requirements. Solutions to all issues discovered during testing are in the process of being implemented and will be verified during future ground tests.
Current and Planned Missions: SPICA
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ESI: the far-infrared instrument for the SPICA mission
Bruce Swinyard
The proposed JAXA/ISAS SPICA mission will have a cooled 3.5 m mirror and will be the next step forward in sensitivity in far infrared astronomy. We describe the scientific case for an imaging Far Infrared Spectrometer for the SPICA mission and the ongoing design study being carried out by European scientists.
James Webb Space Telescope: Science and General Overview
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Science with the James Webb space telescope
The scientific capabilities of the James Webb Space Telescope (JWST) fall into four themes. The End of the Dark Ages: First Light and Reionization theme seeks to identify the first luminous sources to form and to determine the ionization history of the universe. The Assembly of Galaxies theme seeks to determine how galaxies and the dark matter, gas, stars, metals, morphological structures, and active nuclei within them evolved from the epoch of reionization to the present. The Birth of Stars and Protoplanetary Systems theme seeks to unravel the birth and early evolution of stars, from infall onto dust-enshrouded protostars, to the genesis of planetary systems. Planetary Systems and the Origins of Life theme seeks to determine the physical and chemical properties of planetary systems around nearby stars and of our own, and investigate the potential for life in those systems. To enable these for science themes, JWST will be a large (6.5m) cold (50K) telescope with four instruments, capable of imaging and spectroscopy from 0.6 to 29 microns wavelength.
Coronagraphic Exploration Camera (CorECam)
The CorECam Instrument Concept Study (ICS) addressed the requirements and science program for the Terrestrial Planet Finder Coronagraph's (TPF-C) primary camera. CorECam provides a simple interface to TPF-C's Starlight Suppression System (SSS) which would be provided by the TPF-C Program, and comprises camera modules providing visible, and near-infrared (NIR) camera focal plane imaging. In its primary operating mode, CorECam will conduct the core science program of TPF-C, detecting terrestrial planets at visible wavelengths. CorECam additionally provides the imaging capabilities to characterize terrestrial planets, and conduct an extended science program focused on investigating the nature of the exosolar systems in which terrestrial planets are detected. In order to evaluate the performance of CorECam we developed a comprehensive, end-to-end model using OSCAR which has provided a number of key conclusions on the robustness of the TPF-C baseline design, and allows investigation of alternative techniques for wavefront sensing and control. CorECam recommends photon counting detectors be baselined for imaging with TPF-C since they provide mitigations against the background radiation environment, improved sensitivity and facilitate alternative WFSC approaches.
James Webb Space Telescope: Testing
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New approach to cryogenic optical testing the James Webb Space Telescope
The James Webb Space Telescope is a 6.5 meter segmented cryogenic telescope scheduled to be launched in 2013. A key development challenge has been the cost and complexity of cryogenic optical testing of the telescope and observatory. A new approach to cryogenic optical testing the telescope and observatory has been developed that eliminates the need for a complex and expensive cryogenic optical test tower and which also allows all critical test equipment to be external to the chamber and accessible during testing. This paper summarizes the motivation for this change, the conceptual design of it, and status of implementing it.
The JWST backplane stability test article: a critical technology demonstration
Jonathan Arenberg, Larry Gilman, Nick Abbruzze, et al.
The unprecedented stability requirements of JWST structures can only be conclusively verified by a combination of analysis and ground test. Given the order of magnitude of the expected motions of the backplane due to thermal distortion and the high level of confidence required on such a large and important project, the demonstration of the ability to verify the thermal distortion analysis to the levels required is a critical need for the program. The demonstration of these analysis tools, in process metrology and manufacturing processes increases the technology readiness level of the backplane to required levels. To develop this critical technology, the Backplane Stability Test Article (BSTA) was added to the JWST program. The BSTA is a representative substructure for the full flight backplane, manufactured using the same resources, materials and processes. The BSTA will be subject to environmental testing and its deformation and damping properties measured. The thermally induced deformation will be compared with predicted deformations to demonstrate the ability to predict thermal deformation to the levels required. This paper will review the key features and requirements of the BSTA and its analysis, the test, measurement and data collection plans.
Demonstration of the James Webb Space Telescope commissioning on the JWST testbed telescope
D. Scott Acton, Timothy Towell, John Schwenker, et al.
The one-meter Testbed Telescope (TBT) has been developed at Ball Aerospace to facilitate the design and implementation of the wavefront sensing and control (WFS&C) capabilities of the James Webb Space Telescope (JWST). The TBT is used to develop and verify the WFS&C algorithms, check the communication interfaces, validate the WFS&C optical components and actuators, and provide risk reduction opportunities for test approaches for later full-scale cryogenic vacuum testing of the observatory. In addition, the TBT provides a vital opportunity to demonstrate the entire WFS&C commissioning process. This paper describes recent WFS&C commissioning experiments that have been performed on the TBT.
James Webb Space Telescope: Optical Telescope Element (OTE)
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James Webb Space Telescope Observatory stray light performance
The James Webb Space Telescope (JWST) is a large space based astronomical telescope that will operate at cryogenic temperatures. The architecture has the telescope exposed to space, with a large sun shield providing thermal isolation and protection from direct illumination from the sun. The instruments will have the capability to observe over a spectral range from 0.6μm to 29 μm wavelengths. The following paper will present the stray light analysis results characterizing the stray light getting to the instrument focal planes from the full galactic sky, zodiacal background, bright objects near the line of sight, and scattered earth and moon shine. The amount of self-generated infrared background from the Observatory that reaches the instrument focal planes will also be presented.
Status of the JWST optical telescope element
Charlie Atkinson, Scott Texter, Robert Hellekson, et al.
Significant progress has been made in the development of the Optical Telescope Element (OTE), one of three elements of the James Webb Space Telescope (JWST) Observatory. To achieve the 25 square meters of collecting area, JWST will employ the first segmented, deployed optical telescope, requiring a wavefront sensing and control (WFS&C) system to align and phase the telescope's optics, while operating at cryogenic temperatures. The OTE is comprised of the optical components of the three mirror anastigmat and a steering mirror, the structure to deploy and support the optics, the WFS&C system to determine the adjustments necessary to align them, the electronics to control them, and the thermal components to manage the OTE temperatures. Technology development and risk reduction hardware are being produced to address critical technical areas. Subsystem development has progressed with the successful completion of several key design reviews and significant progress on the production of the flight Primary Mirror Segment Assemblies.
BLISS for SPICA: far-IR spectroscopy at the background limit
We present concepts for the background-limited infrared-submillimeter spectrograph (BLISS) for the Japanese SPICA mission to launch early next decade. SPICA will be a 3.5-meter telescope cooled to below 5 K, and offers the potential for far-IR observations limited only by the zodiacal dust emission. BLISS will provide moderate-resolution (R 1000) spectroscopy at this background limit throughout the 40-600 μm band. With sensitivities below 10-20 Wm2 in modest integrations, BLISS-SPICA will enable the first survey spectroscopy of the redshift 0.5 to 5 galaxies which produce the far-IR background. Both WaFIRS waveguide grating spectrometers, and new compact cross-dispersed echelle grating designs are under consideration. Detectors must have sensitivities around 3x10-20 W/√Hz and have good efficiency. The most promising near-term approaches to cover the full band are transition-edge bolometers cooled to ~50 mK with an adiabatic demagnetization refrigerator.
An overview of optical fabrication of the JWST mirror segments at Tinsley
Glen C. Cole, Robert Garfield, Tracy Peters, et al.
The context, preparation, and facilitization of Tinsley to produce the 18 JWST primary mirror segments are described, and an overview of the Project at Tinsley is presented. The mirror segments are aggressively lightweighted, approximately hexagonal, and approximately 1.32m flat-to-flat. While the optical finishing approach is strongly seated in Tinsley's Computer Controlled Optical Surfacing (CCOSTM) technology, extensions have been implemented to address safe and efficient nearly simultaneous flow of the high value mirror segments through numerous cycles of optical finishing, processing and metrology steps. JWST will operate at cryogenic temperatures, and Tinsley will do final figuring from a "hit map" made during cryogenic testing at the NASA MSFC X-Ray Calibration Facility (XRCF). A formal beryllium safety protocol has been established throughout. Extensive handling fixtures assure that the mirrors are moved from station to station experiencing low accelerations. A rigorous qualification process is applied to each new fixture, machine and instrument. Special problems of cryo figuring, and co-finishing the segments to stringent specifications are described.
Point-spread function modeling for the James Webb Space Telescope
Colin Cox, Philip Hodge
We describe software which models the Point Spread Function of the James Webb Space Telescope. The software is designed to be expandable to incorporate optical and instrument data as they become available. An initial model of the detector used in the Near Infra-red Camera has been used to generate realistic stellar images.
James Webb Space Telescope: Wavefront Sensing and Control
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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
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. 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. WFS&C design architecture includes using the Near-Infrared Camera (NIRCam) to provide imagery for ground-resident image processing algorithms which determine the optimal alignment of the telescope. There are two distinct mission phases for WFS&C, both of which use algorithms and NIRCam imagery to determine the required segment updates. For the first phase, WFS&C commissioning, the telescope is taken from its initial deployed state with each of the 18 primary mirror segments acting like independent telescopes, to its final phased state with each segment acting in concert as a part of a single mirror. The second phase, Wavefront Monitoring and Maintenance, continues for the rest of the mission. Here the wavefront quality is evaluated, and when needed, the mirror positions are updated to bring it back to an optimal configuration. This paper discusses the concept of operations for the commissioning and on-going maintenance of the telescope alignment using WFS&C.
Performance of dispersed fringe sensor in the presence of segmented mirror aberrations: modeling and simulation
Dispersed Fringe Sensing (DFS) is an efficient and robust method for coarse phasing of a segmented primary mirror such as the James Webb Space Telescope (JWST). In this paper, modeling and simulations are used to study the effect of segmented mirror aberrations on the DFS fringe image, its signals, and the piston detection accuracy. The simulations show that due to the pixilation spatial filter effect from DFS signal extraction the effect of wavefront error is reduced. In addition, the DFS algorithm is more robust against wavefront aberration when the multi-trace DFS approach is used. We have also studied the JWST Dispersed Hartmann Sensor (DHS) performance in presence of wavefront aberrations caused by the gravity sag and we have used the scaled gravity sag to explore the JWST DHS performance relationship with the level of the wavefront aberration. As a special case of aberration we have also included the effect from line-of-sight jitter in the JWST modeling study.
Verification of the James Webb Space Telescope coarse phase sensor using the Keck Telescope
Marc Albanese, Allan Wirth, Andrew Jankevics, et al.
The James Webb Space Telescope (JWST) Coarse Phase Sensor utilizes Dispersed Hartmann Sensing (DHS)1 to measure the inter-segment piston errors of the primary mirror. The DHS technique was tested on the Keck Telescope. Two DHS optical components were built to mate with the Keck optical and mechanical interfaces. DHS images were acquired using 20 different primary mirror configurations. The mirror configurations consisted of random segment pistons applied to 18 of the 36 segments. The inter-segment piston errors ranged from phased (approximately 0 μm) to as large as ±25 μm. Two broadband exposures were taken for each primary mirror configuration: one for the DHS component situated at 0°, and one for the DHS component situated at 60°. Finally, a "closed-loop" DHS sensing and control experiment was performed. Sensing algorithms developed by both Adaptive Optics Associates (AOA) and the Jet Propulsion Laboratory (JPL)2 were applied to the collected DHS images. The inter-segment piston errors determined by the AOA and JPL algorithms were compared to the actual piston steps. The data clearly demonstrates that the DHS works quite well as an estimator of segment-to-segment piston errors using stellar sources.
James Webb Space Telescope primary mirror deployment ambiguity effects
The James Webb Space Telescope (JWST) is a large space based astronomical telescope employing a primary mirror constructed of 18 hexagonal segments to create its large collecting area, and an image based wavefront sensor at the telescope focal plane to provide knowledge of system alignment. The combination of image sensing at the focal plane over a subset of the telescope's field of view and the resolution of the wavefront sensing system gives rise to a global alignment ambiguity between the primary and secondary mirror. This paper describes the possible magnitude of wavefront error impact outside the alignment region of the FOV for various global alignment modes under the constraint of the various ambiguity limiting factors at the currently estimated wavefront sensing resolution limit.
Phase retrieval algorithm for JWST Flight and Testbed Telescope
An image-based wavefront sensing and control algorithm for the James Webb Space Telescope (JWST) is presented. The algorithm heritage is discussed in addition to implications for algorithm performance dictated by NASA's Technology Readiness Level (TRL) 6. The algorithm uses feedback through an adaptive diversity function to avoid the need for phase-unwrapping post-processing steps. Algorithm results are demonstrated using JWST Testbed Telescope (TBT) commissioning data and the accuracy is assessed by comparison with interferometer results on a multi-wave phase aberration. Strategies for minimizing aliasing artifacts in the recovered phase are presented and orthogonal basis functions are implemented for representing wavefronts in irregular hexagonal apertures. Algorithm implementation on a parallel cluster of high-speed digital signal processors (DSPs) is also discussed.
Focus determination for the James Webb Space Telescope science instruments: a survey of methods
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.
James Webb Space Telescope: Instruments
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The James Webb Space Telescope integrated science instrument module
Matthew A. Greenhouse, Leslye A. Boyce, Stuart D. Glazer, et al.
The Integrated Science Instrument Module of the James Webb Space Telescope is described from a systems perspective with emphasis on unique and advanced technology aspects. The major subsystems of this flight element are described including: structure, thermal, command and data handling, and software.
The MIRI Medium Resolution Spectrometer for the James Webb Space Telescope
M. Wells, D. Lee, A. Oudenhuysen, et al.
The MIRI Medium Resolution Spectrometer (MIRI-MRS) will increase the sensitivity of astronomical spectroscopy at thermal infrared wavelengths (from 5 to 28 microns), by a factor of 1000 over the best that can be achieved by existing ground-based instruments. This leap in performance is further enhanced by the first use at these wavelengths of all reflective Integral Field Units (image slicers) to provide the spectrometer with a rectangular field of view with a shortest dimension of 3.5 arcseconds. We describe the optical design of the MRS and present predictions for its delivered image quality.
Terrestrial Planet Finder: Coronagraphy I
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A nulling coronagraph for TPF-C
The nulling coronagraph is one of 5 instrument concepts selected by NASA for study for potential use in the TPF-C mission. This concept for extreme starlight suppression has two major components, a nulling interferometer to suppress the starlight to ~10-10 per airy spot within 2 λ/D of the star, and a calibration interferometer to measure the residual scattered starlight. The ability to work at 2 λ/D dramatically improves the science throughput of a space based coronagraph like TPF-C. The calibration interferometer is an equally important part of the starlight suppression system. It measures the measures the wavefront of the scattered starlight with very high SNR, to 0.05nm in less than 5 minutes on a 5mag star. In addition, the post coronagraph wavefront sensor will be used to measure the residual scattered light after the coronagraph and subtract it in post processing to 1~2x10-11 to enable detection of an Earthlike planet with a SNR of 5~10.
Toward 1010 contrast for terrestrial exoplanet detection: demonstration of wavefront correction in a shaped-pupil coronagraph
The Shaped Pupil Coronagraph (SPC) is a high-contrast imaging system pioneered at Princeton for detection of extra-solar earthlike planets. It is designed to achieve 10-10 contrast at an inner working angle of 4λ/D. However, a critical requirement in attaining this contrast level in practice is the ability to control wavefront phase and amplitude aberrations to at least λ/104 in rms phase and 1/1000 rms amplitude, respectively. Furthermore, this has to be maintained over a large spectral band. The High Contrast Imaging Testbed (HCIT) at the Jet Propulsion Lab (JPL) is a state-of-the-art facility for studying high contrast imaging systems and fine wavefront control methods. It consists of a vacuum chamber containing a configurable coronagraph setup with a Xinetics deformable mirror. In this paper, we present the results of testing Princeton's SPC in JPL's HCIT. In particular, we present the achievement of 4x10-8 contrast using a speckle nulling algorithm, and demonstrate that this contrast is maintained across wavelengths of 785, 836nm, and for broadband light having 10% bandwidth around 800nm.
The visible nulling coronagraph: architecture definition and technology development status
We describe the advantages of a nulling coronagraph instrument behind a single aperture space telescope for detection and spectroscopy of Earth-like extrasolar planets in visible light. Our concept synthesizes a nulling interferometer by shearing the telescope pupil into multiple beams. They are recombined with a pseudo-achromatic pi-phase shift in one arm to produce a deep null on-axis, attenuating the starlight, while simultaneously transmitting the off-axis planet light. Our nulling configuration includes methods to mitigate stellar leakage, such as spatial filtering by a coherent array of single mode fibers, balancing amplitude and phase with a segmented deformable mirror, and post-starlight suppression wavefront sensing and control. With diffraction limited telescope optics and similar quality components in the optical train (λ/20), suppression of the starlight to 10-10 is readily achievable. We describe key features of the architecture and analysis, present the status of key experiments to demonstrate wide bandwidth null depth, and present the status of component technology development.
Extrasolar planetary imaging coronagraph (EPIC)
Mark Clampin, Gary Melnick, Richard Lyon, et al.
The Extrasolar Planetary Imaging Coronagraph (EPIC) is a proposed NASA Discovery mission to image and characterize extrasolar giant planets in orbits with semi-major axes between 2 and 10 AU. EPIC will provide insights into the physical nature of a variety of planets in other solar systems complimenting radial velocity (RV) and astrometric planet searches. It will detect and characterize the atmospheres of planets identified by radial velocity surveys, determine orbital inclinations and masses, characterize the atmospheres around A and F type stars which cannot be found with RV techniques, and observe the inner spatial structure and colors of debris disks. EPIC has a proposed launch date of 2012 to heliocentric Earth trailing drift-away orbit, with a 3 year mission lifetime (5 year goal), and will revisit planets at least three times at intervals of 9 months. The robust mission design is simple and flexible ensuring mission success while minimizing cost and risk. The science payload consists of a heritage optical telescope assembly (OTA), and visible nulling coronagraph (VNC) instrument. The instrument achieves a contrast ratio of 109 over a 4.84 arcsecond field-of-view with an unprecedented inner working angle of 0.14 arcseconds over the spectral range of 440-880 nm, with spectral resolutions from 10 - 150. The telescope is a 1.5 meter offaxis Cassegrain with an OTA wavefront error of λ/9, which when coupled to the VNC greatly reduces the requirements on the large scale optics, compressing them to stability requirements within the relatively compact VNC optical chain. The VNC features two integrated modular nullers, a spatial filter array (SFA), and an E2V-L3 photon counting CCD. Direct null control is accomplished from the science focal mitigating against complex wavefront and amplitude sensing and control strategies.
Speckle nulling for exoplanet detection with space-based coronagraphic telescopes
To detect Earth-like planets in the visible with a coronagraphic telescope, two major noise sources have to be overcome: the photon noise of the diffracted star light, and the speckle noise due to the star light scattered by instrumental defects. Coronagraphs tackle only the photon noise contribution. In order to decrease the speckle noise below the planet level, an active control of the wave front is required. We have developed analytical methods to measure and correct the speckle noise behind a coronagraph with a deformable mirror. In this paper, we summarize these methods, present numerical simulations, and discuss preliminary experimental results obtained with the High-Contrast Imaging Testbed at NASA's Jet Propulsion Laboratory.
Decreasing the inner working angle in high-contrast imaging by pupil replication
Imaging for exo-planet detection requires both high contrast and a small inner working angle. We show that, for several of the techniques proposed so far to achieve this, the inner working angle can be reduced by adding pupil replication between the telescope and the high contrast imaging system. Using pupil replication, the on-axis image of the star is decreased to a size smaller than the diffraction limit of the telescope, and off axis the point spread function of the planet undergoes minor changes, contained within the envelope of the point spread function of the telescope; the spectrum remains unchanged. The principle of pupil replication was proven experimentally and can be effected by a small-sized, high throughput optical system added between the telescope and the high contrast imaging system. High contrast imaging systems to which pupil replication has been found to be applicable so far include apodisation techniques like pupil apodisation, aperture masks, image plane masks, coronagraphs and combinations. Mathematical assessment and simulations of the sensitivity of pupil replication to optical errors show that the requirements for this system are the same as those for the primary telescope - pupil replication effectively remaps the output pupil of the telescope to the input pupil of the high contrast imaging system. Our results in this paper aim to show, in a realistic set-up, the feasibility of an improvement of the inner working angle by a factor of 4 using four-fold replication optics while maintaining the contrast performance. We do this through analysis of the pupil replication principle including off axis behavior when applied to high contrast imaging systems using pupil apodisation or a shaped mask. We specifically look at the situations similar to that of the Terrestrial Planet Finder Coronagraph and Darwin. We found that an inner working angle of 30 mas can be achieved with a contrast of 10-10 and a large field of view without increasing the requirements except for the pointing.
Hybrid pupil mapping/masking systems for high-contrast imaging
Pupil mapping, also known as phase induced amplitude apodization or PIAA, has emerged as an interesting design concept for NASA's Terrestrial Planet Finder space telescope. However, in a previous paper it was demonstrated that diffraction effects limit the best achievable contrast to about 10-5, which is 5 orders of magnitude short of the required level. Recent work by Olivier Guyon and his collaborators shows that a certain hybrid system can restore the contrast to the required level without degrading significantly the attractive throughput, achromaticity, and inner working angle advantages. In this paper, efficient computational tools are described that can be used to evaluate such designs. It is shown that a design similar to the one proposed by Guyon does indeed meet the contrast requirement.
Imaging extrasolar terrestrial planets from space with a PIAA coronagraph
Olivier Guyon, Eugene A. Pluzhnik, Stephen Ridgway, et al.
The Phase-Induced Amplitude Apodization Coronagraph (PIAAC) uses a lossless beam apodization, performed by aspheric mirrors, to produce a high contrast PSF. This concept offers a unique combination of high throughput (almost 100%), high angular resolution (λ/D), small inner working angle (IWA = 1.5 λ/D), excellent achromaticity (the apodization is performed by geometric reflection on mirrors) and low sensitivity to pointing errors or stellar angular diameter. These characteristics make the PIAAC an ideal choice for direct imaging of extrasolar terrestrial planets (ETPs) from space. We quantify the performance of the PIAAC and other coronagraph designs both in terms of "raw" coronagraphic performance (throughput, IWA etc...) and number of stars around which extrasolar terrestrial planets (ETPs) can be observed. We also identify the fundamental performance limit that can be achieved by coronagraphy, and show that no other coronagraph design is as close to this limit as the PIAAC. We find that in the photon noise limited regime, a 4m telescope with a PIAA coronagraph is able to detect Earth-like planets around 30 stars with 1hr exposure time per target (assuming 25% throughput and exozodi levels similar to our solar system). With a smaller 1 to 2-m diameter telescope, more massive rocky planets could be detected in the habitable zones of a few nearby stars, and an imaging survey of Jupiter-like planets could be performed. Laboratory results and detailed simulations confirm the large potential of this concept for direct imaging of ETPs. A prototype high contrast PIAAC system is currently being operated to demonstrate the coronagraph's performance.
Astronomical near-neighbor detection with a four-quadrant phase mask (FQPM) coronagraph
Pierre Haguenauer, Eugene Serabyn, Bertrand Mennesson, et al.
Direct detection of planets around nearby stars requires the development of high-contrast imaging techniques, because of their very different respective fluxes. We thus investigated the innovative coronagraphic approach based on the use of a four-quadrant phase mask (FQPM). Simulations showed that, combined with high-level wavefront correction on an unobscured off-axis section of a large telescope, this method allows high-contrast imaging very close to stars, with detection capability superior to that of a traditional coronagraph. A FQPM instrument was thus built to test the feasibility of near-neighbor observations with our new off-axis approach on a ground-based telescope. In June 2005, we deployed our instrument to the Palomar 200-inch telescope, using existing facilities as much as possible for rapid implementation. In these initial observations, using data processing techniques specific to FQPM coronagraphs, we reached extinction levels of the order of 200:1. Here we discuss our simulations and on-sky results obtained so far.
Terrestrial Planet Finder: Coronagraphy II
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The Terrestrial Planet Finder Coronagraph optical surface requirements
We derive the requirements on the surface height uniformity and reflectivity uniformity of the Terrestrial Planet Finder Coronagraph telescope and instrument optics for spatial frequencies within and beyond the spatial control bandwidth of the wave front control system. Three different wave front control systems are considered: a zero-path difference Michelson interferometer with two deformable mirrors at a pupil image; a sequential pair of deformable mirrors with one placed at a pupil image; and the Visible Nuller spatially-filtered controller. We show that the optical bandwidth limits the useful outer working angle.
Development of binary image masks for TPF-C and ground-based AO coronagraphs
Jian Ge, Justin Crepp, Andrew Vanden Heuvel, et al.
We report progress on the development of precision binary notch-filter focal plane coronagraphic masks for directly imaging Earth-like planets at visible wavelengths with the Terrestrial Planet Finder Coronagraph (TPF-C), and substellar companions at near infrared wavelengths from the ground with coronagraphs coupled to high-order adaptive optics (AO) systems. Our recent theoretical studies show that 8th-order image masks (Kuchner, Crepp & Ge 2005, KCG05) are capable of achieving unlimited dynamic range in an ideal optical system, while simultaneously remaining relatively insensitive to low-spatial-frequency optical aberrations, such as tip/tilt errors, defocus, coma, astigmatism, etc. These features offer a suite of advantages for the TPF-C by relaxing many control and stability requirements, and can also provide resistance to common practical problems associated with ground-based observations; for example, telescope flexure and low-order errors left uncorrected by the AO system due to wavefront sensor-deformable mirror lag time can leak light at significant levels. Our recent lab experiments show that prototype image masks can generate contrast levels on the order of 2x10-6 at 3 λ/D and 6x10-7 at 10 λ/D without deformable mirror correction using monochromatic light (Crepp et al. 2006), and that this contrast is limited primarily by light scattered by imperfections in the optics and extra diffraction created by mask construction errors. These experiments also indicate that the tilt and defocus sensitivities of high-order masks follow the theoretical predictions of Shaklan and Green 2005. In this paper, we discuss these topics as well as review our progress on developing techniques for fabricating a new series of image masks that are "free-standing", as such construction designs may alleviate some of the (mostly chromatic) problems associated with masks that rely on glass substrates for mechanical support. Finally, results obtained from our AO coronagraph simulations are provided in the last section. In particular, we find that: (i) apodized masks provide deeper contrast than hard-edge masks when the image quality exceeds 80% Strehl ratio (SR), (ii) above 90% SR, 4th-order band-limited masks provide higher off-axis throughput than Gaussian masks when generating comparable contrast levels, and (iii) below ~90% SR, hard-edge masks may be better suited for high contrast imaging, since they are less susceptible to tip/tilt alignment errors.
Terrestrial Planet Finder: Interferometry
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The Fourier-Kelvin Stellar Interferometer: a low-complexity low-cost space mission for high-resolution astronomy and direct exoplanet detection
R. K. Barry, W. C. Danchi, L. D. Deming, et al.
The Fourier-Kelvin Stellar Interferometer (FKSI) is a mission concept for a spacecraft-borne nulling interferometer for high-resolution astronomy and the direct detection of exoplanets and assay of their environments and atmospheres. FKSI is a high angular resolution system operating in the near to mid-infrared spectral region and is a scientific and technological pathfinder to the Darwin and Terrestrial Planet Finder (TPF) missions. The instrument is configured with an optical system consisting, depending on configuration, of two 0.5 - 1.0 m telescopes on a 12.5 - 20 m boom feeding a symmetric, dual Mach- Zehnder beam combiner. We report on progress on our nulling testbed including the design of an optical pathlength null-tracking control system and development of a testing regime for hollow-core fiber waveguides proposed for use in wavefront cleanup. We also report results of integrated simulation studies of the planet detection performance of FKSI and results from an in-depth control system and residual optical pathlength jitter analysis.
Pegase: a space-based nulling interferometer
The space based mission Pegase was proposed to CNES in the framework of its call for scientific proposals for formation flying missions. This paper presents a summary of the phase-0 performed in 2005. The main scientific goal is the spectroscopy of hot Jupiters (Pegasides) and brown dwarfs from 2.5 to 5 μm. The mission can extend to other objectives such as the exploration of the inner part of protoplanetary disks, the study of dust clouds around AGN,... The instrument is basically a two-aperture (D=40 cm) interferometer composed of three satellites, two siderostats and one beam-combiner. The formation is linear and orbits around L2, pointing in the anti-solar direction within a +/-30° cone. The baseline is adjustable from 50 to 500 m in both nulling and visibility measurement modes. The angular resolution ranges from 1 to 20 mas and the spectral resolution is 60. In the nulling mode, a 2.5 nm rms stability of the optical path difference (OPD) and a pointing stability of 30 mas rms impose a two level control architecture. It combines control loops implemented at satellite level and control loops operating inside the payload using fine mechanisms. According to our preliminary study, this mission is feasible within an 8 to 9 years development plan using existing or slightly improved space components, but its cost requires international cooperation. Pegase could be a valuable Darwin/TPF-I pathfinder, with a less demanding, but still ambitious, technological challenge and a high associated scientific return.
The Fourier-Kelvin Stellar Interferometer (FKSI) nulling testbed II: closed-loop path length metrology and control subsystem
The Fourier-Kelvin Stellar Interferometer (FKSI) is a mission concept for an imaging and nulling interferometer in the near to mid-infrared spectral region (3-8 microns), and will be a scientific and technological pathfinder for upcoming missions including TPF-I/DARWIN, SPECS, and SPIRIT. At NASA's Goddard Space Flight Center, we have constructed a symmetric Mach-Zehnder nulling testbed to demonstrate techniques and algorithms that can be used to establish and maintain the 104 null depth that will be required for such a mission. Among the challenges inherent in such a system is the ability to acquire and track the null fringe to the desired depth for timescales on the order of hours in a laboratory environment. In addition, it is desirable to achieve this stability without using conventional dithering techniques. We describe recent testbed metrology and control system developments necessary to achieve these goals and present our preliminary results.
Terrestrial Planet Finder: Other Concepts
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Darwin: a mission overview
Darwin is a mission under study by the European Space Agency, ESA. The mission objectives are detection and characterization of exo-planets, with special emphasize on the planets likely to harbour earthlike life. The mission cancels the light from the target star by nulling interferometry, while the light collected from any orbiting planets will interfere constructively. In this way absorption features in the planetary light can be detected and analysed. In the preceding years ESA has developed the required technology and elaborated on and evaluated different mission concepts with the aim of reducing over-all mission cost. This has resulted in a number of mission architectures, and various interferometric beam recombination techniques. To consolidate the study results two parallel mission assessment studies were initiated September 2005, taking benefit from the large number of technology developments as conducted since 2000. This article reviews the Darwin mission and its architecture evolution from the feasibility study up to the currently ongoing system assessment studies.
New design for additional sensitivity to extrasolar planet detection by stellar hallo cancellation
The proposed design includes 3 new ideas to increase the signal-noise ratio of instruments for the detection and study of extra-solar planets in space and on the ground. The instrument is to be added to systems that cancel the stellar halo, for example coronagraphs with adaptive speckle cancellation using integral field low resolution spectroscopy for speckle detection. The new design then gives an additional sensitivity to other hallo cancellation methods by hardware and/or software. The first part of the instrument spectrally splits the image into 50 to 100 narrowband images with independent optimal bandwidths and central wavelengths. This permits to have for example a uniform spectral resolution by making each bandwidth proportional to the wavelength or to adjust some bandwidths and central wavelengths to specifically target important lines. It also gives in each narrowband image optimum independent spatial sampling, for example 2 pixel per diffraction limit. This cannot be done with field sampling integral field systems as image slicers and TIGER type lens arrays. Another advantage is that there is very little contamination between spectral pixels as opposed to a slit spectrograph where the slit has a significant width compared to the pixel size, being in fact usually larger. Consequently, if a TIGER type lens array is added at the input, all 3 dimensions of the 3-D data box have very little contamination. In the second part of the instrument, the darker regions around the speckles of the narrowband images are reflected back into the spectrograph to reconstruct a white light image with a far higher contrast than at the input. The total additional gain should be equivalent to at least an order of magnitude increase in throughput. Finally, instead of reconstructing one white light image, a small number of images each with its own carefully chosen bandwidth and central wavelength can be reconstructed for specific programs as detection of life. Groups of bandwidths can also be reconstructed into white light in individual images. The system can be used as much in space than on the ground.
Characterization of a star/planet simulator for evaluating extrasolar planet detection techniques
Stephen E. Kendrick, Christopher Robb, Dennis Ebbets, et al.
Precise testbeds are required to investigate the physics and engineering aspects of suppressing extrasolar starlight sufficiently to discern faint companion planets. In addition, testbeds that can simultaneously produce star and planet stimuli will be necessary ground support equipment for evaluating instruments designed for imaging and characterizing extrasolar planets. Integral to this is the ability to represent the broad spectral bands and relative geometry of stars and planets. We have built upon the Terrestrial Planet Finder Coronagraph (TPF-C) requirements as well as those of programs like Extrasolar Planet Imaging Coronagraph (EPIC) and Eclipse to develop a star/planet simulator (SPS) that, in conjunction with other testbed modules, can facilitate the pursuit of pertinent questions. The star/planet simulator developed has a broadband visible light source that illuminates independently adjustable star and planet sources (angular separation and orientation, relative magnitude). It is capable of providing either collimated or direct imaged light to proposed instruments and can be configured to produce the source stimuli in a vacuum environment. We will describe the physical set-up, measurements, and initial observations as well as the plans for combining with a coronagraphic testbed.
Telescope to Observe Planetary Systems (TOPS): a high throughput 1.2-m visible telescope with a small inner working angle
Olivier Guyon, James R. P. Angel, Charles Bowers, et al.
The Telescope to Observe Planetary Systems (TOPS) is a proposed space mission to image in the visible (0.4- 0.9 μm) planetary systems of nearby stars simultaneously in 16 spectral bands (resolution R≈20). For the ≈10 most favorable stars, it will have the sensitivity to discover 2RΕ rocky planets within habitable zones and characterize their surfaces or atmospheres through spectrophotometry. Many more massive planets and debris discs will be imaged and characterized for the first time. With a 1.2m visible telescope, the proposed mission achieves its power by exploiting the most efficient and robust coronagraphic and wavefront control techniques. The Phase-Induced Amplitude Apodization (PIAA) coronagraph used by TOPS allows planet detection at 2λ/d with nearly 100% throughput and preserves the telescope angular resolution. An efficient focal plane wavefront sensing scheme accurately measures wavefront aberrations which are fed back to the telescope active primary mirror. Fine wavefront control is also performed independently in each of 4 spectral channels, resulting in a system that is robust to wavefront chromaticity.
Future Missions: Mission and Telescope Concepts I
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Architecture concept for a 10m UV-optical space telescope
Dennis Ebbets, James DeCino, James Green
The scientific achievements of the Hubble Space Telescope have motivated interest in a larger and more powerful successor that can operate at ultraviolet and optical wavelengths. NASA recently supported a Visions Mission study called the Modern Universe Space Telescope. The scientific goals require the angular resolution expected from a 10m aperture in visible light and the sensitivity provided by 50m2 of collecting area. The approach developed by the MUST study team uses a segmented primary mirror that can be assembled in space. Assembly offers advantages over deployment with regard to mass and volume efficient stowage in the launch vehicle fairing, and simplicity of the mechanical and structural design. If the system is designed thoughtfully from the beginning, then robotic techniques such as those investigated for HST servicing might be used to great advantage. Alternatively, if the space operations infrastructure included in the Vision for Space Exploration is developed, then either astronaut EVA or telerobotic assembly techniques could be employed. In either case, in-space assembly enables a telescope that is substantially larger than the diameter of the launch vehicle.
A Lunar Liquid Mirror Telescope (LLMT) for deep-field infrared observations near the lunar pole
Roger Angel, Dan Eisenstein, Suresh Sivanandam, et al.
We have studied the feasibility and scientific potential of a 20 - 100 m aperture astronomical telescope at the lunar pole, with its primary mirror made of spinning liquid at less than 100K. Such a telescope, equipped with imaging and multiplexed spectroscopic instruments for a deep infrared survey, would be revolutionary in its power to study the distant universe, including the formation of the first stars and their assembly into galaxies. The LLMT could be used to follow up discoveries made with the 6 m James Webb Space Telescope, with more detailed images and spectroscopic studies, as well as to detect objects 100 times fainter, such as the first, high-red shift stars in the early universe. Our preliminary analysis based on SMART-1 AMIE images shows ridges and crater rims within 0.5° of the North Pole are illuminated for at least some sun angles during lunar winter. Locations near these points may prove to be ideal for the LLMT. Lunar dust deposited on the optics or in a thin atmosphere could be problematic. An in-situ site survey appears necessary to resolve the dust questions.
The New Worlds Observer: using occulters to directly observe planets
We discuss the progress that has been made in the understanding of the use of external occulters to observe exoplanetary systems. We show how a starshade can be designed and built in a practical and affordable manner to fully remove starlight and leave only planet light entering a telescope. When coupled to a powerful observatory like the James Webb Space Telescope, an occulter can extinguish the starlight and reveal basic details of the planetary systems around our closest, neighboring stars.
New Worlds Occulter performance: a first look
We have performed a large trade study of the factors affecting the performance of the New Worlds Observer occulter. This external occulter has a multidimensional requirement space and a multidimensional parameter space. Additional engineering constraints of an external occulter spacecraft makes finding the optimal occulter parameters a complicated problem. We present here the requirements space, specifically, requirements that lead to an exoplanet detection mission. We also present the occulter parameter space, factors that lead to changes in the occulter performance. We find that it is possible in almost all cases to find a solution, meaning a set of occulter parameters, which can meet requirements for an exoplanet hunting program. We present our methodology for defining and finding the solution space.
Future Missions: Mission and Telescope Concepts II
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Science promise and conceptual mission design for SAFIR: the single aperture far-infrared observatory
We report on completion of the SAFIR Vision Mission study, as organized by the NASA Science Mission Directorate. This study resulted in a focused baseline design for this large aperture space observatory that capitalizes on architectures being actively developed for JWST and other missions. Special opportunities for achieving thermal performance of this <10 K telescope are reviewed, as well as efforts to understand capabilities and needs for focal plane instrument and I and T on this large (10 m-class) telescope.
DUNE: the Dark Universe Explorer
Understanding the nature of Dark Matter and Dark Energy is one of the most pressing issues in cosmology and fundamental physics. The purpose of the DUNE (Dark UNiverse Explorer) mission is to study these two cosmological components with high precision, using a space-based weak lensing survey as its primary science driver. Weak lensing provides a measure of the distribution of dark matter in the universe and of the impact of dark energy on the growth of structures. DUNE will also include a complementary supernovae survey to measure the expansion history of the universe, thus giving independent additional constraints on dark energy. The baseline concept consists of a 1.2m telescope with a 0.5 square degree optical CCD camera. It is designed to be fast with reduced risks and costs, and to take advantage of the synergy between ground-based and space observations. Stringent requirements for weak lensing systematics were shown to be achievable with the baseline concept. This will allow DUNE to place strong constraints on cosmological parameters, including the equation of state parameter of the dark energy and its evolution from redshift 0 to 1. DUNE is the subject of an ongoing study led by the French Space Agency (CNES), and is being proposed for ESA's Cosmic Vision programme.
ESPRIT: a space interferometer concept for the far-infrared
W. Wild, Th. de Graauw, F. Helmich, et al.
In the far-infrared (FIR) / THz regime the angular (and often spectral) resolution of observing facilities is still very restricted despite the fact that this frequency range has become of prime importance for modern astrophysics. ALMA (Atacama Large Millimeter Array) with its superb sensitivity and angular resolution will only cover frequencies up to about 1 THz, while the HIFI instrument for ESA'a Herschel Space Observatory will provide limited angular resolution (10 to 30 arcsec) up to 2 THz. Observations of regions with star and planet formation require extremely high angular resolution as well as frequency resolution in the full THz regime. In order to open these regions for high-resolution astrophysics we propose a heterodyne space interferometer mission, ESPRIT (Exploratory Submm Space Radio-Interferometric Telescope), for the Terahertz regime inaccessible from ground and outside the operating range of the James Webb Space Telescope (JWST).
SPECS: the submillimeter probe of the evolution of cosmic structure
The concept for the Submillimeter Probe of the Evolution of Cosmic Structure (SPECS) was investigated through NASA Vision Missions Program. In the course of this study, a compelling need for high spatial-resolution far-infrared/submillimeter observations with high angular resolution (50 milliarcseconds) was identified. In order to achieve these scientific goals, a kilometer-baseline far-infrared/submillimeter Michelson stellar interferometer is required, operating in the 40-640 micron range with fully cryogenically cooled optics and photon-limited detectors. There are significant technological challenges to developing this mission, including controllable tethered flight, detector development, and large cryogenic mechanisms. We present here a concept for SPECS and discuss some of the relevant technical aspects of the mission.
Update on the Wide-Field Infrared Survey Explorer (WISE)
Amanda K. Mainzer, Peter Eisenhardt, Edward L. Wright, et al.
The Wide-field Infrared Survey Explorer (WISE), a NASA MIDEX mission, will survey the entire sky in four bands from 3.3 to 23 microns with a sensitivity 1000 times greater than the IRAS survey. The WISE survey will extend the Two Micron All Sky Survey into the thermal infrared and will provide an important catalog for the James Webb Space Telescope. Using 10242 HgCdTe and Si:As arrays at 3.3, 4.7, 12 and 23 microns, WISE will find the most luminous galaxies in the universe, the closest stars to the Sun, and it will detect most of the main belt asteroids larger than 3 km. The single WISE instrument consists of a 40 cm diamond-turned aluminum afocal telescope, a two-stage solid hydrogen cryostat, a scan mirror mechanism, and reimaging optics giving 5" resolution (full-width-half-maximum). The use of dichroics and beamsplitters allows four color images of a 47'x47' field of view to be taken every 8.8 seconds, synchronized with the orbital motion to provide total sky coverage with overlap between revolutions. WISE will be placed into a Sun-synchronous polar orbit on a Delta 7320-10 launch vehicle. The WISE survey approach is simple and efficient. The three-axis-stabilized spacecraft rotates at a constant rate while the scan mirror freezes the telescope line of sight during each exposure. WISE has completed its mission Preliminary Design Review and its NASA Confirmation Review, and the project is awaiting confirmation from NASA to proceed to the Critical Design phase. Much of the payload hardware is now complete, and assembly of the payload will occur over the next year. WISE is scheduled to launch in late 2009; the project web site can be found at www.wise.ssl.berkeley.edu.
Architectures for space astronomical telescopes using Fresnel optics
We have developed a novel chromatic correction scheme for a large aperture space astronomy telescope, using a Fresnel lens as the primary aperture. Systems built around Fresnel optics hold the possibility of drastically reducing mission costs. The use of a Fresnel optic allows a light weight primary lens which results in lighter systems, which in turn can be flown on smaller, less expensive launchers. Costs are also reduced in the manufacture of the primary lens. The performance of the telescope will be given and the tolerancing of the system discussed. The key issue of the mitigation of the intrinsic chromatic aberration will be discussed in detail, as well as deployment methods of a large monolithic lens. It will be shown that architectures based on Fresnel optics can be considered viable and should be considered in the technology selection for future missions.
Photon sieve telescope
Geoff Andersen, Drew Tullson
In designing next-generation, ultra-large (>20m) apertures for space, many current concepts involve compactable, curved membrane reflectors. Here we present the idea of using a flat diffractive element that requires no out-of-plane deformation and so is much simpler to deploy. The primary is a photon sieve - a diffractive element consisting of a large number of precisely positioned holes distributed according to an underlying Fresnel Zone Plate (FZP) geometry. The advantage of the photon sieve over the FZP is that all the regions are connected, so the membrane substrate under simple tension can avoid buckling. Also, the hole distribution can be varied to generate any conic or apodization for specialized telescope requirements such as exo-solar planet detection. We have designed and tested numerous photon sieves as telescope primaries. Some of these have over 10 million holes in a 0.1 m diameter aperture and all of them give diffraction limited imaging. While photon sieves are diffractive elements and thus suffer from dispersion, we will present two successful solutions to this problem.
Future Missions: Solar System Telescopes
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Formation flying applied to solar coronal diagnostics: the ASPIICS coronagraph
S. Vivès, P. Lamy, P. Levacher, et al.
Classical externally-occulted coronagraphs are presently limited in their performances by the distance between the external occulter and the front objective. The diffraction fringe from the occulter and the vignetted pupil which degrades the spatial resolution prevent observing the inner corona inside typically 2-2.5 solar radii. Formation flyers open new perspectives and allow to conceive giant, externally-occulted coronagraphs using a two-component space system with the external occulter on one spacecraft and the optical instrument on the other spacecraft at approximately 100-150 m from the first one. ASPIICS (Association de Satellites Pour l'Imagerie et l'Interfromtrie de la Couronne Solaire) is a payload proposed to ESA in the framework of the PROBA-3 mission of formation flyers presently under study. ASPIICS is composed of a single coronagraph which performs high spatial resolution imaging of the corona as well as 2-dimensional spectroscopy of several emission lines (in particular the forbidden line of Fe XIV at 530.285 nm) from the coronal base out to 3 solar radii ( R). Thus ASPIICS will address the main questions of the coronal physics. The classical design of an externally occulted coronagraph is adapted to the detection of the very inner corona as close as 1.01 R and the addition of a Fabry-Perot interferometer using a so-called etalon.
The Near-Earth Orbit Surveillance Satellite
Brad Wallace, Robert (Lauchie) Scott, Donald Bedard, et al.
Defence Research and Development Canada (DRDC) and the Canadian Space Agency (CSA) are jointly working to place a microsatellite, equipped with a small optical telescope, on orbit to detect and track both "deep-space" earth orbiting objects (orbital altitudes > 5000 km), and inner-earth orbit (IEO) asteroids. The satellite will be named the Near Earth Orbit Surveillance Satellite (NEOSSat), is baselined for launch in 4th Q 2008, and will be equipped with a 15cm diameter telescope capable of detecting 19.5th magnitude stars over a 100s integration. Other important design requirements of this telescope include the ability to observe to within 45 degrees of the sun (to better detect IEO asteroids) and the ability to observe to within 20 degrees of the anti-sun direction and remain power-positive. The mission is expected to cost $11M CDN (launch costs included, but operating and ground-station costs excluded). The scientific aims of the NEOSSat mission will be described and the results of the NEOSSat Phase-A will be presented. Test observations have been conducted using the MOST ("Microvariability and Oscillations of STars") microsatellite, the inspiration for NEOSSat, and the results of these observations will be shown here; these tests validate both the general concept of using a microsatellite for these types of observations, as well as the expected performance.
A novel optical design for planetary surface stereo-imaging: preliminary design of the stereoscopic imaging channel of SIMBIOSYS for the BepiColombo ESA mission
The optical design of the STereoscopic imaging Channel (STC) of the imaging/spectroscopic system SIMBIOSYS for the ESA BepiColombo mission is presented. The main aim of this system is the global stereo mapping of planet Mercury surface during the BepiColombo mission lifetime. The instrument consists of two identical cameras looking at ±20° from nadir which are sharing some optical components and the detector. The instrument has a 23"/pixel scale factor, corresponding to 50 m/px at 400 km from the surface, on a 4°x 4° FoV; imaging in four different spectral bands, between 540 nm and 890 nm, is foreseen. The STC optical characteristics guarantee global stereo mapping of the whole Mercury surface with all the filters. The coupling of an achromatic air-spaced doublet with a relay lens system allows good aberration balancing over all the field of view: the diffraction Ensquared Energy inside one pixel of the detector is of the order of 80%. In addition, an intermediate field stop gives the possibility of designing an efficient baffling system for straylight rejection. To cope with the hazardous radiation environment in which the spacecraft will be immersed in during the mission, all the glasses selected for the design are rad-hard type. A preliminary tolerance analysis has also been undertaken showing a low criticality level for manufacturing, alignment and stability of the system.
Future Missions: Joint Dark Energy Mission
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Destiny: a candidate architecture for the Joint Dark Energy Mission
⪅Destiny is a simple, direct, low cost mission to determine the properties of dark energy by obtaining a cosmologically deep supernova (SN) type Ia Hubble diagram. Its science instrument is a 1.65m space telescope, featuring a grism-fed near-infrared (NIR) (0.85-1.7 μm) survey camera/spectrometer with a 0.12 square degree field of view (FOV) covered by a mosaic of 16 2k x 2k HgCdTe arrays. For maximum operational simplicity and instrument stability, Destiny will be deployed into a halo-orbit about the Second Sun-Earth Lagrange Point. During its two-year primary mission, Destiny will detect, observe, and characterize ~3000 SN Ia events over the redshift interval 0.4 < z < 1.7 within a 3 square degree survey area. In conjunction with ongoing ground-based SN Ia surveys for z < 0.8, Destiny mission data will be used to construct a high-precision Hubble diagram and thereby constrain the dark energy equation of state. The total range of redshift is sufficient to explore the expansion history of the Universe from an early time, when it was strongly matter-dominated, to the present when dark energy dominates. The grism-images will provide a spectral resolution of R≡λ/Δλ=75 spectrophotometry that will simultaneously provide broad-band photometry, redshifts, and SN classification, as well as time-resolved diagnostic data, which is valuable for investigating additional SN luminosity diagnostics. Destiny will be used in its third year as a high resolution, wide-field imager to conduct a multicolor NIR weak lensing (WL) survey covering 1000 square degrees. The large-scale mass power spectrum derived from weak lensing distortions of field galaxies as a function of redshift will provide independent and complementary constraints on the dark energy equation of state. The combination of SN and WL is much more powerful than either technique on its own. Used together, these surveys will have more than an order of magnitude greater sensitivity (by the Dark Energy Task Force's (DETF) figure of merit) than will be provided by ongoing ground-based projects. The dark energy parameters, w0 and wa, will be measured to a precision of 0.05 and 0.2 respectively.
Illuminating dark energy with the joint efficient dark-energy investigation (JEDI)
Edward Cheng, Yun Wang, Edward Baron, et al.
The Universe appears to be expanding at an accelerating rate, driven by a mechanism called Dark Energy. The nature of Dark Energy is largely unknown and needs to be derived from observation of its effects. JEDI (Joint Efficient Dark-energy Investigation) is a candidate implementation of the NASA-DOE Joint Dark Energy Mission (JDEM). It will probe the effects of Dark Energy in three independent ways: (1) using Type Ia supernovae as cosmological standard candles over a range of distances, (2) using baryon acoustic oscillations as a cosmological standard ruler over a range of cosmic epochs, and (3) mapping the weak gravitational lensing distortion by foreground galaxies of the images of background galaxies at different distances. JEDI provides crucial systematic error checks by simultaneously applying these three independent observational methods to derive the Dark Energy parameters. The concordance of the results from these methods will not only provide an unprecedented understanding of Dark Energy, but also indicate the reliability of such an understanding. JEDI will unravel the nature of Dark Energy by obtaining observations only possible from a vantage point in space, coupled with a unique instrument design and observational strategy. Using a 2 meter-class space telescope with simultaneous wide-field imaging (~ 1 deg2, 0.8 to 4.2 μm in five bands) and multi-slit spectroscopy (minimum wavelength coverage 1 to 2 μm), JEDI will efficiently execute the surveys needed to solve the mystery of Dark Energy.
The Joint Efficient Dark-energy Investigation (JEDI): measuring the cosmic expansion history from type Ia supernova
M. M. Phillips, Peter Garnavich, Yun Wang, et al.
JEDI (Joint Efficient Dark-energy Investigation) is a candidate implementation of the NASA-DOE Joint Dark Energy Mission (JDEM). JEDI will probe dark energy in three independent methods: (1) type Ia supernovae, (2) baryon acoustic oscillations, and (3) weak gravitational lensing. In an accompanying paper, an overall summary of the JEDI mission is given. In this paper, we present further details of the supernova component of JEDI. To derive model-independent constraints on dark energy, it is important to precisely measure the cosmic expansion history, H(z), in continuous redshift bins from z ~ 0-2 (the redshift range in which dark energy is important). SNe Ia at z > 1 are not readily accessible from the ground because the bulk of their light has shifted into the near-infrared where the sky background is overwhelming; hence a space mission is required to probe dark energy using SNe. Because of its unique near-infrared wavelength coverage (0.8-4.2 μm), JEDI has the advantage of observing SNe Ia in the rest frame J band for the entire redshift range of 0 < z <2, where they are less affected by dust, and appear to be nearly perfect standard candles. During the first year of JEDI operations, spectra and light curves will be obtained for ~4,000 SNe Ia at z < 2. The resulting constraints on dark energy are discussed, with special emphasis on the improved precision afforded by the rest frame near-infrared data.
Future Missions: Infrastructure
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Concept for a large scalable space telescope: in-space assembly
W. R. Oegerle, L. R. Purves, J. G. Budinoff, et al.
We present a conceptual design for a scalable (10-50 meter segmented filled-aperture) space observatory operating at UV-optical-near infrared wavelengths. This telescope is designed for assembly in space by robots, astronauts or a combination of the two, as envisioned in NASA's Vision for Space Exploration. Our operations concept for this space telescope provides for assembly and check-out in an Earth Moon L2 (EML2) orbit, and transport to a Sun-Earth L2 (SEL2) orbit for science operations and routine servicing, with return to EML2 for major servicing. We have developed and analyzed initial designs for the optical, structural, thermal and attitude control systems for a 30-m aperture space telescope. We further describe how the separate components are packaged for launch by heavy lift vehicle(s) and the approach for the robot assembly of the telescope from these components.
On-orbit assembly and servicing of future space observatories
NASA's experience servicing the Hubble Space Telescope, including the installation of optical elements to compensate for a mirror manufacturing error; replacement of failed avionics and worn-out batteries, gyros, thermal insulation and solar arrays; upgrades to the data handling subsystem; installation of far more capable instruments; and retrofitting the NICMOS experiment with a mechanical cryocooler has clearly demonstrated the advantages of on-orbit servicing. This effort has produced a unique astronomical observatory that is orders of magnitude more capable than when it was launched and can be operated for several times its original design life. The in-space operations capabilities that are developed for NASA's Exploration Program will make it possible to assemble and service spacecraft in space and to service them in cis-lunar and L2 orbits. Future space observatories should be designed to utilize these capabilities. This paper discusses the application of the lessons learned from HST and our plans for servicing the Advanced X-ray Astrophysical Observatory with the Orbital Maneuvering Vehicle and the Space Station Freedom Customer Servicing Facility to future space observatories, such as SAFIR and LifeFinder that are designed to operate in heliocentric orbits. It addresses the use of human and robotic in-space capabilities that would be required for on-orbit assembly and servicing for future space observatories, and describes some of our design concepts for these activities.
Advanced Technologies: Instruments
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Space qualified mid-infrared illumination sources
We present details of a new illumination source, suitable for use on mid-infrared satellite instruments. The device is based around an electrically heated tungsten filament. The source is compact, and dissipates typically 9 mW for an effective black-body temperature of 1000 K. A typical device design will warm from 4 K to 1000 K in around 1 s, and cool from 1000 K to 4 K in around 2.5 s. We present results for a range of device designs, and discuss the range of parameter space (e.g. power dissipation, time constant, photon flux) to which these devices can be tuned. A device of this type is currently in qualification for flight on JWST-MIRI1, and similar devices are being considered for use on JWST-NIRSPEC and SPICA2-ESI3.
Behavior of Si:As and Si:Sb detectors in space
Daniel Devost, Gregory C. Sloan
We present an analysis of the behavior of the detectors on the Infrared Spectrograph (IRS)1 onboard Spitzer.2 The detectors of the IRS have been subjected to a 2.5 years of harsh space environments. We found that the number of protons hitting the IRS detectors is approximately 1 every second. We also present a simple analysis that shows that the Si:Sb detectors are about a factor 3 to 6 times more sensitive to the space environment than the Si:As detectors.
Lithium niobate Fabry-Perot etalons in double-pass configuration for spectral filtering in the visible imager magnetograph IMaX for the SUNRISE mission
A Álvarez-Herrero, T. Belenguer, C. Pastor, et al.
The Imaging MAgnetograph eXperiment, IMaX, is one of the three postfocal instruments of the Sunrise mission. The Sunrise project consists of a stratospheric balloon with a 1 m aperture telescope, which will fly from the Antarctica within the NASA Long Duration Balloon Program. IMaX should work as a diffraction limited imager and it should be capable to carry out polarization measurements and spectroscopic analysis with high resolution (50.000-100.000 range). The spectral resolution required will be achieved by using a LiNbO3 (z-cut) Fabry-Perot etalon in double pass configuration as spectral filter. Up to our knowledge, few works in the literature describe the associated problems of using these devices in an imager instrument (roughness, off-normal incidence, polarization sensitivity...). Because of that, an extensive and detailed analysis of etalon has been carried out. Special attention has been taken in order to determine the wavefront transmission error produced by the imperfections of a real etalon in double pass configuration working in collimated beam. Different theoretical models, numeric simulations and experimental data are analysed and compared obtaining a complete description of the etalon response.
Laboratory simulation of cosmic radiation effects on stressed Ge:Ga detectors at L2 and curing
Jutta M. Stegmaier, Stephan M. Birkmann, Ulrich Grözinger, et al.
The Photodetector Array Camera and Spectrometer (PACS) is one of three science instruments on board the Herschel space observatory to be launched in 2008. It will perform imaging photometry and spectroscopy in the wavelength range from 57 μm to 210 μm. The integral field spectrometer contains two 25 x 16 pixel cameras of Gallium doped Germanium crystals (Ge:Ga). By stressing these crystals, cutoff wavelengths of 127 μm (low-stressed, 200 N) and 205 μm (high-stressed, 800 N) are reached. The characterization of these detectors (responsivity, noise equivalent power (NEP), dark current,...) is carried out at the Max-Planck-Institutes for Astronomy (MPIA, Heidelberg) and Extraterrestrial Physics (MPE, Garching). Both test facilities allow simulation of the in-flight operational conditions of the arrays and provide accurate IR fluxes by means of external/internal black bodies and calibrated cold attenuation filters. A radioactive 137Cs source is used at MPIA to simulate the steady cosmic radiation impact on the photoconductor arrays in order to study the radiation induced changes in responsivity, noise, and the transient behavior. The goal is to determine the optimal operating parameters (temperature, bias, integration time,..) for the operation at the L2 orbit, the best curing method, curing frequency and calibration procedure for high photometric accuracy. The "lessons learned" on operating, curing, deglitching and calibrating stressed Ge:Ga detectors during the ISO mission are applied as well as the relevant reports from IRAS and Spitzer.
Remapping the pupil
Correction of the influence of phase corrugations in the pupil plane is a fundamental issue in achieving high dynamic range imaging. We present here an imaging system which, thanks to non-redundant pupil remapping and spatial filtering, allows a perfect determination of the Optical Transfer Function. We do show that such a system would allow image reconstruction free from phase perturbations, photon noise limited, and with high dynamic range.
Space qualification and performance results of the SIDECAR ASIC
The SIDECAR ASIC is a fully integrated FPA controller system-on-a-chip. Compared to conventional control electronics, it requires significantly less power, less space and less weight. The SIDECAR ASIC, which can operate at ambient and cryogenic temperatures, is currently being space-qualified for integration in the science instruments of the James Webb Space Telescope (JWST). This paper gives an overview of the SIDECAR architecture and its supporting drive electronics. It describes the JWST flight configuration including the custom packaging approach. Test results obtained as part of the space qualification effort are presented. CDS noise of the ASIC itself amounts to less than 25 μV for full 2K x 2K data frames. The noise reduces to less than 6 μV for up-the-ramp-sampling with 88 frames. Based on the existing qualification results and a number of additional tests in the next few months, NASA Technology Readiness Level 6 (TRL6) will be demonstrated by August 2006.
Astronomy FPA advancements at Rockwell Scientific
Advancements in space and ground-based astronomy focal plane array (FPA) technology at Rockwell Scientific Company (RSC) are presented. The review covers the broad base of astronomy work at RSC for both present and next generation FPAs, and details recent achievements in detector, readout, and packaging technologies. RSC astronomy FPA progress includes: RSC FPA delivery for NASA's successful Deep Impact mission, progress on RSC's programs supplying H-2RG FPAs for James Webb Space Telescope (JWST) instruments JWST NIRCam, NIRSpec and FGS; selection of RSC's SIDECAR Application Specific Integrated Circuit (ASIC) for use on JWST instruments NIRCam, NIRSpec and FGS and the development of the JWST SIDECAR space flight package; first silicon on the 16 million pixel HAWAII-4RG (4Kx4K); optimization of NIR FPAs for space telescope missions; construction of multiple 16 million pixel 2x2 mosaic FPAs using the HAWAII-2RG readouts, and the development of the Microlensing Planet Finder (MPF) very large, 150 million pixel FPA.
Laser frequency stabilization to molecular resonances for TPF-C, LISA, and MAXIM
A number of future space observatories will rely on interferometric length measurements to meet mission requirements. A necessary tool for these measurements is a frequency stabilized laser. We present the use of molecular resonances for the frequency stabilization reference for the TPF-C, LISA, and MAXIM missions. For the TPF-C terrestrial planet finder coronagraph mission we have stabilized a 1542nm fiber laser to acetylene and exceeded the required sensitivity for length measurements of less than 25nm over a length scale of 12m and a time scale of 8 hours. For the LISA gravitational wave interferometer mission we have stabilized a frequency doubled 1064nm NPRO laser to molecular iodine. The laser system meets the frequency noise requirements of 30Hz/√(Hz) at mHz frequencies and shows robustness to temperature and alignment fluctuations. It also supplies an absolute reference frequency which is important for lock acquisition of lasers on separate spacecraft. The radiation hardness of the frequency doubling crystal for iodine stabilization was studied. In addition, simplified optical configurations have also been investigated, where the need for auxiliary modulators was eliminated. For MAXIM, we have constructed a stabilized laser system for stabilization of the position of the x-ray optics in the GSFC prototype testbed, and we report some initial results in the testbed operation.
Advanced Technologies: Materials
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CESIC: a new technology for lightweight and cost effective space instrument structures and mirrors
Alcatel Alenia Space, #1 in Europe for satellite systems and at the forefront of orbital infrastructures has been interested in the development of a new material to produce lightweight, stiff, stable and cost-effective structures and mirrors for space instrument. Cesic® from ECM has been selected for its intrinsic properties (high specific modulus, high thermal conductivity, quite low thermal expansion coefficient and high fracture toughness for a ceramic material), added to flexible manufacturing capabilities. Under ESA contract, a flight representative optical bench of Cesic® has been designed, manufactured and tested. The optical bench has been submitted with success to intensive vibration tests up to 80 g on a shaker without problem and was tested down to 30 K showing very high stability. Cesic® is also envisaged for large and lightweight space telescope mirrors. Optical coatings for Cesic® substrates have been developed and qualified for the most stringent optical conditions. To prove the lightweight capability, a large Cesic® mirror D=950 mm with an areal density of less than 25 kg/m2 has been designed, sufficiently strong to withstand launch loads and meet stringent WFE requirements, and then successfully manufactured. Cesic® is also envisaged for large future focal planes holding a large number of detectors assuring high stability thanks to its high thermal conductivity. A full size Cesic® focal plane has been already successfully built and tested. Based on these successful results, Alcatel Alenia Space is now in position to propose for space projects this technology mastered in common with ECM both for mirrors and structures with new innovative concepts thanks to the manufacturing capabilities of this technology.
Lightweight instrument mirrors from single-crystal silicon
Vincent T. Bly, Maria D. Nowak, David O. Moore
We describe a process for fabricating lightweight mirrors from single crystal silicon. We also report ambient and cryogenic test results on a variety of mirrors made by this process. Each mirror is a monolithic structure from a single crystal of silicon. Masses are typically 1/3rd to 1/4th that of an equal diameter solid quartz mirror. We avoid print through of the supporting structure by lightweighting after the optical surface has been formed. Because of the extraordinary homogeneity of single crystal silicon, distortion of the optical surface by the lightweighting process is negligible for most applications (<1/40th wave RMS @ 633nm). This homogeneity also accounts for the near zero distortion at cryogenic temperatures.
Chemical vapor composite silicon carbide for space telescopes
Components for space telescopes using high quality silicon carbide (SiC) produced via the chemical vapor composite (CVC) process are currently under development. This CVC process is a modification of chemical vapor deposition (CVD) and results in a dramatic reduction in residual stress of the SiC deposit. The resultant CVC SiC material has high modulus, high thermal conductivity and can be polished to better than 1nm RMS surface roughness, making it ideal for space telescopes requiring lightweight, stiff and thermally stable components. Moreover, due to its lower intrinsic stress, CVC SiC is much more readily scaled to large sizes and manufactured into the complex geometries needed for the telescope assemblies. Results are presented on the optical figure for a lightweight 15cm CVC SiC mirror demonstrating low wavefront error (<30nm peak-to-valley and <5.1nm rms). Theoretical and experimental modal analysis measured the first four resonant modes of the mirror and found a first modal frequency in the vicinity of 2100 Hz, representing a highly stiff mirror.
Advanced Technologies: Modeling
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A parametric design tool for large space telescope sunshields
We have developed a thermal-optical-mechanical model of a representative sunshield and telescope assembly, appropriate to 10-m class far-infrared large space telescopes such as SAFIR, SPECs, SPIRIT, and CMBPol. The model provides a tool for sensitivity analysis for design parameters, including material properties and structural configuration, provides performance predictions, and has been used to direct technology development for large space telescope structures and materials. The sunshield model incorporates a flight-like design support structure for the five-layer combined sunshield and V-groove radiator, including temperature-dependent thermal, mechanical, and optical properties for the structure and deployed sunshield layers. Heat lift from mechanical cryocoolers is included, in fixed-temperature or power-balance conditions, at arbitrary points on the sunshields and support structure. The model properly accounts the wavelength dependence of radiative transfer between surfaces of widely different temperature, which capacity has not been available from commercial codes for the infrared thermal band (source temperatures 300 K-15 K) until very recently. A simplified model of the zodiacal background to be experienced at the Sun-Earth L2 point is used which, with the wavelength-dependent thermal transfer, improves the fidelity of temperature and heat lift requirements predictions for the coldest sunshield layer and telescope assembly.
Parametric modeling of space telescope architectures
Elizabeth Jordan, Andrzej Stewart, Scott A. Uebelhart, et al.
Development of low-cost, lightweight space imaging systems requires a combination of technologies including lightweight optics to reduce the areal density of the mirrors and application of controls-structures technologies to compensate for the increased flexibility of these systems. These new design technologies have led to many new possibilities for architectures of large space telescopes, creating a necessity for new design tools during the conceptual design phase. The MIT Space Systems Laboratory (MIT-SSL) is examining alternative architectures for a Modular Optical Space Telescope (MOST) by developing a tool to automatically generate unique realizations of a spacecraft based upon parametric inputs to the model. This tool allows system metrics to be evaluated across combinations of design variables so that promising architecture families utilizing different technologies can be identified on the basis of system performance. This paper will describe advances to the structural components of the MOST model, particularly the primary mirror and secondary support tower. Lightweight, rib-stiffened mirrors and a variety of geometries for a lightweight secondary support tower have been modeled. Both of these parameterized sub-components can be analyzed to determine the effects of changing geometries on the structural stiffness. These advanced components can then be used in the system in order to more fully understand the effects of lightweight structures on the system performance metrics.
Innovative image analysis software as a technology driver for advances in space telescope design
Innovative image analysis software has the potential to act as a technology driver for advancing the state-of-the- art in the design of space telescopes and space-based instrumentation. Total mission costs can sometimes be significantly reduced by using innovative compact optical designs that create ugly Point Spread Functions. Most traditional astronomical image analysis techniques, like precision stellar photometry and astrometry, were developed for the analysis of ground-based image data and many photometric reduction codes cleverly take full advantage of the blurring caused by the Earth's atmosphere. Image data from space-based cameras, however, is typically characterized by having significant amounts of power at high spatial frequencies. Mission designers have a penchant to approve of optical designs that are undersampled. Although excellent justifications can often be made for using complex optical designs that have ugly Point Spread Functions (e.g., reduced total mission cost) or for using detectors that are too big at a given wavelength (e.g., giving a wider field-of-view), the analysis of resultant image data from these designs is frequently problematical. Reliance upon traditional ground-based image analysis codes may preclude the use of innovative space-based optical designs if such designs are rejected during the design review process for the very practical reason that there is no proven way to accurately analyze the resultant image data. I discuss ongoing research efforts to develop new image analysis algorithms specifically for space-based cameras that may help NASA and ESA to enhance the scientific returns from future astrophysical missions while possibly lowering total mission costs.
Advanced Technologies: Other
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Interferometric testbed for sub-nanometer stabilization of environmental motions for testing of advanced space telescopes
In several future space telescope missions, high long-term relative stability between optics is required for testing on the ground, as well as achieving the sensitivity goal in flight. Typically, thermal and seismic drifts on the ground are on the order of 1 μm over few hours, orders of magnitude above the testing requirements. To suppress these environmental motions, we developed a control system that is composed of interferometric sensors and PZT-based actuator. The system provides a stable environment to allow ground testing of the mission requirements. Our results show that this kind of system can provide picometer level stability at long timescale and that it should have many applications.
Pointing and image stability for spaceborne sensors: from comet impactors to observations of extrasolar planets
Stephen E. Kendrick, Jeremy Stober, Ian Gravseth
From hitting a comet to long-term observations to find and characterize extrasolar planets, the spacecraft platform pointing accuracy and stability are fundamental. We describe the pointing requirements for Deep Impact, Kepler, and future extrasolar planet missions such as EPIC, and the approach to allow stable long-term measurements. The guidance, navigation, and control system consists of a suite of systems which can include star trackers, gyros, fine guidance sensors, reaction wheels, fast steering mirrors, and active and passive isolation features. One-fifth to one-twentieth of a pixel attitude determination may be needed with stabilities an order of magnitude tighter for observations that may last thousands of seconds. 1.5 milliarcsecond 3-sigma pointing stability can be achieved for the observatory enabling precision measurements by the scientific payloads.
Novel in-space manufacturing concepts for the development of large space telescopes
There is a continuous demand for larger, lighter, and higher quality telescopes. Over the past several decades, we have seen the evolution from launchable 2 meter-class telescopes (such as Hubble), to today's demand for deployable 6 meter-class telescopes (such as JWST), to tomorrow's need for up to 150 meter-class telescopes. As the apertures continue to grow, it will become much more difficult and expensive to launch assembled telescope structures. To address this issue, we are seeing the emergence of new novel structural concepts, such as inflatable structures and membrane optics. While these structural concepts do show promise, it is very difficult to achieve and maintain high surface figure quality. Another potential solution to develop large space telescopes is to move the fabrication facility into space and launch the raw materials. In this paper we present initial in-space manufacturing concepts to enable the development of large telescopes. This includes novel approaches for the fabrication of the optical elements. We will also discuss potential optical designs for large space telescopes and describe their relation to the fabrication methods. These concepts are being developed to meet the demanding requirements of DARPA's LASSO (Large Aperture Space Surveillance Optic) program which currently requires a 150 meter optical aperture with a 16.6 degree field of view.
Poster Session: Current and Planned Missions
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SHIFTS: simulator for the Herschel imaging Fourier transform spectrometer
John V. Lindner, David A. Naylor, Bruce M. Swinyard
The Spectral and Photometric Imaging Receiver (SPIRE) is one of three scientific instruments on the European Space Agency's (ESA) Herschel Space Observatory (HSO). The medium resolution spectroscopic capabilities of SPIRE are provided by an imaging Fourier transform spectrometer (IFTS). A software simulator of the SPIRE IFTS was written to create realistic data products, making use of available qualification and test data. A graphical user interface (GUI) provides fast and flexible access to the simulation engine. We present the design and integration of the simulator, as well as results from the simulator predicting the instrument performance under varying operational conditions.
A comparison of the theoretical and measured performance of the Herschel/SPIRE imaging Fourier transform spectrometer
Locke D. Spencer, David A. Naylor, Bruce M. Swinyard
The Spectral and Photometric Imaging Receiver (SPIRE) is one of three scientific instruments on ESA's Herschel Space Observatory. An imaging Fourier transform spectrometer (IFTS) provides the medium resolution spectroscopic capabilities of SPIRE. This paper compares the measured performance of the SPIRE IFTS, as determined from flight model instrument verification tests, with theoretical expectations. This analysis includes a discussion of the instrument line shape, signal-to-noise, resolution, field of view and spectrometer sensitivity.
Performance evaluation of the Herschel/SPIRE imaging Fourier transform spectrometer
David A. Naylor, Jean-Paul Baluteau, Peter Davis-Imhof, et al.
The Spectral and Photometric Imaging Receiver (SPIRE) is one of three scientific instruments on ESA's Herschel Space Observatory. An imaging Fourier transform spectrometer, of the Mach-Zehnder configuration, provides low to medium resolution spectroscopic capability for SPIRE. The performance of the instrument is being evaluated during a series of test campaigns of the flight model before delivery to ESA. In this paper we present preliminary performance characteristics of the SPIRE spectrometer from the first test campaign of the flight model. We verify the instrument's conformance with fundamental design specifications such as spectral coverage and resolution. In addition, we identify, quantify, and explain some instrumental artefacts that have been observed during these tests.
Spectral and imaging performance of WFC3 interference filters
M. A. Quijada, R. Boucarut, R. Telfer, et al.
The Wide Field Camera 3 (WFC3) is a panchromatic imager that will be deployed in the Hubble Space Telescope (HST). The mission of the WFC3 is to enhance the imaging capability of HST in the ultraviolet, visible and near-infrared spectral regions. Together with a wavelength coverage spanning 2000 Angstrom to 1.7 μm, the WFC3 high sensitivity, high spatial resolution, and large field-of-view provide the astronomer with an unprecedented set of tools for exploring all types of exciting astrophysical terrain and for addressing many key questions in astronomy today. The filter complement, which includes broad, medium, and narrow band filters, naturally reflects the diversity of astronomical programs to be targeted with WFC3. The WFC3 holds 61 UVIS filter elements, 15 IR filters, and 3 dispersive elements. During ground testing, the majority of the UVIS filters were found to exhibit excellent performance consistent with or exceeding expectations; however, a subset of filters showed considerable ghost images; some with relative intensity as high as 10-15%. Replacement filters with band-defining coatings that substantially reduce these ghost images were designed and procured. A state-of-the-art characterization setup was developed to measure the intensity of ghost images, focal shift, wedge direction, transmitted uniformity and surface features of filters that could affect uniformity in flat-field images. We will report on these filter characterization methods, as well as the spectral performance measurements of the in-band transmittance and out-of-band blocking.
Filters for HST Wide Field Camera 3
S. Baggett, T. Brown, R. Boucarut, et al.
Wide-Field Camera 3 (WFC3) has been built for installation on the Hubble Space Telescope (HST) during the next servicing mission. The WFC3 instrument consists of both a UVIS and an IR channel, each with its own complement of filters. On the UVIS side, a selectable optical filter assembly (SOFA) contains a set of 12 wheels that house 48 elements (42 full-frame filters, 5 quadrant filters, and 1 UV grism). The IR channel has one filter wheel which houses 17 elements (15 filters and 2 grisms). While the majority of UVIS filters exhibited excellent performance during ground testing, a subset of filters showed filter ghosting; improved replacements for these filters have been procured and installed. No filter ghosting was found in any of the IR filters; however, the new IR detector for WFC3 will have significantly more response blueward of 800 nm than the original detector, requiring that two filters originally constructed on a fused silica substrate be remade to block any visible light transmission. This paper summarizes the characterization of the final complement of the WFC3 UVIS and IR filters, highlighting improvements in the replacement filters and the projected benefit to science observations.
An integral field spectrograph for the SNAP mission
A. Ealet, E. Prieto, A. Bonissent, et al.
A well-adapted spectrograph concept has been developed for the SNAP (SuperNova/Acceleration Probe) experiment. The goal is to ensure proper identification of Type Ia supernovae and to standardize the magnitude of each candidate by determining explosion parameters. The spectrograph is also a key element for the calibration of the science mission. An instrument based on an integral field method with the powerful concept of imager slicing has been designed and is presented in this paper. The spectrograph concept is optimized to have high efficiency and low spectral resolution (R~100), constant through the wavelength range (0.35-1.7μm), adapted to the scientific goals of the mission.
An integral field spectrograph demonstrator based on slicer technology for the SNAP mission
A dedicated optimized spectrograph based on an integral field unit adopting an imager slicing concept has been developed for the SNAP (SuperNova/Acceleration Probe) experiment. A prototype for the SNAP application is undergoing test at Marseille (France) between LAM (INSU) and CPPM/IPNL(IN2P3) to provide the verification of the optical performances associated with the development of a complete simulation of the instrument. The goal of this demonstrator is to prove the optical and functional requirements of the SNAP spectrograph: diffraction losses, spectrophotometric calibration, image quality and straylight.
Development of NIR detectors and science-driven requirements for SNAP
M. G. Brown, C. Bebek, G. Bernstein, et al.
Precision near infrared (NIR) measurements are essential for the next generation of ground and space based instruments. The SuperNova Acceleration Probe (SNAP) will measure thousands of type Ia supernovae up to a redshift of 1.7. The highest redshift supernovae provide the most leverage for determining cosmological parameters, in particular the dark energy equation of state and its possible time evolution. Accurate NIR observations are needed to utilize the full potential of the highest redshift supernovae. Technological improvements in NIR detector fabrication have lead to high quantum efficiency, low noise detectors using a HgCdTe diode with a band-gap that is tuned to cutoff at 1.7 μm. The effects of detector quantum efficiency, read noise, and dark current on lightcurve signal to noise, lightcurve parameter errors, and distance modulus fits are simulated in the SNAPsim framework. Results show that improving quantum efficiency leads to the largest gains in photometric accuracy for type Ia supernovae. High quantum efficiency in the NIR reduces statistical errors and helps control systematic uncertainties at the levels necessary to achieve the primary SNAP science goals.
Development of an MIR coronagraph for the SPICA mission
Keigo Enya, Shinichiro Tanaka, Takao Nakagawa, et al.
We present the status of the development of a coronagraph for the Space Infrared telescope for Cosmology and Astrophysics (SPICA). SPICA is the next generation infrared space-borne telescope missions led by Japan. The SPICA satellite will be equipped with a telescope that has a 3.5 m diameter monolithic primary mirror and the whole telescope will be cooled to 4.5 K. The satellite is planed be launched early in the 2010s into the sun-earth L2 libration halo orbit and execute infrared observations at wavelengths mainly between 5 and 200 micron. The SPICA mission gives us a unique opportunity for coronagraph observations, because of the large telescope aperture, a simple pupil shape, capability of infrared observations from space and the early launch. We have started development of the SPICA coronagraph in which the primary target is direct observation of extra-solar Jovian planets. The main wavelengths of observation, the required contrast and the inner working angle (IWA) of the SPICA coronagraph instrument are set to be 5-20 micron, 106, and approximately 5 λ/D respectively, whereλ is the observation wavelength and D is the diameter of the telescope aperture. Coronagraphs using a checkerboard mask and a concentric ring mask have been investigated. We found some solutions for the SPICA pupil, which has a large obstruction due to the secondary mirror and its supports. We carried out laboratory experiments to examine coronagraphs obtained using checkerboard-type pupil masks with a central obstruction. Nano-fabrication technology with electron beam was applied to manufacture a high precision mask consisting of a patterned aluminum film on a glass substrate and its performance was confirmed by experiments with visible light. Contrast higher than 106 was achieved. In the future, we will be developing a cryogenic mid-infrared test-bed to investigate the SPICA coronagraphs.
DPhot photometry method for the Spitzer Space Telescope
DPhot is a "deep photometry" computer program for measuring faint point sources from an overlapping set of astronomical images without making a mosaic. A grid of points is written on the sky. The point response function is used to calculate influence coefficients between the grid points and the pixels. A least-squares fit to the pixel data gives flux density measurements at small groups of grid points overlying images of sources. Summing and centroiding the groups of measurements gives a source list of flux densities and coordinates.
Poster Session: JWST
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Detectors for the James Webb Space Telescope near infrared spectrograph (NIRSpec)
Bernard J. Rauscher, Torsten Böker, Craig Cabelli, et al.
The Near Infrared Spectrograph (NIRSpec) will be the James Webb Space Telescope's (JWST's) primary near-infrared spectrograph. NIRSpec is a multi-object spectrograph with fixed-slit and integral field modes. EADS/Astrium is building NIRSpec for the European Space Agency (ESA), with NASA is providing the detector subsystem and programmable multi-aperture mask. In this paper, we summarize recent progress on the detector subsystem including tests demonstrating that JWST's Rockwell HAWAII-2RG sensor chip assemblies have achieved Technology Readiness Level 6 (TRL-6). Achieving TRL-6 is an important milestone because TRL-6 is required for flight.
Onboard calibration sources for the mid-infrared instrument (MIRI) on the James Webb space telescope
A. Glasse, D. Lee, P. Parr-Burman, et al.
We have developed a novel light source for flat fielding and transmission monitoring of the Mid-Infrared Instrument on the JWST. The source uses a hot tungsten filament, mounted in a hemispherical, non-imaging flux concentrator. The design is compact, with the hemisphere having a diameter of 20 mm, and dissipates only 10 milliWatts of electrical power when operating. We describe the most important features of the design, and present the first measurements of its photometric performance.
Mounting MIRI's double prism
MIRI, the Mid-InfraRed Instrument, is one of the 4 instruments currently under development for the NASA/ESA James Webb Space Telescope. Together with the US, MIRI is built by a consortium of 28 European institutes under the lead-management of ESA. The instrument consists of two main modules, a spectroscopic and an imaging part. The imager will allow imaging, coronography and low resolution spectroscopy. The latter mode will use a ZnS-Ge-double-prism assembly as dispersive element. In this contribution, we present the design concept for the mounting of this double prism assembly which places the prisms into the optical path of the imager via an interface to the imager's filterwheel. Despite the very limited available space in the filterwheel and the high weight of the prisms (in comparison to the other filters in the filterwheel), the kinematic mounting of the individual prisms guarantees exact placement with smallest possible induced forces into the prisms. The here presented design of the development model of the double prism assembly is based upon GEM calculation. Experimental thermal and vibrational tests will be performed by the time of this conference.
Development of robust thermo-optical thin-film membranes for the James Webb Space Telescope sunshield
The James Webb Space Telescope (JWST) observatory is the first segmented, deployed optical telescope with optical elements exposed to a space environment that will be thermally controlled to operate at cryogenic temperatures. A multilayered sunshield comprised of layers of polyimide film coated with alloyed silicon and multilayered aluminum based coatings has been developed to control the operating temperature of and minimize stray light seen by the Optical Telescope Element (OTE). The key requirements of the membrane material are to control thermal stability and steady-state thermal performance of the OTE, limit solar and infrared light transmission, meet ESD grounding requirements, have low contaminant levels, and to have highly durable, robust coatings. The testing that was done to evaluate the durability of the membrane material and to show that it will survive the fabrication, integration, test, and launch environments will be explored.
Stray light from galactic sky and zodiacal light for JWST
The open telescope design of the James Webb Space Telescope (JWST) allows light from off-axis sources to scatter into the instrument field of view. The significant sources of stray light in the near IR and the mid-infrared waveband are galactic light and reflected sunlight and thermal emission from the zodiacal dust. The stray light from these sources was calculated with the ASAP software. Backward ray tracing was efficiently used in the prediction of the stray light from the sky. Since the galactic and zodiacal light is distributed over the whole sky, the sky was divided into 7200 patches of size 3 degrees by 3 degrees, and the contribution from each patch was calculated. The instrument geometric susceptibility for each sky patch was calculated with backward ray tracing. Multiplying the geometric susceptibility and the sky radiance, we are able to calculate the stray light from each sky patch. Total stray light from the full sky is then calculated by summing the individual patch contributions. The stray light from the galactic sky and zodiacal light has been calculated for different orientations of the observatory relative to the sky.
The JWST infrared Scanning Shack Hartman System: a new in-process way to measure large mirrors during optical fabrication at Tinsley
Tinsley, under JWST funding, has led the team that has developed a novel and highly versatile piece of ground support equipment for optical surface testing of JWST beryllium mirror segments during optical fabrication. The infrared Scanning Shack Hartmann System (SSHS) offers the advantage of being able to characterize mid-to-high spatial frequency structure on a mirror from early stages of fabrication when slopes may be high and surface irregular, eliminating the need for an extra polishing step before metrology. Working at 9.3μm, the system will accept and measure a wide dynamic range of surface characteristics, including roll-off near the edge of the segment. Knowledge of these surface features at the early grinding stage is imperative if characteristics such as mirror edge roll-off are to be minimized. WaveFront Sciences, producer of commercial COAS and Columbus Shack Hartmann systems, has provided systems engineering and component support for the SSHS system. The SSHS system is based around a special Long Wave Infrared (LWIR) wavefront sensor developed by WaveFront Sciences that is scanned over the mirror surface, making sub-aperture measurements. The smaller, high-resolution measurements are then stitched together to provide high-resolution measurement of the entire mirror surface, even though the surface is in a rough ground state. The system leverages technology from smaller visible instrumentation produced by Wavefront Sciences, especially those for surface sub-aperture measurements of semiconductor wafers. This paper will describe the implementation of the first infrared scanning Shack Hartmann system at Tinsley to address optical fabrication optimization of the JWST Primary Mirror Segments.
Preliminary evaluation of the vibration environment within JSC Chamber A using a simultaneous phase-shifting interferometer
James B. Hadaway, Ron Eng, John Speed, et al.
The vibration environment in and around the Space Environment Simulation Laboratory Chamber A at the Johnson Space Center was recently characterized via accelerometer measurements in support of the thermal-vacuum testing of the James Webb Space Telescope (JWST). Interferometric measurements were also conducted in order to (i) evaluate the ability to make valid measurements with a high speed interferometer within the chamber, (ii) coarsely evaluate the vibration sources, and (iii) provide some correlation between the accelerometer data & the interferometer data. A simultaneous phase-shifting interferometer was used for the measurements. Measurements were made, using a 2" collimated beam & return flat, at various places in and around the chamber, including: across the high-bay floor outside the chamber, across the payload table at the ground floor level of the chamber, from the top of the chamber to the payload table, and from the top to the 3rd floor catwalk. Measurements were made in quiet mode, with a roughing pump on, with exhaust fans on, and with both the pump & fans on. Accelerometer data was taken simultaneously with the interferometer data. The fringe motion was well within capture range of the interferometer for all measurements. The fringes were the most stable across the payload table and the least stable from the top to the catwalk, but the difference was not extreme. The quality of the interferometer data was essentially the same for all configurations (top-to-bottom, top-to-catwalk, etc.) and cases (pump/fans on/off). The results of these measurements will be used to help implement the thermal-vacuum testing of the JWST.
Wave-optics analysis of pupil imaging
Pupil imaging performance is analyzed from the perspective of physical optics. A multi-plane diffraction model is constructed by propagating the scalar electromagnetic field, surface by surface, along the optical path comprising the pupil imaging optical system. Modeling results are compared with pupil images collected in the laboratory. The experimental setup, although generic for pupil imaging systems in general, has application to the James Webb Space Telescope (JWST) optical system characterization where the pupil images are used as a constraint to the wavefront sensing and control process. Practical design considerations follow from the diffraction modeling which are discussed in the context of the JWST Observatory.
Poster Session: TPF
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Study of coronagraphic techniques
Volker Tolls, Michael Aziz, Robert A. Gonsalves, et al.
Smithsonian Astrophysical Observatory (SAO) has set up a program to study coronagraphic techniques. The program consists of the development of new fabrication methods of occulter masks, characterization of the manufactured masks, and application of the masks to study speckle reduction technique. Our occulter mask fabrication development utilizes a focused ion beam system to directly shape mask profiles from absorber material. Initial milling trials show that we can shape nearly Gaussian-shaped mask profiles. Part of this development is the characterization of absorber materials, poly(methyl methacrylate) doped with light-stable chromophores. For the characterization of the masks we have built a mask scanner enabling us to scan the transmission function of occulter masks. The real mask transmission profile is retrieved applying the maximum entropy method to deconvolve the mask transmission function from the beam profile of the test laser. Finally, our test bed for studying coronagraphic techniques is nearing completion. The optical setup is currently configured as a classical coronagraph and can easily be re-configured for studying speckle reduction techniques. The development of the test bed control software is under way. This paper we will give an update of the status of the individual program elements.
Performance of TPF's high-contrast imaging testbed: modeling and simulations
The performance of the high-contrast imaging testbed (HCIT) at JPL is investigated through optical modeling and simulations. The analytical tool is an optical simulation algorithm developed by combining the HCIT's optical model with a speckle-nulling algorithm that operates directly on coronagraphic images, an algorithm identical to the one currently being used on the HCIT to actively suppress scattered light via a deformable mirror. It is capable of performing full three-dimensional end-to-end near-field diffraction analysis on the HCIT's optical system. By conducting extensive speckle-nulling optimization, we clarify the HCIT's capability and limitations in terms of its contrast performance under various realistic conditions. Considered cases include non-ideal occulting masks, such as a mask with parasitic phase-delay errors (i.e., a not band-limited occulting mask) and one with damped ripples in its transmittance profiles, as well as the phase errors of all optics. Most of the information gathered on the HCIT's optical components through measurement and characterization over the last several years at JPL has been used in this analysis to make the predictions as accurate as possible. Our simulations predict that the contrast values obtainable on the HCIT with narrow-band (monochromatic) illumination at 785nm wavelength are Cm=1.58x10-11 (mean) and C4=5.11x10-11(at 4λ/D), in contrast to the measured results of Cm~6×10-10 and C4~8×10-10, respectively. In this paper we report our findings about the monochromatic light performance of the HCIT. We will describe the results of our investigation about the HCIT's broad-band performance in an upcoming paper.
The effects of instrumental elliptical polarization on stellar point spread function fine structure
We present a status report on a study on the effects of instrumental polarization on the fine structure of the stellar point spread function (PSF). These effects are important to understand because the the aberration caused by instrumental polarization on an otherwise diffraction-limited PSF will likely have have severe consequences for extreme high contrast imaging systems such as NASA's proposed Terrestrial Planet Finder (TPF) mission and the proposed NASA Eclipse mission. The report here, describing our efforts to examine these effects, includes two parts: 1) a numerical analysis of the effect of metallic reflection, with some polarization-specific retardation, on a spherical wavefront; 2) an experimental approach for observing this effect, along with a status report on preliminary laboratory results. The numerical analysis indicates that the inclusion of polarization-specific phase effects (retardation) results in a point spread function (PSF) aberration more severe than the amplitude (reflectivity) effects previously recorded in the literature. Preliminary in-lab results are consistent with our numerical predictions.
Fabrication and characteristics of free-standing shaped pupil masks for TPF-coronagraph
Direct imaging and characterization of exo-solar terrestrial planets require coronagraphic instruments capable of suppressing star light to 10-10. Pupil shaping masks have been proposed and designed1 at Princeton University to accomplish such a goal. Based on Princeton designs, free standing (without a substrate) silicon masks have been fabricated with lithographic and deep etching techniques. In this paper, we discuss the fabrication of such masks and present their physical and optical characteristics in relevance to their performance over the visible to near IR bandwidth.
Studying a simple TPF-C
The NASA Terrestrial Planet Finder Coronagraph (TPF-C) mission envisions using a space telescope with an approximately 8 m by 3 m diameter primary mirror to image and spectroscopically characterize at visible wavelengths Earth-like planets orbiting nearby stars. Such terrestrial planets have intensities of 10-10 relative to their stars at separations of a fraction of an arcsecond, requiring extremely high-contrast imaging capabilities. A simple optical system with a minimal number of surfaces will likely have the best chance to image a very faint source near a bright star. A proposed version of a TPF-C integrated starlight suppression system and camera called SpeckleCam encompasses such a design. It incorporates two high-density deformable mirrors to control phase and amplitude wavefront errors, a coronagraph to suppress the stellar diffraction pattern, and simultaneous imaging in three passbands. We use the SpeckleCam concept to examine the utility of the PROPER modeling package, a set of IDL routines that simulate wavefront propagation in an optical system.
Nulling and adaptive optics for very high dynamic range coronagraph
We have started demonstrating a technique for high dynamic range observations in the lab. This method, proposed by Nishikawa et al., combines a nulling interferometer, a wavefront compensator, and a coronagraph. In the experiments, two beams are generated by a beam splitter and they are combined by another beam splitter under an intensity-unbalanced nulling condition. After the unbalanced nulling interferometer (UNI), normal wavefront sensor and two deformable mirrors are applied for phase and amplitude correction (PAC). Wavefront errors of the two original beams, large errors after the UNI, and compensated errors after the PAC by the deformable mirrors will be measured. After the UNI-PAC method is applied, a downstream coronagraph optics will be set to see that the peak intensity of the central star is dimmed and speckle noise level is also reduced relative to off-axis planet intensity. Possible applications of the method are also discussed.
Pointing control system for the Eclipse mission
Paul B. Brugarolas, Tooraj Kia, Diane Li, et al.
This paper describes the high precision pointing control system for the Eclipse telescope. Eclipse is a mission under study at the Jet propulsion Laboratory. Eclipse is a space telescope that uses a coronagraph for high-contrast optical astronomy to study planets around nearby stars. Eclipse observations require very precise pointing, 0.01 arcseconds (3- σ) during the exposure periods that could be as long as 1000 seconds. This study shows a two layer pointing approach for achieving these requirements. In the first layer, the spacecraft ACS stabilizes the line-of-sight to 0.15 arcseconds (3- σ). In the second layer, a Fine Steering Mirror centers the star in the occulting mask to the 0.01 arcseconds (3-σ). The knowledge needed to achieve the desired pointing accuracy is provided by a Fine Guidance Camera. In addition, structural and thermal induced jitter is minimized by design, and through the use of reaction wheel isolators and operational constraints.
PIAA coronagraph design: system optimization and first optics testing
Eugene Pluzhnik, Olivier Guyon, Mark Warren, et al.
An optical system capable of extremely high contrast imaging (about 10-10) at separations comparable to the telescope's diffraction limit is critical for direct imaging of extrasolar terrestrial planets. The PIAA coronagraph (Guyon 2003) based on pupil apodization by geometrical remapping of the flux in the pupil plane seems to be especially adopted for the exoplanet imaging. Although this technique combines many of the advantages found separately in other coronagraphs, two serious concerns remain unanswered: optics manufacturability and effects of diffraction propagation. We describe here a hybrid PIAA/CPA (Classical Pupil Apodization) design in which the apodization is shared between a remapping system (the main apodizer) and "classical" apodizers (auxillary apodizers). In this scheme, optics become easier to manufacture and diffraction effects can be decreased to a level consistent with a 10-10 PSF contrast in a wide spectral band. We show how the parameters of hybrid PIAA/CPA system can be optimized and present some results of optical testing for the high optical quality prototype of PIAA coronagraph.
Polarization and spectral differential imager using channeled spectrum
The light from an exoplanet is expected to be different from that of its parent star in regard to polarization and spectral features. Thus, polarization or spectral differential technique will be a powerful tool for direct detection of exoplanets. We propose a novel technique that enables to detect both polarization and spectral differential images. This technique will be used in combination with the other high-contrast imagers to enhance the performance. This approach uses two Wollaston prisms (WPs) and a thick retarder (TR) inserted between the WPs. Two WPs generate four images and make it possible to obtain polarization differential images. Spectra of these four images have sinusoidal patterns (channeled spectra) due to the WP-TR-WP system. By inserting an interference filter, this system works as bandpass filters whose center wavelengths are different between the images. Therefore, both polarization and spectral differential images can be obtained. Furthermore, we propose to use two variable retarders (VRs) to remove differential aberrations caused by different optical paths of these four images. One VR is inserted in front of WP-TR-WP system to modulate the polarized light beams, and the other one is inserted between WPs to modulate the channeled spectra. By modulating the retardations of the VRs, it becomes possible to remove the differential aberrations. We present the principle of this method. Currently, we are conducting the preliminary laboratory experiment. The results of the laboratory demonstrations will be also reported.
Exoplanet transit analysis using the point spread function
George Tremberger Jr., A. Portnov, E. Cheung, et al.
The behavior of the point spread function could be analyzed in images of stars with known exoplanets. A transform plot of the log intensity versus the Gaussian or sinc function value was used in the analysis. The intercept was extrapolated for brightness information and the slope or adjacent log intensity difference was also fitted. The robustness of the algorithm was evaluated using a bootstrap statistical method that does not require the error to follow a Gaussian distribution. The bootstrap confidence interval was used to assess the changes in the signal before and during transit with simulations that include Gaussian errors as well as non-Gaussian ones. Simulations using Gaussian noise suggested that transit signal changes at about 1-sigma noise level are detectable with a 90% confidence interval, while non-Gaussian noise simulations suggested a lower confidence level. This bootstrap method and the standard Chi-square method used in the analysis of the point spread function of data taken with space telescopes such as Spitzer was compared. The impact of using under-sampled CCD observations with super-sampled point spread functions on the bootstrap analysis is discussed. The analysis of images such as HD 209548 (captured by our 16-inch telescope) suggested that the point spread function approach is comparable to the photometric approach but requires fewer images. The application to other images from telescopes such as Hubble is also discussed.
Fractal characteristics of exoplanet transit time series data
George Tremberger Jr., H. Yao, A. Flamholz, et al.
Exoplanet transit time series photometric data usually contain noise levels that are comparable to the transit signal jumps. The analysis that assumes Gaussian noise and extensive data averaging calibrated to a reference star has been the traditionally used algorithm. This paper studied the fractal property of the time series and found that the fractal dimension changes for time series data that contain transits. The Higuchi fractal method, where the length of the increment in various time lags is plotted against the lags, was used in this study. (Higuchi, T., "Approach to an irregular time series on the basis of fractal theory", Physica D, vol 31, 277-283, 1988). The fractal algorithm was calibrated with the Weierstrass function. Simulations using Gaussian noise suggested that a transit jump signal at about 1-sigma noise level would produce changes in fractal dimension, while non-Gaussian noise simulations suggested a higher transit jump signal. The fractal algorithm was applied to data collected on HD 209458 as well as on published data. The transit caused a fractal dimension change of about 0.06. An over-exposed CCD dataset with much noise was also analyzed and a fractal dimension change of about 0.02 was obtained. The result suggests that fractal dimension analysis, without the assumption of error normality, is an alternative method for identifying transits in time series photometric data.
A hand-held near-infrared slit spectrograph for Earth observations
Srikrishna Kanneganti, Chan Park, Heather Hershley, et al.
We describe the optical and mechanical design of a simple hand-held near infrared spectrograph constructed to produce observations of the spectrum of scrambled light from the Earth from aboard the International Space Station. Observing the Earth in this manner simulates the changing perspective on an extra-solar terrestrial planet observed as a point source by the Terrestrial Planet Finder. A Sensors Unlimited, Inc. SU320-M InGaAs(0.86 - 1.72μm) camera detects the dispersed spectrum and outputs NTSC video to be recorded and also permits frame grabbing. One of the three copies of the instrument is currently aboard the International Space Station. The optical and mechanical design was conceived and executed by graduate and undergraduate students at the University of Virginia.
Estimated performance of a symmetric nulling coronagraph for exoplanet imaging
D. Ren, E. Serabyn
The direct detection of the earth-similar planets nearby bright stars needs high-contrast imaging. We proposed a nulling coronagraph that can, in principle, totally cancel the on-axis point-source starlight for broadband high-contrast imaging. The nulling coronagraph also features close angular distance imaging and high throughput. Equipped with a telescope with only 1.5-m aperture size, it has the potentiality to be able to resolving and directly detecting earth-similar planets at 0.1" (1 λ/D) close-distance in the visible wavelength range. The requirement for a small telescope is a significant advantage for future space missions. We discuss the working principle, instrument realization, error and sensitivity analysis, and the estimated performance of the nulling coronagraph.
Poster Session: Future Mission Concepts
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The Space Infrared Interferometric Telescope (SPIRIT): mission study results
David Leisawitz, Charles Baker, Amy Barger, et al.
We report results of a recently-completed pre-Formulation Phase study of SPIRIT, a candidate NASA Origins Probe mission. SPIRIT is a spatial and spectral interferometer with an operating wavelength range 25 - 400 μm. SPIRIT will provide sub-arcsecond resolution images and spectra with resolution R = 3000 in a 1 arcmin field of view to accomplish three primary scientific objectives: (1) Learn how planetary systems form from protostellar disks, and how they acquire their chemical organization; (2) Characterize the family of extrasolar planetary systems by imaging the structure in debris disks to understand how and where planets form, and why some planets are ice giants and others are rocky; and (3) Learn how high-redshift galaxies formed and merged to form the present-day population of galaxies. Observations with SPIRIT will be complementary to those of the James Webb Space Telescope and the ground-based Atacama Large Millimeter Array. All three observatories could be operational contemporaneously.
JASMINE simulator
We explain simulation tools in JASMINE project (JASMINE simulator). The JASMINE project stands at the stage where its basic design will be determined in a few years. Then it is very important to simulate the data stream generated by astrometric fields at JASMINE in order to support investigations into error budgets, sampling strategy, data compression, data analysis, scientific performances, etc. Of course, component simulations are needed, but total simulations which include all components from observation target to satellite system are also very important. We find that new software technologies, such as Object Oriented(OO) methodologies are ideal tools for the simulation system of JASMINE(the JASMINE simulator). In this article, we explain the framework of the JASMINE simulator.
JASMINE: galactic structure surveyor
We introduce a Japanese plan of infrared(z-band:0.9μm) space astrometry(JASMINE-project). JASMINE is the satellite (Japan Astrometry Satellite Mission for INfrared Exploration) which will measure distances and apparent motions of stars around the center of the Milky Way with yet unprecedented precision. It will measure parallaxes, positions with the accuracy of 10 micro-arcsec and proper motions with the accuracy of ~ 4microarcsec/ year for stars brighter than z=14mag. JASMINE can observe about ten million stars belonging to the bulge components of our Galaxy, which are hidden by the interstellar dust extinction in optical bands. Number of stars with σ/π < 0.1 in the direction of the Galactic central bulge is about 1000 times larger than those observed in optical bands, where π is a parallax and σ is an error of the parallax. With the completely new "map of the bulge in the Milky Way", it is expected that many new exciting scientific results will be obtained in various fields of astronomy. Presently, JASMINE is in a development phase, with a target launch date around 2015. We adopt the following instrument design of JASMINE in order to get the accurate positions of many stars. A 3-mirrors optical system(modified Korsch system)with a primary mirror of~ 0.85m is one of the candidate for the optical system. On the astro-focal plane, we put dozens of new type of CCDs for z-band to get a wide field of view. The accurate measurements of the astrometric parameters requires the instrument line-of-sight highly stability and the opto-mechanical highly stability of the payload in the JASMINE spacecraft. The consideration of overall system(bus) design is now going on in cooperation with Japan Aerospace Exploration Agency(JAXA).
CCD centroiding experiment for JASMINE and ILOM
Taihei Yano, Hiroshi Araki, Naoteru Gouda, et al.
JASMINE and ILOM are space missions which are in progress at the National Astronomical Observatory of Japan. These two projects need a common astrometric technique to obtain precise positions of star images on solid state detectors to accomplish the objectives. We have carried out measurements of centroid of artificial star images on a CCD to investigate the accuracy of the positions of the stars, using an algorithm for estimating them from photon weighted means of the stars. We find that the accuracy of the star positions reaches 1/300 pixel for one measurement. We also measure positions of stars, using an algorithm for correcting the distorted optical image. Finally, we find that the accuracy of the measurement for the positions of the stars from the strongly distorted image is under 1/150 pixel for one measurement.
Nano-JASMINE: a 10-kilogram satellite for space astrometry
Yukiyasu Kobayashi, Naoteru Gouda, Takuji Tsujimoto, et al.
The current status of the nano-JASMINE project is presented. Nano-JASMINE - a very small satellite weighing less than 10 kg - aims to carry out astrometry measurements of nearby bright stars. This satellite adopts the same observation technique that was used by the HIPPARCOS satellite. In this technique, simultaneous measurements in two different fields of view separated by an angle that is greater than 90° are carried out; these measurements are performed in the course of continuous scanning observations of the entire sky. This technique enables us to distinguish between an irregularity in the spin velocity and the distribution of stellar positions. There is a major technical difference between the nano-JASMINE and the HIPPARCOS satellites-the utilization of a CCD sensor in nano-JASMINE that makes it possible to achieve an astrometry accuracy comparable to that achieved by HIPPARCOS by using an extremely small telescope. We developed a prototype of the observation system and evaluated its performance. The telescope (5cm) including a beam combiner composed entirely of aluminum. The telescope is based on the standard Ritchey- Chretien optical system and has a composite f-ratio of 33 that enables the matching of the Airy disk size to three times the CCD pixel size of 15μm. A full depletion CCD will be used in the time delay integration (TDI) mode in order to efficiently survey the whole sky in wavelengths including the near infrared. The nano-JASMINE satellite is being developed as a piggyback system and is hoped for launch in 2008. We expect the satellite to measure the position and proper motion of bright stars (mz < 8.3) with an accuracy of 1 mas, this is comparable to the accuracy achieved with the HIPPARCOS satellite.
Aluminum-made 5-cm reflecting telescope for Nano-JASMINE
We report an outline and a current status of developing a small, all-aluminum made telescope for Nano-JASMINE. Nano-JASMINE is a nano-size astrometry satellite that will demonstrate some key technologies required for JASMINE (Japan Astrometry Satellite Mission for Infrared Exploration) in a real space environment and will measure absolute positions of bright stars (z ≤ 8 mag) with accuracies about 1 milli-arcsecond in a few years mission. It has a Ritchey-Chretien type telescope with a 5-cm effective aperture, a 167-cm focal length and a field of view of 0.5x0.5 degree. The telescope only occupies a volume about 15x12x12 cm, and weighs two kilograms or less. Almost all of the structures and the optical elements of the telescope, including two aspherical mirrors three flat mirrors and a dual-angled flat mirror that combines the beam from a relative angle of 99.5 degrees into the primary mirror, are made out of aluminum alloy, being figured by diamond turning machines. The Bread Board Model (BBM) of the telescope was now measured to be achieving a diffraction-limited performance at room temperature.
Laser interferometric high-precision angle monitor for JASMINE
Yoshito Niwa, Koji Arai, Masaaki Sakagami, et al.
The JASMINE instrument uses a beam combiner to observe two different fields of view separated by 99.5 degrees simultaneously. This angle is so-called basic angle. The basic angle of JASMINE should be stabilized and fluctuations of the basic angle should be monitored with the accuracy of 10 microarcsec in root-mean-square over the satellite revolution period of 5 hours. For this purpose, a high-precision interferometric laser metrogy system is employed. One of the available techniques for measuring the fluctuations of the basic angle is a method known as the wave front sensing using a Fabry-Perot type laser interferometer. This technique is to detect fluctuations of the basic angle as displacement of optical axis in the Fabry-Perot cavity. One of the advantages of the technique is that the sensor is made to be sensitive only to the relative fluctuations of the basic angle which the JASMINE wants to know and to be insensitive to the common one; in order to make the optical axis displacement caused by relative motion enhanced the Fabry-Perot cavity is formed by two mirrors which have long radius of curvature. To verify the principle of this idea, the experiment was performed using a 0.1m-length Fabry-Perot cavity with the mirror curvature of 20m. The mirrors of the cavity were artificially actuated in either relative way or common way and the resultant outputs from the sensor were compared.
Programmatics and development update for the Orion MIDEX star formation survey mission
The Orion MIDEX mission is a 1.2m UV-visual observatory orbiting at L2 that will conduct the first-ever high spatial resolution survey of a statistically significant sample of visible star-forming environments in the Solar neighborhood in emission lines and continuum. This survey will be used to characterize the star and planet forming environments within 2.5 kpc of the Sun, infer global properties and star formation histories in these regions, understand how environment influences the process of star and planet formation, and develop a classification scheme for star forming regions. Based on these findings a similar survey will be conducted of large portions of the Magellanic Clouds, extending the classification scheme to new types of regions common in external galaxies, allowing the characterization of low mass star forming environments in the Magellanic Clouds, study of the spatial distribution of star forming environments and tracing of star formation history. Finally the mission will image a sample of external galaxies out to ~5 Mpc. The distribution of star forming region type will be mapped as a function of galactic environment to infer the distribution and history of low-mass star formation over galactic scales, and characterize the stellar content and star formation history of galaxies. We present in this paper an update on the development of the mission and the hardware necessary to deliver its required performance.
Poster Session: Future Telescope Concepts
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Off-axis reflecting telescope with axially-symmetric optical property and its applications
The basic concept and fundamental result of a recently developed geometric aberration theory for classical off-axis reflecting telescopes and imaging systems are presented. It is shown that a classical off-axis reflecting telescope can be designed to have practically axially-symmetric optical property by eliminating the dominant aberration (linear astigmatism) caused by the asymmetric geometry. A simple closed-form equation for elimination of linear astigmatism is presented. Also, to show how the developed aberration theory can be applied to current and future telescopes, several off-axis reflecting telescopes and imaging systems are designed and analyzed.
Zero distortion three mirror telescope designed for the Dark Universe Explorer (DUNE) space mission
Robert Grange, Bruno Milliard, Sébastien Vivès, et al.
A feasibility study is presently led by CNES for the Dark UNiverse Explorer (DUNE), a space mission designed to provide unprecedented constraints on dark matter and dark energy using weak gravitational lensing measurements over a very large region of the sky (20 000 square degrees). To achieve this scientific goal, the instrument requires a stable 0.23 arc second FWHM PSF with very low ellipticity (6%) over a field of view of 0.55 square degree. To perform the survey we adopted the drift scan mode which brings many advantages in this type of mission but adds the unusual requirement of a zero distortion optical design. We will present the optical performances of a 1.2 meters Korsch three mirror telescope concept (called NODI for NO DIstortion) where the third mirror works with an atypical large magnification and a slightly curved focal surface to obtain zero distortion over an annular 1.7 degrees field of view. A mosaic of 64 CCD detectors of 8 Mega pixels each is shown to pave the curved focal surface without significant degradation of the distortion.
Analysis of the optical design for the SAFIR telelscope
Paul Goldsmith, Behrouz Khayatian, Matt Bradford, et al.
SAFIR, the Single Aperture Far Infra Red Observatory, is a very powerful space mission that will achieve background-limited sensitivity in the far infrared-submillimeter spectral region. Many processes of enormous interest to astronomers can best be studied in this wavelength range, but require the demanding combination of high sensitivity, good angular resolution, and spectroscopic capability. SAFIR is a 10m class telescope offering good angular resolution, cooled to below 5 K in order to achieve background-limited sensitivity, and equipped with a complement of large-format cameras and broadband spectrometers. Successful operation of such a facility is critically dependent on achieving the level of sensitivity expected, but this is rendered difficult by potential pickup from unwanted sources of radiation. This problem is exacerbated by the fact that the emission from the optical system itself is minimal due to its low temperature, thus emphasizing the importance of minimizing pickup from unwanted astronomical sources of radiation, including the emission from dust in our solar system (analogous to the zodiacal light, hence "zodi"), and the emission from warm dust in the Milky Way (Galactic "cirrus"). The extreme sensitivity of SAFIR to these unwanted sources of radiation makes it essential to understand the relative sensitivity of the telescope/detector system to radiation coming from angles far outside the main beam, and to develop designs which minimize this pickup. In this paper we analyze in some detail the relative telescope sensitivity (referred to as the antenna pattern by microwave engineers) for different designs of SAFIR. These calculations include edge diffraction from the secondary and primary reflector, and also the effect of blockage by the secondary and blockage and scattering by support legs in a symmetric system. By convolving the antenna pattern with the brightness of the sky due to the zodi and cirrus, we can calculate the power received when the antenna is pointed in any specified direction. We can also compare the undesired pickup for different designs, in particular symmetric vs. asymmetric (off-axis or unblocked) antenna configurations. These considerations are vital for achieving the most efficient SAFIR design possible, in terms of achieving maximum sensitivity while being able to observe over a large fraction of the sky.
Experiment and modal analysis on the primary mirror structure of Space Solar Telescope
Primary mirror with Φ 1m and f 3.5m is the most important optical part in Space Solar Telescope (SST), which is designed to make observations of transient and steady state solar hydrodynamic and magnetohydrodynamic processes and is being researched and manufactured by National Astronomical Observatories. The primary mirror structure(PMS), a crucial linker for the optical and other subsystems, includes primary mirror and its supporting frame. Therefore, this part must satisfy the optical sufficient strength, stiffness, and thermal stability requirements under the space environment and in the launching process. In this paper the primary mirror structure and its connection are described. The scheme of modal analysis and experiment is built, according to the specific dynamic requirements of the primary mirror structure in Space Solar Telescope. The dynamic response on the primary mirror structure is analyzed with MSC.NASTRAN software. Comparing these results with mode parameters obtained from modal experiment analysis. Modal experiment uses freely hanging primary mirror structure, simple input multi-output, and modal parameter identification through CADA-X software. Both results provide evidences to develop this satellite design.
Poster Session: Advanced Technologies
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Detailed design of the imaging magnetograph experiment (IMaX): a visible imager magnetograph for the Sunrise mission
A. Álvarez-Herrero, T. Belenguer, C. Pastor, et al.
In this work, it is described the Imaging Magnetograph eXperiment, IMaX, one of the three postfocal instruments of the Sunrise mission. The Sunrise project consists on a stratospheric balloon with a 1 m aperture telescope, which will fly from the Antarctica within the NASA Long Duration Balloon Program. IMaX will provide vector magnetograms of the solar surface with a spatial resolution of 70 m. This data is relevant for understanding how the magnetic fields emerge in the solar surface, how they couple the photospheric base with the million degrees of temperature of the solar corona and which are the processes that are responsible of the generation of such an immense temperatures. To meet this goal IMaX should work as a high sensitivity polarimeter, high resolution spectrometer and a near diffraction limited imager. Liquid Crystal Variable Retarders will be used as polarization modulators taking advantage of the optical retardation induced by application of low electric fields and avoiding mechanical mechanisms. Therefore, the interest of these devices for aerospace applications is envisaged. The spectral resolution required will be achieved by using a LiNbO3 Fabry-Perot etalon in double pass configuration as spectral filter before the two CCDs detectors. As well phase-diversity techniques will be implemented in order to improve the image quality. Nowadays, IMaX project is in the detailed design phase before fabrication, integration, assembly and verification. This paper briefly describes the current status of the instrument and the technical solutions developed to fulfil the scientific requirements.
Performance modeling and development of an L3-CCD camera system for high cadence imaging with maximum efficiency
High-cadence imaging is required in several astronomical scenarios. These include: studies of rapidly varying sources, achieving maximum signal-to-noise observations of bright objects, and high dynamic range scenarios, such as faint objects embedded in a crowded field of bright objects. Conventional CCDs have drawbacks in this regime, because many short exposures are needed (either for timeseries sampling, or simply to avoid saturation), with extended readout times between exposures. Consequently, the duty cycle (ratio of exposure time to readout time) dramatically worsens as exposures get shorter. However, Low Light Level CCDs (L3-CCDs) offer low readout noise, high readout rates, and 100% duty cycle. Coupled with its fast frame-transfer mechanism (~2ms to shift the image to the storage area), an L3-CCD can sustain essentially continuous open-shutter time. Our models demonstrate that for a fixed observing time, the L3-CCD will deliver a better signal to noise performance in the high-cadence imaging regime when compared to similar CCDs, even when the latter's performance is optimised by windowing and binning. We also demonstrate that the improved duty cycle reduces the photometric impact of atmospheric scintillation, for any given aperture of telescope. We outline the integration of an L3-CCD into our camera system for high cadence imaging.
Improved cryogenic testing capability at Marshall Space Flight Center's X-ray Cryogenic Facility
Jeff Kegley, Mark Baker, Jay Carpenter, et al.
Marshall Space Flight Center's X-ray Cryogenic Facility (XRCF) has been performing optical wavefront testing and thermal structural deformation testing at sub-liquid nitrogen cryogenic temperatures since 1999. Recent modifications have been made to the facility in support of the James Webb Space Telescope (JWST) program. The test article envelope and the chamber's refrigeration capacity have both been increased. A new larger helium-cooled enclosure has been added to the existing enclosure increasing both the cross-sectional area and the length. This new enclosure is capable of supporting six JWST Primary Mirror Segment Assemblies. A second helium refrigeration system has been installed essentially doubling the cooling capacity available at the facility. Modifications have also been made to the optical instrumentation area. Improved access is now available for both the installation and operation of optical instrumentation outside the vacuum chamber. Chamber configuration, specifications, and performance data will be presented.
Wavefront sensing and control architecture for the Spherical Primary Optical Telescope (SPOT)
Bruce H. Dean, Jeff S. Smith, Jason G. Budinoff, et al.
Testbed results are presented demonstrating high-speed image-based wavefront sensing and control for a spherical primary optical telescope (SPOT). The testbed incorporates a phase retrieval camera coupled to a 3-Mirror Vertex testbed (3MV) at the NASA Goddard Space Flight Center. Actuator calibration based on the Hough transform is discussed as well as several supercomputing architectures for image-based wavefront sensing. Timing results are also presented based on various algorithm implementations using a cluster of 64 TigerSharc TS101 DSP's (digital-signal processors).