Orbiting Astronomical Satellite for Investigating Stellar Systems (OASIS) is a space-based, MIDEX-class mission concept that employs a 17-meter diameter inflatable aperture with cryogenic heterodyne receivers, enabling high sensitivity and high spectral resolution (resolving power ≥106) observations at terahertz frequencies. OASIS science is targeting submillimeter and far-infrared transitions of H2O and its isotopologues, as well as deuterated molecular hydrogen (HD) and other molecular species from 660 to 80 μm, which are inaccessible to ground-based telescopes due to the opacity of Earth’s atmosphere. OASIS will have <20x the collecting area and ~5x the angular resolution of Herschel, and it complements the shorter wavelength capabilities of the James Webb Space Telescope. With its large collecting area and suite of terahertz heterodyne receivers, OASIS will have the sensitivity to follow the water trail from galaxies to oceans, as well as directly measure gas mass in a wide variety of astrophysical objects from observations of the ground-state HD line. OASIS will operate in a Sun-Earth L1 halo orbit that enables observations of large numbers of galaxies, protoplanetary systems, and solar system objects during the course of its 1-year baseline mission. OASIS embraces an overarching science theme of “following water from galaxies, through protostellar systems, to oceans.” This theme resonates with the NASA Astrophysics Roadmap and the 2010 Astrophysics Decadal Survey, and it is also highly complementary to the proposed Origins Space Telescope’s objectives.
The Gamow Explorer will use Gamma Ray Bursts (GRBs) to: 1) probe the high redshift universe (z < 6) when the first stars were born, galaxies formed and Hydrogen was reionized; and 2) enable multi-messenger astrophysics by rapidly identifying Electro-Magnetic (IR/Optical/X-ray) counterparts to Gravitational Wave (GW) events. GRBs have been detected out to z ~ 9 and their afterglows are a bright beacon lasting a few days that can be used to observe the spectral fingerprints of the host galaxy and intergalactic medium to map the period of reionization and early metal enrichment. Gamow Explorer is optimized to quickly identify high-z events to trigger follow-up observations with JWST and large ground-based telescopes. A wide field of view Lobster Eye X-ray Telescope (LEXT) will search for GRBs and locate them with arc-minute precision. When a GRB is detected, the rapidly slewing spacecraft will point the 5 photometric channel Photo-z Infra-Red Telescope (PIRT) to identify high redshift (z < 6) long GRBs within 100s and send an alert within 1000s of the GRB trigger. An L2 orbit provides < 95% observing efficiency with pointing optimized for follow up by the James Webb Space Telescope (JWST) and ground observatories. The predicted Gamow Explorer high-z rate is <10 times that of the Neil Gehrels Swift Observatory. The instrument and mission capabilities also enable rapid identification of short GRBs and their afterglows associated with GW events. The Gamow Explorer will be proposed to the 2021 NASA MIDEX call and if approved, launched in 2028.
KEYWORDS: Sensors, Telescopes, Electronics, James Webb Space Telescope, Gamma radiation, Infrared telescopes, Monte Carlo methods, Electromagnetism, Control systems, Aerospace engineering
The Photo-z InfraRed Telescope (PIRT) is an instrument on the Gamow Explorer, currently proposed for a NASA Astrophysics Medium Explorer. PIRT works in tandem with a companion wide-field instrument, the Lobster Eye X-ray Telescope (LEXT), that will identify x-ray transients likely to be associated with high redshift gamma-ray bursts (GRBs) or electromagnetic counterparts to gravitational wave (GW) events. PIRT will gather the necessary data in order to identify GRB sources with redshift z >6, with an expected source localization better than 1 arcsec. A near real-time link to the ground will allow timely follow-up as a target of opportunity for large ground-based telescopes or the James Webb Space Telescope (JWST). PIRT will also allow localization and characterization of GW event counterparts. We discuss the instrument design, the on-board data processing approach, and the expected performance of the system.
SOFIA, the Stratospheric Observatory for Infrared Astronomy, is a joint project between NASA and the German Aerospace Center DLR to provide infrared and sub-millimeter observing capabilities to the worldwide astronomical community. With a wide range of instruments that cover both imaging and spectroscopy, SOFIA has produced unique scientific results that could not be obtained with a ground-based facility. In the coming decade, SOFIA will be a critical complement to the other major facilities for astronomical research, the James Webb Space Telescope (JWST) and the Atacama Large Millimeter/submillimeter Array (ALMA) by filling in the otherwise unobservable wavelength range of 30–300 μm. SOFIA provides a wide range of instrumentation, and this paper will describe some of the new capabilities in heterodyne spectroscopy, direct detection spectroscopy, and polarimetry.
The joint U.S. and German Stratospheric Observatory for Infrared Astronomy (SOFIA), project has been operating airborne astronomy flights from Palmdale, California since 2011. The observatory consists of a modified 747-SP aircraft with a 2.5-meter telescope in its aft section. SOFIA has a suite of eight science instruments spanning visible to far-infrared wavelengths. For the majority of the year SOFIA operates out of the Armstrong Flight Research Center in Palmdale, California, giving access to Northern Hemisphere targets. SOFIA’s mobility also allows observations in the Southern Hemisphere (Christchurch, New Zealand), of objects such as the Large and Small Magellanic Clouds, the Galactic Center, and Eta Carinae In 2016, SOFIA added polarimetry capability on SOFIA, with HAWC+ commissioning flights. Selected science results, current instrument suite status, new capabilities, and some expectations of future instrument developments over the lifetime of the observatory will be discussed.
The Stratospheric Observatory for Infrared Astronomy (SOFIA) is the world’s largest airborne observatory, featuring a
2.5 meter effective aperture telescope housed in the aft section of a Boeing 747SP aircraft. SOFIA’s current instrument
suite includes: FORCAST (Faint Object InfraRed CAmera for the SOFIA Telescope), a 5-40 μm dual band
imager/grism spectrometer developed at Cornell University; HIPO (High-speed Imaging Photometer for Occultations), a
0.3-1.1μm imager built by Lowell Observatory; GREAT (German Receiver for Astronomy at Terahertz Frequencies), a
multichannel heterodyne spectrometer from 60-240 μm, developed by a consortium led by the Max Planck Institute for
Radio Astronomy; FLITECAM (First Light Infrared Test Experiment CAMera), a 1-5 μm wide-field imager/grism
spectrometer developed at UCLA; FIFI-LS (Far-Infrared Field-Imaging Line Spectrometer), a 42-200 μm IFU grating
spectrograph completed by University Stuttgart; and EXES (Echelon-Cross-Echelle Spectrograph), a 5-28 μm highresolution
spectrometer designed at the University of Texas and being completed by UC Davis and NASA Ames
Research Center. HAWC+ (High-resolution Airborne Wideband Camera) is a 50-240 μm imager that was originally
developed at the University of Chicago as a first-generation instrument (HAWC), and is being upgraded at JPL to add
polarimetry and new detectors developed at Goddard Space Flight Center (GSFC). SOFIA will continually update its
instrument suite with new instrumentation, technology demonstration experiments and upgrades to the existing
instrument suite. This paper details the current instrument capabilities and status, as well as the plans for future
instrumentation.
SOFIA is a joint project between NASA and DLR, the German Aerospace Center, to provide the worldwide astronomical community with an observatory that offers unique capabilities from visible to far-infrared wavelengths. SOFIA consists of a 2.7-m telescope mounted in a highly modified Boeing 747-SP aircraft, a suite of instruments, and the scientific and operational infrastructure to support the observing program. This paper describes the current status of the observatory and details the General Investigator program. The observatory has recently completed major development activities, and it has transitioned into full operational status. Under the General Investigator program, astronomers submit proposals that are peer reviewed for observation on the facility. We describe the results from the first two cycles of the General Investigator program. We also describe some of the new observational capabilities that will be available for Cycle 3, which will begin in 2015.
The Stratospheric Observatory for Infrared Astronomy (SOFIA) is an airborne observatory, carrying a 2.5 m telescope onboard a heavily modified Boeing 747SP aircraft. SOFIA is optimized for operation at infrared wavelengths, much of which is obscured for ground-based observatories by atmospheric water vapor. The SOFIA science instrument complement consists of seven instruments: FORCAST (Faint Object InfraRed CAmera for the SOFIA Telescope), GREAT (German Receiver for Astronomy at Terahertz Frequencies), HIPO (High-speed Imaging Photometer for Occultations), FLITECAM (First Light Infrared Test Experiment CAMera), FIFI-LS (Far-Infrared Field-Imaging Line Spectrometer), EXES (Echelon-Cross-Echelle Spectrograph), and HAWC (High-resolution Airborne Wideband Camera). FORCAST is a 5–40 μm imager with grism spectroscopy, developed at Cornell University. GREAT is a heterodyne spectrometer providing high-resolution spectroscopy in several bands from 60–240 μm, developed at the Max Planck Institute for Radio Astronomy. HIPO is a 0.3–1.1 μm imager, developed at Lowell Observatory. FLITECAM is a 1–5 μm wide-field imager with grism spectroscopy, developed at UCLA. FIFI-LS is a 42–210 μm integral field imaging grating spectrometer, developed at the University of Stuttgart. EXES is a 5–28 μm high-resolution spectrograph, developed at UC Davis and NASA ARC. HAWC is a 50–240 μm imager, developed at the University of Chicago, and undergoing an upgrade at JPL to add polarimetry capability and substantially larger GSFC detectors. We describe the capabilities, performance, and status of each instrument, highlighting science results obtained using FORCAST, GREAT, and HIPO during SOFIA Early Science observations conducted in 2011.
John Wilson, F. Hearty, M. Skrutskie, S. Majewski, R. Schiavon, D. Eisenstein, J. Gunn, J. Holtzman, D. Nidever, B. Gillespie, D. Weinberg, B. Blank, C. Henderson, S. Smee, R. Barkhouser, A. Harding, S. Hope, G. Fitzgerald, T. Stolberg, J. Arns, M. Nelson, S. Brunner, A. Burton, E. Walker, C. Lam, P. Maseman, J. Barr, F. Leger, L. Carey, N. MacDonald, G. Ebelke, S. Beland, T. Horne, E. Young, G. Rieke, M. Rieke, T. O'Brien, J. Crane, M. Carr, C. Harrison, R. Stoll, M. Vernieri, M. Shetrone, C. Allende-Prieto, J. Johnson, P. Frinchaboy, G. Zasowski, A. Garcia Perez, D. Bizyaev, K. Cunha, V. Smith, Sz. Meszaros, B. Zhao, M. Hayden, S. D. Chojnowski, B. Andrews, C. Loomis, R. Owen, M. Klaene, J. Brinkmann, F. Stauffer, D. Long, W. Jordan, D. Holder, F. Cope, T. Naugle, B. Pfaffenberger, D. Schlegel, M. Blanton, D. Muna, B. Weaver, S. Snedden, K. Pan, H. Brewington, E. Malanushenko, V. Malanushenko, A. Simmons, D. Oravetz, S. Mahadevan, S. Halverson
The Apache Point Observatory Galactic Evolution Experiment (APOGEE) uses a dedicated 300-fiber, narrow-band
near-infrared (1.51-1.7 μm), high resolution (R~22,500) spectrograph to survey approximately 100,000 giant stars across
the Milky Way. This three-year survey, in operation since late-summer 2011 as part of the Sloan Digital Sky Survey III
(SDSS III), will revolutionize our understanding of the kinematical and chemical enrichment histories of all Galactic
stellar populations. We present the performance of the instrument from its first year in operation. The instrument is
housed in a separate building adjacent to the 2.5-m SDSS telescope and fed light via approximately 45-meter fiber runs
from the telescope. The instrument design includes numerous innovations including a gang connector that allows
simultaneous connection of all fibers with a single plug to a telescope cartridge that positions the fibers on the sky,
numerous places in the fiber train in which focal ratio degradation had to be minimized, a large mosaic-VPH (290 mm x
475 mm elliptically-shaped recorded area), an f/1.4 six-element refractive camera featuring silicon and fused silica
elements with diameters as large as 393 mm, three near-infrared detectors mounted in a 1 x 3 mosaic with sub-pixel
translation capability, and all of these components housed within a custom, LN2-cooled, stainless steel vacuum cryostat
with dimensions 1.4-m x 2.3-m x 1.3-m.
SOFIA, the Stratospheric Observatory for Infrared Astronomy, is an airborne observatory with a 2.7-m telescope that is
under development by NASA and the German Aerospace Center DLR. From late 2010 and through the end of 2011,
SOFIA conducted a series of science demonstration flights, Early Science, using FORCAST (the Faint Object InfraRed
Camera for the SOFIA Telescope), HIPO (the High-speed Imaging Photometer for Occultations), and GREAT (the
German REceiver for Astronomy at Terahertz frequencies). Flying at altitudes as high as 13.7 km (45,000 ft), SOFIA
operates above more than 99.8% of the water vapor in the Earth’s atmosphere, opening up most of the far-infrared and
sub-millimeter parts of the spectrum. During Early Science, 30 science missions were flown with results in solar system
astronomy, star formation, the interstellar medium, the Galactic Center, and extragalactic studies. Many of these
investigations were conducted by the first group of SOFIA General Investigators, demonstrating the operation of SOFIA
as a facility for the astronomical community. This paper presents some recent highlights from Early Science.
SOFIA, the Stratospheric Observatory for Infrared Astronomy, is a specially modified Boeing 747SP aircraft with a 2.7-
m telescope. Flying above more than 99% of the water vapor in the Earth's atmosphere, SOFIA will enable observations
of large regions of the infrared and submillimeter that are normally opaque to terrestrial observatories. A joint project of
NASA and DLR, SOFIA has completed a series of major flight tests leading up to the Initial Science Flights this year. In
particular, SOFIA has recently completed its first observations through the telescope. This paper gives an overview of
the facility and reports on the recent progress in the development of this major astronomical facility including the First
Light observations with the FORCAST infrared camera.
The Apache Point Observatory Galactic Evolution Experiment (APOGEE) will use a dedicated 300-fiber, narrow-band
(1.5-1.7 micron), high resolution (R~30,000), near-infrared spectrograph to survey approximately 100,000 giant stars
across the Milky Way. This survey, conducted as part of the Sloan Digital Sky Survey III (SDSS III), will revolutionize
our understanding of kinematical and chemical enrichment histories of all Galactic stellar populations. The instrument,
currently in fabrication, will be housed in a separate building adjacent to the 2.5 m SDSS telescope and fed light via
approximately 45-meter fiber runs from the telescope. The instrument design includes numerous technological
challenges and innovations including a gang connector that allows simultaneous connection of all fibers with a single
plug to a telescope cartridge that positions the fibers on the sky, numerous places in the fiber train in which focal ratio
degradation must be minimized, a large (290 mm x 475 mm elliptically-shaped recorded area) mosaic-VPH, an f/1.4 sixelement
refractive camera featuring silicon and fused silica elements with diameters as large as 393 mm, three near-within a custom, LN2-cooled, stainless steel vacuum cryostat with dimensions 1.4 m x 2.3 m x 1.3 m.
Our group has developed the first 1024×1024 high background Si:As detector array, the Megapixel Mid-Infrared array
(MegaMIR). MegaMIR is designed to meet the thermal imaging and spectroscopic needs of the ground-based and airborne
astronomical communities. MegaMIR was designed with switchable capacitance and windowing capability to
allow maximum flexibility. We report initial test results for the new array.
The full potential of far infrared and submillimeter detectors, operating at deep cryogenic temperatures (<4.2K), is only realized if large, two-dimensional arrays of these detectors are developed. The technology for fabricating suitable readouts for such detectors has been one of the main impediments in achieving this objective. In this paper, we present the design parameters of the first 2-side buttable, 32x32 (64x64 mosaic) readout multiplexer, specifically designed for direct-hybrid far IR detector arrays. The readout employs a high open-loop gain, capacitive transimpedance unit-cell design with eight outputs. It features eight selectable gain settings, AC coupling (auto zero) for better input uniformity, sample-and-hold circuitry, and provision to limit the readout glow. A special, 2-micron cryo-CMOS process has been adopted to prevent freeze out and ensure low noise and proper operation at deep cryogenic temperatures. Based on the performance of its predecessors, CRC696 and SBRC190, this device is expected to have CDS read noise of better than 100e- at 2K.
The Megapixel Mid-infrared Instrument (MegaMIR) is a proposed Fizeau-mode camera for the Large Binocular Telescope operating at wavelengths between 5 and 28 μm. The camera will be used in conjunction with the Large Binocular Telescope Interferometer (LBTI), a cryogenic optical system that combines the beams from twin 8.4-m telescopes in a phase coherent manner. Unlike other interferometric systems, the co-mounted telescopes on the LBT satisfy the sine condition, providing diffraction-limited resolution over the 40" field of view of the camera. With a 22.8-m baseline, MegaMIR will yield 0.1" angular resolution, making it the highest resolution wide field imager in the thermal infrared for at least the next decade. MegaMIR will utilize a newly developed 1024 x 1024 pixel Si:As detector array that has been optimized for use at high backgrounds. This new detector is a derivative of the Wide-field Infrared Survey Explorer (WISE) low-background detector. The combination of high angular resolution and wide field imaging will be a unique scientific capability for astronomy. Key benefits will be realized in planetary science, galactic, and extra-galactic astronomy. High angular resolution is essential to disentangle highly complex sources, particularly in star formation regions and external galaxies, and MegaMIR provides this performance over a full field of view. Because of the great impact being made by space observatories like the Spitzer Space Telescope, the number of available targets for study has greatly increased in recent years, and MegaMIR will allow efficient follow up science.
We present a description of a new 1024×1024 Si:As array designed for ground-based use from 5 - 28 microns. With a maximum well depth of 5e6 electrons, this device brings large-format array technology to bear on ground-based mid-infrared programs, allowing entry to the megapixel realm previously only accessible to the near IR. The multiplexer design features switchable gain, a 256×256 windowing mode for extremely bright sources, and it is two-edge buttable. The device is currently in its final design phase at DRS in Cypress, CA. We anticipate completion of the foundry run in October 2005. This new array will enable wide field, high angular resolution ground-based follow up of targets found by space-based missions such as the Spitzer Space Telescope and the Widefield Infrared Survey Explorer (WISE).
E. Young, G. Rieke, M. Blaylock, J. Cadien, C. Engelbracht, K. Gordon, D. Kelly, K. Misselt, J. Morrison, J. Muzerolle, J. Stansberry, K. Su, D. Fadda, D. Frayer, A. Noriega-Crespo, J. Rho
The far-infrared detectors on the Multiband Imaging Photometer for Spitzer (MIPS) represent a significant advancement in both format and sensitivity. We describe some of the operational experience since launch in August 2003. MIPS has three infrared detector arrays, a 128x128 format Si:As impurity band conduction detector operating at 24 μm, a 32x32 format Ge:Ga array operating at 70 μm and a 2x20 format stressed Ge:Ga array operating at 160 μm. Since both germanium detectors utilize conventional bulk photoconductors, they are subject to a number of non-ideal behaviors
that are inherent in these types of devices when operated in ultra-low backgrounds. The principal problems are nonlinear time response, changing responsivity in a radiation environment, and flux non-linearities. We describe observing strategies that are used on MIPS to minimize the impact of these effects.
George Rieke, Erick Young, James Cadien, Charles Engelbracht, Karl Gordon, Douglas Kelly, Frank Low, Karl Misselt, Jane Morrison, James Muzerolle, G. Rivlis, John Stansberry, Jeffrey Beeman, Eugene Haller, David Frayer, William Latter, Alberto Noriega-Crespo, Deborah Padgett, Dean Hines, J. Douglas Bean, William Burmester, Gerald Heim, Thomas Glenn, R. Ordonez, John Schwenker, S. Siewert, Donald Strecker, S. Tennant, John Troeltzsch, Bryce Unruh, R. Warden, Peter Ade, Almudena Alonso-Herrero, Myra Blaylock, Herve Dole, Eiichi Egami, Joannah Hinz, Emeric LeFloch, Casey Papovich, Pablo Perez-Gonzalez, Marcia Rieke, Paul Smith, Kate Su, Lee Bennett, David Henderson, Nanyao Lu, Frank Masci, Misha Pesenson, Luisa Rebull, Jeonghee Rho, Jocelyn Keene, Susan Stolovy, Stefanie Wachter, William Wheaton, Paul Richards, Harry Garner, M. Hegge, Monte Henderson, Kim MacFeely, David Michika, Chris Miller, Mark Neitenbach, Jeremiah Winghart, R. Woodruff, E. Arens, Charles Beichman, Stephen Gaalema, Thomas Gautier, Charles Lada, Jeremy Mould, Gerry Neugebauer, Karl Stapelfeldt
The Multiband Imaging Photometer for Spitzer (MIPS) provides long wavelength capability for the mission, in imaging bands at 24, 70, and 160 microns and measurements of spectral energy distributions between 52 and 100 microns at a spectral resolution of about 7%. By using true detector arrays in each band, it provides both critical sampling of the Spitzer point spread function and relatively large imaging fields of view, allowing for substantial advances in sensitivity, angular resolution, and efficiency of areal coverage compared with previous space far-infrared capabilities. The Si:As BIB 24 micron array has excellent photometric properties, and measurements with rms relative errors of 1% or better can be obtained. The two longer wavelength arrays use Ge:Ga detectors with poor photometric stability. However, the use of 1.) a scan mirror to modulate the signals rapidly on these arrays, 2.) a system of on-board stimulators used for a relative calibration approximately every two minutes, and 3.) specialized reduction software result in good photometry with these arrays also, with rms relative errors of less than 10%.
We describe the process by which the NASA Spitzer Space Telescope (SST) Cryogenic Telescope Assembly (CTA) was brought into focus after arrival of the spacecraft in orbit. The ground rules of the mission did not allow us to make a conventional focus sweep. A strategy was developed to determine the focus position through a program of passive imaging during the observatory cool-down time period. A number of analytical diagnostic tools were developed to facilitate evaluation of the state of the CTA focus. Initially, these tools were used to establish the in-orbit focus position. These tools were then used to evaluate the effects of an initial small exploratory move that verified the health and calibration of the secondary mirror focus mechanism. A second large move of the secondary mirror was then commanded to bring the telescope into focus. We present images that show the CTA Point Spread Function (PSF) at different channel wavelengths and demonstrate that the telescope achieved diffraction limited performance at a wavelength of 5.5 μm, somewhat better than the level-one requirement.
SAFIR is a large (10 m-class), cold (4-10 K) space telescope for wavelengths between 20 microns and 1 mm. It will provide sensitivity a factor of a hundred or more greater than that of Spitzer and Herschel, leveraging their capabilities and building on their scientific legacies. Covering this scientifically critical wavelength regime, it will complement the expected wavelength performance of the future flagship endeavors JWST and ALMA. This vision mission will probe the origin of stars and galaxies in the early universe, and explore the formation of solar systems around nearby young stars. Endorsed as a priority by the Decadal Study and successive OSS roadmaps, SAFIR represents a huge science need that is matched by promising and innovative technologies that will allow us to satisfy it. In exercising those technologies it will create the path for future infrared missions. This paper reviews the scientific goals of the mission and promising approaches for its architecture, and considers remaining technological hurdles. We review how SAFIR responds to the scientific challenges in the OSS Strategic Plan, and how the observatory can be brought within technological reach.
Karl Gordon, Charles Engelbracht, James Muzerolle, John Stansberry, Karl Misselt, Jane Morrison, George Rieke, James Cadien, Erick Young, Herve Dole, Douglas Kelly, Almudena Alonso-Herrero, Eiichi Egami, Kate Su, Casey Papovich, Paul Smith, Dean Hines, Marcia Rieke, Myra Blaylock, Pablo Perez-Gonzalez, Emeric Le Floch, Joannah Hinz, William Latter, Ted Hesselroth, David Frayer, Alberto Noriega-Crespo, Frank Masci, Deborah Padgett
The first six months of flight data from the Multiband Imaging Photometer for Spitzer (MIPS) were used to test MIPS reduction algorithms based on extensive preflight laboratory data and modeling. The underlying approach for the preflight algorithms has been found to be sound, but some modifications have improved the performance.
The main changes are scan mirror dependent flat fields at 24 μm, hand processing to remove the time dependent stim flash latents and fast/slow response variations at 70 μm, and the use of asteroids and other sources instead of stars for flux calibration at 160 μm due to a blue "leak." The photometric accuracy of flux measurements is currently 5%, 10%, and 20% at 24, 70, and 160 μm, respectively. These numbers are expected to improve as more flight data are analyzed and data reduction algorithms refined.
We present the on-orbit performance results of the Pointing Calibration and Reference Sensor (PCRS) for the Spitzer Space Telescope. A cryogenic optical (center wavelength 0.55 um) imager, the PCRS serves as the Observatory's fine guidance sensor by providing an alignment reference between the telescope boresight and the external spacecraft attitude determination system. The PCRS makes precision measurements of the positions of known guide stars; these are used to calibrate measurements from Spitzer's star tracker and gyroscopes to obtain the actual pointing of the Spitzer telescope. The PCRS calibrates out thermomechanical drifts between the 300 K spacecraft bus and the 5.5 K telescope. By using only 16 pixels, the PCRS provides high precision centroiding with extremely low (~64 uW) power dissipation, resulting in minimal impact to Spitzer's helium lifetime. We have demonstrated that the PCRS meets its centroiding accuracy requirement of 0.14 arcsec 1-s radial, which represents ~1/100 pixel centroiding. The Spitzer Space Telescope was launched on 25 August, 2003 and completed its In-Orbit Checkout phase two months later; the PCRS has been operating failure-free ever since.
We present the performance results of the as-built Pointing Calibration and Reference Sensor (PCRS) for the Space Infrared Telescope Facility (SIRTF). A cryogenic optical (center wavelength 0.55 microns) imager, the PCRS serves as the Observatory's fine guidance sensor by providing an alignment reference between the telescope boresight and the external spacecraft attitude determination system. The PCRS makes precision measurements of the positions of known guide stars; these are used to calibrate measurements from SIRTF's star trackers and gyroscopes to obtain the actual pointing of the SIRTF telescope. The PCRS calibrates out thermomechanical drifts between the 300 K spacecraft bus and the 5.5 K telescope. We have demonstrated that the PCRS meets its centroiding accuracy requirement of 0.14 arcsec 1-σ radial. The PCRS was installed inside the SIRTF Cryo-Telescope Assembly in July, 2000 and has logged over 1000 hours of failure-free operation ever since. We have verified that the PCRS has survived all box-level environmental requirements, including the 1.4 K operating temperature, random vibration, pyroshock, and EMI/EMC, necessary to survive launch and operations over SIRTF's 2.5 year lifetime. Currently, the PCRS is undergoing testing as part of the recently integrated Observatory in preparation for a January, 2003 launch.
We describe the ground testing and characterization of the Multiband Imaging Photometer for SIRTF (MIPS). This instrument is a camera with three focal plane arrays covering broad spectral bands centered at 24 μm, 70 μm, and 160 μm. The instrument features a variety of operation modes that permit accurate photometry, diffraction-limited imaging, efficient mapping, and low resolution spectral energy distribution determinations. The observational philosophy of MIPS relies heavily on the frequent use of internal relative calibration sources as well as a high level of redundancy in the data collection. We show that by using this approach, users of MIPS can expect very sensitive, highly repeatable observations of astronomical sources. The ground characterization program for MIPS involved a number of facilities including test dewars for focal-plane level testing, a specialized cryostat for instrument-level testing, and tests in the flight SIRTF Cryo-Telescope Assembly
The science program for the Next Generation Space Telescope (NGST) relies heavily on a high performance nearinfrared imager. A design which supports the observations outlined in the Design Reference Mission (DRM) and which also supports enhanced searches for "first light" objects and planets has been developed. Key features of the design include use of refractive optics to minimize the volume and mass required, tunable filters for spectroscopic imaging, and redundant imagers for fail-safe wavefront sensing.
KEYWORDS: Sensors, Multiplexers, Space telescopes, Telescopes, Photoresistors, Capacitors, Cryogenics, Electrons, Signal to noise ratio, Error control coding
We describe the development of a cryogenic multiplexer for far-infrared (FIR) photoconductor detectors operating at moderate backgrounds. The device is called the SBRC 190. Its architecture and basic functions are based on the 1×32-channel CRC 696 CMOS device used on SIRTF. The SBRC 190 is designed to accommodate the higher backgrounds to be encountered on SOFIA and Herschel, to tolerates a wider range of backgrounds, to permit faster sampling, and to facilitate synchronization of sampling with chopping. Major design differences relative to the CRC 696 which have been incorporated in the SBRC 190 design are: (a) an AC coupled, capacitive feedback transimpedence unit cell, which minimizes input offset effects, thereby enabling low detector biases, (b) selectable feedback capacitors to enable operation over a wide range of backgrounds, and (c) clamp and sample-and-hold output circuits to improve sampling efficiency, which can be a concern at the relatively high readout rates required. A relationship between sampling efficiency and noise performance needed to achieve background-limited instrument performance (BLIP) is derived. Requirements for use on SOFIA, the basic circuit design, fabrication, and operation are discussed.
We have been developing the high throughput hard X-ray telescope, using reflectors coated with the depth graded multilayer known as supermirror, which is considered to be a key technology for future satellite hard X-ray imaging missions. InFOC(mu) $S, the International Focusing Optics Collaboration for (mu) -Crab Sensitivity is the project of the balloon observation of a cosmic hard X-ray source with this type of hard X-ray telescope and CdZnTe pixel detector as a focal plane imager. For the fist InFOC(mu) S balloon experiment, we developed the hard X-ray telescope with outermost diameter of 40cm, focal length of 8m and energy band pass of 20-40 keV, for which Pt/C multilayer was used. From the pre-flight X-ray calibration, we confirmed its energy band and imaging capability of 2 arcmin HPD and 10 arcmin FOV of FWHM, and a effective area of 50 cm2 for 20-40 keV X-ray. We report the current status of our balloon borne experiment and performance of our hard X-ray telescope.
We describe the test approaches and results for the Multiband Imaging Photometer for SIRTF. To verify the performance within a `faster, better, cheaper' budget required innovations in the test plan, such as heavy reliance on measurements with optical photons to determine instrument alignment, and use of an integrating sphere rather than a telescope to feed the completed instrument at its operating temperature. The tests of the completed instrument were conducted in a cryostat of unique design that allowed us to achieve the ultra-low background levels the instrument will encounter in space. We controlled the instrument through simulators of the mission operations control system and the SIRTF spacecraft electronics, and used cabling virtually identical to that which will be used in SIRTF. This realistic environment led to confidence in the ultimate operability of the instrument. The test philosophy allowed complete verification of the instrument performance and showed it to be similar to pre-integration predictions and to meet the instrument requirements.
In June 1997, NASA made the decision to extend the end of the Hubble Space Telescope (HST) mission from 2005 until 2010. As a result, the age of the instruments on board the HST became a consideration. After careful study, NASA decided to ensure the imaging capabilities of the HST by replacing the Wide Field Planetary Camera 2 with a low-cost facility instrument, the Wide Field Camera 3. This paper provides an overview of the scientific goals and capabilities of the instrument.
This paper summarizes the findings of the Next Generation Space Telescope (NGST) Detector Requirements Review Panel. This panel was comprised of NGST Integrated Science Instrument Module study representatives, detector specialists, and members of the NGST project science team. It has produced a report that recommends detector performance levels, and has provided rationale for deriving these levels from basic, anticipated NGST science goals and programs. Key parameters such as detector array format, quantum efficiency, and noise are discussed and prioritized.
The Multiband Imaging Photometer for SIRTF (MIPS) provides the space IR telescope facility (SIRTF) with imaging, photometry, and total power measurement capability in broad spectral bands centered at 24, 70, and 160 micrometers , and with low resolution spectroscopy between 50 and 95 micrometers . The optical train directs the light from three zones in the telescope focal plane to three detector arrays: 128 by 128 Si:As BIB, 32 by 32 Ge:Ga, and 2 by 20 stressed Ge:Ga. A single axis scan mirror is placed at a pupil to allows rapid motion of the field of view as required to modulate above the 1/f noise in the germanium detectors. The scan mirror also directs the light into the different optical paths of the instrument and makes possible an efficient mapping mode in which the telescope line of sight is scanned continuously while the scan mirror freezes the image motion on the detector arrays. The instrument is designed with pixel sizes that oversample the telescope Airy pattern to operate at the diffraction limit and, through image processing, to allow superresolution beyond the traditional Rayleigh criterion. The instrument performance and interface requirements, the design concept, and the mechanical, optical, thermal, electrical, software, and radiometric aspects of MIPS are discussed in this paper. Solutions are shown to the challenge of operating the instrument below 3K, with focal plane cooling requirements done to 1.5K. The optical concept allows the versatile operations described above with only a single mechanism and includes extensive self-test and on- board calibration capabilities. In addition, we discuss the approach to cryogenic end-to-end testing and calibration prior to delivery of the instrument for integration into SIRTF.
The SIRTF requires a visible light sensor at its focal plane to 1) calibrate the alignment between the externally mounted star trackers and the telescope boresight; 2) to establish the correspondence between the telescope coordinate system and the absolute J2000 reference frame; and 3) to provide starting attitudes for high accuracy absolute offset maneuvers. The Pointing Calibration and Reference Sensor (PCRS) functions as the primary absolute attitude reference for the SIRTF telescope. It measures the J2000 position of Tycho Catalogue stars to an accuracy of 0.14 arcsec 1-s per axis. To accurately measure Tycho objects, we have selected a silicon PIN photodiode operating in the Johnson V band, which we use with a cryogenic readout developed for the MIPS instrument on SIRTF. The PCRS employs a 4 by 4 Si:PIN detector array, using the outer rings for acquisition and the inner four pixels for precise measurements. Operation in the SIRTF focal plane presents us with several unique problems. Since the detector thermally links directly to the cryostat helium bath, it must operate at a temperature of 1.4K. Additionally, the power dissipation must be less than 0.1 mW to minimize the impact on helium lifetime. We describe low temperature characterization of Si'PIN detectors and readouts to verify their operability in the PCRS environment. Since the beryllium optics of the SIRTF telescope are diffraction limited only at 6.5 microns and longward, they yield a complicated point spread function at visible wavelengths. We present operational solutions to these and other challenges that allow the PCRS to meet its accuracy requirements with minimal impact on the rest of the SIRTF mission.
We describe the design, construction, and performance of the 32 X 32 Ge:Ga imaging array being built at the University of Arizona for the Multiband Imaging Photometer for SIRTF (MIPS). The array will support a number of operational modes in the MIPS instrument including natural background-limited mapping at 70 micrometers , super-resolution observations at 70 micrometers , and spectral energy distribution measurements between 50 and 100 micrometers . The array is constructed in a modular manner using eight 4 X 32 pixel building blocks. To meet the sensitivity and stability requirements, the array must have excellent photometric repeatability, low noise, and robustness to the effects of the ionizing radiation environment in space. Key elements in attaining this level of performance are the Ge:Ga detectors materials and the cryogenic CRC-696 readout electronics. We present laboratory data for a 16 X 32 prototype of the array, and describe the plans for the construction of the qualification and flight units.
The short wavelength spectrometer (SWS) is one of the four instruments on-board of ESA's IR SPace Observatory (ISO), launched on 15 November 1995. It covers the wavelength range of 2.38-45.2 microns with a spectral resolution ranging from 1000-2000. By inserting Fabry-Perot filters the resolution can be enhanced by a factor 20 for the wavelength range from 11.4-44.5 microns. After the successful launch the instrument was tested and calibrated during a period of spacecraft checkout and performance verification. The opto- mechanical construction of the instrument appears to behave extremely well. The instrument performance is on all aspects as expected, except for the detector sensitivity where the noise is dominated by effects of particle radiation. We given here an overview of the in-orbit performance, discuss the calibration and present some result from trend analysis of the most important instrument and detector parameters.
Stressed Ge:Ga is currently the most suitable detector type for very low background operation in the 115 to 200 micrometers range. Nonetheless, substantial advances have been required to develop stressed Ge:Ga detectors that work at the background limit in SIRTF. Both dark current and read noise have been improved significantly for the SIRTF devices. The design also takes account of space flight requirements such as the necessity to anneal the focal plane thermally using a minimum of cryogenic power dissipation, and the desire that any failures not propagate through an entire focal plane. The SIRTF 2 X 20 pixel focal plane will have dark current of about 200 e/s, read noise of 100 e rms, and responsivity > 7 A/W. As a result, even in the darkest parts of the sky, it will reach the background limit in less than 4 seconds of integration.
NASA's Stratospheric Observatory for IR Astronomy (SOFIA) will enable unprecedented IR acuity at wavelengths obscured from the ground. To help open this new chapter in the exploration of the IR universe, we are developing the Airborne IR Echelle Spectrometer (AIRES) as a facility science instrument. Full funding was awarded for a four year development in October, 1997. The instrument is scheduled to come on-line with the observatory in the Fall of 2001. It will be used to investigate a broad range of phenomena that occur in the interstellar medium. AIRES will use a 1200 mm long, 76 degree blaze angle echelle to combine high resolution spectroscopy with diffraction-limited imaging in the cross-dispersion direction. Its three 2D detector arrays will prove good sensitivity over a decade in wavelength. An additional array will be used as a slit viewer for (lambda) <EQ 28 micrometers to image source morphology and to verify telescope pointing. Our scientific motivation, preliminary optical design and packaging, focal plane configuration, echelle prototyping, and cryostat layout are described.
We report on the design, modeling, and construction of far-infrared focal plane array modules for the Space Infrared Telescope Facility (SIRTF). The modules consist of 4 X 32 detector elements, readout electronics, and interconnections. The modules, which are of Z- plane architecture, may be stacked to produce imaging arrays of at least 32 X 32 format. These arrays are the largest available operating in the wavelength range 50 - 120 micrometers . The design takes advantage of the Hughes CRC-696 readout which was specifically developed for use with far-infrared photoconductive detectors. Since the readouts have excellent performance at temperatures below 2 K, a simplified construction concept using the proven interconnection methods of wire boding and multilayer ceramic boards are used. We report on additional design considerations such as minimization of parasitic capacitance at the input node and accommodation of thermal annealing of the detectors.
We present the design for the multiband imaging photometer for SIRTF (MIPS). MIPS is a versatile instrument that provides diffraction-limited imaging at 30 micrometers , 70 micrometers , and 160 micrometers . MIPS also provides low resolution (5%) spectroscopy in the 50 - 100 micrometers wavelength range to allow the determination of far-infrared spectral energy distributions. The 70 micrometers array can also be used in a special high resolution mode that supports image reconstruction techniques for improved angular resolution. The one cryogenic mechanism on MIPS is a scanning mirror based on a space-qualified design used on the Infrared Space Observatory. We describe modifications to the scan mechanism to optimize it for use at very long wavelengths.
We present initial test results for far-infrared arrays built at the University of Arizona using Ge:Ga photoconductors and low temperature readouts operating at a temperature of 2 K. We also present separate test results for the Hughes CRC-696 multiplexer used in this program. The two array configurations considered are a 1 X 32 based on an older heated readout concept and a new 4 X 32 module that takes advantage of the benefits of having a true cryogenic readout. Based on these results, performance meeting the SIRTF goal of background-limited imaging can be expected for the 32 X 32 array under construction.
The far-infrared is a key wavelength regime for astronomical observations. Until recently, however, development of useful large format arrays at these wavelengths has been hampered by the lack of suitable readouts that operate well at the very low temperatures required by these detectors. We report on the initial characterization of CRC-696 readouts fabricated at the Hughes Technology Center (Carlsbad CA) specifically built to operate at 4 K and lower. These devices have been optimized to work with extrinsic germanium photoconductors. At these low temperatures, the fully multiplexed 32-channel readouts has a read noise below 30 electrons at a power dissipation of 1 (mu) W per channel. We also report on the testing of the first complete focal plane module fabricated with these devices. This module is operating at a level of performance (dark current, noise, stability, and power dissipation) that make arrays built with this technology suitable candidates for the next generation of space infrared observatories.
We report on progress in the construction of highly sensitive arrays of germanium photoconductors for operation at wavelengths between 40 to 120 micrometers . This technology is being developed for future astronomical missions in the far infrared such as SIRTF. We are evaluating construction techniques that will allow us to build 32 X 32 format arrays that are reliable and suitable to be qualified for space flight, while retaining the excellent performance of a prototype we have built and tested previously. We review the technical issues in constructing large format far infrared arrays, along with a description of the approaches that have been adopted in a prototype array to deal with these issues. We report on the development of two advanced methods to interconnect the detectors and readouts, that allow the extension of the Z-plane concept to larger formats: (1) Flex cable and (2) tape automated bonding. Both methods are being evaluated in a detailed series of laboratory experiments, including the electrical performance of the integrated readout/interconnect systems, thermal performance, ease of assembly of completed arrays, and mechanical ruggedness. These approaches will be discussed in terms of their use both with readouts that need to operate at temperatures above those acceptable for the detectors (approximately 20 K) and with readouts that can operate close to the detector temperature (approximately 2 K).
As part of a program to extend the wavelength response of infrared array technology beyond the cutoff of extrinsic silicon photoconductivity, we have calculated the optimum parameters for a front-illuminated two dimensional array of Ge:Be detectors. Detector arrays to this prescription have been produced by indium bump bonding onto sapphire fanouts. We report a preliminary performance evaluation of these arrays.
Mattheus de Graauw, Douwe Beintema, Willem Luinge, Jan Wijnbergen, Klaas Wildeman, G. Ploeger, J. Evers, Erick Young, Theo Kamperman, C. van Dijkhuizen, P. de Groene, M. Frericks, R. van der Linden, S. Czempiel, Helmut Feuchtgruber, Leo Haser, Reinhard Katterloher, F. Melzner, H. Spath, Jakob Stoecker, Huib Visser, Kees Smorenburg, H. van Agthoven
The Short-Wavelength Spectrometer (SWS) for ISO operates in the wavelength range from 2.4 to 45 micrometers. It consists of two, almost identical, grating spectrometers that provide resolving powers varying between 1000 to 2000. In the wavelength region from 12 to 45 micrometers a much larger (>20.000) resolution can be obtained with a pair of Fabry-Perot interferometers. This paper describes the design of the SWS.
This paper presents a brief review of mid and long-wavelength (6 micrometers - 200 micrometers ) infrared detector technology used on space borne astronomical missions. Examples of the focal plane designs from the Infrared Astronomical Satellite (IRAS), Cosmic Background Explorer (COBE), Infrared Space Observatory (ISO), and the Space Infrared Telescope Facility (SIRTF) are presented. The major technical innovations considered are low background photoconductors, self-heated amplifiers, Impurity Band Conduction (IBC) detectors, large format arrays, and true cryogenic readout electronics. The impacts of the changing technology base on the kinds of scientific investigations possible are discussed.
Germanium photoconductors are currently the most sensitive detectors for use in low background, far infrared applications. In particular, between the wavelengths of 40 micrometers and 200 micrometers , these detectors have been used in a number of existing or planned systems for space infrared astronomy. We describe briefly the physical mechanisms of photoconductivity, including a discussion of various non-ideal behaviors seen at low backgrounds. The requirements for specialized cryogenic electronics are discussed along with some current implementations. Examples of past focal plane array designs are given, and the extension of the technology to large format imaging arrays is described.
We describe the development of sensitive extrinsic germanium focal plane arrays for the Space Infrared Telescope Facility (SIRTF). The cryogenic telescope of SIRTF will be used for natural-background-limited astronomical observations, an application that requires arrays of far-infrared sensors of unprecedented sensitivity. For the 30 -55 tm wavelength range, we describe the development of monolithic Ge:Be arrays with associated readouts bump-bonded to a common substrate. For the 55 - 120 im wavelength range, we describe arrays based on a 1 x32 building block that can be stacked into fully-filled two-dimensional arrays. We show results from tests of a 3 x 32 demonstration array that operates at the SIRTF performance levels. This array demonstrates solutions to the problems of 1) maintaining the required detector operating temperature ( < 2K ) ; 2) isolating the array from the heat and photon emission of the readout; 3) achieving long absorption paths in the detectors; and 4) maintaining constant detector bias and low noise from the readout amplifier. The array design permits stacking into the full 32x32 format required for SIRTF The array thermally isolates the readout from the detectors to take advantage of the improved electronics noise performance at the elevated temperature of 20 K. We also show designs for improved versions of the array that emphasize manufacturability and the ability to be space qualified
The Amber Engineering AE 152 readout is a 32-channel multiplexer built as part of the far-infrared focal plane array development effort for the Space Infrared Telescope Facility (SIRTF). The design of the device addresses a number of constraints peculiar to the operation of germanium photoconductors. In particular, the need for a very high level of bias stability is solved by a non-switched operation of the first stage. Additionally, the readout was optimized for the detector capacitance expected of large bulk photoconductors ( 0.7 pF) and for the slow operating speeds anticipated for this astronomical application. Fabricated in a 1 .25 jim C-MOS process, the circuit utilizes a cascode input stage to provide gain at the front end while avoiding the Miller effect. The AE 152 also includes an internal offset correction and a shift register multiplexer for the output. We present test data for this device at a variety of temperatures, and show read noises as low as 8 electrons at a temperature of 77 K
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