SPHEREx, a mission in NASA’s Medium Explorer (MIDEX) program recently selected for Phase-A implementation, is an all-sky survey satellite that will produce a near-infrared spectrum for every 6 arcsecond pixel on the sky. SPHEREx has a simple, high-heritage design with large optical throughput to maximize spectral mapping speed. While the legacy data products will provide a rich archive of spectra for the entire astronomical community to mine, the instrument is optimized for three specific scientific goals: to probe inflation through the imprint primordial non-Gaussianity left on today’s large-scale cosmological structure; to survey the Galactic plane for water and other biogenic ices through absorption line studies; and to constrain the history of galaxy formation through power spectra of background fluctuations as measured in deep regions near the ecliptic poles. The aluminum telescope consists of a heavily baffled, wide-field off-axis reflective triplet design. The focal plane is imaged simultaneously by two mosaics of H2RG detector arrays separated by a dichroic beamsplitter. SPHEREx assembles spectra through the use of mass and volume efficient linear variable filters (LVFs) included in the focal plane assemblies, eliminating the need for any dispersive or moving elements. Instead, spectra are constructed through a series of small steps in the spacecraft attitude across the sky, modulating the location of an object within the FOV and varying the observation wavelength in each exposure. The spectra will cover the wavelength range between 0.75 and 5.0 µm at spectral resolutions ranging between R=35 and R=130. The entire telescope is cooled passively by a series of three V-groove radiators below 80K. An additional stage of radiative cooling is included to reduce the long wavelength focal plane temperature below 60K, controlling the dark current. As a whole, SPHEREx requires no new technologies and carries large technical and resource margins on every aspect of the design.
ATLAST is a particular realization of the Large Ultraviolet Optical Infrared telescope (LUVOIR), a ∼10-m diameter space telescope being defined for consideration in the 2020 Decadal Review of astronomy and astrophysics. ATLAST/LUVOIR is generally thought of as an ambient temperature (∼300 K) system, and little consideration has been given to using it at infrared wavelengths longward of ∼2 μm. We assess the scientific and technical benefits of operating such a telescope further into the infrared, with particular emphasis on the study of exoplanets, which is a major science theme for ATLAST/LUVOIR. For the study of exoplanet atmospheres, the capability to work at least out to 5.0 μm is highly desirable. Such an extension of the long wavelength limit of ATLAST would greatly increase its capabilities for studies of exoplanet atmospheres and provide powerful capabilities for the study of a wide range of astrophysical questions. We present a concept for a fiber-fed grating spectrometer, which would enable R=200 spectroscopy on ATLAST with minimal impact on the other focal planet instruments. We conclude that it is technically feasible and highly desirable scientifically to extend the wavelength range of ATLAST to at least 5 μm.
The Spitzer Space Telescope, which has operated very successfully since 2003 in its unique Earth-trailing solar orbit, is NASA's Great Observatory for infrared astronomy. We provide a quick overview of the optical characteristics of Spitzer and review the observatory design. The main emphasis is on two unique on-orbit activities used to optimize the scientific return from Spitzer: 1. an unusual approach to focusing the telescope that minimized the use of the cryogenic focus mechanism, and 2. a methodology for extending the cryogenic lifetime of Spitzer by actively controlling the telescope temperature.
A key to the success of the Spitzer Space Telescope (formerly SIRTF) Mission was a unique management structure that
promoted open communication and collaboration among scientific, engineering, and contractor personnel at all levels of
the project. This helped us to recruit and maintain the very best people to work on Spitzer. We describe the management
concept that led to the success of the mission. Specific examples of how the project benefited from the communication
and reporting structure, and lessons learned about technology are described.
We are developing the Background-Limited Infrared-Submillimeter Spectrograph (BLISS) for SPICA to provide
a breakthrough capability for far-IR survey spectroscopy. SPICAs large cold aperture allows mid-IR to submm
observations which are limited only by the natural backgrounds, and BLISS is designed to operate near this
fundamental limit. BLISS-SPICA is 6 orders of magnitude faster than the spectrometers on Herschel and
SOFIA in obtaining full-band spectra. It enables spectroscopy of dust-obscured galaxies at all epochs back to
the rst billion years after the Big Bang (redshift 6), and study of all stages of planet formation in circumstellar
BLISS covers 35 - 433 microns range in ve or six wavelength bands, and couples two 2 sky positions simultaneously.
The instrument is cooled to 50 mK for optimal sensitivity with an on-board refrigerators. The detector
package is 4224 silicon-nitride micro-mesh leg-isolated bolometers with superconducting transition-edge-sensed
(TES) thermistors, read out with a cryogenic time-domain multiplexer. All technical elements of BLISS have
heritage in mature scientic instruments, and many have own. We report on our design study in which we are
optimizing performance while accommodating SPICAs constraints, including the stringent cryogenic mass budget.
In particular, we present our progress in the optical design and waveguide spectrometer prototyping. A
companion paper in Conference 7741 (Beyer et al.) discusses in greater detail the progress in the BLISS TES
We present an overview of the calibration and properties of data from the IRAC instrument aboard the Spitzer Space
Telescope taken after the depletion of cryogen. The cryogen depleted on 15 May 2009, and shortly afterward a two-month-
long calibration and characterization campaign was conducted. The array temperature and bias setpoints were
revised on 19 September 2009 to take advantage of lower than expected power dissipation by the instrument and to
improve sensitivity. The final operating temperature of the arrays is 28.7 K, the applied bias across each detector is 500
mV and the equilibrium temperature of the instrument chamber is 27.55 K. The final sensitivities are essentially the
same as the cryogenic mission with the 3.6 μm array being slightly less sensitive (10%) and the 4.5 μm array within 5%
of the cryogenic sensitivity. The current absolute photometric uncertainties are 4% at 3.6 and 4.5 μm, and better than
milli-mag photometry is achievable for long-stare photometric observations. With continued analysis, we expect the
absolute calibration to improve to the cryogenic value of 3%. Warm IRAC operations fully support all science that was
conducted in the cryogenic mission and all currently planned warm science projects (including Exploration Science
programs). We expect that IRAC will continue to make ground-breaking discoveries in star formation, the nature of the
early universe, and in our understanding of the properties of exoplanets.
We describe our ongoing project to build a far-infrared polarimeter for the HAWC instrument on SOFIA. Far-IR
polarimetry reveals unique information about magnetic fields in dusty molecular clouds and is an important
tool for understanding star formation and cloud evolution. SOFIA provides flexible access to the infrared as
well as good sensitivity to and angular resolution of continuum emission from molecular clouds. We are making
progress toward outfitting HAWC, a first-generation SOFIA camera, with a four-band polarimeter covering 50 to
220 microns wavelength. We have chosen a conservative design which uses quartz half-wave plates continuously
rotating at ~0.5 Hz, ball bearing suspensions, fixed wire-grid polarizers, and cryogenic motors. Design challenges
are to fit the polarimeter into a volume that did not originally envision one, to minimize the heating of the
cryogenic optics, and to produce negligible interference in the detector system. Here we describe the performance
of the polarimeter measured at cryogenic temperature as well as the basic method we intend for data analysis.
We are on track for delivering this instrument early in the operating lifetime of SOFIA.
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.
Multi-wavelength imaging polarimetry at far-infrared wavelengths has proven to be an excellent tool for studying
the physical properties of dust, molecular clouds, and magnetic fields in the interstellar medium. Although these
wavelengths are only observable from airborne or space-based platforms, no first-generation instrument for the
Stratospheric Observatory for Infrared Astronomy (SOFIA) is presently designed with polarimetric capabilities.
We study several options for upgrading the High-resolution Airborne Wideband Camera (HAWC) to a sensitive
FIR polarimeter. HAWC is a 12 × 32 pixel bolometer camera designed to cover the 53−215 μm spectral range
in 4 colors, all at diffraction-limited resolution (5−21 arcsec). Upgrade options include: (1) an external set of
optics which modulates the polarization state of the incoming radiation before entering the cryostat window;
(2) internal polarizing optics; and (3) a replacement of the current detector array with two state-of-the-art
superconducting bolometer arrays, an upgrade of the HAWC camera as well as polarimeter. We discuss a range
of science studies which will be possible with these upgrades including magnetic fields in star-forming regions
and galaxies and the wavelength-dependence of polarization.
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).
The Spitzer Space Telescope (formally known as SIRTF) was successfully launched on August 25, 2003, and has completed its initial in-orbit checkout and science validation and calibration period. The measured performance of the observatory has met or exceeded all of its high-level requirements, it entered normal operations in January 2004, and is returning high-quality science data. A superfluid-helium cooled 85 cm diameter telescope provides extremely low infrared backgrounds and feeds three science instruments covering wavelengths ranging from 3.6 to 160 microns. The telescope optical quality is excellent, providing diffraction-limited performance down to wavelengths below 6.5 microns. Based on the first helium mass and boil-off rate measurements, a cryogenic lifetime in excess of 5 years is expected. This presentation will provide a summary of the overall performance of the observatory, with an emphasis on those performance parameters that have the greatest impact on its ultimate science return.
The Space Infrared Telescope Facility (SIRTF) was successfully launched on August 25, 2003. SIRTF is an observatory for infrared astronomy from space. It has an 85cm diameter beryllium telescope operating at 5.5 K and a projected cryogenic lifetime of 4 to 6 years based on early flight performance. SIRTF has completed its in-orbit checkout and has become the first mission to execute astronomical observations from a solar orbit. SIRTF's three instruments with state of the art detector arrays provide imaging, photometry, and spectroscopy over the 3-180 micron wavelength range. SIRTF is achieving major advances in the study of astrophysical phenomena from the solar system to the edge of the Universe. SIRTF completes NASA's family of Great Observatories and serves as a cornerstone of the Origins program. Over 75% of the observing time will be awarded to the general scientific community through the usual proposal and peer review cycle. SIRTF has demonstrated major advances in technology areas critical to future infrared missions. These include lightweight cryogenic optics, sensitive detector arrays, and a high performance thermal system, combining radiative and cryogenic cooling, which allows a telescope to be launched warm and to be cooled in space. These thermal advances are enabled by the use of an Earth-trailing solar orbit which will carry SIRTF to a distance of ~0.6 AU from Earth in 5 years. The SIRTF project is managed for NASA by the Jet Propulsion Laboratory which employs a novel JPL-industry team management approach. This paper provides an overview of the SIRTF mission, telescope, cryostat, instruments, spacecraft, orbit, operations and project management approach; and this paper serves as an introduction to the accompanying set of detailed papers about specific aspects of SIRTF.
The Spitzer Space Telescope is an 85-cm telescope with three cryogenically cooled instruments. Following launch, the observatory was initialized and commissioned for science operations during the in-orbit checkout (IOC) and science verification (SV) phases, carried out over a total of 98.3 days. The execution of the IOC/SV mission plan progressively established Spitzer capabilities taking into consideration thermal, cryogenic, optical, pointing, communications, and operational designs and constraints. The plan was carried out with high efficiency, making effective use of cryogen-limited flight time. One key component to the success of the plan was the pre-launch allocation of schedule reserve in the timeline of IOC/SV activities, and how it was used in flight both to cover activity redesign and growth due to continually improving spacecraft and instrument knowledge, and to recover from anomalies. This paper describes the adaptive system design and evolution, implementation, and lessons learned from IOC/SV operations.
SIRTF, -the Space Infrared Telescope Facility, is to be launched by NASA early in 2003. SIRTF will be an observatory for infrared astronomy from space with an 85cm aperture telescope operating at 5.5K and a 2.5-to-5 year cryogenic lifetime. SIRTF's three instruments with state of the art detector arrays will provide imaging, photometry, and spectroscopy over the 3-180um wavelength range. SIRTF will provide major advances for the study of astrophysical problems from the solar system to the edge of the Universe. SIRTF will complete NASA's family of Great Observatories and serve as a cornerstone of the Origins program. Over 75% of the observing time will be awarded to the general scientific community through the usual proposal and peer review cycle. SIRTF will demonstrate major advances in technology areas critical to future infrared missions. These include lightweight cryogenic optics, sensitive detector arrays, and a high performance thermal system, combining radiative and cryogenic cooling, which allows the telescope to be launched warm and to cool in space. These thermal advances are enabled by the use of an Earth-trailing solar orbit which carries SIRTF to a distance of ~0.6 AU from Earth in 5 years. This paper will provide an overview of the SIRTF mission, -telescope, cryostat, instruments, spacecraft, orbit, and operations - in preparation for an accompanying set of detailed technical presentations.
The Astrobiology Explorer (ABE) is a MIDEX mission concept, currently under Concept Phase A study at NASA's Ames Research Center in collaboration with Ball Aerospace & Technologies, Corp., and managed by NASA's Jet Propulsion Laboratory. ABE will conduct infrared spectroscopic observations to address important problems in astrobiology, astrochemistry, and astrophysics. The core observational program would make fundamental scientific progress in understanding the distribution, identity, and evolution of ices and organic matter in dense molecular clouds, young forming stellar systems, stellar outflows, the general diffuse ISM, HII regions, Solar System bodies, and external galaxies. The ABE instrument concept includes a 0.6 m aperture Ritchey-Chretien telescope and three moderate resolution (R = 2000-3000) spectrometers together covering the 2.5-20 micron spectral region. Large format (1024 x 1024 pixel) IR detector arrays will allow each spectrometer to cover an entire octave of spectral range per exposure without any moving parts. The telescope will be cooled below 50 K by a cryogenic dewar shielded by a sunshade. The detectors will be cooled to ~7.5 K by a solid hydrogen cryostat. The optimum orbital configuration for achieving the scientific objectives of the ABE mission is a low background, 1 AU Earth driftaway orbit requiring a Delta II launch vehicle. This configuration provides a low thermal background and allows adequate communications bandwidth and good access to the entire sky over the ~1.5 year mission lifetime.
A long-wavelength large format Quantum Well Infrared Photodetector (QWIP) focal plane array has been successfully used in a ground based astronomy experiment. QWIP arrays afford greater flexibility than the usual extrinsically doped semiconductor infrared (IR) arrays. Recently, we operated an infrared camera with a 256x256 QWIP array sensitive at 8.5 μm at the prime focus of the 5-m Hale telescope, obtaining the images. The remarkable noise stability - and low 1/f noise - of QWIP focal plane arrays enable camera to operate by modulating the optical signal with a nod period up to 100 s. A 500 s observation on dark sky renders a flat image with little indication of the low spatial frequency structures associated with imperfect sky substration or detector drifts. At low operating temperatures for low-background irradiance levels, high resistivity of thick barriers in the active region of QWIPs impeded electrons from entering the detector from the opposite electrode. This could lead to a delay in refilling the space-charge buildup, and result in a lower responsitivity at high optical modulation frequencies. In order to overcome this problem we have designed a new detector structure, the blocked intersubband detector (BID) with separate active quantum well region and blocking barrier.
A long-wavelength large format Quantum Well Infrared Photodetector (QWIP) focal plane array has been successfully used in a ground based astronomy experiment. QWIP arrays afford greater flexibility than the usual extrinsically doped semiconductor infrared arrays. The wavelength of the peak response and cutoff can be continuously tailored over a range wide enough to enable light detection at any wavelength range between 6 - 20 micrometers .
One of the simplest device realizations of the classic particle- in-the-box problem of basic quantum mechanics is the Quantum Well Infrared Photodetector (QWIP). In this paper we discuss the effect of focal plane array non-uniformity on the performance, optimization of the detector design, material growth and processing that has culminated in realization of large format long-wavelength QWIP cameras, holding forth great promise for many applications in 6-18 micron wavelength range in science, medicine, defense and industry. In addition, we present the recent developments in long-wavelength/very long-wavelength dualband QWIP imaging camera for various applications.
This paper reports on the status of SIRTF--the Space Infrared Telescope Facility. SIRTF will be a cryogenically- cooled space telescope instrumented with large-format, state of the art infrared detector arrays. SIRTF will complete NASA's family of Great Observatories and also serve as a cornerstone of the Origins program. SIRTF will be launched in 2001, carrying a complement of imaging and spectroscopic instrumentation, for a mission approximately 5 yr in duration. SIRTF will be placed in an earth-trailing heliocentric orbit; the very favorable thermal environment of this orbit has enabled a novel warm-launch architecture for the cryogenic system. More than 75% of the observing time on SIRTF will be available to the general scientific community. The community involvement in SIRTF began in June of 2000 with the formal release of the call for Legacy Science proposals.
Quantum Well IR Photodetectors (QWIPs) afford greater flexibility than the usual extrinsically doped semiconductor IR detectors. The wavelength of the peak response and cutoff can be continuously tailored over a range wide enough to enable light detection at any wavelength range between 6-20 micrometers . The spectral band width of these detectors can be tuned from narrow to wide allowing various applications. Also, QWIP device parameters can be optimized to achieve extremely high performance sat lower operating temperatures due to exponential suppression of dark current. Furthermore, QWIPs offer low cost per pixel and highly uniform large format focal plane arrays (FPAs) mainly due to mature GaAs/AlGaAs growth and processing technologies. The other advantages of GaAs/AlGaAs based QWIPs are higher yield, lower 1/f noise and radiation hardness. Recently, we operated an IR camera with a 256 by 256 QWIP array sensitive at 8.5 micrometers at the prime focus of the 5-m Hale telescope, obtaining the images. The remarkable noise stability - and low 1/f noise - of QWIP focal plane arrays enable camera to operate by modulating the optical signal with a nod period up to100 s. A 500 s observation on dark sky renders a flat image with little indication of the low spatial frequency structures associated with imperfect sky subtraction or detector drifts.
One of the simplest device realizations of the classic particle-in-the-box problem of basic quantum mechanics is the Quantum Well Infrared Photodetector (QWIP). In this paper we discuss the effect of focal plane array non-uniformity on the performance, optimization of the detector design, material growth and processing that has culminated in realization of large format long-wavelength QWIP cameras, holding forth great promise for many applications in 6 - 18 micron wavelength range in science, medicine, defense and industry. In addition, we present the recent developments in long-wavelength/very long-wavelength dualband QWIP imaging camera for various applications.
The Space IR Telescope Facility (SIRTF), the last of NASA's 'Great Observatories' is entering its development phase. Ongoing advances in IR detector technology, coupled with innovative choices in orbit and system architecture, have maintained the vitality of SIRTF's scientific capability at a small fraction of the original development cost. The great sensitivity of SIRTF and its high observing efficiency promise to yield a rich legacy of science results. SIRTF is on a fast-track development schedule, with launch in December 2001. While the current baseline calls for a minimum 2.5-year cryogenic lifetime, recent programmatic and engineering development suggest that a 5-year lifetime is within reach. More than 75 percent of the SIRTF observing time will be available to the general community. We summarize the scientific capabilities and the technical specifications for the mission, including descriptions of the three-instrument payload. We will focus on the SIRTF science observations concepts, and describe SIRTF's seven observing modes - the modes by which the community will interface with the Observatory. The pre- and post-launch user services available at the SIRTF Science Center will also be presented. We include a listing of events likely to be of interest to potential SIRTF users between now and launch.
In recent years, many research groups in the world have demonstrated large format quantum well IR photodetector (QWIP) focal pane arrays for various thermal imaging applications. QWIPs as opposed to conventional low bandgap IR detectors, are limited by thermionic dark current and not tunneling current down to 30K or less. As a result the performance of QWIPs can be substantially improved by cooling from 70K to 30K. Cooling does not induce any nonuniformity or 1/f noise in QWIP focal plane arrays. In this paper, we discuss the development of highly uniform long-wavelength QWIPs for astronomical applications.
One of the simplest device realizations of the classic particle-in-the-box problem of basic quantum mechanics is the Quantum Well Infrared Photodetector (QWIP). In this paper we discuss the optimization of the detector design, material growth and processing that has culminated in realization of 15 micron cutoff 128 X 128 QWIP focal plane array camera, hand-held and palmsize 256 X 256 long-wavelength QWIP cameras and 648 X 480 long-wavelength camera, holding forth great promise for myriad applications in 6 - 25 micron wavelength range in science, medicine, defense and industry. In addition, we present the recent developments in broadband QWIPs, mid-wavelength/long-wavelength dualband QWIPs, long- wavelength/very long-wavelength dualband QWIPs, and high quantum efficiency QWIPs for low background applications in 4 - 26 micrometer wavelength region for NASA and DOD applications.
The Space Infrared Telescope Facility (SIRTF) will explore the birth and evolution of the Universe with unprecedented sensitivity. SIRTF will be the first mission to combine the high sensitivity achievable from a cryogenic space telescope with the imaging and spectroscopic power of the new generation of infrared detector arrays. The scientific capabilities of this combination are so great that SIRTF was designated the highest priority major mission for all of U.S. astronomy in the 1990s. The astronomical community will use SIRTF to explore the infrared universe with a depth and precision complementary to that achieved by NASA's other great observatories -- the Hubble Space Telescope (HST), the Advanced X-ray Astrophysics Facility (AXAF), and the Compton Gamma Ray Observatory (GRO) in their respective spectral bands. The launch of SIRTF in 2001 will permit contemporaneous observations with HST to study forefront problems of astrophysics. This paper provides a comprehensive review of the SIRTF program -- the science, the mission design, the facility, the instruments, and the implementation approach. Emphasis is placed on those features of the program including the use of a solar (heliocentric) orbit and the adoption of a novel warm-launch cryogenic architecture -- which will allow us to realize the great scientific potential of SIRTF in a resource- constrained environment.
A revised baseline mission concept for the Space Infrared Telescope Facility (SIRTF) has been developed by the SIRTF science and engineering teams over the past year. This mission, which would be carried into solar orbit by a Delta 7920 launch vehicle, retains the key scientific capabilities of earlier mission concepts at a fraction of the mass and cost. We review the scientific and technical innovations which have enabled this development.
This paper describes the status of NASA's Space Infrared Telescope Facility (SIRTF) program. SIRTF will be a cryogenically cooled observatory for infrared astronomy from space and is planned for launch early in the next decade. We summarize a newly modified baseline SIRTF mission and provide and overview of SIRTF's scientific programs.
The Space Infrared Telescope Facility -- SIRTF -- will be a cryogenically cooled observatory for infrared astronomy from space and is planned for launch early in the next decade. SIRTF will build on the scientific and technical results obtained by IRAS, COBE and ISO, but it will go beyond these cryogenic space missions by making extensive use -- for both imaging and spectroscopy -- of large-format detector arrays. This paper discusses a newly modified baseline SIRTF mission and its scientific capabilities.
The Space Infrared Telescope Facility (SIRFT) is a one-meter-class, liquid-helium-cooled, earth-orbiting astronomical observatory that will be the infrared component of NASA's family of Great Observatories. SIRTF will investigate numerous scientific areas including formation and evolution of galaxies, stars, and other solar systems; supernovae; phenomena in our own solar system; and, undoubtedly, topics that are outside today's scientific domain. SIRTF's three instruments will permit imaging at all infrared wavelengths from 1.8 to 1200 microns and spectroscopy from 2.5 to 200 microns. The observatory will operate at an altitude of 100,000 km where it will achieve a five-year lifetime and operate with better than 80 percent on-target efficiency. The scientific importance and technical and programmatic readiness of SIRTF has been recognized by the 1991 report of the National Research Council's Astronomy and Astrophysics Survey Committee which recently identified SIRTF as the highest priority major new initiative in all of astronomy for the coming decade.