Wavefront sensing and control technology for submillimeter and far infrared space telescopes
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wavefront sensing and control segmented mirrors sp↗
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Wavefront Sensing and Control Technology for Submillimeter and Far-Infrared Space Telescopes
The NGST wavefront sensing and control system will be developed to TRL6 over the next few years, including testing in a cryogenic vacuum environment with traceable hardware. Doing this in the far-infrared and submillimeter is probably easier, as some aspects of the problem scale with wavelength, and the telescope is likely to have a more stable environment; however, detectors may present small complications. Since this is a new system approach, it warrants a new look. For instance, a large space telescope based on the DART membrane mirror design requires a new actuation approach. Other mirror and actuation technologies may prove useful as well.
Redding, Dave↗
Fixed-Tuned Submillimeter Waveguide Multipliers Using MMIC Technology
In preparation for the insturment ammouncement of opportunity for the Far Infrared and Submillimeter Space Telescope, and ESA/NASA space astrophysics observatory mission, local oscillator sources at high frequencies (1200 GHz) are being developed. As part of a multiplier chain beginning at ~100 GHz we are developing single and multiple diode waveguide circuits up to 640 GHz.
Far Infrared Submillimeter Space Telescope↗
Bolometric detector systems for IR and mm-wave space astronomy
Recent developments in bolometric detector systems for millimeter and submillimeter wave space astronomy are described. Current technologies meet all the requirements for the high frequency instrument onboard the cosmic background radiation anisotropy satellite/satellite for the measurement of background anisotropies (COBRAS/SAMBA) platform. It is considered that the technologies that are currently being developed will significantly reduce the effective time constant and/or the cooling requirements of bolometric detectors. These technologies lend themselves to the fabrication of the large format arrays required for the Far Infrared and Submillimeter Space Telescope (FIRST). The scientific goals and detector requirements of the COBRAS/SAMBA platform that will use infrared bolometers are reviewed and the baseline detector system is described, including the feed optics, the infrared filters, the cold amplifiers and the warm readout electronics.
Church, S. E.↗
Micro-spec: an Integrated Direct-detection Spectrometer for Far-infrared Space Telescopes
The far-infrared and submillimeter portions of the electromagnetic spectrum provide a unique view of the astrophysical processes present in the early universe. Our ability to fully explore this rich spectral region has been limited, however, by the size and cost of the cryogenic spectrometers required to carry out such measurements.Micro-Spec (μ-Spec) is a high-sensitivity, direct-detection spectrometer concept working in the 450-1000 (micrometers) wavelength range which will enable a wide range of flight missions that would otherwise be challenging due tothe large size of current instruments with the required spectral resolution and sensitivity. The spectrometer design utilizes two internal antenna arrays, one for transmitting and one for receiving, superconducting microstrip transmission lines for power division and phase delay, and an array of microwave kinetic inductance detectors (MKIDs) to achieve these goals. The instrument will be integrated on a approximately 10 sq cm silicon chip and can therefore become an important capability under the low background conditions accessible via space and high-altitude borne platforms. In this paper, an optical design methodology for micro-Spec is presented, with particular attention given to its two-dimensional diffractive region, where the light of different wavelengths is focused on the different detectors. The method is based on the maximization of the instrument resolving power and minimization of the RMS phase error on the instrument focal plane. This two-step optimization can generate geometrical configurations given specific requirements on spectrometer size, operating spectral range and performance.Two point designs with resolving power of 260 and 520 and an RMS phase error less than approximately 0.004 radians were developed for initial demonstration and will be the basis of future instruments with resolving power up to about 1200.
Far-infrared↗
Novel Multiplexing Technique for Detector and Mixer Arrays
Future submillimeter and far-infrared space telescopes will require large-format (many 1000's of elements) imaging detector arrays to perform state-of-the-art astronomical observations. A crucial issue related to a focal plane array is a readout scheme which is compatible with large numbers of cryogenically-cooled (typically < 1 K) detectors elements. When the number of elements becomes of the order of thousands, the physical layout for individual readout amplifiers becomes nearly impossible to realize for practical systems. Another important concern is the large number of wires leading to a 0.1-0.3 K platform. In the case of superconducting transition edge sensors (TES), a scheme for time-division multiplexing of SQUID read-out amplifiers has been recently demonstrated. In this scheme the number of SQUIDs is equal to the number (N) of the detectors, but only one SQUID is turned on at a time. The SQUIDs are connected in series in each column of the array, so the number of wires leading to the amplifiers can be reduced, but it is still of the order of N. Another approach uses a frequency domain multiplexing scheme of the bolometer array. The bolometers are biased with ac currents whose frequencies are individual for each element and are much higher than the bolometer bandwidth. The output signals are connected in series in a summing loop which is coupled to a single SQUID amplifier. The total number of channels depends on the ratio between the SQUID bandwidth and the bolometer bandwidth and can be at least 100 according to the authors. An important concern about this technique is a contribution of the out-of-band Johnson noise which multiplies by factor N(exp 1/2) for each frequency channel. We propose a novel solution for large format arrays based on the Hadamard transform coding technique which requires only one amplifier to read out the entire array of potentially many 1000's of elements and uses approximately 10 wires between the cold stage and room temperature electronics. This can significantly reduce the complexity of the readout circuits.
Karasik, Boris S.↗
New Concepts for Far-Infrared and Submillimeter Space Astronomy
The Second Workshop on New Concepts for Far-Infrared and Submillimeter Space Astronomy aimed to highlight the groundbreaking opportunities available for astronomical investigations in the far-infrared to submillimeter using advanced, space-based telescopes. Held at the University of Maryland on March 7-8, 2002, the Workshop was attended by 130 participants from 50 institutions, and represented scientists and engineers from many countries and with a wide variety of experience. The technical content featured 17 invited talks and 44 contributed posters, complemented by two sixperson panels to address questions of astronomy and technology.
Benford, Dominic J.↗
The Wide-Field Imaging Interferometry Testbed: Progress and Plans
We describe the technique of wide field mosaic imaging for optical/IR interferometers and present early experimental results from a laboratory instrument designed to validate, experiment with, and refine the technique. A conventional single-detector stellar interferometer operating with narrow bandwidth at center wavelength lambda is limited in its field of view to the primary beam of the individual telescope apertures, or approx. lambda/D(sub tel) radians, where is the telescope diameter. Such a field is too small for many applications; often one wishes to image extended sources. We are developing and testing a technique analogous to the mosaic method employed in millimeter and radio astronomy, but applicable to optical/IR Michelson interferometers, in which beam combination is done in the pupil plane. An N(sub pix) x N(sub pix) detector array placed in the image plane of the interferometer is used to record simultaneously the fringe patterns from many contiguous telescope fields, effectively multiplying the field size by N(sub pix)/2, where the factor 2 allows for Nyquist sampling. This mosaic imaging technique will be especially valuable for far IR and submillimeter interferometric space observatories such as the Space Infrared Interferometric Telescope (SPIRIT) and the Submillimeter Probe of the Evolution of Cosmic Structure (SPECS). SPIRIT and SPECS will be designed to provide sensitive, high angular resolution observations of fields several arcminutes in diameter, and views of the universe complementary to those provided by HST, NGST, and ALMA.
Rinehart, S. A.↗
Spectroscopic Capabilities and Possibilities of the Far Infrared and Submillimeter Telescope Mission
The Far Infrared and Submillimeter Telescope (FIRST) mission is the fourth European Space Agency corner stone mission. FIRST will be an observatory with a passively cooled (80 Kelvin) 3.5 meter class telescope and three cryogenic instruments covering the 670 to 80 mm spectral region. The mission is slated for a 4.5 year operational lifetime in an L2 orbit. It will share an Arian 5 launch with PLANCK in early 2007. The three payload instruments include the Spectral and Photometric Imaging Receiver (SPIRE), which is a bolometer array with Martin-Puplett FTS for 200-670 microns, the Photoconductor Array Camera and Spectrometer (PACS), which is a photoconductor array with a grating spectrometer for 80-210 microns and the Heterodyne Instrument for FIRST (HIFI), which is a series of seven heterodyne receivers covering 480-1250 GHz and portions of 1410-1910 GHz and 2400-2700 GHz. FIRST will make many detailed spectral surveys of a wide variety of objects previously obscured by the atmosphere and in regions of the spectrum seldom used for astronomical observations, With all of the spectroscopic capability on FIRST a great deal of laboratory spectroscopic support will be needed for accurate interpretation of the spectral data.
Pearson, J. C.↗
Prospects for Studying Interstellar Magnetic Fields with a Far-Infrared Polarimeter for SAFIR
Polarimetry at mid-infrared through millimeter wavelengths using airborne and ground-based telescopes has revealed magnetic structures in dense molecular clouds in the interstellar medium, primarily in regions of star formation. Furthermore, spectropolarimetry has offered clues about the composition of the dust grains and the mechanism by which they are aligned with respect to the local magnetic field. The sensitivity of the observations to date has been limited by the emission from the atmosphere and warm telescopes. A factor of 1000 in sensitivity can be gained by using instead a cold space telescope. With 5 arcminute resolution, Planck will make the first submillimeter polarization survey of the full Galaxy early in the next decade. We discuss the science case for and basic design of a far-infrared polarimeter on the SAFIR space telescope, which offers resolution in the few arcsecond range and wavelength selection of cold and warm dust components. Key science themes include the formation and evolution of molecular clouds in nearby spiral galaxies, the magnetic structure of the Galactic center, and interstellar turbulence.
Dowell, C. Darren↗
Analysis of the Optical Design for the SAFIR Telescope
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 to 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').
antenna radiation patterns↗
The Next Century Astrophysics Program
The Astrophysics Division within the NASA Office of Space Science and Applications (OSSA) has defined a set of major and moderate missions that are presently under study for flight sometime within the next 20 years. These programs include the: Advanced X Ray Astrophysics Facility; X Ray Schmidt Telescope; Nuclear Astrophysics Experiment; Hard X Ray Imaging Facility; Very High Throughput Facility; Gamma Ray Spectroscopy Observatory; Hubble Space Telescope; Lunar Transit Telescope; Astrometric Interferometer Mission; Next Generation Space Telescope; Imaging Optical Interferometer; Far Ultraviolet Spectroscopic Explorer; Gravity Probe B; Laser Gravity Wave Observatory in Space; Stratospheric Observatory for Infrared Astronomy; Space Infrared Telescope Facility; Submillimeter Intermediate Mission; Large Deployable Reflector; Submillimeter Interferometer; and Next Generation Orbiting Very Long Baseline Interferometer.
Swanson, Paul N.↗
Utilization of Space Station by the Large Deployment Reflector
The Large Deployable Reflector (LDR), a NASA concept of a very large, orbiting, far infrared submillimeter telescope is described. To be launched in the 1990s, LDR has a projected life of 10 years and is to be serviced every 2 to 3 years. A System Concept and Technology Definition Study of LDR for NASA Ames is currently being conducted. Study results indicate that launch of a 20 m LDR, operating in a 700 to 800 km orbit, requires two shuttle loads. The components of LDR are assembled in a lower parking orbit, and the system is checked out and then transferred to the operational orbit. Furthermore, for servicing, LDR may have to be retrieved to the same lower orbit (and later returned to operational altitude) by an orbit transfer vehicle. These requirements bring up the question of a suitable assembly, checkout, and servicing platform. The deployment process is time consuming and may require special equipment not necessarily available from the orbiter itself. The SS is an attractive choice for that platform.
Bandermann, L. W.↗
FIR/THz Space Interferometry: Science Opportunities, Mission Concepts, and Technical Challenges
Sensitive far-IR imaging and spectroscopic measurements of astronomical objects on sub-arcsecond angular scales are essential to our understanding of star and planet formation, the formation and evolution of galaxies, and to the detection and characterization of extrasolar planets. Cold single-aperture telescopes in space, such as the Spitzer Space Telescope and the Herschel Space Observatory, are very sensitive, but they lack the necessary angular resolution by two or more orders of magnitude. Far-IR space interferometers will address this need in the coming decades. Several mission concepts have already been studied, including in the US the Space Infrared Interferometric Telescope (SPIRIT) and the more ambitious Submillimeter Probe of the Evolution of Cosmic Structure (SPECS). This talk will describe science goals and summarize alternative concepts for future FIR/THz space interferometry missions. Small arrays of sensitive, fast, direct detectors are a key enabling technology for SPIRIT and SPECS. I will describe the technology requirements for far-IR interferometry, including the detector requirements, and their derivation from the mission science goals and instrument concepts.
Leisawitz, David↗
An Infrared Telescope for Planet Detection and General Astrophysics
NASA plans to launch a Terrestrial Planet Finder (TPF) mission in 2014 to detect and characterize Earth-like planets around nearby stars, perform comparative planetology studies, and obtain general astrophysics observations. During our recently completed a TPF Mission Architecture study for NASA/JPL we developed the conceptual design for a 28-meter telescope with an IR Coronagraph that meets these mission objectives. This telescope and the technology it embodies are directly applicable to future Far-IR and Submillimeter space missions. The detection of a 30th magnitude planet located within 50 milli-arc-seconds of a 5th (Visual) magnitude star is an exceptionally challenging objective. Observations in the thermal infrared (7-17 microns) are somewhat easier since the planet is "only" 15(sup m) fainter than the star at these wavelengths, but many severe challenges must still be overcome. These challenges include: 1. Designing a coronagraph for star:planet separations less than or equal to lambda/D. 2. Developing the deployment scheme for a 28m space telescope that can fit in an existing launch vehicle payload fairing. 3. Generating configuration layouts for the IR telescope, coronagraph, spacecraft bus, sunshade, solar array, and high-gain antenna. 4. Providing: Structural stability to within 10 microns to support the optics. Thermal control to achieve the necessary structural stability, as well as providing a stable (approx. 30K) thermal environment for the optics. Dynamics isolation from potential jitter sources. 5. Minimizing launch mass to provide the maximum payload for the science mission Interfacing to an EELV Heavy launch vehicle, including acoustic and stress loads for the launch environment. 6. Identifying the key technologies (which can be developed by 2009) that will enable TPF mission to be performed. 7. Generating a manufacturing plan that will permit TPF to be developed at a reasonable cost and schedule. Many of these design challenges result in inherently conflicting requirements on the design of TPF. Drawing on our experience with large space telescopes such as the Chandra X-ray Observatory and the Next Generation Space Telescope, we have created a conceptual design for TPF that successfully meets these challenging requirements. This paper describes our solution to these challenges.
Lillie, C. F.↗
Far-Infrared Space Interferometers: Future Windows on Star and Planet Formation
Far-IR space interferometers will provide observational access to a spectral region containing many important cooling and diagnostic spectral lines and the bulk of the thermal emission from dust at angular scales critical to advancing our understanding of the star and planet formation process. We will describe concepts for the Space Infrared Interferometric Telescope (SPIRIT) and the Submillimeter Probe of the Evolution of Cosmic Structure (SPECS). Both of these candidate NASA missions are imaging and spectral Michelson interferometers operating in the wavelength range -40 - 800 microns. SPIRIT, which could be launched in a decade as a NASA Origins Probe, is built on a deployable boom and has a maximum baseline length of -30 - 50 m, yielding sub-arcsecond resolution in the far-IR. SPIRIT will thus provide far-IR/sub-mm measurements complementary to the near- and mid-IR measurements obtainable with the James Webb Space Telescope (JWST), and well matched to JWST observations in angular resolution. Ultimately SPECS, a NASA Vision Mission, will use formation flying to attain baseline lengths up to 1 km, and thus angular resolution comparable to that of the Hubble Space Telescope and the Atacama Large Millimeter Array. We will report preliminary results of the NASA-sponsored SPIRIT and SPECS mission studies, which are now underway.
Leisawitz, David↗
Developing Wide-Field Spatio-Spectral Interferometry for Far-Infrared Space Applications
Interferometry is an affordable way to bring the benefits of high resolution to space far-IR astrophysics. We summarize an ongoing effort to develop and learn the practical limitations of an interferometric technique that will enable the acquisition of high-resolution far-IR integral field spectroscopic data with a single instrument in a future space-based interferometer. This technique was central to the Space Infrared Interferometric Telescope (SPIRIT) and Submillimeter Probe of the Evolution of Cosmic Structure (SPECS) space mission design concepts, and it will first be used on the Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII). Our experimental approach combines data from a laboratory optical interferometer (the Wide-field Imaging Interferometry Testbed, WIIT), computational optical system modeling, and spatio-spectral synthesis algorithm development. We summarize recent experimental results and future plans.
Leisawitz, David↗
SUBMM wave superconduction hot-electron direct detectors
Recently, we have presented a concept for a hot-electron direct detector (HEDD) capable of counting single millimeter-wave photons. Such a detector meets the needs of future space far-infrared applications and can be used for background-limited detector arrays on missions like SPIRIT, 10-m filled aperture telescope, SAFIR, and SPECS.
hot-electron electron-phonon direct detectors subm↗