The European Space Agency's ISO satellite is a liquid helium cooled space observatory for infrared astronomy. It will be launched for an 18 month mission in 1995 by the Ariane 4 rocket. The payload module contains a 60 cm telescope and 4 focal plane instruments covering the wavelength range 2.4 to 240 micrometers . During the first cold tests early in 1994, ISO's 2300 1 tank was partially filled with superfluid helium. The main purpose of this test was to check all the functions of the instruments and their compatibility in ISO's cryovacuum environment. In addition the straylight level caused by thermal emission of the cryostat's interior was measured by the focal plane instruments.

ASTER is an advanced multispectral imager with a high spatial, spectral and radiometric resolutions for EOS-AM1 platform which will be launched in June 1998. ASTER covers a wide spectral region from visible to thermal infrared by 14 spectral bands. Moreover, ASTER has a stereoscopic viewing capability by a near infrared band. Excellent observational performance can be expected by a pushbroom type visible and near infrared radiometer (VNIR subsystem) with a high spatial resolution of 15 m, a pushbroom type short wave infrared radiometer (SWIR subsystem) with a high spectral resolution and a whiskbroom type thermal infrared radiometer (TIR subsystem) with high spatial, spectral and radiometric resolutions. Long life mechanical cryocoolers are developed to enhance the performances of the SWIR and the TIR subsystems.

The topic is wildly off-axis reflecting systems (Schiefspiegler) which consist of a pair of confocal prolate spheroids. That they are reflecting makes them appropriate for use in the infrared. By wildly off-axis I mean that the angle between the major axes of the two spheroids may be arbitrarily large, a property that makes them particularly useful in the cramped quarters on a satellite. In this construction two foci, one from each of the spheroids, are made to coincide. The remaining two, belonging to each spheroid, are taken as the systems entrance and exit pupils. Thus a chief ray will pass through each of these three points. In previous papers we have defined the pseudo axis as on e of the chief rays about which all other chief rays are symmetric and the conditions for its existence had been derived. Conditions for the formation of particular types of imaging forming systems, or for afocal systems, also have been derived. In this paper we present specific examples of these systems together with analyses of their properties as determined by generalized ray tracing.

This paper describes the original requirement of a light weight, high performance, low cost thermal imager which resulted in the design of the novel coaxial scanner. The early form of imager used a dedicated display to match the original cyclic scan sequence. With the advent of fast digital scan converters and the desire to use standard TV monitors the imager was redesigned and new TV compatible scan sequences devised. A version of this scanner is currently being manufactured by GEC Marconi Avionics, UK, and the paper concludes with examples of its application.

An elegantly simple cryogenic instrument has been proposed to measure far infrared radiation from starburst galaxies. The experiment-known as WIRE- employs a Cassegrain telescope with diamond-turned mirrors to provide a light- weight optical system for photon collection. A dichroic beamsplitter and filter separate the light into two broad, well-defined bands of interest. Two 128- X 128-pixel arsenic-doped silicon focal plane arrays spatially sample the incoming photons. These arrays feature exceptionally low dark current and low read noise, which allows the coaddition of thousands of images. The entire optical section and focal plane arrays are cooled to 12 Kelvin and 7.5 Kelvin, respectively, by a two-stage, solid-hydrogen cryostat. An uncomplicated electronics package provides some on-board coaddition of images, accepts the simple command required by the WIRE instrument, and interfaces the data signals to the SMEX spacecraft for telemetry to the ground.

New type of infrared instruments such as Tunable Etalon Remote Sounder for the Earth (TERSE) and High resolution Limb Infrared Absorption Spectrometer (HLAS) were proposed and studied for the future Japanese earth observation satellite program. This paper describes the results of feasibility study of TERSE and HLAS.

A satellite borne FTIR called IMG (Interferometric Monitor for Greenhouse Gases) is now under development by JAROS (Japan Resources Observation System Organization) deputed by MITI (Ministry of International Trade and Industry). It will be installed on ADEOS (Advanced Earth Observing Satellite) which will be launched in Feb. 1996 by NASDA (National Space Development Agency of Japan). IMG is a very high spectral resolution (0.1 cm^-1) spectrometer which covers a wide range of infrared spectrum (3.3-14 micrometers ). With these features, IMG can detect and monitor spatial and vertical distribution of greenhouse effect gases such as CO₂, CH₄, O₃, etc. over the entire Earth.

Program overview, scientific targets and instrument design of the Improved Limb Atmospheric Spectrometer (ILAS) is described. The ILAS has two grating spectrometers for solar occultation measurement: one is for measurement of infrared band (850-1610 cm^-1, 11.76 micrometers - 6.21 micrometers ) for O₃, HNO₃, NO₂, N₂O, H₂O, CH₄ and CFC11, and the other is for visible band (753-784 nm, O₂ A band) for aerosols, temperature and air density measurement. ILAS will be onboard the ADEOS spacecraft and will observe high-latitude (N55-70, S63-87) ozone layer after February 1996 over 3 years with high vertical resolution (less than or equal to 2 km).

A space infrared astronomy program in Japan is reviewed. The first space infrared telescope, IRTS (Infrared Telescope in Space) will be launched in February of 1994. The IRTS is a small mission onboard the small space platform, SFU and is optimized to observed diffuse infrared emission. Based on the experiences of IRTS, a new space infrared mission, IRIS (Infrared Imaging Surveyor) is now being proposed. The IRIS will be launched by MV rocket which is now under development in ISAS. The IRIS is a new technology telescope which uses mechanical cooler and radiative cooling. With use of large format arrays and 70 cm aperture telescope, new discoveries on cosmology, galaxies, stars, and planetary systems are expected.

In 1999, ADEOS-II is planned to launch. This satellite aims to observe the global changes of environment based on the carbon, water and energy cycle. For this purpose, ADEOS-II will carry several mission equipments. One of them is GLI (GLobal Imager). GLI is the imaging radiometer possible to observe various objects, for example, ocean color, sea surface temperature, vegetation index, cloud distribution, ice on the land and sea. To satisfy these abilities various methods will be applied to GLI. Collecting Optics consists of 2 off-axis parabolic mirrors to avoid the obstruction in the field of view. Interference filter are joined each other to set up many filter in the focal plane. Both faces of scan mirror will be used in terms of extending the integration time of detectors. In this report these methods and mission of GLI will be described.

We have made a submillimeter-wave telescope for a Japanese sounding rocket, S- 520-17, which is dedicated for an observation of cold dust in Orion molecular cloud region. The system is now under test for launch in Jan. 1995. The telescope include an off-axis Gregorian telescope with aperture of 30 cm, focal plane bolometer array, cryogenic cooling system down to 0.3 K, and a star sensor using charge modulation device. A very low emissivity optical arrangement of less than 1% is achieved using pure aluminum mirror, off axis reflector and cold optics. Single moded conical feed horn is effectively coupled with bolometers with efficiency of more than 90%. The focal plane array consists of 12-element bolometers, six for 250 micrometers observation and six for 500 micrometers observation. NEPs of the bolometers are 5 X 10^-17W/√Hz which is read out by AC bridge read-out circuit. Total system gives sensitivities of about 10^-12W/cm² X sr for diffuse objects or 2 Jy for compact objects at 500 micrometers over 100 deg² region with a beam sizes of 10 arcmin. This observation gives unique data on cold dust distribution, which is believed to dominate the dust mass distribution, over Orion Molecular Cloud region.

We have developed an eight-element stressed Ge:Ga linear array. It has a compact and stable structure. The pixel size is 0.9 X 0.9 X 0.9 mm³, the pitch of the array is 1.0 mm, and the total sensitive area is 8.0 mm X 1.0 mm. The longer wavelength cut-off is 200 microns, and the peak responsivity is 100 A/W in a high-background condition including cavity efficiencies. It has been demonstrated that this array has a useful performance in the high-background condition, such as for airborne and balloon-borne instruments. The structure of the stress assembly is provably extendable up to sixteen and more.

A long life spaceborne Stirling cycle cryocooler named 'LS-5A' has been developed for use to cool the detector mounted on the Short Wavelength Infrared Radiometer (SWIR) of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). The cryocooler is applied Stirling cycle, supplies 1.2 watt cooling at the cooling temperature of 70 K, and consist of a twin-opposed piston compressor unit and a expander unit balanced by an active balancer to minimize the self-induced vibration. In order to accomplish 5 years of continuous operation in orbit, the cryocooler has noncontact clearance seals for pistons supported by suspension springs to avoid the wear of seal materials. Cooling performances and self-induced vibration levels were evaluated, and a life test cryocooler has been running for 7300 hours without any performance degradation.

We have been developing a long life spaceborne cryocooler for the thermal infrared radiometer (TIR), an observation system on the advanced spaceborne thermal emission and reflection radiometer (ASTER). ASTER was selected by NASA to fly on the EOS-AM1 platform which will be launched in 1998. The TIR cryocooler was designed to maintain the infrared detector's temperature at 80 Kelvin. And to do this, the cooling capacity is required more than 1.2 W when the cold head is 70 K. The cryocooler must operate continuously for more than 5 years with low mechanical disturbance. To meet these requirement, we used clearance seals and linear electric motors for long life, and back-to-back compressors and an expander with an active balancer for low mechanical disturbance.

The Space Dynamics Laboratory at Utah State University built an infrared imaging radiometer with dual, large-format detector arrays and a passively cooled telescope for low earth orbit. The confocal detector arrays include a 128 X 128 HgCdTe array operating from 4.5 to 7.5 micrometers and a 256 X 256 InSb array operating from 2.0 to 4.5 micrometers . These arrays yield simultaneous dual-band images. A 13 cm aperture, passively cooled telescope with single- axis scan mirror gives high system sensitivity, excellent image quality, and precision tracking of targets and backgrounds without the usual complexity of cooled optics. High speed cryogenic filter wheels with 6 to 8 filters per detector provide for rapid band selection. A modular cooling system allows the detector arrays and filters to be cooled using either a mechanical cryocooler or a solid cryogen cryostat depending on mission requirements. An on-board calibration source performs pixel-to-pixel uniformity correction on- orbit.

The Wide-Field Infrared Explorer is a cryogenically-cooled infrared telescope designed to study the evolution of starburst galaxies. This survey mission, proposed as part of the NASA Small Explorer program, takes advantage of recent advances in infrared detector technology to detect distant galaxies in 12 and 25 micrometers wavelength bands. The WIRE instrument is designed to be integrated with a spacecraft bus provided by Goddard Space Flight Center and launched into a 500 km orbit on a Pegasus XL launch vehicle. Most of the mission will be split between a moderate depth survey requiring 14 minutes exposure time per field and a deep survey requiring 4-8 hours per field. The WIRE telescope has an aperture of 300 mm, focal length of 1105 mm and field of view of 31.6 arcmin. A dichroic beam splitter separates the beam into the two wavelength bands. The two sensors are 128 X 128 Si:As arrays with 75-micrometers pixels operating in the blocked impurity band (BIB) mode. The focal plane arrays are cooled by solid hydrogen to 7.5 K and the optics and baffles are cooled by solid hydrogen to below 19 K.

Space Dynamics Laboratory at Utah State University (SDL/USU) optimized the focus of an off-axis, cryogenically cooled infrared collimator for cryogenic operating temperatures. Historically, collimator focus was optimized at ambient temperatures where interactive focus adjustment and testing could be performed. The focus shift that occurred when the optics were cooled was minimized by collimator design, and the change was negligible compared to the spatial resolution of the IR sensor measuring the collimator's simulated point source. However, the focus determined at ambient temperature does not meet the image quality requirements of state-of-the-art sensors. The method used by SDL to determine optimal focus at cryogenic temperatures applies classical optical techniques to the cryogenically cooled environment. System level interferometric measurements are first made to characterize the system wavefront error. These measurements are then applied to an aberration-free optical model to evaluate system focus for a wavelength of 12 micrometers . The method also uses a knife edge test to refer the interferometric measurements to the aperture located near the focal point of the collimator. This paper discusses the physical test setup, outlines the optical model and analysis procedure, and presents results before and after focus optimization of a multifunction infrared calibrator.

This paper provides an overview of the sounding of the atmosphere using broadband emission radiometer (SABER) instrument proposed by NASA Langley Research Center (LaRC) and the Space Dynamics Laboratory at Utah State University (SDL/USU). SABER is a 12-channel infrared radiometer designed to measure atmospheric emissions in the 1 to 17 micrometers spectral region. Radiometric, optical, thermal, and electronic aspects of the design are discussed.

The calibration of low background IR sensor systems require cryogenically cooled collimators. The need to characterize the output beam angle as a function of pointing position, cryogenic pressure, temperature and liquid level has always been difficult. Historically, manual theodolites have been used to measure these parameters. Because accuracy and repeatability of the manual measurement device is dependent upon user interpretation and manual coupling, the ability to measure small drifts with the thoedolite is not sufficient. The time required to manually characterize the output beam angle as a function of pointing position is so long that the drift of the beam angle begins to dominate the measurement error. A Charge Injection Device (CID) camera with very uniform focal plane pixel spacing and quality optics, can be used to very accurately monitor output beam angles in short intervals. This is accomplished by using sub-pixel centroiding techniques. Resolving a reimaged spot to 1/40 pixel accuracy is accomplished by using a weighted center of area calculation. Automated measurements have two advantages: they are faster, allowing for large numbers of measurements and higher resolution as well as removing human error, resulting in a better understanding of the pointing system. Using a 512 X 512 CID camera, angular resolution of 5 (mu) rad is achieved for a field of view of 6 degrees full angle. The potential for absolute accuracies of the same resolution is achievable if the stability and nonuniformities of the CID camera and optics are calibrated. Typical results obtained from a cryogenic system taken with the CID camera will be presented.

The challenging target position calibration task was accomplished in the recently upgraded AEDC 7V Chamber by use of a newly developed instrument termed the 7V Alignment Monitor System (7V-AMS). The 7V-AMS is essentially a resident, reference sensor consisting of a high quality imaging telescope, staring focal plane array (FPA), and FPA frame data acquisition and image processing system. A sub-pixel image centroiding routine permits accurate and precise determination of target image position. Unorthodox operation of the otherwise off-the-shelf FPA and frame data acquisition system results in a radiometric sensitivity that permits the 7V-AMS to 'see' the high to midrange radiometric levels of all 7V calibration and target simulation sources. This sensitivity range, coupled with its high quality imaging capability, allowed the 7V-AMS to inspect the radiation patterns of the newly activated radiometric calibration and target simulation equipment, to pinpoint sources of stray radiation, and to detect and display faint ghost images. As part of its primary task, target position calibration, the 7V-AMS was used to precisely define the coordinate axis relationships of all equipment capable of controlling target position. This paper describes the 7V-AMS salient design features and also presents some results of its first application in the 7V Chamber.

The ISO Short Wavelength Spectrometer will open the full 2.4-45 micrometers wavelength range for astronomical spectroscopy. At spectral resolving power approximately equals 1000, most sources detected by IRAS will be within reach. In addition, spectral resolving power approximately equals 30000 is provided for the 12-45 micrometers range. Examples of proposed observations illustrate the SWS capabilities.

Far-infrared (FIR) spectroscopy and photometry provide unique tools to investigate the physical and chemical processes in the moderately warm, dense interstellar medium (ISM) and provide key information about fundamental astrophysical questions like star formation, star burst phenomena, and the formation of galaxies. We describe an imaging Fabry-Perot spectrometer for the Kuiper Airborne Observatory which operates in the wavelength range 40-200 micrometers . It employs 5 X 5 element photoconductive detector arrays and provides spectral resolutions of up to 10⁵. With this instrument we have observed star forming regions and molecular clouds in out Galaxy, the Galactic Center, and the global ISM in external galaxies. The Far Infrared and Submillimeter Space Telescope (FIRST) will open up for study the entire submillimeter and far-infrared band (85-900 micrometers ) including those wavelengths that are inaccessible even from airplanes. Furthermore, it will provide unprecedented angular resolution in the FIR due to its large telescope diameter. It will employ a Multi-Frequency Heterodyne receiver (MFH) and an imaging Far-InfrarRed spectrometer/Spectrophotometer (FIR). The latter instrument will be equipped with multiple Fabry-Perots and photoconductor and bolometer arrays. Its sensitivity and variable spectral resolution will make it suited both for Galactic and extragalactic observations.

A heterodyne receiver system for 700 to 3,000 GHz has been successfully used aboard the Kuiper Airborne Observatory since 1985. With this instrument several first high-resolution detection of CO (J equals 7 - 6, 9 - 8, 11 - 10, 12 - 11, 14 - 13) were performed. The down-converted signal is amplified by low-noise amplifiers and decomposed by an acousto-optical spectrometer. It has a maximum bandwidth of 1,400 MHz with a resolution of 1.5 MHz. At 3,000 GHz this yields an instantaneous velocity range of 170 km/sec with a resolution of 0.2 km/sec. The sensitivity of the whole system is given by the system noise temperature, e.g. T_sys equals 6,400 K (NEP equals 1 X 10^-19 W/Hz) at 2,500 GHz and 2,300 K (3 X 10^-20 W/Hz) at 800 GHz.

The far-infrared filters for the satellite subexperiment ISOPHOT have to fulfil a number of specific requirements. This is a report about the developed filter concept which was used to match all specifications. In a wide wavelength region this concept is capable of defining broad or narrow bandpasses in a flexible way. The filters which have been constructed are robust and survive multiple cryogenic cycles. They combine high passband transmission with extreme stopband rejection. Details are given for some representative ISOPHOT FIR-filters.

ISOPHOT, the photo-polarimeter on the Infrared Space Observatory (ISO) uses high sensitivity doped silicon and germanium photodetectors working in the wavelength range form 2.4 to 240 micrometers . Under low IR-background conditions such detectors show long and non-linear response relaxation to a step change of IR-illumination. We will show that this nonideal behavior can be described with high precision at least for the PHT-S Si:Ga detectors. In space, high- energy radiation will strongly influence the performance of the detectors operated a low temperature. Irradiation tests using a (gamma) -radiation source were performed on our Ge:Ga and stressed Ge:Ga detector simulating the radiation environment on the ISO orbit. We found annealing procedures for the detectors which restore the photometric calibrations to within a few percent.

In the last 20 years German space industry and research institutes have been involved with the development of IR sensors for application in space in the fields of remote sensing and astronomy. Following successful sounding rocket experiments, the first cryogenically-cooled space IR sensor has been successfully flown as part of the SDIO STS 39 mission in April 1991, acquiring valuable data on IR signatures in space. Other instruments operating in the IR currently under development are the ISOPHOT instrument of the European Space Observatory (ISO), the MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) and the SCIAMACHY. The paper will provide an overview of German IR space sensors, their design and performance characteristics.

The first fully space qualified acousto-optical spectrometer (AOS) is described. It is built for the Submillimeter Wave Astronomy Satellite (SWAS) to be launched in July 1995. It has a very large bandwidth from 1400 to 2800 MHz covered by 1365 channels. This corresponds to a nearly 1 MHz channel spacing. The design is optimized for very high stability, which is demonstrated by means of Allan variance stability test. The Allan plot minimum time was found well above 800 seconds. The AOS can operate within a temperature range from -5 to +30 degree(s)C (+5 to +25 degree(s)C nominal) and with temperature variations of up to 2 degree(s)C/h. The performance was verified also after environmental testing such as random vibration (10.2 G rms) and thermal cycling of -30 to +50 degree(s)C. The lightweight mechanical design resulted in a total weight of 7.2 kg including electronics. A detailed optical design study was performed in order to achieve diffraction limited channel resolution, high efficiency and low sensitivity to mechanical distortion. The RF input power needed for full scale is 11 mW. The power consumption is 5.4 Watts (including data pre-averaging and DC-DC converter losses). The development has shown that AOSs are well suited for spaceborne applications.

For the infrared astronomy and earth atmosphere survey helium-cooled telescope and instruments are used since over 15 years. As a national program MBB (now DASA) had developed the GIRL (German Infrared Laboratory) - cryosystem from 1977 to 1985. Bases on the experience from there, the 'Infrared Background Signature Survey' (IBSS) -sensor was built, which flew successfully on Space Shuttle (STS39) in May 1991. Based on GIRL and IBSS DASA built the Payload Module (PLM) for the 'Infrared Space Observatory' (ISO) under ESA-contract. The basic designs of the GIRL-, IBSS-, and ISO-cryostats are described. Besides essential IBSS- flight data, important functional aspects of space cryostats are illustrated at the example of ISO. The flight hardware acceptance status of the ISO-PLM, which shall be launched for its 18-months IR-astronomy mission on an Ariane 4 - launcher in September 1995, is described together with important hardware elements and the total PLM.

The PFS is optimized for studies for the Martian atmosphere and will be also used for investigations of the surface composition. The instrument is a dual Rotational Reflector Interferometer (RRI) and covers both the SWIR (1.25 - 4.5 micrometers ) and the MIR (5.6 - 40 micrometers ) in two channels. The Noise Equivalent Spectral Radiance (NESR) is predicted to characterize the instrument. The NESR depends of the modulation coefficient, the detectivity of the detectors, the other main parameters of the interferometer, and the spectral characteristics of filters and beamsplitters as well. The modulation coefficient takes into account both the most important deviations of the optical elements from the ideal one's and partial misalignment by mechanical tolerance's. Typically estimated values are for the Short Wavelength Channel (LWC): 2 X 10^-8 W/(cm² sr cm^-1) for (sigma) equals 400 cm^-1 respective. Some extreme examples of the Martian surface are given where the recording of spectra is promising due to a satisfying signal to noise ratio and some other one's where measurements will be critically.

The present state of the art for scientific InSb focal planes is the Santa Barbara Research Center (SBRC) 256 X 256 device. In this paper we will present the status of the 1024 X 1024 focal plane development effort, technical details on the design, and both warm and cryogenic test data on the readout multiplexer. As the largest InSb infrared hybrid focal plane in development, this information should be of great interest to many groups. The current status and test data are presented here so that those planning future space instrumentation projects can be brought up to date on this advanced technology.

The CIRS instrument is the Infrared spectrometer of the CASSINI orbiter. The flight and spare models performances of the IR Photovoltaic detector arrays are presented here. We discuss the efforts made to avoid 1/f noise dependent diodes to meet the severe requirements of this mission to Saturn.

Rockwell Science Center and the University of Hawaii have developed a short wavelength infrared (SWIR) 1024 X 1024 focal plane array (FPA). The continuing project is funded by the U.S. Air Force Phillips Laboratory in connection with their Advanced Electro Optical System (AEOS) 3.67 m telescope project on Haleakala, Maui. We have achieved our objective of developing a 1024 X 1024 FPA with a cut-off wavelength of 2.5 micrometers . The device is named the HgCdTe Astronomical Wide Area Infrared Imager (HAWAII). The first hybrids have been characterized, delivered and first light achieved two days ahead of schedule; performance highlights include successful elimination of the reset anomaly (whose presence limited the noise performance of prior astronomical 256 X 256 FPAs), total FPA dark current < 0.1 e-/sec at 77 K, pixel yield > 99%, quantum efficiency > 50%, BLIP-limited sensitivity at low-10⁹ photons/cm²-sec background and operating temperatures to 120 K, and read noise < 10 e-.

In this paper, a general and inclusive framework for understanding and characterizing the atmospheric effects in the thermal infrared in imaging systems is presented. This includes separation of the atmospheric distortions to their main two ingredients: optical turbulence, and scattering and absorption by atmospheric particulates. A basic and correct understanding of those effects enables the development of prediction models for the atmospheric turbulence and aerosol MTFs. Here, both models are implemented for real-time thermal image restoration, with the prior knowledge of standard meteorological parameters, and specifications of the imaging system. Examples of such restorations are presented and the uniqueness of the restoration method is discussed with the inclusion of atmospheric degradation of the received image with and without subsequent image restoration. The most important conclusion is that knowledge of the expected atmospheric MTF is crucial for the system designer.

A 1-5 micron astronomical infrared imaging facility is currently under development at Observatoire de Grenoble for the ADONIS adaptive optics system, a collaborative project of Observatoire de Paris and Observatoire de Grenoble under ESO (European Southern Observatory) contract. This imaging detector will equip the camera to be installed at the F/45 output focus of the 3.6 m telescope operated by ESO at La Silla, Chile. The detector is a 128 X 128 HgCdTe/CCD array optimized in the 3-5 micron range, built by the CEA-LETI-LIR (Infrared Laboratory). The measured readout noise is less 450 electrons at a pixel readout rate of 415 kHz. The detector has a high storage capacity of 6.8 X 10⁶ electrons yielding a dynamic range of about 84 dB. Such a high capacity is very useful, because adaptive optics allows large integration times up to a few minutes without degradation of the images by the atmospheric turbulence. Dark current is not a limitation for these large integration times even at an operation temperature of 77 K. A compact and versatile control electronics is being developed at the Observatoire de Grenoble. We will discuss the overall performances of the detector as well as the data acquisition and control systems built at Grenoble in the framework of astronomical imaging with adaptative optics techniques.

An analytical expression is derived for the complex reflectivity of a corner cube retroreflector, using the complex reflection coefficients for the s- and p-polarization. It incorporates errors in the cube corners, surface finish, and the coating non-uniformity. This expression shows explicitly that the corner cube retroreflector modifies the electric field of the incident beam, according to the path through the retroreflector (the segment). The corner cube retroreflector conjugates the incident beam only in the case of a plane wave with a constant amplitude incident on a "perfect" corner cube retroreflector of infinite dimensions.

We consider the advantages and disadvantages of a rotating and a rotational shearing interferometer for the detection of a planet circling around a nearby star. A rotating, rotational-shearing interferometer is proposed for the detection of a faint object in the vicinity of a very bright object. We derive an expression for the interferometric pattern detected by a rotational shearing interferometer. When the interferometer points at the bright star, the observed fringes are due only to the wavefront originating at the faint planet. A two-aperture interferometric configuration, even though not necessary for the shearing function, is suggested to enhance the stability of a free-flying spaceborne structure.

Los Alamos National Laboratories has begun construction of a visible/infrared radiometric calibration station that will allow for absolute calibration of optical and IR remote sensing instruments with clear apertures less than 16 inches in diameter in a vacuum environment. The calibration station broadband sources will be calibrated at the National Institute of Standards and Technology (NIST) and allow for traceable absolute radiometric calibration to within +/- 3% in the visible and near IR (0.4-2.5 micrometers ), and less than +/- 1% in the infrared, up to 12 micrometers . Capabilities for placing diffraction limited images of for sensor full-field flooding will exist. The facility will also include the calibration of polarization and spectra effects, spatial resolution, field of view performance, and wavefront characterization. The configuration of the vacuum calibration station consists of an off-axis 21 inch, f/3.2, parabolic collimator with a scanning fold flat in collimated space. The sources are placed, via mechanisms to be described, at the focal plane of the off-axis parabola. Vacuum system pressure will be in the 10^-6 Torr range. The broadband white-light source is a custom design by LANL with guidance from Labsphere Inc. The continuous operating radiance of the integrating sphere will be from 0.0-0.006 W/cm²/Sr/micrometers (upper level quoted for approximately 500 nm wavelength). The blackbody source is also custom designed at LANL with guidance from NIST. The blackbody temperature will be controllable between 250-350 degree(s)K. Both of the above sources have 4.1 inch apertures with estimated radiometric instability at less than 1%. The designs of each of these units will be described. The monochromator and interferometer light sources are outside the vacuum, but all optical relay and beam shaping optics are enclosed within the vacuum calibration station. These sources are to be described, as well as the methodology for alignment and characterization.

The Submillimeter Wave Astronomy Satellite (SWAS) mission will study galactic star formation and interstellar chemistry. To carry out this mission, SWAS will survey dense (n_H2 > 10³ cm^-3) molecular clouds within our galaxy in either the ground-state or a low- lying transition of five astrophysically important species: H₂O, H₂¹⁸O, O₂, CI, and ¹³CO. By observing these lines SWAS will: (1) test long-standing theories that predict that these species are the dominate coolants of molecular clouds during the early stages of their collapse to form stars and planets and (2) supply heretofore missing information about the abundance of key species central to the chemical models of dense interstellar gas. During its two-year mission, SWAS will observe giant and dark cloud cores with the goal of detecting to setting an upper limit on the water abundance of 3 X 10^-6 (relative to H₂) and on the molecular oxygen abundance of 2 X 10^-6 (relative to H₂). SWAS is designed to carry all elements of a ground based radiotelescope. The telescope is a highly efficient 54 X 68-cm off-axis Cassegrain antenna with an aggregate surface error less than or equal to 11 micrometers rms. The receiver system consists of two independent heterodyne receivers with second harmonic Schottky diode mixers, passively cooled to approximately equals 150 K. The spectrometer is a single acousto-optical spectrometer (AOS) with 1400 1-MHz channels enabling simultaneous observations of the H₂O, O₂, CI, and ¹³CO lines.

A rotating interferometer has been proposed for the detection of faint signals and the reconstruction of their sources. The performance analysis of a two-dimensional interferometer shows that an mterferometer configuration incorporating a non-redundant aperture spacing need not additionally include a rotational feature. The rotation of a two-aperture interferometer is recommended to sample the pupil plane at a large number of angular spatial frequencies and a single radial spatial frequency. A two-aperture interferometer, either stationary or rotating, will not detect a star and its faint companion. If the starplanet separation is correctly estimated in advance in order to set the aperture separation, then a very slowly rotating two-aperture interferometer may be used for detection of this system. Key Terms : Interferometnc arrays, Pupil-plane interferometry, Faint-signal detection, Signal reconstruction.