This work summarizes the progress in the development and testing of the telescope for a space imaging spectrometer 'OMEGA' of a new stereo-spectral-imaging system ARGUS developed in the frame of the International project for MARS 94/96 missions. The results of the telescope aberration calculation are given. Brief description of the facility for the main optical characteristics measurements are described. The telescope was tested at a special vacuum chamber at the temperature range from 180K to 300K. The results of the telescope investigation are given.

In cryogenic optical-figure measurements for nominal optical flats, we in principle need a dewar-window system with the associated wavefront distortion calibrated for its actual temperature profile. Using traditional approach, this calibration would require a cryogenically calibrated reference flat, whose calibration on the other hand would need a calibrated window system not existing yet. Of course, we cannot reliably calculate the wave-front distortion either because of the following unknown profiles in the glass substrates such as temperature, temperature-dependent non-uniformity of the thermal expansion coefficient, refractive index, mechanical mounting strain, etc. To solve the problem, the author proposes a scheme to characterize and separate the tilt-independent wavefront distortion of the window system from that of the test piece in only one cooldown. The scheme involves interferometric phase map measurements for several lateral locations of the test piece shifted by a cryogenic X-Y translation stage. The data reduction scheme is described in detail.

The composite infrared spectrometer (CIRS) instrument is scheduled to fly on NASA's Cassini Orbiter to Saturn in 1997. CIRS consists of two Fourier transform spectrometers, the mid-IR (MIR) and the far-IR (FIR), which measure a spectral range from 7 to 1000 microns. The optical alignment of CIRS begins with alignment of the optical subsystems which are then integrated and aligned to each other. These subsystems include the 0.5 meter Cassegrain telescope, collimating optics aft of the telescope, the moving mirror scanning mechanism, MIR and FIR interferometers, and the MIR and FIR focal planes. This paper discusses the alignment verification test developed to verify the opto-mechanical alignment of the collimating optics and the fixed mirrors of the interferometers. The verification test utilized the ZYGO Mark IVxp interferometer to test the wavefront of the aligned subsystem. The test set-up, requirements and results are presented.

The CIRS instrument to be flown on the Cassini mission to Saturn is a cryogenic spectrometer with far-IR (FIR) and mid-IR (MIR) channels. The CIRS FIR focal plane consists of focussing optics, an output polarizer/analyzer which splits the output radiation according to polarization. The reflected and transmitted components are imaged by concentrating cones onto gold black foil thermopiles. The focal plane covers the spectral range of 10-600 cm^(-1). The geometric field-of-view requirement is 4.3 mrad. This paper details the assembly, alignment, characterization, cryogenic testing, and flight qualification of the CIRS FIR focal plane.

We present a brief overview of the design and construction of two grating infrared spectrometer, a new 2D array, dual grating spectrometer for the 7.0 to 13.8 micron region, built at the University of Denver (DU). This instrument has been designed to fulfill specific scientific goals in astronomy while utilizing the array to its fullest extent. The instrument uses diamond-turned aluminum optics to allow warm optical alignment and eliminate differential contraction of the optics while operating at cryogenic temperatures. Two gratings are used in the optical design to provide a resolution of about 800. The entire assembly is cooled with a Gifford-McMahon refrigerator so that it may later be adapted for use during remote observing. The array is a Rockwell 128 by 128 Si:As BIB hybrid focal plane array sensitive from optical to 26 microns. The electronics package and software for readout were developed by Wallace Instruments and are already in use on our TNTCAM at DU. 'First light' is scheduled for late summer 1996.

An all aluminum reflective optical system was tested to evaluate its optical performances at near liquid nitrogen temperature. A special cryogenic dewar was designed and fabricated with an optical window made of quartz glass on the front wall of the dewar. The optical system under test and a reference plane mirror, which were mounted into the dewar and cooled by liquid nitrogen, formed a double pass interferometric test schema together with a He-Ne interferometer of Fizeau type outside the dewar. The test results showed that there was little differences between the wavefront errors before and after the optical system is cooled, and in both cases the optical system had a diffraction limited imaging quality.

The SIRTF Telescope Test Facility (STTF) consists of an optical dewar for testing mirrors of up to 1m diameter and f < 6 at temperatures from 300K to 5K and a phase shift interferometer for optical characterization. The STTF was brought on-line in early 1995. The STTF was initially used to cool a 50cm diameter beryllium mirror that had been previously tested at NASA Ames Research Center. The initial tests validated the performance of the STTF by proving that the STTF could cool a mirror to 5K and achieve high quality optical data on the mirror, consistent with the previous results achieved at NASA Ames. The STTF has also been used to provide cryogenic optical testing of the ultra- lightweight 85cm diameter beryllium primary mirror assembly for the Infrared Telescope Technology Testbed (ITTT). Currently the facility is preparing for testing the complete ITTT. Also, the long wavelength photon background in the facility will be measured and characterized in 1996.

This paper addresses the current thermal management techniques of the Sounding of the Atmosphere using broadband emission radiometry (SABER) instrument. The SABER instrument is being developed jointly by NASA Langley and the Space Dynamics Laboratory at Utah State University. This instrument will fly on the Thermosphere-Ionosphere- Mesosphere Energetics and Dynamics spacecraft being built at the Applied Physics Laboratory at John Hopkins University. The infrared sensors on SABER must be cooled to 75 K for a 2 year period and at a 100 percent duty cycle. Because of SABER's stringent mass, size, and power constraints, the TRW miniature pulse tube refrigerator has been baselined to cool the focal plane assembly. A passive radiator will maintain the telescope at an average temperature near 230 K. Heat from the cryo-cooler and electronics will be dissipated by a separate radiator maintained at approximately 273 K. Approaches and advances in thermal management technology currently employed on the SABER instrument to ensure that heat loads and temperature ranges are met are also discussed.

The CIRS instrument to be flown on the Cassini mission to Saturn is a cryogenic spectrometer with far-IR (FIR) and mid-IR (MIR) channels. The CIRS FIR channel is a polarizing interferometer that contains three polarizing grid components. These components are an input polarizer, a polarizing beamsplitter, and an output polarizer/analyzer. THey consist of a 1.5 micron thick substrate with 2 micrometers wide copper wires, with 2 micrometers spacing, photolithographically deposited on the substrate. Mylar and polypropylene were chosen as the flight candidate substrates. After the testing was performed, mylar was chosen over polypropylene for the CIRS instrument due to a better cryogenic reflectance performance. These elements were fabricated at Queen Mary and Westfield College in London. This paper details the flight qualification of the mylar substrate and the characterization of the polypropylene substrate. Performance tests included cryogenic optical flatness, cryogenic polarization sensitive reflectance and transmittance measurements. Environmental tests included vibration, acoustic, humidity, and radiation survivability.

A cryogenically cooled Fabry-Perot etalon for imaging in the 2-2.5 micrometers , K band, spectral region has been constructed. Capacitance sensors monitor the etalon mirror spacing and parallelism and provide the error signals for active cavity control in a feedback loop with piezoelectric actuators. The new K band etalon is designed to be compatible with the Queensgate Instruments Ltd. CS100/ET servo-stabilized Fabry- Perot system. 3-5 micrometers cryogenically cooled etalons have also been made and coatings are also available for the 8-13 micrometers range. Working in the K band range permits the use of water free silica substrates which in turn allows the cavity spacing to be extended beyond the nominal 100 micrometers cavity spacing of the 3-5 micrometers etalons by using specially manufactured optically contacted capacitor pads. Under servo-control at 77K the etalon has a response time of 30ms and a minimum cavity tuning range of +/- 3 micrometers about the nominal cavity length, corresponding to at least 5 orders of interference at a wavelength of 2.5 micrometers . The etalon aperture has a nominal diameter of 50mm.

The wide-field infrared explorer (WIRE) is a small explorer (SMEX) mission that will fly in the fall of 1998. The WIRE mission proposes to conduct a 4-month survey of more than 100 degree² of sky using 12- and 25-micrometers detectors. The instrument requires cryogenic cooling of its focal planes and telescope in order to achieve the required performance sensitivity. In addition, because of the SMEX nature of the experiment, the mass of the cryostat must be less than 60 kg. The most mass efficient system meeting the lifetime requirement was determined to be a dual stage H₂/H₂ cryostat. The focal planes are conductively cooled by the primary H₂ while the telescope is cooled by the secondary H₂. The secondary H₂ also protects the primary H₂ by intercepting the parasitic heat loads. This paper describes the design and performance of the H₂/H₂ cryostat.

Space flight optical instruments and their support hardware must reliably operate in stressing environments for the duration of their mission. They must also survive the mechanical and thermal stresses of transportation, storage and launch. It is necessary to qualify the hardware design through environmental testing and to verify the hardware's ability to perform properly during and/or after some selected environmental tests on the ground. As a rule, flight electronics are subjected to thermal, mechanical and electromagnetic environmental testing. Thermal testing takes the form of temperature cycling over a temperature difference range (Delta) T of up to 100 degrees C for a minimum of six cycles, with additional performance verification testing at the hot and cold extremes. Mechanical testing takes the form of exposure to random vibration, sine sweep vibration, shock spectra and static loading on a centrifuge or by sine burst on a vibration table. A standard series of electromagnetic interference and electromagnetic compatibility testing is also performed.

The successful operation of many space-based systems requires reliable cryogen handling capabilities. Propulsion systems and remote sensor cooling systems that must contain and transfer cryogenic fluids must do so repeatedly and reliably over an extended system lifetime. For maximum utility, these space-based cryogen handling systems must be capable of both programmed control and remote-site control. One critical component of a cryogenic transfer system is a remote-controlled valve. The Space Dynamics Laboratory at Utah State University has developed a stepper-motor- activated cryogenic valve for NASA/Goddard Space Flight Center under contract NASA5-29422. This valve is flight- certified and has proven to be very reliable and rugged. Helium leak rates of less than 1 X 10^-8 sccs at 4 degrees K are consistently obtained after 3000 open-and- close cycles of the valve. This report describes the unique design of the valve and the special material used for the seat and stem to achieve these results.

Presented in this paper are the test results of the engineering test model of integrated cooler experiment. This cooler consists of integrating a small, low-power Stirling cryogenic refrigerator with a small mass of a triple point phase change material (PCM). The advantages of this type of cooler are a closed system; no vibrations during sensor operation; the ability to absorb increased 'spike' heat loads; potentially longer system lifetime; and a lower mass, cost, and power consumption. Experimentation was performed in the laboratory using methanol as the PCM. The goals of the testing were to demonstrate the practical use of new technologies and demonstrate the operation of the total system for simulated sensor scenarios. Presented are the results of the first series of tests.

A novel monolithic device is described which has the capability of resolving angular accelerations in a single axis to 10^-10 rad s^-2 Hz^-1/2. The device consists of a niobium proof mass attached to a housing via a torsional spring, and is operated at a temperature below 9.2 K so that the niobium is superconducting. Angular accelerations cause proportional angular displacements of the proof mass and, because of the Meissner effect in superconductors, changes in the inductance of superconducting coils located near the proof mass. Changes in inductance are sensed by a superconducting quantum interference device through the modulation of persistent currents. The angular accelerometer is being designed for use at frequencies below 1 Hz, so the resonant frequency of the proof mass is on the order of 10Hz. It is intended for use with the University of Maryland's superconducting gravity gradiometer to allow removal of angular and centrifugal acceleration-induced errors. Design parameters, assembly techniques and performance testing are discussed.

Conventional methods for supporting cold components in optical systems and instruments often lead to excessive conductive heat loads. The need for better thermal isolation while maintaining structural rigidity motivated work on a tension system utilizing high performance fibers to support a focal plane assembly in an instrument to be flown in space. Utilizing Kevlar 49 fibers in an approach referred to as fiber support technology, we were able to reduce the conducted parasitic heat loads from 85 mW to less than 2 mW while increasing the 1st resonant frequency form about 50 Hz to 700 Hz. Various radiation suppression and wiring schemes were necessary to further reduce the total parasitic heat loads on this system. This paper outlines the details of this development effort making the use of a low input power miniature mechanical cooler possible. This approach seems consistent with the 'smaller', better, cheaper, faster' attitude of the nineties.

Flexible thermal links play an important role int he thermal management of cryogenically cooled components. The purpose of these links is to provide a means of transferring heat from a cooled component to a cooler reservoir with little increase in temperature. The standard soldered approach although effective proves to be time consuming and contributes to added thermal impedances which degrade the performance of the link. For system with little tolerance for temperature differences between cooled components and a cooling source this is undesirable. The authors of this paper have developed a technique by which thin metal foil or braided wire can be attached to metal end blocks without any solder using the swaging process. Swaging provides a fast, simple method for providing a low thermal impedance between the foils and blocks. This paper describes the characteristics of these thermal links in terms of length, mass, thermal resistance, flexibility, and survivability.

Thermal links are essential to the successful operation of many of today's advanced space systems. The aerospace industry constantly searches for new, more efficient means of moving thermal energy away from sensitive instruments. As current technologies continue to advance, satellites become smaller and better than before. Work must continue, however, to develop more efficient, lightweight thermal links. Recent advances in the construction of carbon based composite fibers now allows the possibility of designing a thermal link with an impressive combination of low mass.

An electrical substitution radiometer cooled to 20K is being developed to determine the total solar irradiance with a ten-fold improvement in terms of absolute accuracy and resolution over existing space-borne radiometers. The radiometer is cooled using a Matra Marconi Space mechanical cooler based on the Stirling cycle with a heat lift of 120 mW at 20K. The instrument weights 74 kg, requires 130 K of power and has an overall envelope size of 453 by 383 by 730 mm. The instrument has been part of the European accommodation study for external payloads on the International Space Station.

The composite infrared spectrometer (CIRS) of the Cassini mission to Saturn has two interferometers covering the far infrared and mid infrared wavelength region. The instrument is aligned at ambient temperature, but operates at 170 Kelvin and has challenging boresight and interferometric alignment tolerances. This paper describes how the aluminium mirrors were aligned to the CIRS optics module to tolerances of .5 milliradians in biaxial tilt and 100 microns in decenter and how the instrument boresight was aligned.

The composite infrared spectrometer (CIRS) of the Cassini mission to Saturn has two interferometers covering the far- IR (FIR) and mid-IR (MIR) wavelength region. The instrument is aligned at ambient temperature, but operates at 170 Kelvin and has challenging interferometric alignment tolerances. Interferometric alignment sensitivity tests of the CIRS FIR breadboard indicated that the instrument was sensitive to alignment perturbations in the few arc second regime; therefore, a cryogenic alignment stability test was designed and implemented to determine the stability of the CIRS optics module. Test beamsplitters were installed in the instrument to allow transmission of HeNe laser beams through both channels of the instrument onto test focal planes consisting of position sensing photodiodes to measure the actual shear and boresight change in the focal planes. Cryogenic vacuum compatible shutters were designed and fabricated to allow separate measurements of the reflected and transmitted components of the test beam. The test determined that the optics bench was distorting an unacceptable amount between ambient and operating temperature, but that the distortion was very repeatable, opening the possibility of performing an interferometric alignment at cryogenic temperature.

The composite infrared spectrometer (CIRS) of the Cassini mission to Saturn has two interferometers covering the far- IR (FIR) and mid-IR (MIR) wavelength region. The instrument is aligned at ambient temperature, but operates at 170 Kelvin and has challenging interferometric alignment tolerances. Interferometric alignment sensitivity tests of the CIRS FIR breadboard indicated that he instrument was sensitive to alignment perturbations in the few arc second regime. Early cryogenic testing indicated that the instrument structure was not stable during cryogenic cycling; therefore, remote alignment of the FIR channel beamsplitter was implemented to recover modulation efficiency. The hardware developed to facilitate the in situ alignment at cryogenic temperatures is described, as are the results of several thermal cycles.

The composite infrared spectrometer (CIRS) of the CAssini mission to Saturn has two interferometers covering the far- IR (FIR) and mid-IR (MIR) wavelength region. The FIR is a polarizing interferometer utilizing dihedral retroreflectors and a polarizing beamsplitter. As such, it is sensitive to extremely small alignment change of the dihedrals and beamsplitter elements. The alignment stability required of the beamsplitter through all cryogenic cycling, handling, test, and launch-induced disturbances is better than 10 arc seconds. The mount is also required to induce minimal distortion to the 1.5-micron-thick mylar polarizing element ont he FIR channel and the potassium bromide beamsplitter/compensator elements on the MIR channel. It is also required to provide biaxial tilt adjustment at the arc second level and translation adjustment of the beamsplitter elements to the few micron level, and must be locked without changing the alignment of the element. This may be the first mount to have achieved these requirements on a cryogenic instrument.