The Cassini spacecraft will to be launched on its mission to Saturn in October 1997. Upon arrival in 2004, Cassini will begin a four-year tour of the Saturnian system, the first visit to that planet since Voyager. Among several remote sensing instruments in its payload, the spacecraft will carry the Composite Infrared Spectrometer (CIRS), to study the atmospheres and surfaces of Saturn and its moons. CIRS will retrieve temperatures and gas compositions in the atmospheres of Saturn and its largest moon, Titan, from deep in their tropospheres to high in their stratospheres. CIRS will also investigate the thermal properties and composition of Saturn’s rings. Studies of Saturn and Titan will tell us about the formation and composition of the early solar system, the evolution of these two very different bodies along different paths, and how, at present, they change diurnally and seasonally. Spectra of the rings and the moon's solid surfaces will help determine their thermal characteristics, mineral compositions, and geological evolutions.

The LRCTF (Laser Ranging Characterization and Test Facility) is a unique facility built at NASA GSFC to provide thermal-optical testing of the next generation GPS LRA (Global Positioning Satellite’s Laser Retroreflector Array) laser ranging target. The 400mm diameter target is an array consisting of 48 total internal reflection retroreflectors and has an optical cross section requirement of 100 MSM (million square meters). To verify that the array meets this requirement during on-orbit conditions, the LRCTF is equipped with a 400mm test beam, a data product output consisting of full aperture FFDPs (Far Field Diffraction Patterns) and a thermal chamber. The FFDPs are used to calculate the OCS. This paper will describe the facility design, alignment approach, and verification process.

The controlled deployment of the Lightweight Flexible Solar Array (LFSA) experiment using the shape memory alloy release and deployment system has been demonstrated. Work remains to be done in increasing the efficiency of Copper Indium Diselinide (CIS) terminations to the flexible harness that carries current from the array to the I-V measurement electronics.

A flight experiment has demonstrated a modular solar concentrator that can be used as a direct substitute replacement for planar photovoltaic panels in spacecraft solar arrays. The light concentrating panel (LCP) uses an orthogrid arrangement of composite mirror strips to form an array of rectangular mirror troughs that reflect light onto standard, high-efficiency solar cells at a concentration ratio of approximately 3:1. The panel area, mass, thickness, and pointing tolerance has been shown to be similar to a planar array using the same cells. Concentration reduces the panel's cell area by 2/3, which significantly reduces the cost of the panel. An opportunity for a flight experiment module arose on NASA's Small Explorer/Wide-Field Infrared Explorer (SMEX/WIRE) spacecraft, which uses modular solar panel modules integrated into a solar panel frame structure. The design and analysis that supported implementation of the LCP as a flight experiment module is described. Easy integration into the existing SMEX LITE wing demonstrated the benefits of technology transparency. Right data shows the stability of the LCP module after nearly one year in low Earth orbit

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 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.

The composite infrared spectrometer (CIRS) is a remote sensing instrument to be flown on the Cassini orbiter. CIRS will retrieve vertical profiles of temperature and gas composition for the atmospheres of Titan and Saturn, from deep in their tropospheres to high in their stratospheres. CIRS will also retrieve information on the thermal properties and composition of Saturn's rings and Saturnian satellites. CIRS consists of a pair of Fourier Transform Spectrometers (FTSs) which together cover the spectral range from 10-1400 cm-1 with a spectral resolution up to 0.5 cm-1. The two interferometers share a 50 cm beryllium Cassegrain telescope. The far-infrared FTS is a polarizing interferometer covering the 10-600 cm-1 range with a pair of thermopile detectors, and a 3.9 mrad field of view. The mid-infrared FTS is a conventional Michelson interferometer covering 200-1400 cm-1 in two spectral bandpasses: 600-1100 cm- 1100-1400 cm(superscript -1 with a 1 by 10 photovoltaic HgCdTe array. Each pixel of the arrays has an approximate 0.3 mrad field of view. The HgCdTe arrays are cooled to approximately 80K with a passive radiative cooler.

Small machine attached to table-top belt sander makes possible to use belt sander to grind glass disk quickly to specified diameter within tolerance of about plus or minus 0.002 in. Intended to be used in place of production-shop glass grinder. Held on driveshaft by vacuum, glass disk rotated while periphery ground by continuous sanding belt.

The Composite Infrared Spectrometer (CIRS) instrument is scheduled to fly on NASA's Cassini mission to Saturn. CIRS operates at 170 Kelvin and utilizes two Michelson interferometers to measure the infrared spectrum between 7.1 and 1000 microns. The Mid-InfraRed interferometer (MIR) is a classical Michelson design operating in the 7.1 to 16.7 micron band. The Far-InfraRed interferometer (FIR) is a polarizing Michelson design measuring the 16.7 to 1000 micron band. Both the MIR and FIR use retroreflector elements rather than flat mirrors. The MIR requires hollow cube corner style retroreflectors while the FIR polarizing nature requires roof-top mirror style retroreflectors. Initial testing of available technology indicated that interferometric quality retroreflectors do exist in ambient temperatures. Tests were performed using commercially available mounted and unmounted cube corners and commercial cube corners mounted to GSFC designed mounts to characterize their cryogenic, interferometric performance. The Goddard Space Flight Center's ambient and cryogenic test and results are presented here.