There is a current trend in space-based remote sensing toward long duration missions that produce hyper-spectral imaging data. One instrument that is uniquely suited to hyperspectral imaging is the infrared Michelson spectrometer. Michelson spectrometers use a translating mirror stage to vary the optical path length of one leg of the interferometer. Infrared applications often require cooling of this stage to achieve optimum performance. This cryogenic mirror stage is a critical spectrometer component that must be designed and constructed to achieve high reliability and performance during long duration missions. This paper concentrates on three specific areas of optimization. First, an accelerated lifetime test was performed on the mirror stage, with particular attention to the flexural pivots in the joints of the structure. There was no change seen over 22 million translation cycles. Second, a vibration model was created to predict the stage's response to launch and operational accelerations. The model's results closely matched measured values obtained during shake tests of the mirror stage. Third, a cryogenic mirror design was improved to decrease its weight and increase its stability over a wide temperature range. The improved design offers excellent performance for cryogenic operation.
Space based optical instruments are evolving toward large apertures and requiring high sensitivity at longer wavelengths. Instruments that collect light at wavelengths longer than about 15 microns often use Potassium Bromide (KBr) as part of the optical system. Since KBr has rather poor mechanical properties, many engineers have been hesitant to design instruments with KBr optics larger than a few centimeters. This problem is made more difficult by the fact that sensors in these longer wavelengths are often operated at cryogenic temperatures to minimize self- emission. The overall objective of this effort was to examine methods of mounting KBr optics to improve their vibrational, optical, and thermal characteristics. A legacy KBr mount is examined and revised to increase its robustness and scalability. Using finite element models and dynamic testing, the limits of the current design was explored. An alternative design using a bonded support was investigated. A new thermally engineered composite material (TECMat) was developed that appears to match the thermal expansion of KBr over a wide temperature range. TECMat's general properties and possible methods of implementing it in optical mount are described.
A geostationary Imaging Fourier Transform Spectrometer (GIFTS) has been selected for the NASA New Millennium Program (NMP) Earth Observing-3 (EO-3) mission. Our paper will discuss one of the key GIFTS NMP mission is designed to demonstrate new and emerging sensor and data processing technologies with the goal of making revolutionary improvements in meteorological observational capability and forecasting accuracy. The GIFTS payload is a versatile imaging FTS with programmable spectral resolution and spatial scene selection that allows radiometric accuracy and atmospheric sounding precision to be traded in near real time for area coverage. The GIFTS sensor combines high sensitivity with a massively parallel spatial data collection scheme to allow high spatial resolution measurement of the Earth's atmosphere and rapid broad area coverage. An objective of the GIFTS mission is to demonstrate the advantages of high spatial resolution on temperature and water vapor retrieval by allowing sampling in broken cloud regions. This small gsd, may require extremely good pointing control. This paper discusses the analysis of this requirement.
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.