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Light-weight structures and optics fabricated from composite
materials, such as carbon-carbon or graphite cyanate ester, combined
with new instrument architectures are capable of reducing the mass of
an Fourier Transform Spectrometer (FTS) instrument such as GIFTS by an
order-of-magnitude over previous FTS instruments. The composites can
also provide thermal management and thermal stability with high
structural strength in a single material.
One of the greatest mass factors in previous spacecraft FTS instruments is their electronics, housings, and interconnects. Technologies have been developed to alleviate the problem by integrating the electronics directly onto ultra-light composite structures of the spacecraft. These technologies, which will be considered in the GIFTS study, include advanced circuitry designs. These are multi-layered flexible circuits, which contain hidden and blind vias and provide for generic spacecraft functions such as power distribution, low-loss connections among subsystems, and enhanced data transfer among on-board microprocessors. Also, incorporating composites into the instrument design to be used for accomplishing this measurement concept has the potential of reducing mass by an order of magnitude over conventional materials, e.g., aluminum. Another area for composite materials that promises to minimize mass is the input telescope. For geosynchronous applications of FTSs, AGS studies have shown that the size of the primary mirror for the input telescope must be approximately 30 centimeters in diameter. Using conventional materials and state-of-the-art techniques, this drives the total instrument mass to unacceptable levels for the small launch vehicles, which are attractive for future missions. Tertiary telescopes, which offer access to the field stop, have the desired pupil location within the interferometer, but add more mass because of the additional optics. Composite materials can reduce areal densities of the optics to approximately ten kilograms per meter squared, thereby offering considerable mass savings. |