A combination of a single mode AIGaAs laser diode and a broadb:md LED was used in a Michelson interferometer to provide reference signals in a Fourier transform spectrometer, the Composite Infrared Spectrometer, on the Cassini mission to Saturn. The narrowband light from the laser produced continuous fringes throughout the travel of the interferometer, which were used to control the velocity of the scan mechanism and to trigger data s,'unpling. Tile broadblmd light from the LED produced a burst

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... of fringes at zero path difference, which was used as a fixed position reference. The system, including the sources, the interferometer, and the detectors, was designed to work both at room temperature and at the instrument operating temperature of 170 Kelvin. One major challenge that was overcome wits preservation, from room temperature to 170 K, of alignment sufficient for high modulation of fringes from the broadband source. Another was the shift of the source spectra atxmt 30 nm toward shorter wavelengths upon cooldown.