Fraunhofer line optical correlator for orbit determination

Abstract: The design of a Fraunhofer line optical correlator is detailed. The instrument described herein correlates a reflected solar spectrum against multiple Fraunhofer absorption lines to estimate the radial velocity of the reflecting body. By using a spatial light modulator (SLM) as a photomask for known solar absorption lines in the visible spectrum, the ratio of Doppler shifted solar energy to the total received energy can be calculated. Although the reflected light from targets in high orbit is weak, signal-to-noise ratio (SNR) is enhanced by the measurement of multiple Fraunhofer lines in a single snapshot image. Simulations indicate that prediction of orbital parameters is improved by incorporation of this velocity information, and in some cases the number of line-of-sight measurements can be reduced from three to two.