Planet and time estimation using star trackers
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This paper presents a methodology to identify an observed visible planet (Venus, Mars, Jupiter, and Saturn) using digital star trackers and with no time information. Once the planet is identified, the paper shows how to estimate the time by a simple linear estimator. The proposed technique to perform planet identification is extremely fast because the adopted approach accessing the 2-Dimensional planet database is based on a 2-Dimensional k-vector technique. The planet identification algorithm never failed during extensive numerical tests. The accuracy of the estimated time is a function of the observed planet, of the particular geometry, and of the database size. For relatively small planet database, and avoiding the rare situations of trajectory knots, the time estimation for the worst geometry and planet (Saturn) is always better than a day. However, ongoing studies, based on Kalman filtering and on cubic Beziér curve best-fitting technique, will estimate the time with, at least, one order of magnitude gain in accuracy.
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