High Accuracy On-ground Attitude Reconstitution for the ESA Astrometry Mission Hipparcos

The ESA space - astrometry mission Hipparcos will provide a uniform and high-precision stellar Catalogue of the whole sky. During 2.5 years 100,000 selected stars will be observed by a special telescope mounted on a satellite placed in earth stationary orbit and their observations will be processed on-ground by two independent scientific Consortia. The data processing requires that the star coordinates in the telescope focal plane be transformed into a common inertial reference frame. To correctly perform this transformation, the satellite three-axes attitude must be reconstituted within a specified accuracy - rms error < 0.1 arcsec on each angle-for the mission lifetime, by processing the data of the on-board attitude sensors: star mapper and gyros. In this paper, after an overview of the Hipparcos mission, the attitude reconstitution is formulated as a Gauss-Markov estimation problem and solved by processing only star mapper data. The Gauss-Markov procedure takes advantage from a guaranteed error linear model describing the attitude evolution over the desired time interval.