On-Ground Attitude Determination In The Hipparcos Mission

An accurate on-ground reconstitution of the satellite three-axes attitude from the downlinked star mapper photon counts is an essential factor in the final accuracy of the Hipparcos Astrometric Catalogue. The reconstitution method developed by the FAST Consortium and currently on use to process Hipparcos data is the concern of this paper. After on outline of the main reconstitution models and algorithms, an accuracy assessment of the estimates, attitude and star coordinates, coming out from the first year data reduction, is presented; the assessment shows that attitude root mean square errors are already around the mission target of 0.1 arcseconds.