An overview is presented on why and how the new reduction of the Hipparcos data was carried out, and in particular on how improved understanding of the dynamics of the Hipparcos satellite was obtained and made the new reduction possible. A brief description is given of the main torques acting on the spacecraft and some peculiar features in the satellite dynamics, such as rate and scan-phase discontinuities. An overview is also presented of the dynamic attitude modeling, and the role it played in the iterative solution that established the new astrometric catalogue. Some examples of the potential impact of the new reduction on the scientific results of the mission are given. Finally, the relevance of this study for the Gaia mission is briefly discussed.