Huygens probe entry trajectory and attitude estimated simultaneously with Titan atmospheric structure by Kalman filtering

Space probes entering planetary atmospheres are used for in situ study of their physical structures. During the entry phase aerodynamic forces exerted on the probe depend on atmospheric density. As a consequence accelerations measured by on-board sensors can be used to derive probe trajectory as well as atmospheric density, pressure and temperature profiles. In this work acceleration data acquired by the Huygens Atmospheric Structure Instrument (HASI) have been used to reconstruct the probe trajectory and the Titanʹs atmospheric structure from ≈ 1545 km down to ≈ 155 km of altitude. An accurate six degree of freedom model of Huygens during the entry phase has been developed and a new reconstruction technique based on Kalman filtering is presented. This technique estimates simultaneously the probe trajectory, the attitude profile consistent with measured data and the atmospheric density, pressure and temperature.