Huygens' entry and descent through Titan's atmosphere-Methodology and results of the trajectory reconstruction

The European Space Agency's Huygens probe separated from the NASA Cassini spacecraft on 25 December 2004, after having been attached for a 7-year interplanetary journey and three orbits around Saturn. The probe reached the predefined NASA/ESA interface point on 14 January 2005 at 09:05:52.523 (UTC) and performed a successful entry and descent sequence. The probe softly impacted on Titan's surface on the same day at 11:38:10.77 (UTC) with a speed of about 4.54 m/s. The probe entry and descent trajectory was reconstructed from the estimated initial state vector provided by the Cassini Navigation team, the probe housekeeping data, and measurements from the scientific payload. This paper presents the methodology and discuss the results of the reconstruction effort. Furthermore the probe roll rate was reconstructed prior to the main entry phase deceleration pulse and throughout the entire descent phase under the main and drogue parachute.