Orbit determination results and trajectory reconstruction for the Cassini/Huygens Mission

During Cassini’s third orbit around Saturn, the Huygens Probe was successfully released on a trajectory that resulted in the probe entering Titan’s atmosphere on 14January-2005, making it both the most distant spacecraft landing and the first spacecraft to successfully land on the moon of another planet. The navigation requirements for the probe that had to be met included the flight path angle (-65° ± 3° at the 99% confidence level) and the angle of attack (less than 5° at the 99% confidence level). Considering that there was no control of the probe after release and that the probe was released 21 days before entry, which was before Saturn apoapsis and before a 127,000 km flyby of Iapetus, the most stringent navigation requirement on the probe was the flight path angle. However, the reconstructed estimate of –65.4° ± 0.7° (99%) shows that the probe was delivered well within the entry angle corridor. Additional navigation requirements were imposed on the Cassini orbiter to ensure that the orbiter’s pointing was accurate enough to maintain the telemetry link from Huygens to Cassini for the probe relay. The navigation contribution to this pointing error could not exceed 3.0 mrad (at the 99% confidence level). The reconstruction indicates that the maximum navigation induced pointing error during the probe relay timeframe was 1.2 mrad with a 0.03 mrad uncertainty