Characterization of the spin and attitude of the ESA Huygens probe during its descent onto Titan using the engineering dataset

The Huygens probe is the ESA’s main contribution to the Cassini-Huygens mission, carried out jointly by the ESA, the NASA and the ASI. It was designed to descent into the atmosphere of Titan, Saturn’s largest moon, on January 14, 2005, providing surface images of the farthest object a man-made probe has ever landed on. Its main purpose was to study Titan’s atmosphere during the descent phase.
Of course, priority has been given to the scientific instruments for data recovery but a small engineering dataset was also sent back to Earth. The goal of the present work was, using these engineering data, to characterize the instantaneous orientation of the Huygens probe during its descent, in order to allow correct analysis of the scientific data.
The methods used concern evaluation of reduced accelerometer data, analysis of the telecommunication link’s power level using the accurately known antenna gain pattern and a comparison between the Huygens mission and the more fully instrumented SM2 test probe which was dropped in the Earth’s atmosphere in 1995. Some basic dynamic modelization has also been done to investigate likely behaviours and try to identify consistent approximations.
In addition to this report, the results of my work include Excel r files containing probe orientation (support) data as well as a MATLAB r routine which allows to compute a probe’s azimuth from the (manually pre-processed) telemetry link gain and the positioning dataset. A user-friendly program for the visualization of the evolution of all involved variables - including a 3D probe orientation display - was also planned, but could not be finished since a complete characterization of the probe’s attitude (tilt-related motions) was not achieved yet before writing the present report.
As a whole bunch of people spread over the world were working on the subject of the probe’s orientation using different information, the conclusions of all teams had to be compared. This was continually done by e-mail while working on the subject; a final meeting on April 22 & 23, 2005 was meant to clarify the situation before publishing first official results.