For a consistent interpretation and correlation of results from all the probe science experiments, and to provide confidence in ground-truth calibrations of orbiter remote sensing measurements, an accurate reconstruction of the probe entry and descent trajectory is needed. Without a common and consistent descent profile, each probe experiment team would need to develop a profile independently thereby causing a significant duplication of effort and expenditure of resources, and making correlation and comparison of results from different experiments somewhat suspect and therefore less meaningful. Furthermore, direct (in situ) atmospheric sampling by the probe will provide "ground truth"' verification of orbiter observations of Titan. Without a means to tie the measured atmospheric properties to the probe altitude, location, and velocity at specific times, the value of ground-truth support for orbiter science at Titan would be significantly compromised.

The goal of the Huygens trajectory reconstruction effort is therefore

• to provide a common trajectory for all experiment teams to use when interpreting their respective data sets. This will also eliminate the need for each team to perform the task independently and thereby offering a more economical use of limited resources,
• to provide a common basis for interpretation and correlation of data from different experiments. For example, the existence of atmospheric turbulence and wind shear, evident from the unique signatures in the HASI accelerometer data can only be correlated with other atmospheric properties such as temperature gradients, winds, and cloud decks if a common probe trajectory profile is utilized by all the experiment teams,
• to provide the atmospheric properties along the probe entry and descent path for use by the orbiter experiment teams as a means of "ground-truthing" remote sensing measurements, and
• to provide precise measurements of the probe position and velocity throughout descent, required for the DWE recovery of the zonal winds by Doppler tracking of the Huygens probe.

 

The responsibility of developing analysis techniques by which the Huygens entry and descent trajectory will be reconstructed from the official NASA/ESA hand-off point at the interface altitude of 1270 km to the surface is given to the Huygens Descent Trajectory Working Group (DTWG), chartered in 1996 as a subgroup of the Huygens Science Working Team (HSWT). The membership of the DTWG includes the Huygens and Cassini project scientists, The Huygens Operations Scientist, and representatives from each of the probe science instrument teams and contributing orbiter teams.

IWF is co-chairing the DTWG since 2003 under contract with ESA and is responsible for

• the development of a framework between experiment teams and the Huygens Mission Team for sharing and exchanging data relevant to the descent trajectory analysis and modeling,
• the development and testing of methodologies and tools by which the probe descent trajectory and attitude can be accurately reconstructed from the probe and orbiter science and engineering data and
• the reconstruction, analysis, and archiving of the Huygens entry and descent trajectory from the actual probe measurements in January 2005.