The bottom of the Huygens probe was equipped with a set of vanes to control its spin profile (magnitude and direction) under parachute. But unexpectly, the spin rate started to decrease and eventually reversed (Lebreton, 2005) (Pérez-Ayucar, et al. 2005) during descent.

Post-flight engineering evaluation of the anomalous spin were not conclusive. An industrial study led by Vorticity in 2014-2015 concluded that the vanes torque was not strong enough to control the spin, and described a situation where one of the two HASI instrument booms would not deploy during the whole descent. 

Further investigations were done in the framework of the Huygens close-out activities under ESA Contract in October 2017. The main objective was to characterize the individual torques applied by the spin vanes, by each of the fixed appendages, and the HASI instrument booms in different deployment configurations. A mock-up of the Huygens probe was studied in a subsonic wind tunnel. Two research laboratories were involved: the Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E, CNRS-University of Orléans) and the Laboratory Pluridisciplinaire de Recherche en Ingénierie des Systèmes, Mécaniques et Energétiques (PRISME) of the University of Orléans. The amplitude of the negative torque created by the fixed appendages (enhanced by the flow deviation by vanes) turned out to be larger than the torque created by the vanes. The negative effect of the appendages is augmented by the fact that the gas flow around them is deviated by the vanes. The effect of each of the HASI booms is slightly higher than the vanes, and should compensate under nominal deployed configuration. 

The full report and its conclussions is available here:



Contact: miguel.perez.ayucar@esa.int, jean-pierre.lebreton@cnrs-orleans.fr, nicolas.altobelli@sciops.esa.int

Other references:

- Lebreton, Jean-Pierre. «An overview of the descent and landing of the Huygens probe on Titan.» Nature 438, n° 90 (2005): 785-791.

- Pérez-Ayúcar, Miguel, A. Sarlette, P. Couzin, T. Blancquaert, O. Witasse, et J.-P. Lebreton. «Huygens attitude reconstruction based on flight engineering parameters.» 3rd annual International Planetary Probe Workshop IPPW-2005, 2005.