PPI results from the balloon drop experiment of the HASI pressure profile instrument

At December 1995 a balloon drop experiment was conducted at Leon, Spain, fo r the HASI (Huygens Atmospheric Structure Instrument) instrument of the Huy gens probe. A part of HASI is the Pressure Profile Instrument (PPI) which w ill measure the atmospheric pressure profile of Titan during the descent at Nov-ember 2004. The experiment platform was carried by a balloon to an alt itude of 30 km and it made a subsequent parachute-assisted descent. The pre ssure instrument functioned basically as expected. The vertical flight traj ectory and pressure profile was reconstructed by using the collected data o f the pressure instrument and the simultaneous temperature measurements. Th e calculated flight trajectory was in agreement with independent measuremen ts with Omega and GPS. Some turbulence was detected near the surface and ot her dynamic behaviour in the upper part of the trajectory. The experiment d emonstrated the nominal performance of the PPI instrument and serves as a r eal-like test flight for the actual mission. (C) 1998 Elsevier Science Ltd. All rights reserved.