Titan wind effects on the descent trajectory of the ESA Huygens probe

Details Titan wind effects on the descent trajectory of the ESA Huygens probe Titan wind effects on the descent trajectory of the ESA Huygens probe

Oct 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002esasp.514..191k&link_type=abstract

In: Earth-like planets and moons. Proceedings of the 36th ESLAB Symposium, 3 - 8 June 2002, ESTEC, Noordwijk, The Netherlands. E

Computer Science

2

Space Missions: Saturn, Titan Atmosphere

Scientific paper

The Huygens Probe is the ESA-provided element of the joint NASA/ESA Cassini/Huygens mission to Saturn and Titan. The Cassini/Huygens spacecraft was launched on 15 October 1997 and will arrive at Saturn on the 1st of July 2004. The Huygens probe will be released on 24 December 2004 and enter the atmosphere of Titan on 14 January 2005. A recently discovered design flaw in the Huygens radio receiver onboard Cassini led to a significant redesign of the mission geometry by both the Huygens and Cassini project teams. In this new scenario the Orbiter will pass Titan at high altitude (i.e., 60,000 km) on the retrograde side of Titan and will trail the Probe by only about 2.1 hours instead of the originally planned 1250 km flyby altitude on the prograde side of Titan and a 4 hour delay time. Among the factors governing the duration and quality of the Cassini/Huygens communication window during the descent is the Probe drift caused by zonal winds. Existing Titan wind models have been reevaluated and compared to recent ground-based observations. Simulations of the Probe entry and descent show a drift from ~300 km up to ~430 km away from the "no wind" landing point, depending on the wind model. At the end of the nominal mission this difference in wind drift (assuming prograde winds) causes a difference of up to 1.7 dB (within a margin of 3 to 4 dB, resulting from the receiver design flaw) in the received signal strength to zonal winds and their directions is due to the steep decrease of the Probe antenna gain when the Cassini spacecraft (with the Huygens receiver) as seen from the Probe moves to increasingly higher elevation angles. A simulation of the Probe atmospheric entry phase shows that the zonal wind direction also impacts the shape of the deceleration profile and its peak value. The deceleration profile will be accurately measured during the entry phase by accelerometers onboard the Probe. From this data set the density profile of the upper Titan atmosphere will be inferred. This will complement the orbiter instrument measurements planned during the early Titan flybys for validation of the upper Titan atmosphere model and evaluation of the drag force that will act on the Cassini spacecraft at subsequent low altitude Titan flybys (~950 km).

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