Cassini-Huygens prepare for a titanic plunge

Original post on 23/12/2004

In less than 24 hours, the European dare-devil probe to Saturn’s moon Titan will leave its mothership. The ‘green for go’ decision was taken on 23 December. After a 7-year journey, the moment of truth approaches. Mankind will be discovering another world with revelations, perhaps, on the true nature of this enigmatic moon, shrouded in a thick veil of mystery.

The Cassini orbiter is due to release Europe’s “flying-saucer” – as one of ESA’s former Directors of Science has called it – early on Christmas morning, at 04:08 CET European time. If successfully separated it will then head for Titan, arriving there on 14 January. Meanwhile the Cassini orbiter will change its collision course on 27 December so as to be in position to relay the Huygens descent data back to Earth.

On this occasion, to better understand the objectives of the Cassini-Huygens’ mission, we publish a series of articles describing the way the probe and orbiter instruments work. They carry accronyms that are sometimes obscure, sometimes evocative. (We particularly appreciated the gallic sounding ‘MIMI’, and its team leader). Indeed, it is also an occasion to show a few faces behind the mission, those of the principal investigators and team leaders, most of whom we have been honoured to meet. These coming days as the probe approaches its target, we will better understand their expectations… and anxieties.

We focus first on the Huygens instruments

The Descent Imager/Spectral Radiometer contains four cameras, which will capture the brightness of Titan’s sky and send back panoramic, pie-shaped photo mosaics of its surface.
The Huygens Atmospheric Structure Instrument contains sensors that will measure the physical and electrical properties of Titan’s atmosphere. Temperature and pressure sensors will measure the atmosphere’s heat. The Doppler Wind Experiment will improve communication with the probe by giving it a stable carrier frequency. The probe drift caused by winds in Titan’s atmosphere will induce a measurable Doppler shift in the carrier signal. The swinging of the probe beneath its parachute due to atmospheric properties may also be detected.
A Gas Chromatograph Mass Spectrometer will identify and measure chemicals in Titan’s atmosphere. It is equipped with samplers that will be filled at high altitude for analysis.
The Aerosol Collector and Pyrolyser will draw in and analyze particles from clouds in the atmosphere through a system of filters and portable ovens.
A Surface Science Package houses sensors designed to determine whether Titan’s surface at the landing site is solid or liquid. A tilt sensor will measure any pendulum motion during the descent and will show any motion due to waves. If the surface is liquid, other sensors will measure its density, temperature and other characteristics.

And there are the Cassini orbiter instruments

For further details on the mission progress and to see images already obtained by the Cassini instruments since arrival around Saturn last July, please consult the agencies’ web sites:
European Space Agency – Cassini-Huygens
NASA-JPL Cassini-Huygens