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The Cassini-Huygens Mission to Saturn and Titan



Artist's conception of the Huygens Probe descending through Titan's atmosphere (Spilker).

This artist's rendering illustrates the Cassini Orbiter's radar as it maps swaths of Titan's surface (Spilker).

Launched on October 6, 1997, the Cassini-Huygens spacecraft is scheduled to be inserted in Saturn's orbit on July 1, 2004 and is expected to take 4 years to complete. This mission is an international collaboration of 17 countries including the United States, France, Germany, Italy, Great Britain, Netherlands, Austria, Finland, Norway, Sweden, Hungary, Ireland, Spain, Czech Republic, Switzerland, Denmark, and Belgium.

Once in Saturn's orbit, the Cassini Orbiter will release the Huygens Probe on November 6, 2004. During its descent, the probe will measure a variety of data in Titan's atmosphere. A summary of the instruments used, and their purpose is shown below:

Location Instrument Purpose
Probe Atmospheric Structure Instrument measure temperature, density, and pressure over a range of altitudes; measure the electrical properties of the atmosphere and detect lightning
Probe Aerosol Collector and Pyrolyser vaporize aerosols, then direct the resulting gas to the Gas Chromatograph and Mass Spectrometer
Probe Gas Chromatograph and Mass Spectrometer provide a detailed inventory of the major and minor atmospheric species, including organic molecules and noble gases - in particular argon
Probe Doppler Wind Experiment track the course of the descending probe, giving wind direction and speed at various altitudes
Probe Descent Imager and Spectral Radiometer take pictures and record spectra of the clouds and surface
Orbiter Ultraviolet Imaging Spectrograph detect argon and establish Titan's deuterium-hydrogen ratio
Orbiter Visible and Infrared Mapping Spectrometer study the circulation of Titan's atmosphere
Orbiter Imaging Science Subsystem Camera track clouds
Orbiter Composite Infrared Spectrometer develop temperature profiles with help of Radio Science Instrument
Orbiter radar map the surface through the clouds wigh high-resolution swaths; provide data on the extent of liquid versus dry land and map surface features


The probe will complete its descent to Titan's surface on november 27, 2004. After the probe has hit the surface, the Cassini Orbiter will continue to listen for 30 minutes, in the event that tranmission continues after landing. After the Cassini Orbiter has completed collecting information from the probe, it will transmit the data to Earth. When data is received on Earth, the probe mission will be completed and the orbiter tour will begin.

The orbiter portion of the mission will last four years and consist of 74 orbits around Saturn with various orientations. The orientations will range from 7 to 155 days and Saturn-centered periapsis will range from 2.6 to 15.8 Saturn radii. Inclinations will range from 0 to 75 degrees.

During the orbiter tour, 43 Titan flybys will occur ranging from 2500 km to 8000 km in altitude. This is done to control the orbit of the spacecraft around Saturn as well as to collect more scientific data from Titan. Titan flybys are crucial in controlling Cassini's orbit around Saturn because a close flyby could increase velocity by hundreds of meters per second, thus saving propellent for other adjustments of the spacecraft. The tour will also contain close and distant flybys of 36 icy satellites in Saturn's orbit.

"When the Cassini Orbiter and Huygens Probe arrive at Titan, they will provide us with our first close-up view of Saturn's largest satellite. With the Probe's slow descent through Titan's atmosphere - with images of the surface and chemical composition data - and the Orbiter's radar maps of the moon's surface, we will once again be shown another world" (Spilker).





Cassini Science Objectives at Titan


  • Determine the abundance of atmospheric constituents (including any noble gases), establish isotope ratios for abundant elements, and constrain scenarios of the formation and evolution of Titan and its atmosphere (Spilker).
  • Observe the vertical and horizontal distributions of trace gases, search for more complex organic molecules, investigate energy sources for atmospheric chemistry, model the photochemistry of the stratosphere, and study the formation and composition of aerosols (Spilker).
  • Measure the winds and global temperatures, investigate cloud physics, general circulation and seasonal effects in Titan's atmosphere, and search for lightning discharges (Spilker).
  • Determine the physical state, topography and compostion of the surface, infer the internal structure of the satellite (Spilker).
  • Investigate the upper atmosphere, its ionization and its role as a source of neutral and ionized material for the magnetosphere of Saturn (Spilker).

Copyright (C) 2003 by Dan Taylor