Large site logo

To Open The Sky

The Front Pages of Christopher P. Winter

The Cassini Mission to Saturn

A personal view


The Mission and the Science

Updated February 2003

Cassini was launched in 1997. Three years later, in the autumn of 2000, engineers discovered a shortcoming in the receiver aboard Cassini that is to pick up the data from the Huygens probe as it descends to Titan. Simply put, the receiver would not have been able to handle the apparent change in frequency (the Doppler shift) of the radio signal from the probe as it slowed down relative to Cassini.

ESA and NASA engineers and scientists formed a joint Huygens Recovery Task Force. After six months of analysis, they came up with a plan to save the mission: Send Cassini cruising past Titan at a larger distance, so the Doppler shift is not so great. The plan, endorsed by senior management from both agencies and by members of the Cassini-Huygens scientific community, also changes the timeline of the Huygens mission. Separation of the probe will be delayed by seven weeks, to 14 January 2005, and Cassini will make three passes by Titan beforehand, instead of the two originally planned.

The timeline below gives both the original and revised dates for the main events of Cassini's mission. Mission elapsed time corresponds to the revised timeline.

MISSION
EVENT
ORIGINAL
DATE
REVISED
DATE
DAYS FROM
LAUNCH
See also Cassini-Huygens Mission Timeline on Wikipedia.
Launch 15 October 1997 6 October 1997 0
Aphelion 1   1 November 1997 26
Perihelion 1   23 March 1998 169
Venus swingby #1 21 April 1998 21 April 1998 198
Deep space maneuver 2 December 1998 2 December 1998 423
Aphelion 2   4 December 1998 426
HGA Window begins   16 December 1998 436
HGA Window ends   10 January 1999 461
Venus swingby #2 20 June 1999 20 June 1999 622
Perihelion 2   27 June 1999 629
Earth swingby 16 August 1999 16 August 1999 680
HGA permanently deployed   29 January 2000 969
Jupiter swingby 30 December 2000 30 December 2000 1181
Science observations begin 1 June 2004 1 January 2004 2277
Insertion into Saturn orbit 1 July 2004 1 July 2004 2460
First flyby of Titan 27 November 2004 26 October 2004 2577
Second flyby of Titan   13 December 2004 2625
Third flyby of Titan   25 December 2004 2637
Huygens probe release 6 November 2004 25 December 2004 2637
Huygens on Titan 27 November 2004 14 January 2005 2659
End of nominal mission 1 July 2008 1 July 2008 3921

Once Cassini reaches Saturn, the plan goes as follows: Science observations begin on 1 June with a close flyby of Phoebe as the first event. Following this, Cassini will decelerate into an orbit aimed for the general neighborhood where Titan will be four months hence. This path gets fine-tuned on 12 September. When Huygens is cut loose, its internal timer is loaded with the exact intervals for its planned sequence of events. Rotating at 7 rpm for stability, Huygens will drift for 22 days, finally entering Titan's atmosphere at a high-latitude point on the sunlit side. Things happen fast after that. Its heat shield will protect it as it barrels into the atmosphere at 20,000 km/hr, slowing to 1,400 km/hr in a mere three minutes. Next, a series of parachutes will complete the deceleration, and the heat shield will drop away. The probe will ultimately come to rest, gathering data from 6 science packages and sending it up to Cassini. Whether Titan's surface is solid or liquid, Huygens is designed to stay upright and afloat. It should complete its mission in under three to four hours.

Cassini, meanwhile, will point its high-gain antenna at Titan for those few hours, storing any data received for later relay to Earth. After this period, Huygens having done its own thing, the mother ship will turn away and begin its four-year mission.

In brief, that mission will be to gather data on the plasma, dust, radio waves and magnetic fields present in the vicinity of Saturn, to observe its rings and icy moons, and to map the geometry of the Saturn system as accurately as possible.

The complements of scientific instruments and their principal investigator (PI) or team leader (TL) are:

Cassini

  1. Composite Infrared Spectrometer (CIRS)
    PI: Mr. Virgil G. Kunde (NASA-Goddard)
    temperature profiles & new chemical signatures
  2. Imaging Science Subsystem (ISS)
    PI: Dr. Carolyn C. Porco (University of Arizona)
    • Narrow Angle Camera
    • Wide Angle Camera
  3. Ultraviolet Imaging Spectrograph (UIS)
    PI: Dr. Larry Esposito (University of Colorado)
  4. Visible & Infrared Mapping Spectrometer
    PI: Dr. Robert H. Brown (University of Arizona)
    • Winds on Saturn & Titan
    • Saturn Deep Atmosphere
    • Ring Composition & Structure
    • Composition of Icy Moon Surfaces
  5. Radar
    TL: Dr. Charles Elachi (NASA-JPL)
    Uses high-gain antenna to determine:
    • distribution & presence of oceans on Titan
    • topography of Titan solid surface
    • topography of icy satellites
  6. Radio Science Subsystem (RSS)
    TL: Dr. Aruydas J. Kliore (NASA-JPL)
  7. Cassini Plasma Spectrometers (CAPS)
    PI: Dr. David E. Young (Southwest Research Institute)
    measures ion flux as function of mass & charge
  8. Cosmic Dust Analyzer (CDA)
    PI: Dr. Eberhard Grün (Max Planck Institut fur Kernphysic)
  9. Ion & Neutral Mass Spectrometer (INMS)
    TL: Dr. Hunter Waite
  10. Dual Technique Magnetomer (MAG)
    PI: Dr. David J. Southwood (Imperial College of Science & Technology)
  11. Magnetospheric Imaging Instrument (MIMI)
    PI: Dr. Stamatios M. Krimigis (APL)
  12. Radio & Plasma Wave Science (RPWS)
    PI: Dr. Donald A. Gurnett (University of Iowa)

Huygens

  1. Huygens Atmosphere Structure Instrument (HASI)
    M. Fulchignoni (Universite di Roma)
  2. Gas Chromatograph -- Mass Spectrograph (GCMS)
    H. B. Niemann (NASA-GSFC)
  3. Aerosol Collector Pyrolyser (ACP)
    G. M. Israel (CNRS Service d'Aeronomie)
  4. Descent Imager / Spectral Radiometer
    M. G. Tomasko (University of Arizona)
  5. Doppler Wind Experiment
    M. K. Bird (Universitat Bonn)
  6. Surface Science Package
    J. C. Zarnecki (University of Kent)
Valid CSS! Valid HTML 4.01 Strict To contact Chris Winter, send email to this address.
Copyright © 1997-2015 Christopher P. Winter. All rights reserved.
This page was created in 1997. Its contents were last modified on 25 October 2015.