The Cassini Orbiter's mission consists of delivering a probe called Huygens, provided
by ESA, to Titan, and then remaining in orbit around Saturn for detailed studies of the
planet and its rings and satellites.
Cassini Orbiter
The spacecraft was originally planned to be the second three-axis stabilized,
RTG-powered Mariner Mark II, a class of spacecraft developed for missions beyond the orbit
of Mars. However, various budget cuts, the cancellation of CRAF and rescopings of the project have forced a more
special design, postponing indefinitely any implementation of the Mariner Mark II
series.
The principal objectives are to:
- determine the three-dimensional structure and dynamical behavior of the rings;
- determine the composition of the satellite surfaces and the geological history of each
object;
- determine the nature and origin of the dark material on Iapetus' leading
hemisphere;
- measure the three-dimensional structure and dynamical behavior of the
magnetosphere;
- study the dynamical behavior of Saturn's atmosphere at cloud level;
- study the time variability of Titan's clouds and hazes; and,
- characterize Titan's surface on a regional scale.
Following instruments are on board of Cassini:
- Radio Frequency Instrument Subsystem
- Dual Technique Magnetometer
- Science Calibration Subsystem
- Imaging Science (narrow-angle camera)
- Imaging Science (wide-angle camera)
- Visible and Infrared Mapping Spectrometer
- Radio and Plasma Wave Science
- Ion and Neutral Mass Spectrometer
- Magnetospheric Imaging Instrument
- Cosmic Dust Analyzer
- Cassini Radar
- Cassini Plasma Spectrometer
- Ultraviolet Imaging Spectrograph
- Composite Infrared Spectrometer
Cassini took a similar tour of the solar system as did Galileo, referred to as a VVEJGA
(Venus-Venus-Earth-Jupiter Gravity Assist) trajectory. Several opportunities exist for
Cassini to make observations of asteroids, although exact encounters remain to be
determined after the spacecraft has been launched as it depends on the launch date.
Cassini entered orbit around Saturn on 1 July 2004 after a 96 min burn of the primary
main engine. Shortly after entering orbit around Saturn, Huygens will separate from the
Cassini orbiter and begin its entry into the atmosphere of Titan. Cassini is then expected
to make at least 30 loose elliptical orbits of the planet, each optimized for a different
set of observations.
Cassini's instrumentation consists of: a radar mapper, a CCD imaging system, a
visible/infrared mapping spectrometer, a composite infrared spectrometer, a cosmic dust
analyzer, a radio and plasma wave experiment, a plasma spectrometer, an ultraviolet
imaging spectrograph, a magnetospheric imaging instrument, a magnetometer, an ion/neutral
mass spectrometer. Telemetry from the communications antenna as well as other special
transmitters (an S-band transmitter and a dual frequency Ka-band system) will also be used
to make observations of the atmospheres of Titan and Saturn and to measure the gravity
fields of the planet and its satellites.
Cassini ended its mission on 15 September 2017, when it entered Saturn's atmosphere after 13 years in orbit.
Huygens Titan probe
The Huygens probe is an atmospheric probe designed to make in situ observations of the
Saturnian satellite Titan. ESA's contribution to the Cassini mission, Huygens' objectives
are to:
- determine the physical characteristics (density, pressure, temperature, etc.) of Titan's
atmosphere as a function of height;
- measure the abundance of atmospheric constituents;
- investigate the atmosphere's chemistry and photochemistry, especially with regard to
organic molecules and the formation and composition of aerosols;
- characterize the meteorology of Titan, particularly with respect to cloud physics, lightning discharges, and general circulation; and,
- examine the physical state, topography, and composition of the surface.
Huygens is a 1.3 m diameter descent module with a spherical nose and a conical aft
section. A thermal protection aeroshell surrounds the descent module, decelerating it from
6 Km/s at arrival to 400 m/s in about two minutes and protecting it from the intense heat
of entry. A parachute will then be deployed and the aeroshell jettisoned. The probe will
float down through the atmosphere making measurements.
Instrumentation for the probe will include:
- an aerosol collector and pyrolyzer,
- a descent imager and spectral radiometer,
- a Doppler wind experiment,
- a gas chromatograph/mass spectrometer,
- an atmospheric structure instrument, and
- a surface science package.
Huygens was separated from Cassini on 25.12.2004 and landed successfully on Titan on
14.01.2005. The probe transmitted images and data during decent and after landing from the
surface. Huygens operated for about 2 hours after landing.