CASSINI / HUYGENS - Remote sensing probe to Saturn
The joint ESA/NASA mission CASSINI/HUYGENS is the first Medium Mission of
ESA's Horizon 2000 program.
It will study the planet Saturn and its largest moon Titan.
Following launch in 1997 using a NASA Titan IV rocket with Centaur upper stage
the spacecraft will make two flybys of Venus and then flybys of Earth and
Jupiter.
It will reach the Saturnian system in 2004.
The spacecraft comprises an orbiter (CASSINI), which will orbit Saturn for at
least three years with numerous flybys of Titan, and a probe (HUYGENS), which
will descend to the surface of the moon Titan.
The Pioneer (1979) and two Voyager (1980/81) spacecraft resulted in the
first close at hand observations and detailed images of Saturn, its rings
and satellites.
The results from the CASSINI/HUYGENS mission will build on the knowledge
obtained from these investigations and greatly advance our understanding of
the Saturnian system.
The mission will provide the UK scientific community with its first
opportunity to land an instrument on another planetary body.
British scientists have been involved in building five instruments on
CASSINI, taking the leading role in one of them.
There are a further two instruments where Britain has had a scientific input.
The Composite Infrared Spectrometer will analyse the composition of
Titan's and Saturn's atmospheres remotely from the Cassini orbiter and will
measure temperatures and cloud properties.
Research into the nitrogen and carbon compounds on Titan is particularly
important, as this may help to understand what the Earth was like before life
began.
The Dual Technique Magnetometer will provide information on the
magnetic field around Saturn and the electric and magnetic interactions
between the planet and its rings.
Titan does not have a magnetic field and this means that its atmosphere is
continually being blown away by the Solar wind.
The DTM will be able to study this process.
The Cosmic Dust Analyser will measure the physical and chemical make up
of small dust particles.
This will improve our understanding of Saturn's rings.
Measurements taken during the journey from Earth will provide the first in-situ
chemical data on the dust in space, especially around the asteroid belt and
Jupiter.
This will help to identify the origins of interplanetary dust particles.
RAL has a hardware involvement in this experiment.
The Cassini Plasma Electron Spectrometer will study the interaction of
the Solar wind with the Saturnian system.
The effect of the Solar wind on the large amounts of dust near the rings
should help us to understand how planets were formed in the early dusty Solar
system.
RAL also has a hardware involvement in this instrument.
RPWS
This instrument will measure Radio and Plasma Waves.
Propagating radiowaves can be used to sense remotely many phenomena, such as
lightning and electron resonances.
Plasma waves will be studied locally to understand the physical processes
taking place.
CISS
The UK involvement in the Cassini Imaging Science Subsystem is through
software developed at the CIC.
At the CIC software is being developed to aid in the choice of CCD for the
ISS cameras, data compression and image analysis.
Software is also being developed for ring, satellite and asteroid dynamics
and to generate ephemerides for Saturnian satellites.
TRM
This project is developing models, techniques and software using altimeter
data from sources, (both terrestrial and space), in support of the Cassini
RADAR facility instrument.
RADAR will provide radar imaging and altimetry of the surface of Titan with a
view to determining its nature, especially the existence of liquid oceans and
lakes.
HUYGENS
One of the Voyager discoveries was that Titan, which is the size of a small
planet, has a nitrogen dominated atmosphere containing many carbon compounds.
One puzzle is why methane is present in Titan's atmosphere.
The study of Titan could provide information on the early atmosphere of the
earth, before life began, and tell us where the nitrogen and water on earth
came from.
As it approaches Titan's surface the Hugyens probe, with six instruments on
board, will analyse the chemical composition of the atmosphere, the weather,
and the surface.
Britain is taking the leading role in the surface measurements and is involved
in building another instrument on the probe.
The Surface Science Package will perform direct measurements of the
previously unobserved surface of Titan, which is shrouded by an orange haze.
It is not known whether Huygens will hit solid ground or splash into a cold
sea of liquid methane.
This package of instruments will tell us how hard and flat the landing site is.
If it lands in an ocean it will be able to measure the ocean's depth, density,
and the speed at which sound and light travels through it.
From these data, scientists will be able to tell what the ocean is made of
and whether the ocean is as old as Titan.
RAL has a hardware involvement in this instrument.
The Huygens Atmospheric Structure Instrument will measure the temperature,
pressure, density and electrical properties of the atmosphere, as the probe
descends slowly by parachute.
Accelerometers will measure the winds buffeting the probe and a microphone
will listen for thunder and other noises.
Jim Lang, lang@solg2.bnsc.rl.ac.uk, 19-Feb-97