UK Scientists To Probe Saturn's Mysterious Moon Titan
UK scientists are eagerly awaiting the launch of a probe to a world possibly resembling a deep-frozen primitive Earth aboard the most ambitious space mission ever attempted. In mid- October, a heavy-lift Titan IV-Centaur rocket is scheduled to send the Cassini-Huygens spacecraft on its way to the distant reaches of the Solar System, at the beginning of a seven-year odyssey to the planet Saturn and its cloud-covered satellite, Titan.
The European Space Agency's Huygens probe is designed to unveil the secrets of planet-sized Titan. After slamming into Titan's upper atmosphere at 6 km/s, the 350-kg probe will be slowed by friction. Once its velocity has been reduced to around 400 m/s, three parachutes will be deployed in sequence - a drogue, the main chute (about 8 metres in diameter), and a stabiliser parachute. Development and testing of the all- important parachutes and pyrotechnic devices used during the descent has been carried out by Martin Baker Ltd. of Higher Denham, UK.
The successful return of data also depends on the probe's software, developed by Logica plc. of London. This commands the probe during its controlled descent, initiates the various experiments and controls data transmission back to the orbiter. Logica has also provided software on the Cassini orbiter which will control the radio receiver to match frequency and data rate as the relative position and velocity of the two craft change.
Titan Atmospheric Science
Huygens will slowly drop through the dense nitrogen atmosphere for two and a half hours, unveiling the secrets of the smog-shrouded moon. The University of Kent has helped to develop the Huygens Atmospheric Structure Instrument, which will measure the ways in which Titan's atmospheric pressure, temperature and density change with altitude during the descent. Some information on wind and possible lightning will also be returned. The university has prime responsibility for the accelerometry sub-system which incorporates a single axis, high sensitivity servo and lower sensitivity three axis piezo-resistant accelerometers.
The probe carries six scientific experiments, one of which has been principally designed to make measurements on Titan's surface. This is the Surface Science Package (SSP), designed and built by a team under the leadership of Dr John Zarnecki from the University of Kent. Other members of the team include scientists from Rutherford Appleton Laboratory, the Southampton Oceanography Centre, and the University of Manchester Institute of Science and Technology, as well as institutions in France, Poland, Holland and the USA.
Touchdown on Titan is expected to be fairly gentle, at around 5 m/s. On arrival, the SSP is designed to measure various physical characteristics of the surface, including its temperature, density and electrical properties. For a touchdown on land, a penetrometer will be used to measure surface hardness while a tiltmeter will determine the angle of slope. If the probe strikes liquid, an acoustic sounder will measure its depth while the tiltmeter will measure the height and frequency of any wind- generated waves. The package will have to operate at a temperature of about -180 degrees Celsius and will have to gather and return its data to the orbiter within half an hour, before its batteries run out of power and the orbiter moves out of range.
The mission is divided into two parts. While the American Cassini orbiter will spend four years studying the Saturnian system (see RAS press notice 97/35), the most exciting single event will be the despatch of the European Space Agency's Huygens probe into the orange smog of hydrocarbons which smothers the giant moon Titan. The probe is designed to unveil Titan's secrets as it parachutes towards the unseen surface, returning a stream of data about atmospheric conditions and, hopefully, the nature of the underlying terrain.
Arriving at Saturn in July 2004, the Cassini spacecraft will fire its engines to brake into orbit around the ringed planet. Four months later, Huygens will be released from the mother craft and sent on a collision course with Titan. The slumbering probe will coast for three weeks towards its target. It will then be awakened by onboard alarm clocks just 15 minutes before plunging into the moon's upper atmosphere at a velocity of 6 km/sec.
Protected by a special shield from the searing heat of entry, the probe will be slowed by friction until its main parachute can be deployed. During a two-and-a-half-hour descent, Huygens will transmit more than 1,000 images and directly sample the dense atmosphere. Scientists expect the probe to send back fascinating new information about the rain of methane or ethane falling from the clouds, the nitrogen-rich atmosphere, and the unique terrain on which it will touch (or splash) down.
No-one knows how long the Huygens Surface Science Package will operate, even if it survives the landing. Estimates vary from 3 minutes to a maximum of 30 minutes.
The Cassini spacecraft must lift-off from Cape Canaveral Air Station, Space Launch Complex 40 between 6 October and 15 November. The launch is currently scheduled for Monday 13 October with a launch window which opens at 4.55 a.m. and closes at 7.15 a.m. (E.D.T.) corresponding to 10.55-13.15 European Time. The voyage to Saturn will take 6.7 years.
The Huygens probe is named after the 17th century Dutch astronomer Christiaan Huygens, who discovered Titan in 1655.
The Cassini mission is an international venture involving the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA), and the Italian Space Agency (ASI), as well as several European academic and industrial partners. The United States is responsible for the main Cassini spacecraft which will be inserted into orbit around Saturn in July 2004. Attached to the mother craft is the European-built Huygens probe, whose task is to parachute onto the unexplored surface of Titan, the largest of Saturn's moons.
UK investment in the Cassini-Huygens mission amounts to 7.4 million pounds of which 4.48 million pounds is being spent on the orbiter experiments and 2.92 million pounds on the probe investigations. Most of this is provided by the Particle Physics and Astronomy Research Council (PPARC).
PPARC is the UK Government-funded body providing support for basic research in elementary particles and the forces of Nature; planetary and solar research, including space physics; astronomy, astrophysics and cosmology.
Further information on the Huygens mission can be found on these Web pages:
Dr Jacqueline Mitton, RAS Public Relations Officer
Phone: Cambridge ((0)1223) 564914
FAX: Cambridge ((0)1223) 572892
Peter Bond, Space Science Advisor