Introduction
- localization - Formation - Composition
Cassini-Huygens - Earth and Titan ?
- Conclusion
1. Introduction
2. Launching of the Huygens-Cassini mission
3. What is happening during the Huygens-Cassini mission ?
1. Introduction
On Sunday, November 12. 1980, Voyager I flew over Saturn, its rings and its 18 satellites… Eighteen hours and five minutes before the planet arrived, the robot came near an unidentified object. The Earth-controlled probed turned to it and Titan, Saturn's satellite, appeared in front of the measuring instruments…
The fog surrounding Titan puzzled all the mission's investigators. But after a single day of calculations, the researchers' perplexity gave way to amazement, because Titan's atmosphere is made up of 90 % of nitrogen, but also of hydrocarbons and nitrogen compounds such as hydrocyanic acid, cyanogen and cyanacetylene. Such a number of different elements could be a could criterium for living conditions.
The pictures taken during the Voyagers I and II missions only show a thck, impenetrable, orange-coloured mist covering Titan's soil (Voyager II had been launched 9 months after Voyager I but had been 100 times as far). In 1988, the ESA decided to build the Huygens probe in order to penetrate the mystery of a possible " pre-biotic formation " on Titan's soil.
Cassini-Huygens
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2. Launching of the Huygens-Cassini mission
The
NASA then decided to finance the Cassini project, launching a large, unoccupied
probe towards Saturn in order to study this planet, its rings and satellites
from the probe's orbit. The Huygens probe will then be released when reaching
the vicinity of Titan. Both probes weigh 5.8 tons in total and are as big
as a small lorry.
They were launched on October 13., 1997 from Cape Kennedy Center in Florida, by the American rocket Titan IV - Centaur (whose name is actually mere coincidence).
The total cost of the project, including the cost of the flight and of the ground staff until 2008, has been estimated to 120 billion Francs (3 billion Euros). The European share it this cost is of about 15 billion Francs (0.38 billion Euros).
3. What is happening during the Huygens-Cassini mission ?
Cassini will take a roundabout way : Titan IV is not powerful enough to throw a huge machine as Cassini directly into Saturn's sphere of influence, that is why il will follow a complex route by using the own gravity of several planets.
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On October 23. 1997, space navigation and trans mission systems were successfully checked by the space centre for ESA's operations. Huygens' descent upon Titan should take place on November 27. 2004.
On April 26. 1998, the probe flew over Venus for the first time, at an height of 284 km from the planet's soil. The probe began then to fly at a speed of 39 km/sec.
On December 3. 1998, the first correction on the probe's flight path was made.
On January 21. 1999, all measuring instruments were inspected. They still worked.
On June 22. 1999, the probe flew over Venus for the second time, but at a height of 600 km this time. A few scientific observations were made on this occasion.
In July 1999, according to astronomers from the Lawrence Livermore National Laboratory in California, oceans of hydrocarbons and rocky-icy continents were seen on Titan's surface.
On August 18. 1999, the probe flew over Planet Earth and measured its magnetical field after taking pictures of the Moon. American anti-nuclear associations protested against it, finding it dangerous that the probe should fly over the Earth, because of the possibility of a crash (but they didn't say anything about the 32 kg plutonium contained in the probe).
On April 15. 2000, Cassisni was heading for Saturn, after safely breaking through the asteroid belt between Mars and Jupiter. The probe passed at 1.5 million km from the 2685 Masursky Asteroid, a very tiny object, and managed to measure its size and albedo.
In September 2000, the probe's data transmission stopped functioning.
In October 2000, a test was made to check Cassini's camera system. It was successful.
In December 2000, Cassini-Huygens swang by Jupiter at a distance of 9.72 million km. It sent magnificent high-resolution images of Jupiter to Earth.
In July 2001, Cassini shifted its course after a major problem in Huygens' data recovery system was discovered.
In April 2002, the main engine's ignition corrected the probe's route during 9.8 sec while Cassini Huygens was 3 million km away from Earth. This operation, which is the thirteenth to be achieved since the rocket was launched, allowed the navigators to practise a manoeuver that is going to become common as soon as the probe is in orbit around Saturn, since they will have to switch on the engine every five days.
Cassini should theoretically work until 2008, maybe even longer. During the last four years spent in the vicinity of Saturn, it will achieve almost 60 revolutions around the planet, amongst which 33 will allow it to fly over Titan.
On
November 27. 2004, the Huygens probe will be dropped by parachute into Titan's
thick atmosphere. During its descent, it will take pictures whick hopefully
will show something else than a foggy cloud. It will also measure the temperature,
the atmospheric pressure and the speed of the wind. The probe will also search
for possible lightnings and will carry out a chemical analysis of the atmosphere's
composition. All these results will be sent by radio to the Cassini ship that
will send them to Earth afterwards. Nobody can tell what Huygens will come
across at the end of this long descent : the soil could be solid, or liquid.
The probe could land on a rocky floor but could also dive into a methane or
ethane ocean, or in a thick layer of " chemical humus ".
Huygens' designers tried to take each possibility into account.
The device is robust enough to survive to a landing on a rocky soil, but also
light enough to float if it falls into one of these oceans. It was designed
to resist the wind's - and even the lightnings' - attacks. If there is no
light on Titan, a powerful lamp was provided. Huygens is equipped with an
instrument that can measure the soil's hardness, and another one can measure
the waves' impacts in the sea. In the case that there would be some noise
on Titan, a microphone has also been provided. The Huygens team hopes that
the probe will " survive " during at least half an hour after its
landing, so it will be possible to get the data from it.
Cassini and Huygens will not only bring scientific instruments. Thousands
of signatures and messages from all over the world are also travelling through
the universe inside the probe. The NASA and the ESA have given the possibility
to send their signature into space for free to anybody who would like to.
The messages are stocked as electronic data on two compact discs.
On the European CD carried by the Huygens probe, the following message can
for instance be found :
" I"m a French Earthman (1m83), looking for a tall,
attractive and preferably romantic Martian Girl. "
Introduction
- localization - Formation - Composition
Cassini-Huygens - Earth and Titan ?
- Conclusion