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Rosetta - Masterpiece of Technology with a Cosmic Message

* Rosetta's cosmic message
* New upper stage for a complicated flight path
* Demanding requirements even during "hibernation"
* "Digging" in the cosmic archive

Friedrichshafen/Bremen/Kourou, 12 February 2004

Two weeks before launch of the European comet probe Rosetta, the final preparations are underway at the launch site Kourou, French-Guyana. Under the management of space technology engineers of the European space company EADS Astrium, the spacecraft has been thoroughly tested and integrated into Ariane 5. This requires meticulous care since the launch window for the start to a journey lasting ten years will open for the first time on February 26, 2004. Rosetta will be the first spacecraft to orbit the nucleus of the comet 67P/Churyumov-Gerasimenko and to deploy a lander on the comet's surface.

With a volume of approximately 330 million euros, EADS Astrium was the industrial prime contractor for the European Space Agency ESA. The overall costs of the mission amount to approx. 770 million euros. On the whole, about 200 EADS Astrium engineers and technicians from Germany, France and the U.K. have been involved in the development and construction of the comet probe. Challenging technical efforts were required for that purpose, as Rosetta will have to carry out autonomous monitoring and control for many years. It will be the first probe ever to be supplied with energy from solar arrays at a distance of approx. 800 million kilometres from the Sun. These are only some of the technical novelties in this project.

Rosetta's cosmic message

Rosetta is composed of two elements, i.e. the main probe, which will orbit the comet Churyumov-Gerasimenko, and the lander, which is to land on the celestial body. Both spacecraft will exist until the comet either disintegrates or collides with a planet in the far future. For that reason, Rosetta is carrying a message on board. A small nickel disk attached to the outside of the main probe contains the first three chapters of "Genesis" engraved in a thousand languages. This corresponds to approximately 7,000 pages in standard format. They have been produced by the San Francisco-based institution "Rosetta project to save the variety of languages".

The parallel to the "Rosetta stone" discovered in 1799 by a soldier of the Napoleonic Army in Egypt is as follows: The basalt rock with a weight of 760 kilogrammes shows an inscription in three different languages. Since two of the three languages were known, it was possible to decipher the third unknown language, the hieroglyphics. The U.S. Rosetta project fears that 95 per cent of all languages will die out this century and many of them will no longer be available in written form. The aim of the project is to create a "global Rosetta stone". It contains several texts that have been translated into all known languages. This will make it possible to decipher unknown languages in the future.

With this inscription Rosetta follows a tradition in space technology. For example, the NASA spacecraft Pioneer 10 and 11 launched in 1972 and 1973, are equipped with engraved metallic plates at the exterior containing information about man and our cosmic home. Each of the spacecraft Voyager 1 and 2 launched in 1977 is equipped with a gold-plated record including a record player. It contains 27 pieces of music from Louis Armstrong to Johann Sebastian Bach, as well as messages in many languages.

The probe duo Cassini/Huygens launched in 1997 also carries a cosmic message on board. Cassini and Huygens are equipped with a CD-ROM containing messages of greeting, signatures and short compositions which have been transmitted to ESA and NASA by people from all over the world via Internet. Huygens, which is integrated at (today's) EADS Astrium in Ottobrunn, is to explore Titan, Saturn's moon and its atmosphere and land there in January 2005.

New upper stage for a complicated flight path

In order to bring Rosetta on its right way to "67P", the Ariane 5 upper stage, for the first time, accelerates to a speed of almost 40,000 kilometres per hour, i.e. to escape speed, on this mission. Only this speed allows leaving of the Earth's orbit and starting its journey through deep space. For being able to carry out this demanding manoeuvre, EADS SPACE Transportation had to re-qualify and modify the upper stage. Instead of igniting immediately after separation from the main stage as usual, the EPS (Etage Propulsion Stockables) upper stage – developed and built under the leadership of EADS SPACE Transportation – and its Rosetta payload will start a 105-minute coasting flight first. Then, it will be ignited to achieve the escape speed after a burning time of about 16 minutes.

Even this additional boost is not sufficient to inject the spacecraft directly on its way to the comet which will be close to Jupiter's orbit during the rendezvous with the probe. For that reason, the spacecraft must gather momentum four times in the gravity fields of Mars (March 2007)) and the Earth ( 2005 , 2007 and 2009) in order to get into the outer regions of the planetary system.

Demanding requirements even during "hibernation"

Before Rosetta approaches the comet Churyumov-Gerasimenko in May 2014, there will be a phase (from July 2011 to January 2014) during which the probe is put into deep sleep. Nevertheless, its "brain" must not be switched off completely during that time. The on-board computers must continuously monitor the state of all instruments and make sure the temperature in the probe varies within certain limits only. "The software development turned out to be one of the greatest challenges“, says project manager Rainer Best of EADS Astrium, Friedrichshafen. In order to cover all possible cases, the software was tested intensively for two years by means of two completely equipped probe models. In an emergency, the system must be able to put itself to a safe mode or to switch on spare components in case of a failure.

Even for minimum operation, the probe requires a power of approximately 390 watts. So far, all spacecraft moving away from the Sun beyond Mars' orbit have received their energy from "radioactive" batteries. There, the heat from disintegrating radioactive substances is directly transformed into electrical energy. In an extensive research programme carried out for Rosetta from 1990 to 1996, solar arrays were developed which are optimised for conditions with very low light intensity and very low temperatures. Rosetta is equipped with two solar-array wings with a length of 15 metres each and an overall surface of 68 square metres. At a distance of 800 million kilometres from the Sun, where the light intensity decreases to about four per cent of the intensity near the Earth, they generate about 450 watts – more than originally planned. In the summer of 2015, when Rosetta has approached the Sun to a distance of approximately 150 million kilometres (according to the radius of the Earth' orbit), the solar arrays will supply the entire electrical energy of 8,700 watts.

Thermal control of the probe represents another technical challenge. Rosetta's distance to the Sun will vary between approx. 150 and 800 million kilometres. That means, the spacecraft is heated with an intensity varying according to the Sun's radiation (-270°C/+100°C). Furthermore, the instruments and computers will heat the probe's interior depending on their operational state. Despite these considerably changing conditions, the temperature inside the probe must not vary too much. According to EADS Astrium project manager Rainer Best "The instruments prefer a temperature of about +20 degrees Centigrade. To guarantee this, special louvers opening and closing automatically as a function of the temperature have been developed for the first time in Europe".

The dust emanated by the cometary nucleus could present a problem. During its flight and in the orbit around the comet, Rosetta orientates itself by means of the stars. A small telescope, the so-called star tracker, is used for that purpose. However, if Rosetta orbits the comet Churyumov-Gerasimenko at a distance of just one kilometre, dust will probably obstruct the view of the telescope. "Normal" software would not be able to distinguish the small particles from stars and would thus inevitably lose orientation. This problem was solved by the development of intelligent software which is able to recognise the constellations even if up to a thousand "false" stars irritate the computer.

In May 2014, Rosetta will be so close to the comet that the probe itself can determine its position. The relative velocity between Rosetta and the comet will then be reduced to 10 km/h, and Rosetta will slowly approach its destination. In August 2014, it will insert itself into an orbit and carry out a detailed investigation of the cometary nucleus with a presumable size of three by five kilometres from a distance of just one kilometre.

During that process, a suitable terrain for the lander will also be selected. Landing could be performed in November 2014. At the time of separation from the probe, the lander will be exactly aligned and fly passively – attracted by the low gravity of the comet – until it lands on the comet's surface. As soon as the device touches the ground, harpoons attached with ropes will be ejected in order to anchor it firmly.

The lander will take samples of the soil with a drill at a depth of up to 20 centimetres and analyse them. A sensor will measure the composition of the ground, the probe will investigate the internal structure by means of radio waves and six micro-cameras will take panoramic pictures which will be transmitted to Earth via the "relay station" Rosetta. The lander is equipped with a battery providing it with electrical energy for a period of 68 hours. This period is required for the main programme of the scientific investigations. Additionally, it is equipped with solar arrays, extending its lifetime, provided they are optimally aligned to the Sun.

While Rosetta continues to orbit the comet, the latter will steadily approach the Sun. It will start to heat up and the matter will evaporate and form the typical tail. Until December 2015, Rosetta is to observe how the planet wakes up from the icy cold, then the mission will be regarded as officially terminated.
"Digging" in the cosmic archive

For the scientific community, the Rosetta mission is comparable to a journey to primeval times of our solar system. In contrast to planets, where tectonics and erosion have permanently changed the rocks, the material inside comets has remained unchanged since its formation 4.6 billion years ago. The tailed stars can be regarded as deep-freeze archives which scientists will now try to decipher.

EADS Astrium is the leading satellite company in Europe. It is wholly owned by EADS SPACE. In 2002, EADS SPACE had a turnover of approximately 2.2 billion euros and 12,300 employees in Germany, France, the United Kingdom and Spain. The satellite activities of EADS Astrium cover complete civil and military telecommunications and Earth observation, science and navigation programmes, and all spacecraft avionics and equipment.

Press Contact
Mathias Pikelj
EADS Astrium GmbH, Press & Information
Tel.: 07545/ 8-9123
Fax: 07545/ 8-5589
mailto: presse-de@astrium.eads.net

Kirsten Leung
EADS SPACE Transportation, Press & Information
Tel.: 0421/ 539 5326
Fax: 0421/ 539 4534
mailto: kirsten.leung@space.eads.net

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