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Rosetta - a Spacecraft in Search of Pristine Matter

Berlin/Friedrichshafen, 01 May 2002

In January 2003, the European spacecraft Rosetta is to set off in search of pristine matter. It will be launched on its long flight to the comet "Wirtanen" by the European launch vehicle Ariane 5. For approximately one year, it will orbit this tailed star at a distance of one kilometre and explore it in detail. At the same time, a probe will land on the comet's surface for surface-science investigations and analysis.

At Astrium, which is the industrial prime contractor, extensive activities are underway for this challenging project of the European Space Agency ESA. Work on the flight model has been in full swing since early 2001. All experiments and the lander have been completed. At present, the satellite is being tested in so-called environmental tests in ESA's Technology Centre ESTEC, in Noordwijk/The Netherlands. This inspection phase will last until July 2002. The overall volume of this contract totals about € 300 million.

Rosetta Tacking through the Planetary System

Rosetta is the third of four major Planetary Cornerstone missions of the European Space Agency ESA. In terms of engineering, it ranks among the most difficult projects that are feasible today. It will further expand Europe's commanding position in cometary research which it had attained with the fly-by of Halley's Comet by the space probe Giotto in 1986.

The flight path itself already calls for new technical solutions. Even the thrust of the powerful Ariane 5 is not sufficient to directly inject the spacecraft on its way to the comet. The probe must rather gather momentum three times in the gravity fields of Mars and the Earth in order to get onto the right track. According to current planning this will take place in 2005 at Mars and the Earth and once again at the Earth in 2008. Only after the third swing-by manoeuvre will Rosetta be catapulted into the outer regions of the planetary system, where it will encounter the comet "Wirtanen". Thus, Rosetta reaches a maximum distance of approximately 800 million kilometres to the Sun and a distance of about one billion kilometres to the Earth. It is the first time ever a solar-powered probe will have ventured such distances.

In between these events, Rosetta will be largely on its own. This is the reason why the technically most complex workshare for industry is the so-called avionics pack, which is also delivered by Astrium. It contains the software for the onboard computers and the attitude control system. Mind and body must operate faultlessly and to a large degree autonomously. The biggest single item under this contract, however, is the instrument platform, which is also under the responsibility of Astrium.

The Asteroids Otawara and Siwa

Before its encounter with the comet, however, Rosetta will pass close to two asteroids. In 2006, it will pass Otawara at a distance of 2,200 kilometre, and in 2008, after a second fly-by of the Earth, it will pass Siwa at a distance of 3,500 kilometres. Asteroids are bits of rock which orbit the Sun primarily in the area between Mars and Jupiter. They are probably the building blocks for a planet which could not be formed on account of Jupiter's enormous gravitational forces. Therefore, these bodies are also called planetoids or minor planets. Astronomers know very little about them and expect to obtain valuable information on their composition and creation from the data delivered by Rosetta.

Comet Wirtanen

The rendezvous manoeuvre with comet Wirtanen will be initiated in November of 2011. In September 2012, more than nine years after launch, Rosetta will have reached its destination and insert itself into an orbit around the comet. Only then will the most thrilling part of the venture start. At that time, Wirtanen will be at a distance of nearly 400 million kilometres to the Earth and 500 million kilometres to the Sun. Here, in the icy cold of deep space, the comet is still inactive, which means it does not emanate any gases which could form a coma or tail.

During that time the surface will be imaged from a distance of approximately one kilometre. For the first time, scientists, and of course the public, will be able to clearly see a cometary surface. Details down to one metre are expected to be discernible. The camera will be built by the Max-Planck Institute for Aeronomy in Katlenburg/Lindau, the experts who also developed the successful camera for Giotto.

Simultaneously, spectrometers will scan the surface in various spectral ranges down to the infrared range. This data will be used to determine the mineral and chemical composition of the surface material. The surface is expected to have the appearance of a dirty, crusted icy desert.

Halley's Comet revealed long canyons, wide craters and up to 900-metre high hills. Nobody knows whether Wirtanen might look similar.

The German camera will also look for level terrain, since Rosetta will deploy a lander on the surface some time after having reached the comet.

This vehicle will land softly on the surface and will then have to be anchored. The reason for this is that the comet, measuring only a few kilometres, has extremely low gravity. Its force of attraction is so low that a coin thrown in the air would disappear forever.

The lander will carry a series of complex instruments for the analysis of surface samples. Additionally, a camera will take panoramic pictures. The camera is a co-operative development between the Institute for Planetary Exploration of the German Aerospace Centre (DLR) in Berlin and French scientists. It is even planned to lower a micro-camera into the bore-hole to determine the structure of the cometary crust.

While Rosetta orbits the comet, the latter will steadily approach the Sun. Wirtanen will wake up from the icy cold and start to heat up. Gases will evaporate from its surface and inside. They will drag along dust particles, and Wirtanen will thus form a coma and a tail. The 13 measuring instruments on board Rosetta will then begin the study of gas and dust. Approximately one year after Rosetta's encounter with the comet, Wirtanen will have reached the orbital point nearest the Sun, where it is most active. Shortly thereafter, the spacecraft mission will be completed. Wirtanen will then withdraw again into the outer and icy regions of the planetary system.

For the first time, scientists will thus have the opportunity to see "live" how a cometary surface evolves in the course of the "seasons". The pictures taken by Giotto already showed that, apparently, huge gas jets spout out of the crevasses in the surface. Rosetta will show this process in much more detail and thus help unravel further mysteries that surround the comets.

Comets - the Archives of Primeval Times

The gathered data will be of inestimable value to the scientific community, as the instruments on board the lander, in a way, will tap an archive which has preserved unaltered material from the time of formation of the solar system. Pristine matter can be found on no other celestial body, with the possible exception of some asteroids. On the Earth and also on other planets, source material from which the planets were formed, continuously evolved in the course of the last 4.6 billion years. Chemical, geological and biological processes transformed the atmosphere and rocks thereby destroying any information from primeval times.

Comets, by comparison, are so small that no geological processes such as erosion or plate tectonics take place. There are presumably billions of cometary nuclei that slowly move around the Sun far outside Pluto's orbit. It is only when one of them ventures into the inner solar system that it will heat up so that gas will evaporate and it will appear as a tailed star in the sky.

Comets spend most of their "life" in the outer regions of the solar system where temperatures drop to nearly absolute zero. The cometary material is thus preserved in a deep-freeze state. Scientists therefore hope that Rosetta will help them determine the chemical composition of protosolar nebula in order to further explore the creation of our solar system and thus of the Earth. In other words: Rosetta will be looking for the roots of our existence.

Rosetta

This also explains the name of the spacecraft. It refers to the "Rosetta Stone", an Egyptian inscription stone, discovered by a soldier in the Napoleonic Army in 1799, near the Egyptian city Rosetta. By means of the inscription on that stone, the French scholar, Jean-François Champollion, detected the first clues to deciphering the Egyptian hieroglyphics, thereby opening the historians' way to our cultural roots.

Friedrichshafen, May 2002/02021

For further information:

Astrium
Earth Observation & Science
Mathias Pikelj
Tel.:+49 7545/ 8-9123
Fax: +49 7545/ 8-5589
presse-eo@astrium-space.com