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 kilometer and
explore it in detail. At the same time, a probe will land on the cornet’s
surface for surface-science investigations and analysis.

At Astrium, which is the industrial primecontractor, extensive activities
are underway for this challenging project of the European Space Agency ESA.
Work on the flight model are in full swing since the beginning of this year.
All experiments and the lander shall be completed by early July. The
satellite will be integrated and tested until the end of September; the
so-called environmental tests will then follow in ESA’s Technical Center
Estec in Noordwijk/The Netherlands. This inspection phase will last until
April of next year. The overall volume of this contract, which will run
until mid-2002, totals about half a billion German marks.

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 maneuver will Rosetta be catapulted into the outer regions of
the planetary system, where it will encounter comet Wirtanen.

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 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 750 kilometers,
and in 2008, after a second fly-by of the Earth, it will pass Siwa at a
distance of 1,600 kilometers. 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 maneuver with comet Wirtanen will be initiated in the spring
of 2011 and, in the spring of 2012, that is more than nine years after
launch, the spacecraft will have reached its destination. And only then will
the most thrilling part of the venture start. At that time Wirtanen will be
at a distance of nearly 600 million kilometers to the Earth and 750 million
kilometers 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 kilometer. For the first time scientists, and of course the public, will
be able to clearly see a cometary surface. Details down to one meter are
expected to be discernible. The camera will be built by the Max-Planck
Institute for Aeronomy in Katlenburg/Lindau, the experts that 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-meter 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.
Originally, two landers had been planned. One, called Champollion, was to be
jointly built by France and the USA, the other one, Roland (Rosetta Lander),
was planned as an exclusive German project. After the Americans’ decision to
withdraw from the project, Germany and France will jointly build one lander.
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
kilometers, has an 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 cooperative development between the Institute for Planetary
Exploration of the German Aerospace Center (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 onboard 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 OT 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-Francois Champollion,
detected the first clues to deciphering the Egyptian hieroglyphics, thereby
opening the historians’ way to our cultural roots.

Paris/Le Bourget, June 2001/01011

For further information: Astrium

Earth Observation & Science Mathias Pikelj

tel.:+49 7545/ 8-9123

fax: +49 7545/ 8-5589