The countdown to Rosetta’s rendezvous in space began on 1 March 1997. At
the end of February 2004, seven years and not a few headaches later, the
European Space Agency (ESA) probe will at last be setting off on its
journey to meet Comet Churyumov-Gerasimenko. The long-planned get-together
will not however take place until the middle of 2014. A few months after
arriving at the comet, Rosetta will release a small lander onto its
surface. Then, for almost two years it will investigate
Churyumov-Gerasimenko from close up.

Dr Gerhard Schwehm, lead scientist for the Rosetta project, explains that,
"With this mission we will be breaking new ground – this will be the first
protracted cometary encounter." The trip to the meeting place in space
will certainly be a long one, located as it is some 4.5 astronomical units
from the Sun, which translates into something like 675 million kilometres.
Rosetta will be on the road for ten years, during which time it will clock
up in excess of five billion kilometres.

Launch in February 2004

Rosetta will be waved off on 26 February when it lifts off from the space
centre in Kourou, French Guiana aboard an Ariane 5 launcher. Shortly after
the spacecraft’s release, its solar panels will be deployed and turned
towards the Sun to build up the necessary power reserves. Its various
systems and experiments will be gradually brought into operation and
tested. Just three months into the mission the first active phase will be
over, followed by final testing of the experiments in October 2004.
Rosetta will then spend the following years flying a lonely path to the
comet, passing by the Earth, Mars, the Earth and the Earth again.

There is no alternative to this detour, for even Ariane 5, the most
powerful launcher on the market today, lacks the power to hurl the probe
on a direct route to the comet. To get the required momentum, it will rely
on swing-by maneuvres, using the gravitation pull of Mars (in 2007) and
the Earth (three times, in 2005, 2007 and 2008) to pick up speed.

Asteroids for company

A change is as good as a rest, and a meeting with at least one asteroid
should help break the monotony for Rosetta. The spacecraft will come close
to an asteroid at the end of 2008. Asteroids are, it will be remembered,
rocky bodies, some as large as mountains, some even larger, that orbit the
Sun in much the same way as planets.

"These ‘brief encounters’ are a scientific opportunity and also a chance
to test Rosetta’s instrument payload," says Gerhard Schwehm. But asteroid
exploration also serves an entirely practical purpose: "The more we find
out about them, the better the prospect of being able one day to avert a
possible collision." Following a period of low-activity cruising, the
probe’s course will be adjusted one last time in May 2011. From July 2011,
a further two-and-a-half years’ radio silence will be observed, and
Rosetta, left entirely to its own resources, will fly close to the Jupiter

Link-up in 2014

Finally, in January 2014, the probe will be reactivated and will, by
October 2014, be only a few kilometres distant from Churyumov-Gerasimenko.
This is where the dream of so many scientists becomes reality. Having
deposited its precious lander cargo on the comet’s surface, Rosetta will
continue to orbit Churyumov-Gerasimenko and together they will spend the
next seventeen months flying towards the Sun.

Rosetta was built by an international consortium led by Astrium. The
lander probe was developed in Cologne under the aegis of the DLR,
GermanyĆ­s space agency, with contributions from ESA and research centres
in Austria, Finland, France, Hungary, Ireland, Italy and Great Britain.

The comet explorer carries ten scientific instruments. Their job is to
draw out the secrets of the comet’s chemical and physical composition and
reveal its magnetic and electrical properties. Using a specially designed
camera, the lander will take pictures in the macro and micro ranges and
send all the data thus acquired back to Earth, via Rosetta.

"This will be our first ever chance to be there, at first hand, so to
speak, as a comet comes to life," Schwehm goes on to explain. When
Churyumov-Gerasimenko gets to within about 500 million kilometres of the
Sun, the frozen gases that envelop it will evaporate and a trail of dust
will be blown back over hundreds of thousands of kilometres. When
illuminated by the Sun, this characteristic comet tail then becomes
visible from Earth. In the course of the mission, the processes at work
within the cometary nucleus will be studied and measured more precisely
than has ever before been possible, for earlier probes simply flew past
their targets. "As we will be accompanying Churyumov-Gerasimenko for two
years, until the comet reaches the point closest to the Sun on its orbit,
we can at long last hope to acquire new knowledge about comets. We are
confident we will come a step nearer to understanding the origins and
formation of our solar system and the emergence of life on Earth."

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