Rosetta -- a new target to solve planetary mysteries (Forwarded)

European Space Agency
Press Information Note No. 01-2004
Paris, France 26 January 2004

Rosetta -- a new target to solve planetary mysteries

Rosetta is scheduled to be launched on board an Ariane-5 rocket on 26 February
from Kourou, French Guiana.

Originally timed to begin about a year ago, Rosetta's journey had to be
postponed, as a precaution, following the failure of a different version of
Ariane-5 in December 2002. This will be the first mission to orbit and land on a
comet, one of the icy bodies that travel throughout the Solar System and develop
a characteristic tail when they approach the Sun.

This delay meant that the original mission's target, Comet Wirtanen, could no
longer be reached. Instead, a new target has been selected, Comet
67P/Churyumov-Gerasimenko, which Rosetta will encounter in 2014 after a
'billiard ball' journey through the Solar System lasting more than ten years.
Rosetta's name comes from the famous 'Rosetta Stone', from which Egyptian
hieroglyphics were deciphered almost 200 years ago. In a similar way, scientists
hope that the Rosetta spacecraft will unlock the mysteries of the Solar System.

Comets are very interesting objects for scientists, since their composition
reflects how the Solar System was when it was very young and still 'unfinished',
more than 4600 million years ago. Comets have not changed much since then. In
orbiting Comet Churyumov-Gerasimenko and landing on it, Rosetta will collect
information essential to an understanding of the origin and evolution of our
Solar System. It will also help discover whether comets contributed to the
beginnings of life on Earth. In fact comets are carriers of complex organic
molecules that, delivered to Earth through impacts, perhaps played a role in the
origin of living forms. Furthermore, 'volatile' light elements carried by comets
might also have played an important role in forming the Earth's oceans and
atmosphere.

"Rosetta is one of the most challenging missions undertaken so far," says
Professor David Southwood, ESA Director of Science. "No one has ever attempted
such a mission, unique for its scientific implications as well as for its
complex and spectacular interplanetary space manoeuvres." Before reaching its
target in 2014, Rosetta will circle the Sun four times on wide loops in the
inner Solar System. During its long trek, the spacecraft will have to endure
some extreme thermal conditions. Once it is close to Comet
Churyumov-Gerasimenko, scientists will take it through a delicate braking
manoeuvre; the spacecraft will then closely orbit the comet, and gently drop a
lander on it. It will be landing on a small, fast-moving 'cosmic bullet' about
whose 'geography' very little is known yet.

An amazing 10-year interplanetary trek

Rosetta is a three-tonne box-type spacecraft about three metres high, with two
14-metre solar panels. It consists of an orbiter and a lander. The lander is
approximately one metre across and 80 centimetres high. It will be attached to
the side of the orbiter during the journey to Comet Churyumov-Gerasimenko.
Rosetta carries 21 experiments in total, 10 of them on the lander. They will be
kept in hibernation during most of its 10-year trek towards the comet.

Why does Rosetta's cruise need to take so long? To reach Comet
Churyumov-Gerasimenko, the spacecraft needs to go out into deep space as far out
from the Sun as Jupiter. No launcher could possibly get Rosetta there directly.
ESA's spacecraft will gather speed from gravitational 'kicks' provided by four
planetary fly-bys: one of Mars in 2007 and three of Earth in 2005, 2007 and
2009. During the trip, Rosetta will also twice pass through the asteroid belt,
where a fly-by with one or more of these primitive objects is possible. A number
of candidate targets have already been identified, but the final selection will
be made after launch, once the amount of surplus fuel has been verified by
mission engineers. During these encounters, scientists plan to switch on
Rosetta's instruments for scientific studies of these largely unexplored Solar
System bodies.

Long trips in deep space include many hazards, such as extreme changes in
temperature. Rosetta will leave the benign environment of near-Earth space to
the dark, frigid regions beyond the asteroid belt. To manage these thermal
loads, experts have done very tough pre-launch tests to study Rosetta's
endurance. For example, they have heated its external surfaces to more than 150
C, then cooled it to -150 C in the next test.

The spacecraft will be fully reactivated prior to the comet rendezvous manoeuvre
in 2014. Then, Rosetta will orbit the comet -- an object only about 4 kilometres
in diameter -- while it cruises through the inner Solar System at 135 000
kilometres per hour. At the time of the rendezvous -- around 675 million
kilometres from the Sun -- Comet Churyumov-Gerasimenko will hardly show any
surface activity. This means that the characteristic 'coma' (the comet's
'atmosphere') and the tail will not be formed yet, because of the distance from
the Sun. The comet's tail is in fact made of dust grains and frozen gases from
the comet's surface that vaporise because of the Sun's heat.

Over a period of six months, Rosetta will extensively map the comet's surface,
prior to selecting a landing site. In November 2014, the lander will be ejected
from the spacecraft from a height which could be as low as one kilometre.
Touchdown will be at walking speed, about one metre per second. Immediately
after touchdown, the lander will fire a harpoon into the ground to avoid
bouncing off the surface back into space, since the comet's extremely weak
gravity alone would not hold onto the lander. Operations and scientific
observations on the surface will last at least a week, but may continue for many
months. Besides taking close-up pictures, the lander will drill into the dark
organic crust and sample the primordial ices and gases.

During and after the lander operations, Rosetta will continue orbiting and
studying the comet: it will be the first spacecraft to witness at close quarters
the changes taking place in a comet when the comet approaches the Sun and grows
its coma and tail and then travels away from it. The trip will end in December
2015, after 12 years of adventure, when the comet has made its closest approach
to the Sun and is on its way towards the outer Solar System.

Studying a comet on the spot

Rosetta's goal is to examine the comet in great detail. The instruments on the
orbiter include several cameras and spectrometers that work at different
wavelengths: infrared, ultraviolet, visible and microwave. In addition, there
are various other instruments to make in situ analysis. Together, they will
provide, amongst other things, very high-resolution images and information about
the shape, density, temperature and chemical composition of the comet. Rosetta's
instruments will analyse the gases and dust grains in the coma that forms when
the comet becomes active, as well as the interaction with the solar wind.

The ten experiments on the lander will make an on-the-spot analysis of the
composition and structure of the comet's surface and subsurface material. A
drilling system will take samples down to 30 centimetres below the surface and
feed these to the 'composition analysers'. Other instruments will measure
properties such as near-surface strength, density, texture, porosity, ice phases
and thermal properties. Microscopic studies of individual grains will tell us
about the texture.

Ground operations

All scientific data including those relayed from the lander will be stored on
the orbiter for downlink to Earth at the next ground station contact. ESA has
installed a new deep-space antenna at New Norcia, near Perth in Western
Australia, as the main communications link between the spacecraft and ESOC
Mission Control in Darmstadt, Germany. This 35-metre diameter parabolic antenna
allows the radio signal to reach distances of more than a million kilometres
from Earth. The radio signals, travelling at the speed of light, will take up to
50 minutes to cover the distance between the spacecraft and Earth.

Building Rosetta

Rosetta was selected as a mission in 1993. The spacecraft has been built by
Astrium Germany as prime contractor. Major subcontractors are Astrium UK
(spacecraft platform), Astrium France (spacecraft avionics), and Alenia Spazio
(assembly, integration, and verification). Rosetta's industrial team involves
more than 50 contractors from 14 European countries, Canada and the United States.

Scientific consortia from institutes across Europe and the United States have
provided the instruments on the orbiter. A European consortium under the
leadership of the German Aerospace Research Institute (DLR) has provided the
lander. Rosetta has cost ESA EUR 770 million at 2000 economic conditions. This
includes the launch and the entire period of development and mission operations
from 1996 to 2015. The lander and the experiments, the so-called 'payload', are
not included since they are funded by the member states through scientific
institutes.

Note to editors

Europe is a leading pioneer in comet exploration. In 1986, ESA's Giotto
spacecraft performed the closest comet fly-by ever achieved by any spacecraft
(at a distance of 600 kilometres from Halley). It sent back wonderful pictures
and data that showed that comets contain complex organic molecules. These kinds
of compounds are rich in carbon, hydrogen, oxygen, and nitrogen. Intriguingly,
these are the elements which make up nucleic acids and amino acids, which are
essential ingredients for life as we know it. Giotto continued its successful
journey and flew within about 200 km of Comet Grigg-Skjellerup in 1992. Now
scientists will be eagerly waiting to be able to answer some of the fascinating
new questions that arose from analysing the exciting results from Giotto.

Other past missions that have flown by a comet a NASA's ICE mission in 1985,
the two Russian Vega spacecraft and the two Japanese spacecraft Suisei and
Sakigake that were part of the armada that visited Comet Halley in 1986; NASA's
Deep Space 1 flew by Comet Borelly in 2001 and NASA's Stardust, which flew by
Comet Wild 2 earlier this month and has captured samples of the comet's coma to
be returned in 2006. Unfortunately NASA's Contour launched in summer 2002 failed
when it was inserted into its interplanetary trajectory. Later this year we
shall also see the launch of Deep Impact, a spacecraft that will shoot a massive
block of copper into a comet's nucleus.

For more information please contact:

ESA - Communication Department
Media Relations Service
Tel: +33(0)1 53 69 7155
Fax: +33(0)1 53 69 7690

About Rosetta

* Rosetta
http://www.esa.int/SPECIALS/Rosetta/index.html
* Rosetta at a glance
http://www.esa.int/SPECIALS/Rosetta/SEMYMF374OD_0.html

Related links

* ESA Science
http://www.esa.int/esaSC/index.html
* DLR
http://www.dlr.de
* Astrium
http://www.astrium-space.com

IMAGE CAPTIONS:

[Image 1:
http://www.esa.int/export/esaCP/SEMX..._index_1.html]
Rosetta's 11-year expedition will begin in February 2004, with an Ariane-5
launch from Kourou in French Guiana. The three-tonne spacecraft will first be
inserted into a parking orbit around Earth, before being sent on its way towards
the outer Solar System.

Rosetta will be the first spacecraft to orbit a comet's nucleus.

Credits: ESA/AOES Medialab

[Image 2:
http://www.esa.int/export/esaCP/SEMX...html#subhead1]
Deep space hibernation to comet rendezvous (July 2011 - January 2014): after a
large deep-space manoeuvre, the spacecraft goes into hibernation. During this
period, Rosetta records its maximum distances from the Sun (about 800 million
kilometres) and Earth (about 1 thousand million kilometres). The spacecraft is
reactivated prior to the comet-rendezvous manoeuvre, during which the thrusters
fire for several hours to slow the relative drift rate of the spacecraft and
comet to about 25 metres per second.

Credits: ESA/AOES Medialab

[Image 3:
http://www.esa.int/export/esaCP/SEMX...html#subhead2]
Image of Comet 67P/Churyumov-Gerasimenko.

Our tiny corner of the Universe -- the Solar System -- is home to one star, nine
planets and dozens of planetary satellites. It also contains millions of
asteroids and comets -- the left-over debris from the cosmic construction site
that created the planets and their moons. Rosetta's task is to study these
primitive building blocks at close quarters so that scientists may gain new
insights into the events that took place 4600 million years ago, during the
birth of the Earth and its planetary neighbours.

Credits: ESA and European Southern Observatory

[Image 4:
http://www.esa.int/export/esaCP/SEMX...html#subhead3]
The Orbiter's scientific payload includes 11 experiments, in addition to the
Lander. Scientific consortia from institutes across Europe and the United States
have provided these state-of-the-art instruments. All of them are located on the
side of the spacecraft that will permanently face the comet during the main
scientific phase of the mission.

Credits: ESA/AOES Medialab

[Image 5:
http://www.esa.int/export/esaCP/SEMX...html#subhead5]
The picture shows the Rosetta in preparation for thermal testing in the Large
Space Simulator at ESA's ESTEC facility, The Netherlands.

Credits: ESA/A.Van Der Geest