[meteorite-list] Rosetta - A Space Sophisticate

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:31:23 2004
Message-ID: <200402171820.KAA29075_at_zagami.jpl.nasa.gov>

Paris, 16 February 2004
European Space Agency
Information Note
N° 04-2004

ROSETTA N° 2

Hi-tech in space - Rosetta - a space sophisticate

The European Space Agency's Rosetta mission will be getting under way in
February 2004. The Rosetta spacecraft will be pairing up with Comet
67P/Churyumov-Gerasimenko and accompanying it on its journey,
investigating the comet's composition and the dynamic processes at work as
it flies sunwards. The spacecraft will even deposit a lander on the comet.
"This will be our first direct contact with the surface of a comet," said
Dr Manfred Warhaut, Operations Manager for the Rosetta mission at ESA's
European Space Operations Centre (ESOC) in Darmstadt, Germany.

The trip is certainly not short: Rosetta will need ten years just to reach
the comet. This places extreme demands on its hardware; when the probe
meets up with the comet, all instruments must be fully operational,
especially since it will have been in "hibernation" for 2 and a half years
of its journey. During this "big sleep", all systems, scientific
instruments included, are turned off. Only the on-board computer remains
active.
 
Twelve cubic metres of technical wizardry

Rosetta's hardware fits into a sort of aluminium box measuring just 12
cubic metres. The scientific payload is mounted in the upper part, while
the subsystems - on-board computer, transmitter and propulsion system -
are housed below. The lander is fixed to the opposite side
of the probe from the steerable antenna. As the spacecraft orbits the
comet, the scientific instruments will at all times be pointed towards its
surface; the antenna and solar panels will point towards the Earth and Sun
respectively.

For trajectory and attitude control and for the major braking maneuvres,
Rosetta is equipped with 24 thrusters each delivering 10 N. That
corresponds to the force needed here on Earth to hold a bag containing 10
apples. Rosetta sets off with 1650 kg of propellant on board, accounting
for more than half its mass at lift-off.

Just 20% of total mass is available for scientific purposes. So when
developing the research instruments the same rule applied as for
supermodels: make every gram count. The calculation seems to have worked
out right: the main probe will be carrying 11 scientific instruments and
the Rosetta lander a further ten. They will analyse the composition and
structure of the comet's nucleus and study its interaction with the solar
wind and the interplanetary plasma.

Rosetta - unplugged

"To provide the probe with the power it needs in space, we have given it
the biggest solar panels ever carried by a European satellite," Manfred
Warhaut explained. "These cells are its only source of electricity." They
span 32 metres tip to tip while, at 64 m2 the surface area is comparable
to that of a two-bedroom flat. The panels may be rotated through 180° to
catch the maximum amount of sunlight.

These dimensions are also essential because when Rosetta meets
Churyumov-Gerasimenko it will be 675 million kilometres away from the Sun.
At that distance solar radiation is very weak and the solar collectors
will supply only 440 W of power - compared with 8000 W towards the end of
the mission when the two companions come closest to the Sun (at some 150
million kilometres from our star distance). "The probe is also equipped
with a set of four 10-amp-hour batteries to maintain power supply while
Rosetta flies in the shadow of the comet."

Rosetta lander - standing on its own three legs

The Rosetta lander is another of the mission's technical highlights. Using
its scientific instruments, its job will be to investigate the comet's
surface on location. Thanks to a mechanical arm, the lander will operate
in a two-metre radius. The soft landing is a particular problem given the
extremely weak gravitational force exerted by the very small comet
nucleus; the lander, weighing in at 100 kg on Earth, will on the comet be
as light as a sheet of paper . If there were the slightest recoil, it
would bounce back uncontrollably like a rubber ball. To make sure this
doesn't happen, the lander's three legs are equipped with special
shock-absorbers which take up most of the kinetic energy. The legs are
also fitted with ice pitons; these bore into the ground immediately on
touchdown.

At the same moment, the lander fires a harpoon to anchor it to the ground
- an opportunity also to investigate the mechanical properties of the
surface. "If everything goes according to plan, the mission results could
well fundamentally expand our knowledge of comets, just as the Rosetta
Stone, after which the probe is named, helped unravel the mystery of
Egyptian hieroglyphics," said Manfred Warhaut.

For further information on Rosetta and ESA projects, please consult our
portal at: http://www.esa.int/science or directly at
http://www.esa.int/rosetta

For further information, please contact :
ESA, Media Relations Service
Tel: +33(0)1.53.69.7155
Fax: +33(0)1.53.69.7690
Received on Tue 17 Feb 2004 01:20:09 PM PST