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(meteorobs) Excerpt from "CCNet 85/2001 - 10 July 2001"
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From: Peiser Benny <B.J.Peiser@livjm.acdot uk>
To: cambridge-conference <cambridge-conference@livjm.acdot uk>
Subject: CCNet 85/2001 - 10 July 2001
Date: Tue, 10 Jul 2001 10:25:17 +0100
CCNet 85/2001 - 10 July 2001
---------------------------
[...]
(2) ROSETTA'S CONSERT HEADS FOR A REAL COOL VENUE
Andrew Yee <ayee@nova.astro.utorontodot ca>
[...]
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(2) ROSETTA'S "CONSERT" HEADS FOR A REAL COOL VENUE
>From Andrew Yee <ayee@nova.astro.utorontodot ca>
ESA Science News
http://sci.esa.int
05 Jul 2001
What is a comet really like? What is its interior like? Could it be a fluffy
agglomeration of snow and dirt? Or perhaps it is solid all the way through
like an iceberg encrusted with black organic material? Some have even
likened it to a chocolate cake with a dark surface overlying a mixture of
porous and solid material! Identifying the nature of a comet is just one of
the key questions ESA's Rosetta mission is intended to answer, and the Comet
Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) instrument
on the Rosetta Orbiter and Lander will play a major role in revealing the
true nature of these cosmic wanderers.
CONSERT has already made its mark by becoming the first of the scientific
experiments that will fly on the Rosetta Orbiter to be delivered to Alenia
Spazio in Turin. The remainder of the comet chaser's state-of-the-art
payload will follow in the coming weeks, paving the way for the start of the
Orbiter's payload integration phase.
Sounding a comet with radar
CONSERT's mass is limited to only 3 kg, but there is nothing lightweight
about its mission to gently probe the interior of a comet -- something that
has never before been attempted.
The experiment, built in France and in Germany, will reveal the internal
structure of Comet Wirtanen's nucleus by using an ingenious radar sounding
technique. As the Rosetta Orbiter swings around the tiny ice world at a
distance of less than 30 km, a transmitter on board the spacecraft sends a
radio 'pulse' towards the comet nucleus at a frequency close to 90 MHz.
The Lander, which is sitting on the far side of the nucleus, behaves rather
like a mirror. It receives the signal after it has travelled through the icy
nucleus and transmits a new 'pulse' back towards the Orbiter. This
re-transmitted signal eventually arrives back at the Orbiter, where it is
compressed and stored for off-line scientific analysis.
Some 3000 of these measurements will be taken during each orbit of Comet
Wirtanen. By studying the time delays as the signals pass through the
nucleus from different directions, the scientists will be able to estimate
the dielectric constant of the materials inside the comet (a measure of its
ability to reflect the radio signals and their velocity). They will then be
able to determine the internal structure (if any) of the nucleus -- the
denser the material is, the slower the pulse passes through it.
So will it work?
The experiment's principal investigator, Professor Wlodek Kofman of the
Laboratoire de Planetologie (CNRS-UJF-OSUG) in Grenoble and also affiliated
with the Service d'Aeronomie (CNRS), France, has been studying this problem
for many years.
"Based on our current understanding of the composition of comets, we believe
that electromagnetic waves of the right frequency will pass right through
the nucleus," said Professor Kofman.
"Obviously, we have to try out the technique on Earth in order to see if it
works before we launch it towards a comet or planet," he said. "In 1993 we
actually went to Antarctica to carry out a radar experiment and we found
that we could successfully deduce the structure inside the ice."
"We were intending to fly a radar on the Russian Mars-98 mission in order to
measure the thickness of the Martian permafrost," he continued,
"Unfortunately, the mission was cancelled, so Rosetta will be our first
opportunity to fly an experiment in space."
"We have recently completed a successful test of the CONSERT Electrical
Qualification Models on the roofs of the University of Bochum," he said.
"The two antennae and mock-ups of the Lander and Orbiter were placed on two
different roofs so that we could characterise the radiation pattern of the
antennae with a minimum of interference from the ground and perform the
end-to-end test of the equipment," he explained.
"The 'Lander' was placed on one roof, about 80 metres away from the
'Orbiter', and we picked up the return signal loud and clear," said Kofman.
"When we are in orbit around Wirtanen, we should be able to detect large
structures or layers within the comet, and even recognise small-scale
irregularities," he added.
One of the great unknowns is the lifetime of the experiment, since its
success depends on the continued operation of the Rosetta Lander.
"The life of the Lander is expected to be quite short -- possibly only a few
days or weeks," explained Professor Kofman. "If the Lander survives for a
long time, we will carry out the experiment many times. Obviously, I would
like it to operate for many orbits!"
The CONSERT instrument was developed by three European institutes: the
Service d'Aironomie in Paris; the Laboratoire de Planitologie in Grenoble;
and the Max-Planck-Institut f|r Aeronomie in Lindau. Other contributions
have been made by the European Space Technology Centre (ESTEC) in the
Netherlands and the University of Bochum.
For further information contact:
Professor Wlodek Kofman
Laboratoire de Planitologie de Grenoble, France
Tel: +33 476 514152
E-mail: wlodek.kofman@obs.ujf-grenoble.fr
USEFUL LINKS FOR THIS STORY
* Rosetta home page
http://sci.esa.int/rosetta/
* Rosetta instruments
http://sci.esa.int/content/doc/e5/2277_.htm
IMAGE CAPTIONS:
[Image 1:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=1&cid=1&oid=2748
8&ooid=27694]
The Rosetta Orbiter swoops over the Lander soon after touchdown on the
nucleus of Comet 46P/Wirtanen. (Photo courtesy Astrium).
[Image 2:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=1&cid=1&oid=2748
8&ooid=27518]
The mock-up lander antenna during tests on the roof of the University of
Bochum.
[Image 3:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=1&cid=1&oid=2748
8&ooid=27519]
The mock-up orbiter antenna during tests on the roof of the University of
Bochum.
[Image 4:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=1&cid=1&oid=2748
8&ooid=27680]
Professor Wlodek Kofman, principal investigator of CONSERT. Laboratoire de
Planitologie de Grenoble, France.
[Image 5:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=1&cid=1&oid=2748
8&ooid=27684]
Radar tests at Dumont d'Urville, the French station in Antarctica, showed
that the CONSERT technique works.
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