Fwd: The flybys around Venus and the Earth provided a calibration opportunity for the instruments aboard Huygens and Cassini
tony...@myinternetuk.com
05 May 2000 16:25:26
sci.astro
From: ay...@nova.astro.utoronto.ca
Subject: The flybys around Venus and the Earth provided a calibration
opportunity for the
To: sci.astro
ESA Science News
http://sci.esa.int
04 May 2000
The flybys around Venus and the Earth provided a calibration
opportunity for
the instruments aboard Huygens and Cassini
A very successful session entitled "The Jovian and Saturnian systems:
surfaces and atmospheres -- The Cassini/Huygens mission to Saturn and
Titan" took place from 28 to 29 April, as part of 2000 Assembly of the
European Geophysics Society in Nice. The audience included mission
scientists and their collaborators, who shared the same feelings that
the swingbys around Venus and the Earth had not only allowed an unique
opportunity for calibration operations, but had also been bringing a
considerable amount of science data.
"The Huygens Probe has just landed at Nice airport!" With this
announcement
J.-P. Lebreton, Huygens Project Scientist, opened a very successful
session
on "The Jovian and Saturn systems" which took place as part of XXV
General
Assembly of the European Geophysics Society, held in Nice last week.
In
fact, the actual Probe is still on its cruise toward Saturn and Titan
aboard the Cassini Orbiter, but for this special occasion a joint
effort
by ESA and ALCATEL from Cannes, France, had enabled the display of a
full-scale model of the ESA's Huygens probe at the international
airport
of the Cote Azur.
The session was convened by J-P Lebreton (ESA) and co-convened by D.
Matson
(JPL) and covered many topics regarding surfaces and atmospheres of
the
Jovian and Saturnian systems. A general review of the most recent data
from Cassini/Huygens mission was also presented, as well as future
perspectives for Titan exploration. Two-day oral presentations were
followed by a very lively poster session, which concluded a well
attended
gathering.
Dennis Matson, the Cassini Project Scientist, gave the opening talk,
in
which he pointed out the great event, scheduled for the end of this
year
(30 December), when for the first time two spacecraft, namely Cassini
and
Galileo, will simultaneously observe Jupiter. An unique stereoscopic
study
of the Jovian atmosphere, ionosphere and magnetosphere will be
performed,
also covering the morphology, geology and magnetic field nature of
various
Jupiter's Moon. HST and some terrestrial telescopes will also perform
simultaneous observations. The great planet will be the special guest
at
the New Year's day party which many scientists will be celebrating in
laboratories and mission control centres.
Many papers dealt with the scientific data that have already been
obtained
during the swingbys of Venus and Earth. Mission scientists and their
collaborators shared the same feelings that the two swingbys allowed
an unique opportunity for calibration operations. Without the swingby
opportunity, a considerable amount of time orbiting Saturn and Titan
would have had to be spent, in calibrating all the instruments.
During the poster session included presentations on calibration
results for
the Huygens Atmospheric Structure Instrument (HASI), the main
instrument
aboard the Huygens Probe, obtained during the periodical checkouts
since
its launch in October 1997. The zero-gravity data from the cruise
phase
is of particular interest for an assessment of the errors that
occurred in
accelerometer output. The cruise checkouts have therefore made it
possible
to estimate uncertainties in HASI accelerometers and this will be very
useful during the mission phase.
One of the main issues to be examined was the investigation of
lightning
on Titan, namely the sudden high-current discharge caused by
atmosphere's
electrical breakdown, which occurs in regions of strong vertical
atmospheric
convection, very common on the Earth. During the Voyager flyby of
Titan,
no terrestrial-like lightning discharges were observed, whether
because
lightning flashes occur only locally or because the discharges may
release
energies below the Voyager detection threshold. However this lack of
evidence does not rule out its existence. The Cassini radio and plasma
wave
science instrument (RPWS) onboard the Orbiter and HASI (Huygens
Atmospheric
Structure Instrument) onboard the Probe have to investigate more
precisely
the existence of lightning and, eventually, to determine the
geographical
areas where the probability of lightning generation is higher.
Meanwhile
models and predictions have been developed, some of them were also
discussed
in Nice. Lightning on Titan should be a local phenomenon which occurs
only
near the sub polar point, where the energy input is large. This means
that
Cassini would have no chance to detect Earth-like lightning signals
via
nighttime flybys. An important contribution came from the observations
performed by RPWS during the two Venus flybys, which showed no
evidence of
lightning signals. Due to the very good sensitivity of the
observations,
there are strong constraints on possible Venusian lightning, at least
like
those on Earth, due to the absence of strong vertical convection in
the
dense atmosphere.
Many among scientists convened in Nice are gathering again this week
in
Padua where the HSWT is meeting for the annual session, in order to
review
the 5th checkout results and to prepare next checkout test, scheduled
for
September this year. There will also be discussion about latest
science
features related to the mission and assessment of the payload's
performance.
IMAGE CAPTIONS:
[Image 1:
http://sci.esa.int/content/image/index.cfm?aid=12&cid=35&oid=18635&objecttypename=news&ooid=18630]
Denis Matson Cassini Project manager during his presentation.
[Image 2:
http://sci.esa.int/content/image/index.cfm?aid=12&cid=35&oid=18640&objecttypename=news&ooid=18630]
Jean-Pierre Lebreton & Denis Matson.
[Image 3:
http://sci.esa.int/content/image/index.cfm?aid=12&cid=35&oid=18641&objecttypename=news&ooid=18630]
Huygens model at Nice airport.
--
Andrew Yee
ay...@nova.astro.utoronto.ca
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