Venus Express En Route to Probe the Planet's Hidden Mysteries

http://www.esa.int/SPECIALS/Venus_Ex...6Q638FE_0.html

Venus Express en route to probe the planet's hidden mysteries
European Space Agency
9 November 2005

ESA PR 50-2005. The European spacecraft Venus Express has been
successfully placed into a trajectory that will take it on its journey
from Earth towards its destination of the planet Venus, which it will
reach next April.

A virtual twin sister of the Mars Express spacecraft which has been
orbiting the Red Planet since December 2003, Venus Express is the
second
planet-bound probe to be launched by the European Space Agency.

Venus Express will eventually manoeuvre itself into orbit around Venus
in order to perform a detailed study of the structure, chemistry and
dynamics of the planet's atmosphere, which is characterised by
extremely
high temperatures, very high atmospheric pressure, a huge 'greenhouse
effect' and as-yet inexplicable 'super-rotation' which means that it
speeds around the planet in just four days.

The European spacecraft will also be the first orbiter to probe the
planet's surface while exploiting the 'visibility windows' recently
discovered in the infrared waveband.

The 1240 kg mass spacecraft was developed for ESA by a European
industrial team led by EADS Astrium with 25 main contractors spread
across 14 countries. It lifted off on board a Soyuz- Fregat rocket, the
launch service being provided by Starsem.

The lift-off from the Baikonur Cosmodrome in Kazahkstan this morning
took place at 09:33 local time (04:33 Central European Time).

Initial Fregat upper-stage ignition took place nine minutes into the
flight, manoeuvring the spacecraft into a low-earth parking orbit. A
second firing, one hour and 22 minutes later, boosted the spacecraft to
pursue its interplanetary trajectory.

Contact with Venus Express was established by ESA's European Space
Operations Centre (ESOC) at Darmstadt, Germany approximately two hours
after lift-off. The spacecraft has correctly oriented itself in
relation
to the sun and has deployed its solar arrays.

All on-board systems are operating perfectly and the orbiter is
communicating with the Earth via its low-gain antenna. In three days'
time, it will establish communications using its high-gain antenna.

Full speed ahead for Venus

Venus Express is currently distancing itself from Earth at full speed,
heading on its five-month, 350 million kilometre journey inside our
Solar System. After check-outs to ensure that its on-board equipment
and
instrument payload are in proper working order, the spacecraft will be
'mothballed', with contact with Earth being reduced to once daily. If
needed, trajectory correction manoeuvres can go ahead at the half-way
stage in January.

When making its closest approach, Venus Express will face far tougher
conditions than those encountered by Mars Express on nearing the Red
Planet. For while Venus's size is indeed similar to that of Earth, its
mass is 7.6 times that of Mars, with gravitational attraction to match.

To resist this greater gravitational pull, the spacecraft will have to
ignite its main engine for 53 minutes in order to achieve 1.3 km/second
deceleration and place itself into a highly elliptical orbit around the
planet. Most of its 570 kg of propellant will be used for this
manoeuvre.

A second engine firing will be necessary in order to reach final
operational orbit: a polar elliptical orbit with 12-hour crossings.
This
will enable the probe to make approaches to within 250 km of the
planet's surface and withdraw to distances of up to 66 000 km, so as to
carry out close-up observations and also get an overall perspective.

Exploring other planets to better understand planet Earth

"The launch of Venus Express is a further illustration of Europe's
determination to study the various bodies in our solar system,"
stressed
Professor David Southwood, the Director of ESA's science programmes.

"We started in 2003 with the launch of Mars Express to the Red Planet
and SMART-1 to the Moon and both these missions have amply exceeded our
expectations. Venus Express marks a further step forward, with a view
to
eventually rounding off our initial overview of our immediate planetary
neighbours with the BepiColombo mission to Mercury to be launched in
2013."

"With Venus Express, we fully intend to demonstrate yet again that
studying the planets is of vital importance for life here on Earth,"
said Jean Jacques Dordain, ESA Director General.

"To understand climate change on Earth and all the contributing
factors,
we cannot make do with solely observing our own planet. We need to
decipher the mechanics of the planetary atmosphere in general terms.
With Mars Express, we are studying the Martian atmosphere. With
Huygens,
we have explored that of Saturn's satellite Titan.

"And now with Venus Express, we are going to add a further specimen to
our collection. Originally, Venus and the Earth must have been very
similar planets. So we really do need to understand why and how they
eventually diverged to the point that one became a cradle for life
while
the other developed into a hostile environment."

The Venus Express mission is planned to last at least two Venusian days
(486 Earth days) and may be extended, depending on the spacecraft's
operational state of health.

Twin sister of Mars Express

Venus Express largely re-uses the architecture developed for Mars
Express. This has reduced manufacturing cycles and halved the mission
cost, while still targeting the same scientific goals. Finally approved
in late 2002, Venus Express was thereby developed fast, indeed in
record
time, to be ready for its 2005 launch window.

However, Venusian environmental conditions are very different to those
encountered around Mars. Solar flux is four times higher and it has
been
necessary to adapt the spacecraft design to this hotter environment,
notably by entirely redesigning the thermal insulation.

Whereas Mars Express sought to retain heat to enable its electronics to
function properly, Venus Express will in contrast be aiming for maximum
heat dissipation in order to stay cool.

The solar arrays on Venus Express have been completely redesigned. They
are shorter and are interspersed with aluminium strips to help reject
some solar flux to protect the spacecraft from temperatures topping
250?C.

It has even been necessary to protect the rear of the solar arrays -
which normally remain in shadow - in order to counter heat from solar
radiation reflected by the planet's atmosphere.

An atmosphere of mystery

Following on from the twenty or so American and Soviet missions to the
planet carried out since 1962, Venus Express will endeavour to answer
many of the questions raised by previous missions but so far left
unanswered.

It will focus on the characteristics of the atmosphere, its
circulation,
structure and composition in relation to altitude, and its interactions
with the planet's surface and with the solar wind at altitude.

To perform these studies, it has seven instruments on board: three are
flight-spare units of instruments already flown on Mars Express, two
are
from comet-chaser Rosetta and two were designed specifically for this
mission.

The PFS high-resolution spectrometer will measure atmospheric
temperature and composition at varying altitudes. It will also measure
surface temperature and search for signs of current volcanic activity.

The SPICAV/SOIR infrared and ultraviolet spectrometer and the VeRa
instrument will also probe the atmosphere, observing stellar
occultation
and detecting radio signals; the former will in particular seek to
detect molecules of water, oxygen and sulphuric compounds thought to be
present in the atmosphere.

The VIRTIS spectrometer will map the various layers of the atmosphere
and conduct multi-wavelength cloud observation in order to provide
images of atmospheric dynamics.

Assisted by a magnetometer, the ASPERA 4 instrument will analyse
interaction between the upper atmosphere and the solar wind in the
absence of magnetospheric protection such as that surrounding Earth
(for
Venus had no magnetic field). It will analyse the plasma generated by
such interaction, while the magnetometer will study the magnetic field
generated by the plasma.

The VMC camera will monitor the planet in four wavelengths, notably
exploiting one of the 'infrared windows' revealed in 1990 by the
Galileo
spacecraft (when flying by Venus en route for Jupiter), making it
possible to penetrate cloud cover through to the surface. The camera
will also be used to monitor atmospheric dynamics, notably to observe
the double atmospheric vortex at the poles, the origin of which still
remains a mystery.

For further information, please contact:

ESA Media Relations Division
Tel +33 (0)1 53 69 71 55
Fax +33 (0)1 53 69 76 90