[meteorite-list] Venus Express Gets Ready To Take The Plunge

[Ron Baalke]

http://www.esa.int/Our_Activities/Space_Science/Venus_Express/Venus_Express_gets_ready_to_take_the_plunge

Venus Express Gets Ready To Take The Plunge
European Space Agency
16 May 2014

After eight years in orbit, ESA's Venus Express has completed routine 
science observations and is preparing for a daring plunge into the planet's 
hostile atmosphere.

Venus Express was launched on a Soyuz-Fregat from the Russian Baikonur 
Cosmodrome in Kazakhstan on 9 November 2005, and arrived at Venus on 11 
April 2006.

It has been orbiting Venus in an elliptical 24-hour loop that takes it 
from a distant 66 000 km over the south pole - affording incredible 
global views - to an altitude of around 250 km above the surface at 
the north pole, close to the top of the planet's atmosphere.

With a suite of seven instruments, the spacecraft has provided a comprehensive 
study of the ionosphere, atmosphere and surface of Venus.

"Venus Express has taught us just how variable the planet is on all 
timescales and, furthermore, has given us clues as to how it might have 
changed since its formation 4.6 billion years ago," says Hakan Svedhem, 
ESA's project scientist.

"This information is helping us decipher how Earth and Venus came to 
lead such dramatically different lives, but we've also noticed that 
there are some fundamental similarities."

Venus has a surface temperature of over 450°C, far hotter than a normal 
kitchen oven, and an extremely dense, choking mixture of noxious gases 
for an atmosphere. But from the mission's infrared survey of the chemical 
composition of the rocky surface, we have learned that Venus might have 
once had a plate tectonics system like Earth, and even an ocean of water.

Just like Earth, Venus is losing parts of its upper atmosphere to space 
and Venus Express measured twice as many hydrogen atoms escaping out of 
the atmosphere than oxygen. Because water is made of two hydrogen atoms 
and one oxygen atom, the observed escape indicates that water is being 
broken up in the atmosphere. 

Today, the total amount of water on Earth is 100 000 times that on Venus. 
But because the two planets are about the same size and formed at the 
same time, both may have had similar amounts of the precious liquid in 
their early years.

Meanwhile, the spacecraft's cameras have tracked thousands of features 
in the cloud tops some 70 km above the planet's surface, including an 
enormous swirling vortex at the planet's south pole that shares similarities 
with hurricanes on Earth. The spacecraft also recorded bursts of lightning 
- identified by their electromagnetic signature - generated in clouds 
of sulphuric acid.

Is Venus volcanically active?

Studies of the planet's "super-rotating" atmosphere - it whips 
around the planet in just four Earth-days, much faster than the 243 days 
the planet takes to complete one rotation about its axis - also turned 
up some intriguing surprises. In one study, average wind speeds were found 
to have increased from roughly 300 km/h to 400 km/h over a period of six 
Earth years.

Conversely, a separate study found that the rotation of the planet had 
slowed by 6.5 minutes since NASA's Magellan, which completed its 5-year 
mission at Venus 20 years ago, measured it.

However, it remains unknown if there is a relationship between the increasing 
wind speeds and the slowing rotation.

Magellan's radar survey of the planet revealed that its surface was 
heavily altered in the past by a large number of volcanoes. But Venus 
Express has provided tantalising hints that the planet may well be still 
geologically active today. One study found numerous lava flows that must 
have been created no more than 2.5 million years ago, just yesterday on 
geological timescales, and perhaps much more recently.

Indeed, measurements of sulphur dioxide in the upper atmosphere have shown 
large variations over the course of the mission. Although peculiarities 
in the atmospheric circulation may produce a similar result, it is the 
most convincing argument to date of present-day active volcanism.
Venus Express aerobraking

Now, after eight years in orbit, the fuel supplies necessary to maintain 
the elliptical orbit are running low and will soon be exhausted. Thus, 
routine science operations concluded this week, and the spacecraft is 
being prepared for one final mission: to make a controlled plunge deeper 
into the atmosphere than ever before attempted.

"We have performed previous short "aerodrag" campaigns where we've 
skimmed the thin upper layers of the atmosphere at about 165 km, but we 
want to go deeper, perhaps as deep as 130 km, maybe even lower," says 
Patrick Martin, Venus Express mission manager.

"It is only by carrying out daring operations like these that we can 
gain new insights, not only about usually inaccessible regions of the 
planet's atmosphere, but also how the spacecraft and its components 
respond to such a hostile environment.

This "experimental aerobraking" phase is planned for 18 June - 11 
July, during which time some limited science measurements with the spacecraft's 
magnetic field, solar wind and atom analysing instruments will be possible. 
Also, temperature and pressure sensors will record the conditions that 
the spacecraft is experiencing.

"The campaign also provides the opportunity to develop and practise 
the critical operations techniques required for aerobraking, an experience 
that will be precious for the preparation of future planetary missions 
that may require it operationally," says Paolo Ferri, head of mission 
operations.

Aerobraking can be used as a way of getting into orbit around planets 
without having to carry quite so much fuel, thus reducing the launch mass.

It is possible that the remaining fuel in Venus Express will be exhausted 
during this phase or that the spacecraft does not survive these risky 
operations. But if the spacecraft is still healthy afterwards, its orbit 
will be raised again and limited operations will continue for several 
more months, fuel permitting.

However, by the end of the year, it is likely that Venus Express will 
have made its final descent into the atmosphere of the planet, bringing 
a fantastic scientific endeavour to an end.

"Venus Express has penetrated deeper into the mysteries of this veiled 
planet than anyone ever dreamed, and will no doubt continue to surprise 
us down to the last minute," adds Hakan.

Prior to and during the aerobraking campaign, short updates will be published 
via @esaoperations and/or the Rocket Science blog whenever they are available. 
A final report will be published on the ESA Portal soon after the aerobraking 
campaign.

In depth

Eight mission highlights for eight years in orbit - read more about 
these key mission discoveries:

Shape-shifting polar vortices
Recent volcanism?
Spinning Venus is slowing down
Super-rotation is speeding up
Snow on Venus?
Ozone layer
Water loss
A magnetic surprise

Markus Bauer 
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799 
Mob: +31 61 594 3 954 
Email: markus.bauer at esa.int

Hakan Svedhem 
ESA Venus Express project scientist 
Email: hakan.svedhem at esa.int

Patrick Martin
ESA Venus Express mission manager
Email: pmartin at sciops.esa.int

Paolo Ferri
Head of ESA mission operations 
Email: paolo.ferri at esa.int