[meteorite-list] Venus Express Rises Again

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 11 Jul 2014 14:43:21 -0700 (PDT)
Message-ID: <201407112143.s6BLhLZe029775_at_zagami.jpl.nasa.gov>

http://sci.esa.int/venus-express/54340-venus-express-rises-again/

Venus Express rises again
European Space Agency
11 July 2014

After a month surfing in and out of the atmosphere of Venus down
to just 130 km from the planet's surface, ESA's Venus Express is
about to embark on a 15 day climb up to the lofty heights of 460 km.

Since its arrival at Venus in 2006, the spacecraft has been
conducting science observations from an elliptical 24-hour orbit
that took it from a distant 66 000 km over the south pole -
affording incredible global views - to altitudes around 250 km at
the north pole, just above the top of the planet's atmosphere.

After eight years in orbit and with fuel for its propulsion system
running low, a daring aerobraking campaign was planned as a final
assignment for Venus Express, during which it would dip
progressively lower into the atmosphere on its closest approaches
to the planet.

Thus routine science operations concluded on 15 May, and the
spacecraft's altitude was allowed to drop naturally from the
effect of gravity, culminating in a month 'surfing' between 131 km
and 135 km above the surface.

Additional small thruster burns were used to drop the spacecraft
to lower altitudes, reaching 130.2 km earlier this week. Tomorrow,
it is expected to dip to 129.1 km.

"We have explored uncharted territory, diving deeper into the
atmosphere than ever before," says Hakan Svedhem, ESA's Venus
Express project scientist.

"We've measured the effects of atmospheric drag on the
spacecraft, which will teach us how the density of the atmosphere
varies on local and global scales."

Indeed, the additional drag exerted by the denser atmosphere at
lower altitudes reduced the spacecraft's orbital period by more
than an hour.

Small changes in the spacecraft's acceleration were also recorded
due to variations in the atmospheric density along its orbital
path. Differences in acceleration were also noticed between the
day and night side of the planet.

The forces experienced by the spacecraft at different altitudes
equate to a difference in atmospheric density of about thousand
times between 165 km and 130 km, causing significantly increased
stress on the spacecraft.

Indeed, the Venus Express team monitored the rapid heating that
the spacecraft experienced as it skimmed through the upper reaches
of the atmosphere during each orbit at about 36 000 km/h.

"During several of the 100-second long passages through the
atmosphere, the solar panel temperature sensor reading increased
by over 100??C," describes Adam Williams, ESA's Venus Express
spacecraft operations manager.

"Analysing the spacecraft's response to such rapid heating will
be useful for planning future spacecraft systems and subsystem
design."

Commands have now been sent to the spacecraft ready to begin a
series of 15 manoeuvres that will raise the lowest part of the
orbit to about 460 km. These begin tomorrow and should be
completed by 26 July.

Once Venus Express reaches this higher altitude orbit it will be
allowed to decay naturally, eventually sinking into the atmosphere
by December, ending its mission.

However, it is possible that the remaining fuel will run out
during the thruster burns required to raise its orbit.

If this occurs, it will no longer be possible to communicate with
the craft and its orbit will once again decay.

"We have already gained valuable experience in operating a
spacecraft in these challenging conditions that will be important
for future missions that may require it. Once we have completed
the orbit raise, we look forward to processing and analysing the
scientific data collected on the atmosphere," says Patrick
Martin, ESA's Venus Express mission manager.

For updates during the orbital raising manoeuvres follow the
Rocket Science Blog <http://blogs.esa.int/rocketscience/> and
_at_esaoperations <https://twitter.com/esaoperations> on Twitter.


Notes for Editors

The recorded atmospheric density at an altitude of 165 km was
10^-11 kg/m^3 and at 130 km it was 10^-8 kg/m^3 . While these
values may seem small - atmospheric density at Earth's sea level
is 1 kg/m^3 - the density is a thousand times greater at the
lowest altitudes.

On Monday 7 July, Venus Express completed 3000 orbits around Venus.


For more information, please contact

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

Adam Williams
ESA Venus Express spacecraft operations manager
Email: Adam.Williams at esa.int

Patrick Martin
ESA Venus Express mission manager
Email: pmartin at sciops.esa.int
Received on Fri 11 Jul 2014 05:43:21 PM PDT