Venus Express ends eight year mission
Sen—ESA’s Venus Express has finally ended its eight-year mission. The spacecraft exhausted its fuel during a series of thruster burns earlier this year and will now naturally sink deeper into the atmosphere over the coming weeks.
Since arriving at Venus in 2006, Venus Express has conducted a detailed study of the planet and its atmosphere.
With propellant for its propulsion system running low, the spacecraft was tasked in mid-2014 with a daring aerobraking campaign, during which it dipped progressively lower into the atmosphere on its closest approaches to the planet, allowing an exploration of previously uncharted regions of the atmosphere. This provided important information for future missions as aerobraking can be used to enter orbit around planets with atmospheres without having to carry quite so much propellant.
After ‘surfing’ in and out of the atmosphere the lowest point of the orbit was raised again and by 26 July it was back up to about 460 km. A decision was taken to correct the natural decay under gravity with a new series of raising manoeuvres during 23–30 November, in an attempt to prolong the mission into 2015.
However, as reported earlier by Sen, full contact with Venus Express was lost on 28 November. Since then links had been partially re-established, but they were very unstable and only limited information could be retrieved.
“The available information provides evidence of the spacecraft losing attitude control most likely due to thrust problems during the raising manoeuvres,” says Patrick Martin, ESA’s Venus Express mission manager.
Without propellant it is no longer possible to control the attitude and orient Venus Express towards Earth to maintain communications.
Artist’s impression of an active volcano on Venus. Image credit: ESA/AOES
One of the many highlights from the mission is the hint 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 and possibly even much less than that.
Measurements of sulphur dioxide in the upper atmosphere have shown large variations over the course of the mission. Although atmospheric circulation may produce a similar result, it is the most convincing argument to date of active volcanism.
A survey of the amount of hydrogen and deuterium in the atmosphere suggests that Venus once had a lot of water in the atmosphere, which is now mostly gone, and possibly even oceans of water like Earth’s.
Venus Express also measured twice as many hydrogen atoms escaping out of the atmosphere as oxygen atoms, indicating that water is being broken up in the atmosphere.
When studying the winds, by tracking clouds in images, average wind speeds were found to have increased from roughly 300 km/h to 400 km/h over a period of six Earth years.
A separate study found that the rotation of the planet had slowed by 6.5 minutes since NASA’s Magellan measured it 20 years ago.
“While we are sad that this mission is ended, we are nevertheless happy to reflect on the great success of Venus Express as part of ESA’s planetary science programme and are confident that its data will remain important legacy for quite some time to come,” says Martin Kessler, Head of ESA Science Operations.“The mission has continued for much longer than its planned lifetime and it will now soon go out in a blaze of glory.”