ESA Venus Express climbs to new orbit post aerobraking

Venus Express aerobraking. 

Credit: ESA - C. Carreau

ESA's Venus Express spacecraft has climbed to a new orbit following its daring aerobraking experiment, and will now resume observations of this fascinating planet for at least a few more months.

The orbit-raising followed a month of aerobraking that saw the spacecraft surf in and out of the atmosphere at altitudes typically between 131 km and 135 km for a couple of minutes on each of its closest approaches to the planet.

Before, normal operations involved an elliptical orbit every 24 hours that took Venus Express from 66 000 km over the south pole down to around 250 km at the north pole, just above the top of the atmosphere.

But, after eight years and with propellant running low, the Venus Express team began a daring aerobraking campaign, dipping the craft progressively lower into the atmosphere on its closest approaches.

The experiment directly explored previously uncharted regions of the atmosphere, while also providing information on how a spacecraft responds when encountering the tenuous upper reaches of an atmosphere at high speed.

Aerobraking can be used to reduce the speed of a spacecraft approaching a planet or moon with an atmosphere, allowing it to be captured into orbit, and to move from an elliptical orbit to a more circular one.

Less fuel has to be carried, yielding benefits all round.

The technique will be used on future missions and the Venus Express experiments will help guide their design.

"We have collected valuable data on the Venusian atmosphere in a region difficult to characterise by other means," says Håkan Svedhem, ESA's Venus Express project scientist.

"The results show that the atmosphere seems to be more variable than previously thought for this altitude range, but further analysis will be needed in order to explain these variations properly."

Between altitudes of 165 km and 130 km, the atmospheric density increases by a factor of roughly a thousand, meaning that the forces and stress encountered by Venus Express were much higher than during normal operations.

It also experienced extreme heating cycles, with temperatures rising by over 100°C during several 100 second-long passages through the atmosphere.

In addition, the atmospheric drag at these lower altitudes was so great that the spacecraft's orbital period was reduced by more than an hour.



The Venusian cloud tops during nearly a full orbit of ESA’s Venus Express around the planet. 

The inset shows the corresponding position and relative speed of Venus Express as it approaches from its furthest distance of 66 000 km above the south pole, swooping down to 250 km above the north pole.

The images were captured by the Venus Monitoring Camera on 7–8 January 2012 and are shown in false colour.

Credit: ESA Venus Express

"The spacecraft has proven to be very robust and has apparently experienced no substantial degradation in any area, but a detailed evaluation is still to take place," says Joerg Fischer, Venus Express operations engineer.

At the end of the campaign, 15 thruster burns raised the craft's altitude, preventing it from dropping into the atmosphere.

The last was executed on Thursday evening, boosting Venus Express to a new altitude of 460 km at its closest and 63 000 km at its furthest. This new orbit takes 22 hours 24 minutes to complete.

"During the 15 manoeuvres, each thruster fired more than 8000 pulses and burned a total of about 5.2 kg of propellant to raise the spacecraft to this new altitude," adds Joerg.

This orbit will slowly decay again under gravity, but with only a few kilograms of fuel at most now remaining further altitude-raising manoeuvres may not be possible.

If no further corrections are made, Venus Express will probably reenter the atmosphere again in December, but this time for good, ending the mission.

In the meantime, having survived not only the aerobraking experiment but also the most recent orbit-raising manoeuvres, all of the science experiments will be reactivated, continuing their detailed study of Venus for at least a few more months.

"We are delighted with the success of the experimental aerobraking campaign, and are looking forward to assessing the details over the coming months," says Patrick Martin, mission manager.

"Meanwhile, we are enjoying the view from our new orbit around Venus, and plan to continue augmenting the scientific return of this exciting mission."

ESA Space Weather reports for Venus

This image is part of the Venus space weather report issued 5 June 2014.

During May-August 2014, ground controllers flying ESA's Venus Express will receive daily reports on solar activity issued by experts at ESA’s Space Weather Coordination Centre (SSCC), at the Space Pole in Belgium.

Credit: ESA

The weather updates will deliver the best information from a variety of sources, including ESA’s Proba-2 and solar-orbiting ESA and NASA spacecraft, to the control team as rapidly as possible.

For the first time, ESA is providing regular space-weather reports for a spacecraft orbiting another planet.

When your spacecraft is surfing deep into the atmosphere of an alien world, you need the latest information on conditions that could affect your trajectory.

If that planet is Venus, that means knowing what’s happening on our Sun in real time, because solar activity can greatly influence conditions like atmospheric density and the radiation environment at Earth’s closest neighbour.

Since May, ground controllers flying Venus Express have been receiving daily reports on solar activity issued by experts at ESA’s Space Weather Coordination Centre (SSCC), at the Space Pole in Belgium.

Surfing the Venus atmosphere 
The centre was established by the Agency’s Space Situational Awareness (SSA) programme office, and it began delivering precursor space-weather services for terrestrial clients in last year.

Now that Venus Express has completed its eight-year scientific mission, the reports are especially important as the control team take the satellite through an extraordinary multi-week ‘aerobraking’ campaign.

Artistic vision of Venus Express during the aerobraking manoeuvre, which will see the spacecraft orbiting Venus at an altitude of around 130 km from 18 June to 11 July. 

In the month before, the altitude will gradually be reduced from around 200 km to 130 km. 

If the spacecraft survives and fuel permits, the elevation of the orbit will be raised back up to approximately 450 km, allowing operations to continue for a further few months. 

Eventually, however, the spacecraft will plunge back into the atmosphere and the mission will end.

“Aerobraking means lowering the spacecraft so that for part of each orbit it dips down very low and skims through the very uppermost reaches of the Venusian atmosphere,” notes Adam Williams, Deputy Spacecraft Operations Manager.

“We know that the current state of our Sun can affect Venus’ atmosphere, which could in turn impact the planned orbit of Venus Express as it passes through the atmosphere.”

Adam says that the team do not expect to replan any of the aerobraking orbits based on ‘typical’ solar activity levels.

“The space weather reports will, however, allow us to better understand anomalous behaviour that we may subsequently observe on the spacecraft.

“And in extreme cases, we would be more ready to react to a serious situation. For example, if our startrackers were to be overloaded by radiation.”

ESA Venus express prepared for Daring Dive into Venus' Atmosphere - Video

A European spacecraft will plunge into Venus' thick atmosphere next month in a bold maneuver that may bring its lengthy and productive mission to a dramatic end.

The European Space Agency (ESA) Venus Express probe, which has been circling Earth's hellishly hot "sister planet" for eight years, is running low on fuel.

So mission officials wrapped up routine science operations this week to begin preparing Venus Express for a deep dive into the planet's fast-swirling air.

"We have performed previous short 'aerodrag' campaigns where we've skimmed the thin upper layers of the atmosphere at about 165 kilometers [103 miles], but we want to go deeper, perhaps as deep as 130 kilometers [81 miles], maybe even lower," Venus Express mission manager Patrick Martin said in a statement.

Visualization of Venus Express during the aerobraking maneuver, which will see the spacecraft orbiting Venus at an altitude of around 130 km from 18 June to 11 July. 

If the spacecraft survives and fuel permits, it will be raised back up to approximately 450 km, allowing operations to continue for a few more months. 

Eventually, however, the spacecraft will plunge back into the atmosphere and the mission will end.

Credit: ESA–C. Carreau

"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," Martin added.

Venus Express will take temperature and pressure measurements and gather other science data during the dive, which is scheduled to take place from June 18 through July 11. But mission officials expect the "aerobraking" maneuver will have other benefits as well.

"The campaign also provides the opportunity to develop and practice 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," Paolo Ferri, head of mission operations for Venus Express, said in a statement.