Venus Express took a plunge into the Venus atmosphere
17 July 2014 - Since its arrival at Venus in 2006, VEX has been conducting science observations from an elliptical 24-hour orbit that took it from a distant 66 000 km over the south pole (apoapsis) to altitudes around 250 km at the north pole (periapsis), just above the top of the planet’s atmosphere.
After eight years in orbit, a daring aerobraking campaign took place as a final assignment for Venus Express, during which it dipped progressively lower into the atmosphere on its closest approaches to the planet.
On 15 May 2014 routine science operations were concluded and the spacecraft’s altitude was allowed to drop naturally from the effect of gravity, ‘surfing’ between 131 km and 135 km above the surface. Additional small thruster burns were used to drop the spacecraft to even lower altitudes, reaching 129.1 km on July 12 at the periapsis.
The effects of atmospheric drag on the spacecraft were measured, which will teach us how the density of the atmosphere varies on local and global scales. The additional drag exerted by the denser atmosphere at lower altitudes reduced the spacecraft’s orbital period by more than an hour.
The forces experienced by the spacecraft at different altitudes equate to a difference in atmospheric density of about thousand times between 165 km (10-11 kg/m3) and 130 km (10-8 kg/m3), causing significantly increased stress on the spacecraft. Indeed, the spacecraft experienced a rapid heating as it skimmed through 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 increased by almost 100°C.
Commands have now been sent to the spacecraft to begin a series of 15 manoeuvres, planned between July 12 and July 25, which will raise the periapsis to about 460 km. Once Venus Express reaches this higher altitude orbit, the latter will not be corrected anymore and will naturally decay, until the spacecraft eventually sinks into the atmosphere by December, ending its mission.