ESA’s Venus Express has ended its eight-year mission after far exceeding its planned life. The spacecraft exhausted its propellant during a series of thruster burns to raise its orbit following the low-altitude aerobraking earlier this year.
Since its arrival at Venus in 2006, Venus Express had been on an elliptical 24-hour orbit, travelling 66 000 km above the south pole at its furthest point and to within 200 km over the north pole on its closest approach, conducting a detailed study of the planet and its atmosphere.
However, after eight years in orbit and with propellant for its propulsion system running low, Venus Express 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.
Normally, the spacecraft would perform routine thruster burns to ensure that it did not come too close to Venus and risk being lost in the atmosphere. But this unique adventure was aimed at achieving the opposite, namely reducing the altitude and allowing an exploration of previously uncharted regions of the atmosphere.
The campaign also provided important experience for future missions – aerobraking can be used to enter orbit around planets with atmospheres without having to carry quite so much propellant.
Between May and June 2014, the lowest point of the orbit was gradually reduced to about 130-135 km, with the core part of the aerobraking campaign lasting from 18 June to 11 July.
After this month of ‘surfing’ in and out of the atmosphere at low altitudes, the lowest point of the orbit was raised again through a series of 15 small thruster burns, such that by 26 July it was back up to about 460 km, yielding an orbital period of just over 22 hours.
The mission then continued in a reduced science phase, as the closest approach of the spacecraft to Venus steadily decreased again naturally under gravity.