Change in Venus Express's pericentre altitude with time
This plot shows the change in Venus Express's pericentre altitude (Y-axis) as the mission progresses, from Medium Term Plan 73 to 75 (MTP073 - MTP075; 13 November 2011 to 4 February 2012). The X-axis shows the orbit number; each orbit lasts 24 hours.
The pericentre altitude decreases due to predicted forces experienced by the spacecraft. For the purposes of the Atmospheric Drag Experiment campaign, which started on 8 January 2012, the pericentre altitude is allowed to decrease beyond nominal, down to 175 kilometres. The sharp jump in the pericentre altitude is due to the orbit-raising manoeuvre carried out at the end of the Atmospheric Drag Experiment campaign, bringing it back to nominal on 22 January.