Change in Venus Express pericentre altitude with time from 19 August to 8 December 2012
This plot shows the change in Venus Express's pericentre altitude (Y-axis) as the mission progresses, 19 August to 8 December 2012 (medium term plan (MTP) #83 through medium term plan (MTP) #86). The X-axis shows the orbit number; each orbit lasts 24 hours.
The pericentre altitude decreases due to predicted forces experienced by the spacecraft. The pericentre plateau, where the low pericentre altitude is used for the atmospheric drag experiments, is clearly visible in the beginning and end of the figure. After a series of drag measurements, the pericentre is raised by firing the main spacecraft engine.
For the purposes of the ninth Atmospheric Drag Experiment campaign, which ended on 1 September 2012, the pericentre altitude was allowed to decrease beyond nominal, down to 170 kilometres. The sharp jump in the pericentre altitude was due to the pericentre-raising manoeuvre carried out at the end of the Atmospheric Drag Experiment campaign, bringing the pericentre altitude back to into the nominal range in orbit 2335 on 11 September.