Change in angles between the Sun, Earth and Venus Express around the time of superior conjunction
Change in the Sun-spacecraft-Earth angle (angle between the Sun and Earth as seen from the spacecraft, in blue) and the Sun-Earth-spacecraft angle (angle between the Sun and the spacecraft as seen from Earth, in pink) around the time of superior conjunction, from 27 February to 2 May 2013.
The spacecraft and Venus were in superior conjunction with Earth from 16 to 24 March. The Sun-Earth-spacecraft alignment approached solar conjunction with an angle of 3.2 degrees on 16 March – the Sun was almost directly between Earth and the spacecraft. At this time, the quality of the communications signal was such that it was acceptable only at very low data rates, too low for nominal command uplinks or science data downlinks.
The flight control team therefore decided to shutdown Venus Express science operation downlinks in the period around superior conjunction. Some science observations continued, but were limited by the fact that the data could not be downloaded.
After the end of superior conjunction, from 25 March through 13 April, there were no communications or telemetry checks with the spacecraft as the Sun was still directly in the line-of-sight from Earth.
By 13 April, the Sun-Earth-spacecraft geometry allowed the spacecraft to end the communications shutdown forced by the conjunction. Communications began first only at very low data rates. On 14 April, the data rate was increased and nominal science operations were resumed.