Enforce Illumination Constraints with Fake Ephemerides on Venus Express

Shortly after the orbit insertion of Venus Express, damages by sun exposure were discovered on the Venus monitoring camera. To prevent further degradations, direct illumination of the instrument had to be avoided, thus several issues had to be resolved at the time of Venus quadrature. First existing thermal constraints had to be reviewed to allow Earth pointing; then a modification of the on-board guidance process was required. After dedicated studies, the thermal constraints were adapted and 2 solutions were proposed to adapt the guidance. The "fake ephemerides" solution was selected although it required the modification of an on-board surveillance. Detailed development, including an update of the procedure to swap the high gain antenna and validations were completed before the start of the first quadrature phase. It was then possible to merge these operations and the associated constraints with a complex plan of observations. Smooth executions rewarded the exhaustive preparation and demonstrated that the payload could be preserved throughout the mission.