Rosetta Navigation during the End of Mission Phase

ESA’s Rosetta mission ended on 30 September 2016, after 26 months of operations around the comet 67P/Churyumov-Gerasimenko to characterize it, deploy the Philae lander on its surface, and monitor its evolution during the perihelion passage. The date selected for Rosetta End of Mission (EoM) was immediately before entering superior solar conjunction and at a point in the heliocentric orbit where the increasing distance to both Sun and Earth was already imposing major constraints on the scientific operations, due to limited solar power received on board and downlink data rate. The last two months of Rosetta operations were dedicated to fulfil the high-level mission objective of orbiting the comet as low as possible and terminating the mission with a direct descent and slow impact on the comet’s surface. Flying so close to the comet was extremely challenging for navigation due to the strong orbital perturbations from the gravitational field of such an irregular body. This phase is considered a success and very fruitful in terms of scientific return. Moreover, it was during this period that the lander search campaign finally succeeded to image Philae at rest on its landing site. This paper describes the trajectory design for the EoM scenario, it discusses the encountered navigation challenges and how they were tackled, and it reports the achieved navigation results.