Rosetta status report: close flyby navigation issues

During its most recent close flyby last Saturday, where Rosetta flew within 14 km of the surface of the comet, the spacecraft experienced significant difficulties in navigation. This resulted in its high gain antenna starting to drift away from pointing at the Earth, impacting communications, and was subsequently followed by a ‘safe mode’ event. The spacecraft has now been successfully recovered, but it will take a little longer to resume normal scientific operations. Here is the full report from the mission team: Rosetta has been flying a series of flyby trajectories around Comet 67P/C-G since February, allowing the spacecraft to collect scientific data from a range of distances. Its closest flyby to date took it just 6 km from the surface of the comet – over the Imhotep region on the comet’s large lobe – on 14 February. On Saturday 28 March, Rosetta performed a 16 km flyby (about 14 km from the surface), also over the comet’s large lobe. With activity from the comet increasing as it moves closer to the Sun, operating Rosetta close to the comet means flying through denser regions of outflowing gas and dust. This results in the spacecraft and its large solar arrays being exposed to significantly more drag. Furthermore, as experienced during the 14 February flyby, operating this close to the comet also has another effect: the spacecraft’s star trackers, used to navigate, are confused by mistaking comet debris for stars. Crucially, the star trackers also help control the attitude of the spacecraft: by using an autonomous star pattern recognition function, they provide input to the the onboard Attitude and Orbit Control and Measurement Subsystem used to maintain the spacecraft’s orientation with respect to the stars. This allows the spacecraft to know its orientation with respect to the Sun and Earth. In turn, […]



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