ESA GNC Conference Papers Repository

The Rosetta probe reached its destination comet Churyumov-Gerasimenko in spring 2014 after a ten-year long journey through outer space. After releasing the Philae lander on November 12th of that year, the European Space Operations Center (ESOC) commanded the Rosetta orbiter to lower its orbit to perform low altitude fly-bys for enhanced science. However at that time the comet outgassing activity started to become burdensome to the spacecraft star trackers and the Attitude and Orbit Control System (AOCS) attitude estimation function, up to the point of triggering a safe mode in March 2015. Then, as anticipated, the situation did not improve towards the comet perihelion passage in august 2015, forcing ground operators to retreat the Rosetta orbiter further away from the comet in order to preserve its precious attitude estimation function from the hazardous comet dust environment. As the designer and manufacturer of the Rosetta orbiter, Airbus Defence and Space proposed to ESOC an original engineering support and in-flight expertise trying to better characterize and potentially improve the in-flight behaviour, through an on-ground testing campaign of the 15-year old Rosetta Star Tracker Engineering and Qualification Model (EQM) connected to the spacecraft EQM at ESOC, with a specially adapted in-house Optical Stimulator named the microSTOS. This presentation will first describe the observed attitude estimation in-flight behavior, then present the proposed AOCS SW improvements before detailing the Rosetta EQM test phase carried out at ESOC end 2015. The obtained results allowed to validate the proposed retuning of some SW parameters before patching them in flight before the Rosetta Grand Finale in September 2016 composed of low altitude elliptical orbits and a final descent to the surface, thus contributing to a flawless End Of Mission.