Accurate and autonomous navigation for the ATV

The Automated Transfer Vehicle (ATV) is a European spacecraft intended to service the International Space Station (ISS). It is designed to perform automated phasing, approach, rendezvous and docking to the ISS, then departure and deorbitation manoeuvres. Such an automated rendezvous mission towards a manned facility raises severe performance and safety constraints for the vehicle, which are declined towards the on-board Navigation in terms of availability, accuracy and failure tolerance: the ATV shall be operational after any first failure and safe conditions shall be reached after a second failure. The whole ATV navigation system has been designed to fulfil these very stringent requirements. Based on fully redundant hardware, the navigation algorithms present optimal estimators and multi-layers Failure, Detection, Isolation and Recovery (FDIR) capabilities to ensure the continuity of the state vector in case of failure. Several functions provide state vectors estimations and health reports, according to the flight phase: the attitude and drift estimation function provides the vehicle absolute attitude and angular rate during the whole flight; for the far rendezvous, position and velocity relative to the ISS are estimated by the relative GPS navigation and a dedicated relative navigation with Videometer applies in close rendezvous, in the final approach. All these autonomous navigation functions offer nevertheless a high level of monitoring and control to the ATV Control Centre operators. Thus the ATV innovative navigation chain provides the high level of performance, robustness and autonomy required by modern spacecrafts involved in human programs, today in Earth orbit but also for future space exploration missions. L'ATV (Automated Transfer Vehicle) est un véhicule de service européen pour la Station Spatiale Internationale (ISS). Il est conçu pour réaliser les manœuvres de phasage, d'approche, de rendez-vous et d'arrimage à l'ISS, puis les manœuvres de départ et de désorbitation. Une telle mission automatisée de rendez-vous vers une infrastructure habitée induit pour le véhicule des contraintes très sévères de performance et de sécurité qui sont déclinées vis-à-vis de la navigation embarquée en termes de disponibilité, de précision et de tolérance aux pannes : l'ATV doit rester opérationnel après une première panne quelconque et doit rejoindre des conditions de sécurité après une seconde panne. L'ensemble du système de navigation de l'ATV a été conçu po