ESA GNC Conference Papers Repository

The evolution of the Attitude Determination and Control System (ADCS) for the Airbus Defence and Space Eurostar E3000 telecom platform is driven by: the evolving needs of operators, leading to enhanced pointing, e.g. for Ka multi-beam missions, and mission stringent availability; new launchers availability, leading to full electric transfer, from injection orbit to operational station; and internal product improvements, leading to propose new features to customers. The ADCS architecture is continuously improved to accompany these needs. Right now, a major step forward is to be implemented to answer efficiently these new challenges and boundaries, especially the electric orbit raising (EOR). The ADCS being developed relies heavily on the use of state-of-the-art Active Pixel Sensor (APS) technologybased Star Tracker (STR) for attitude measurement. Although already part of the current ADCS, the use of STR is enlarged: permanent and large angle measurement capability offers simple concept for the attitude determination during the transfer orbit, especially with the attitude required for optimized electric transfer, but also for chemical transfer. And while on station, it allows new 3-axis control without momentum bias, allowing to cope with large in-orbit testing or mission biases. An accurate 3-axis FOG technology-based gyroscope will complement the STR to ensure permanent 3-axis measurements even during potential star tracker unavailability, linked to Earth and Sun blindings on transfer orbit. A new 4-wheel array is implemented to offer increased momentum and torque capacity, to cope with guidance needs during electric transfer. These wheels are connected to the new 100V power supply. In addition, electric propulsion orbit raising and momentum off-loading capability are introduced with the development of a deployable arm, supporting the electric thrusters. This upgraded ADCS involves major novelties in attitude determination and control algorithms. On-board orbit computation provides Sun and Moon ephemerides and predicted eclipses, orbit control-induced velocity increments, satellite precise position and Earth-pointing attitude set-point. Attitude guidance computes smooth attitude profiles to perform large slew maneuvers within actuator allocations, in particular EOR maneuvers. Gyro-stellar hybridization provides optimal attitude determination from star tracker and gyroscope measurements in terms of sensor availability and noise transmission. Control modes are adapted to the use of STR control during all mission phases, allowing a global simplification of ADCS software and flight procedures, while providing improved performances (e.g. pointing accuracy, Earth acquisition duration). In particular, an Earth-pointing backup mode with very large domain of convergence has been developed, to almost avoid any transition to Sun-pointing safe mode. To cover the specific EOR phase where ground visibility is only intermittent, the autonomy and Failure Detection Isolation and Recovery (FDIR) management have been enhanced, with more autonomous decision on-board ensuring maximum continuity of the thrust phases.