ESA GNC Conference Papers Repository

Current core navigation for High dynamics missions in Earth vicinity, such as Launch Vehicles and Re-entry Vehicles, relies on inertial measurements units (IMU). To meet drastic requirements during atmospheric flight, at injection in orbit, parachute opening or landing, the selected IMU shall be ultra-accurate: baseline IMU for ARD or Ariane 5 is in the 0.01°/hr – 50 ?g class. Considering future Ariane missions such as direct GEO payload jettisoning, the possibility to use alternative measurements to support navigation and possibly relax the IMU class has been assessed, and especially the GNSS solution. However, up to now, having the navigation of such vehicles rely on an external element (here the GNSS satellites) has always been considered as an appalling condition, as a loss of GNSS signal in the atmospheric part of flight could endanger the integrity of the vehicles, and possibly the ground integrity. Primary cause of loss of GNSS signal is the unavailability of the GNSS signals (shut-down of GNSS service, or selective availability) ; with the on-going development of Galileo, the availability of GNSS signals will be mastered. Then, two other aspects may cause a loss of GNSS signal: the high dynamics of the vehicle (3rd order Phase loop are sensitive to Jerk and its derivatives) and degraded Signal to Noise ratios conditions (caused by jamming, atmospheric scintillations, blackout).