Fusion of inter-satellite Ranging and Carrier-Phase Differential GPS for autonomous relative navigation in LEO

This paper focuses on the autonomous relative navigation of LEO satellite formations. Specifically, a CDGPS technique is addressed using a cascade-combination of dynamic and kinematic filters which processes double differenced code and carrier measurements on two frequencies to get centimeter-level baseline estimates. In order to improve navigation filter robustness against poor GPS geometry and noisy measurements, the CDGPS filter is augmented by inter-satellite local ranging measurements with decimeter-level range accuracy, as the ones provided by ranging transponders or GNSS-like systems. Performance of the augmented filter is tested by numerical simulations of orbital configurations characterized by short, varying baselines, relevant to next generation Synthetic Aperture Radar missions. Numerical results show that the augmented filter is able to preserve the centimeter-level accuracy of the relative navigation also in the cases in which the CDGPS-only filter exhibits a degraded accuracy due to a poor GDOP or a limited number of GPS satellites in view