CARRIER-BASED DIFFERENTIAL GPS FILTERING APPROACHES FOR PRECISE RELATIVE POSITIONING IN FORMATION FLYING WITH HIGHLY VARIABLE INTER-SATELLITE DISTANCE

A dynamic filtering scheme for carrier-based differential GPS relative navigation of formation flying satellites is described. It relies on an augmented-state Extended Kalman Filter processing double-difference GPS observables and using a non linear model of the relative dynamics. Filter performance is specifically evaluated for formations where the inter-satellite distance largely varies during the mission. The filter provides estimation accuracy ranging from the millimetre to the centimetre level as the baseline grows from a few kilometres to 200 km