Application of High Precision Two-Way S-band Ranging to the Navigation of the Galileo Earth EncountersThe application of high-accuracy S/S-band (2.1 GHz uplink/2.3 GHz dowlink) ranging to orbit determination with relatively short data arcs is investigated for the approach phase of each of the Galileo spacecraft's two Earth encounters (8 December 1990 and 8 December 1992).