Precision relative navigation is an essential aspect of spacecraft formation flying missions, both from an operational and a scientific point of view. In view of the restricted availability of spaceborne dual-frequency receivers, research in this area has so far focused on single-frequency GPS navigation over short baselines. This situation is likely to change, however, with ongoing space receiver developments as well as the implementation of new civil radio navigation signals. The present paper therefore assesses the potential of kinematic relative positioning of spacecraft in low Earth orbit (LEO) making use of dual frequency GPS measurements. The LAMBDA method is chosen to resolve the integer ambiguities of the L1 and L2 carrier phase measurements and the associated wide- and narrow-lane combinations. Thereafter kinmatic relative position fixes with an accuracy limited only by the carrier phase noise and the geometric dilution of precision can be obtained. The feasibility, accuracy and robustness of this processing scheme are illustrated using actual GPS measurements for two spacecraft in low Earth orbit separated by baselines of 10-100 km. Geodetic grade C/A and P2 pseudorange measurements as well as L1 and L2 carrier measurements have been obtained in hardware simulations using a pair of NovAtel OEM4-G2 receivers and a Spirent STR4760 48 channel GPS signal simulator.
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