Simulation Platform for Relative Navigation Using GPS Carrier Phase Measurements for Satellite Formation Flying Missions

The use of Global Positioning System (GPS) technology for satellite formation flying missions has received more attention recently. The Carrier Phase Differential Global Positioning System (CDGPS) technique is generally employed to obtain relative position of a high accuracy. To validate the formation flying CDGPS algorithm, a simulation platform is necessary to simulate the GPS signals received by spaceborne receivers. This paper describes the simulation model of GPS observations for Low-Earth Orbit (LEO) spacecraft. The differences in the error sources between GPS use in space and on the ground are analysed in detail. The ionospheric effects have been identified as the main error source in space applications, especially for long baseline scenarios. Therefore the ionospheric delay model is the focus in the design of the simulation platform. Based on the platform, relative positions between two LEO satellites are derived using the L1-only and the L1/L2 carrier phase measurements. Positioning accuracy is compared with the corresponding accuracy obtained by the hardware simulator. The results show that the simulation platform is suitable for the validation of relative position determination algorithms for spacecraft formation flying missions. The modulated design and flexible parameter initialisation make the platform easily augmented for other GNSS constellations, including Galileo, GLONASS, and Beidou.