GPS-Based Precise Relative Orbit Determination for LEO Satellites Using GPS Double-Differenced Carrier Phases

The GPS-based precise relative orbit determination for Low-Earth Orbiting (LEO) satellites using double-differenced (DD) carrier phases is very important for formation flying missions to satisfy the different relative orbit accuracy requirements. Current methods need either reference stations or reference orbits, which are not convenient, particularly for real-time data processing. Based on this motivation, we investigated the GPS-based precise relative orbit determination for LEO satellites without any reference stations or reference orbits. Additionally, ambiguity resolution is also important for the precise relative orbit determination by using GPS carrier phase observations. Therefore, we also studied the impacts of ambiguity resolution on the precise relative orbit determination. A new approach for ambiguity resolution, which is based on the difference between the estimated and adjusted DD ionosphere free phase biases based on the resolved wide-lane and narrow-lane integers, is presented and implemented in the GPS data processing. Lastly, the effects of the arc length on the relative orbit determination were also investigated. For our study, we used the observations of the GRACE (Gravity Recovery and Climate Experiment) twin satellites, which are equipped with a very precise K-band ranging (KBR) system. The KBR data can be used for assessing the relative orbit accuracy. To determine orbits, the orbits are not only produced, but also assessed. The orbit accuracy is assessed using a number of tests, including analysis of the orbit fits, orbit comparisons, Satellite Laser Ranging (SLR) and KBR residuals.