Robust spacecraft attitude determination using global positioning system receivers

This work presents the development of a new attitude determination system based on global positioning system signals. This new algorithm utilizes signal-to-noise-ratio measurements from canted antennas to produce three-axis attitude solutions. These solutions are then used to determine the integer ambiguities for double-difference carrier-phase measurements. The two measurement types are processed through an extended Kalman filter to produce attitude solutions. The algorithm is tested using both hardware-in-the-loop orbit simulations and static rooftop data. These experiments demonstrate the speed of the integer resolution process and the accuracy of the resulting carrier-phase attitude solutions. Further tests demonstrate that the canting of the antennas has little or no effect on the double-difference carrier-phase measurements for antenna baselines of 1 m. The algorithm is modified to include magnetometer measurements. Simulation demonstrates how this addition further improves the integer resolution. The results of the rooftop and simulation experiments demonstrate that this new algorithm can quickly and accurately resolve the integer ambiguities associated with carrier-phase attitude determination. Once the integers are resolved, the resulting algorithm generates solutions of less than 0.5 deg in accuracy. To conclude this work, some possible future work is discussed.