Robust and Adaptive Nonlinear Attitude Control of a Spacecraft

In the context of the initiative Formation for Atmospheric Science and Technology demonstration (FAST), this dissertation describes the design and comparison of several nonlinear attitude controllers for TU Delft’s micro-satellite. The control requirements include robustness against model uncertainties and disturbances. To this end, five Backstepping schemes are selected for comparison: Standard Static, Static Robust, Integrated Adaptive with tuning functions estimation, Modular Adaptive with nonlinear extended state observation and, finally, Immersion and Invariance Adaptive. The spacecraft model is written using Modified Rodrigues Parameters. Three perturbation sources are considered and applied separately: constant inertia tensor mismatch; saturated reaction wheel; and moving mirror from a payload spectrometer. All perturbations are translated to time-variant disturbance torques and command filters are used in all designs allowing the inclusion of magnitude and rate constraints. Convergence of the tuning functions estimator to the true disturbance value is proved. The Immersion and Invariance Adaptive Backstepping law is here proved input-to-state stable in case of time-variable perturbation. Simulation reveals similar tracking performances of all controlled systems in a disturbance-free case. In all disturbance scenarios the adaptive laws clearly outperform the static ones. This is especially evident in the presence of a faulty reaction wheel and a moving payload. Sampling time analysis shows higher dependence of the adaptive designs on the control frequency. The Modular Adaptive and the Immersion and Invariance Adaptive Backstepping controllers display the best performances. However, the latter design emerges as, not only the easiest to tune, but also as the one with the most consistent performance.