Nanosatellite nonlinear attitude control testing on an air bearing system

While nonlinear attitude control has been explored widely in theory, nanosatellite air-bearing-based spacecraft simulators have not been used to test nonlinear discrete time control techniques. This paper documents development and testing of a nonlinear attitude controller for a next generation nanosatellite. A novel nonlinear control algorithm will be verified with a spherical air bearing system. The stability conditions for robustness against unmatched uncertainties and disturbances are derived using Lyapunov stability theory to establish the regions of asymptotic stabilization. The proposed control method is tested on a three-axis nanosatellite air-bearing system with reaction wheel actuation, and results are compared to numerical simulations to show that precise attitude pointing and tracking can be achieved by dealing with the issues of system nonlinearities, variations in initial conditions, external disturbances, and control force saturation, concurrently. The results will be compared with a combined feedback and feedforward momentum tracking control law in the reference. The attitude control system results will be invaluable to the development and testing of future nanosatellite payloads.