Constrained Attitude Control of a Cubesat with Redundant Reaction Wheel Configurations

Demand for well-performing attitude control systems is increasing with advances in Cubesat technologies. In particular, the problem of stabilizing the attitude of a satellite without fully knowing its inertia and the external disturbances acting on it is quite challenging. The task becomes even more complex when the actuators' dynamics are included. In this paper, an adaptive strategy for three-axis attitude stabilization is proposed with two control loops. The first deals with attitude control in the presence of unknown external disturbances and inertia uncertainty; stability of this controller is proved using Lyapunov's stability theory. In the second loop, a PID controller is used to control the torque of a DC motor in a four-wheel setup. Both pyramidal and NASA configurations are investigated. Additionally, a systematic method for the construction of a reference frame is established based on an alignment and a constraint vector, so that the satellite can efficiently execute its mission. A numerical simulation is performed to test the aptitude of the control strategy, it shows that the designed controllers succeed in reaching their respective objectives regardless of the reaction wheels' configuration. However, a close examination of the results reveals that the pyramid layout is more efficient, saving up to 35% in energy consumption.