Attitude Control of a 2U Cubesat by Magnetic and Air Drag Torques

This paper describes the development of a magnetic attitude control subsystem for a 2U cubesat. Due to the presence of gravity-gradient torques, the satellite dynamics are open-loop unstable near the desired pointing configuration. Nevertheless, the linearized time-varying system is completely controllable, under easily verifiable conditions, and the system's disturbance rejection capabilities can be enhanced by adding air drag panels exemplifying a beneficial interplay between hardware design and control. In this paper, conditions for the complete controllability for the case of a magnetically controlled satellite with passive air drag panels are developed, and simulation case studies with the linear quadratic regulator and model predictive control designs applied in combination with a nonlinear time-varying input transformation are presented to demonstrate the ability of the closed-loop system to satisfy mission objectives despite disturbance torques.