Attitude control of Earth-pointing satellites employing novel hybrid actuator configurations

This paper presents an attitude control system for an Earth-pointing satellite, applicable to both circular and elliptical orbits. Two actuator configurations are proposed in this work: one utilizing two reaction wheels, three magnetorquers, and three pairs of Coulomb shells, and a reduced configuration with a single reaction wheel alongside the same set of magnetorquers and Coulomb shells. The magnetorquers and Coulomb shells, aligned along the principal body axes, rely on the Earth's geomagnetic field, making them inherently underactuated. In the first configuration, the reaction wheels generate torque along two axes, while the magnetorquers and Coulomb shells provide control along the remaining axis. In the reduced configuration, a single reaction wheel controls one axis, requiring the magnetic actuators to handle the other two. A control law is developed to estimate the required torques and efficiently distribute them among the actuators. The global asymptotic stability of this control strategy is shown to be valid for all initial angular velocity conditions. Numerical simulations are performed for both circular and elliptical orbits under varying initial conditions. The results validate the effectiveness of both configurations in achieving stable attitude control while optimizing actuator usage and minimizing system complexity.