Relative roll control of satellite docking using electromagnetic coils

An electromagnetic coil topology and its control strategy, which can be incorporated into the electromagnetic docking device, have been proposed for the relative roll control of two satellites in space. The target satellite and the chaser satellite are respectively embarked with four and six coils evenly arranged around the docking axis. All the coils on the target satellite are Direct Current (DC) energized, while the currents in the coils of the chaser satellite are regulated to achieve the relative roll control. The electromagnetic force/torque model is built by utilizing the frequently-used far field model. Based on the fundamental components extracted from that model, this paper proposes a real-time magnetic moment vector distribution formula that simply generates a constant roll torque. This paper not only presents an equation for calculating the relative roll angle through the Euler angles of two satellites, but also an equation that converts the roll torque setpoint to the setpoints of the coil currents. A 3-closed-loop positioning controller composed of angle, angular velocity, and current loop is developed. The proposed topology is verified by finite element simulation, and the control strategy is validated by dynamics simulation and ground-based tests.