Modeling and Analysis of a 3-DOF Spherical Momentum Exchange Actuator for Spacecraft Attitude Maneuver

This paper describes a prototype and analytical studies of a three-degree of freedom (3-DOF) spherical momentum exchange actuator for three-axis attitude control. Its moving part, without any gimbal structures cascaded, can be directly driven by a stator electromagnetic field instead of servomotors, which sets it apart from conventional control moment gyros. First, the motion of equation and torque exchange model are developed. Analysis shows that the proposed actuator possesses a considerable torque amplification effect. Then a two-level torque-sharing strategy tailored for this device is presented to decouple the command torque into reaction flywheel/gimbal torque and further assign them to each of the stator coils. The physical limit of the rotor's tilt range is investigated and an n-step incremental Euler eigenaxis rotation is resorted to as the solution. Numerical simulation results present a desirable dynamic response, revealing that the single device has the potential to provide limited three-axis control for spacecraft. Finally, the pros and cons of this device are analyzed. This study may serve as a reference on the design and research of new future momentum exchange devices for spacecraft attitude maneuvers. (C) 2015 American Society of Civil Engineers.