Attitude Control of the Low Earth Orbit Satellite with Moving Masses under Strong Aerodynamic Disturbance

This study investigates an attitude control scheme for the satellite with moving masses and reaction wheels to solve the problem of the strong aerodynamic disturbance in low Earth orbit. The moving mass actuator is introduced to minimize the influence of the aerodynamic torque, so as to avoid the frequent saturation of the reaction wheel speed. The rotational dynamic equations of the attitude and the translational dynamic equations of the masses are derived by Newtonian mechanics. The dynamic effects of the mass movement are analyzed. A nonlinear observer is used for the precise estimation of the system disturbance to minimize the effects of the disturbance on attitude control through feedforward compensation. An incremental discrete PID control algorithm is used to slow down the mass movement and reduce the dynamic effects. The aerodynamic torque can be used to actively compensate the system disturbance in y and z axes of the body system without knowing structural parameters of the satellite. The numerical simulation indicates that the satellite is capable of maintaining the attitude convergence accuracy within ±0.1° all the time despite strong and uncertain aerodynamic torque. The results verify the feasibility and effectiveness of the proposed control scheme for the satellite with moving masses and reaction wheels.