Research On Attitude Control Of Small Satellite Based On Spherical Motor

Conventional control moment gyros(CMGs)and reaction wheels(RWs)are widely used in spacecraft attitude control attributing to the rapid response capability,high precision as well as no propellants.However,complex gimbal structures,large servo parts and commonly required redundancy configurations limit their applications to mini satellites.In contrast,multi-DOF electromagnetic actuators have great advantages in weight,size as well as volume because of their higher functional and structural integration,which appears greatly promising in space engineering.This paper focuses on the satellite attitude maneuver using permanent magnet spherical motor.Firstly,a new type momentum exchange spherical actuator was proposed.By analyzing the electrical equation and dynamic equation,this device is a multi-input multi-output strong coupling nonlinear dynamical system.In order to improve the system dynamic response,a decoupling control based on PD feed-forward algorithms was adopted.Then,the full dynamic equations of motion for the spacecraft system are derived by the Newton-Euler method.To facilitate computation,virtual gimbal coordinate frames are established.Next,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.For parallel configuration,a nonlinear control law in terms of quaternions is developed via backstepping method.The proposed control law compensates the coupling torques arising from the spacecraft rotation,and is robust against the external disturbances.Then,the singularity problem is analyzed.To avoid singularities,a modified weighed Moore-Pseudo inverse velocity steering law based on null motion is proposed.The weighted matrices are carefully designed to switch the actuators and redistribute the control torques.The null motion is used to reorient the rotor away from the tilt angle saturation state.Finally,numerical simulations of rest-to-rest maneuvers are performed to validate the effectiveness of the proposed method.