Research On Attitude Control Methods For Fast Maneuver Satellites

As the development of aerospace techonology,current space missions demand the maneuver ability of satellites.In order to solve attitude control issue of large angle fast maneuver,the goal of this paper could be concluded as follow: design attitude controllers to improve system convergence rate while maintaining the steady accuracy at a high level for satellite large angle fast maneuver attitude control,and design controllers robust to system inertia matrix uncertainty and disturbance torque under control torque and angular velocity constraint.The main work done in this paper could be concluded as follow:Design of PID plus controllers.Based on the effect of different terms in PID controller,the integral term is added into the controller when system state approaches its equilibrium point to improve the steady accuracy,and the issue that integral term strengthened state shocking is avoided.Based on the idea of sliding mode control,the product term of angular velocity is added into the controller to ensure system state could converge along the designed sliding mode while the stability of PID controller is maintained.The angular velocity is maintained constantly at the initial stage of sliding mode hence the convergence rate of attitude quaternion could be maintained,and the efficiency of control torque could be improved.The relationship between control parameters and norm of control torque and angular velocity is proved,and the constraints on control parameters are given to ensure that the system state does not exceed its upper bound.The control torque saturation issue is also solved by minifying the PID terms proportionally.Design of sliding mode controllers.The convergence rate of standard sliding mode descends severely sicne the angular velocity descends severely.First,in order to improve the convergence rate of standard sliding mode control,the open loop control algorithm Bang-Bang control is combined with sliding mode control.A two stage sliding mode is constructed and the system angular velocity is maintained constant and the convergence rate of attitude quaternion could be maintained at a high level.The acceleration of angular velocity at slow down is also locked so that the efficiency of control torque could be improved.Then an update law of sliding mode parameter is designed and the parameter could be enlarged as the system state converges to zero,hence the terminal convergence could be largely improved.The relationship between control parameter and control torque and angular velocity is proved and the constraints on control parameters is given to ensure that the system state does not exceed its upper bound.Design of finite time controllers.First,a finite time sliding mode with three stage structure is designed for the large angle maneuver situation.The angular velocity is maintained constant when the system state is far from equilibrium point so that the convergence rate of attitude quaternion could be maintained.The standard sliding mode is modified so that the system could have finite time stability when the system approaches its equilibrium point.The property of Euler Axis is used to avoid the singularity of finite time controller and the control torque saturation issue is solved.Then a finite time controller based on MRP is designed in order to deal with the small angle maneuver situation.The sliding mode is designed based on the derivative of MRP instead of angular velocity so that the singularity issue is solved.Design of trajectory planning algorithm and attitude tracking control algorithm.The solution of current trajectory planning algorithm for satellite attitude maneuver is numerical and the computation is huge for on-board computers.In order to simplify the computation,a trajectory planning algorithm with analytical solution for attitude maneuver with any initial state and target state.The attitude maneuver is detached into three independent single axis maneuvers and the time efficient trajectory is derived based on Bang-Bang control.The total maneuver angle is optimized and the switching point is derived.Then a special situation similar as Horman maneuver is considered and the “rendezvous point” is derived.The accelerate and decelerate stage are reduced based on this method and the efficiency of control torque and system convergence rate is improved.Then an attitude tracking controller is designed to ensure that the system state could converge along the designed trajectory.