Anti-unwinding Sliding Mode Attitude Control For Rigid Spacecraft

Spacecraft attitude control technology is the basis to complete a variety of space missions.It has a very wide range of applications in military and civil,such as Earth topography survey,weather forecast,communication,broadcasting and military investigation,and so on.However,the spacecraft attitude control system is a complex nonlinear system.Thus,the spacecraft attitude controller design faces many problems,such as the uncertainty of spacecraft system parameters and external disturbances.In addition,the spacecraft may suffer the unwinding problem during spacecraft attitude maneuver or tracking.When the initial attitude of the spacecraft is very close to the desired attitude and the error between the initial angular velocity and the desired angular velocity is almost zero,due to the improper design of the attitude control law,the angular velocity of the spacecraft around the Euler axis first increases and the spacecraft rotates away from the expected attitude.Then the angular velocity around the Euler axis decreases,and finally returns to the desired attitude.This phenomenon is called unwinding.The unwinding phenomenon may cause extra fuel consumption.It is a challenge to design an appropriate control law for spacecraft to realize the attitude maneuver and tracking without unwinding phenomenon.For this end,the unwinding phenomenon is taken into consideration,and anti-unwinding attitude control laws are developed.For the rest-to-rest attitude maneuver control of rigid spacecraft described by quaternion,an anti-unwinding sliding mode attitude maneuver control law is designed when the upper bound of the external disturbance is known.First,a novel sliding function is designed by a sine hyperbolic function such that the sliding surface contains two equilibriums.It is proven that the system achieves unwinding-free performance when the system states are on the sliding surface.Then,a new anti-unwinding attitude controller is proposed to guarantee the finite-time convergence of the system states on the reaching phase.Moreover,the unwinding-free performance of the system on the reaching phase is ensured by designing the dynamic parameter of the developed controller.Furthermore,a boundary layer is introduced for the designed controller to avoid the chattering phenomenon.Moreover,the convergence property and unwinding-free performance when the system states within the boundary layer are proven.On the basis of the aforementioned works,a more general attitude tracking control problem is considered.An anti-unwinding terminal attitude controller is developed for the attitude tracking of a rigid spacecraft with external disturbance.A nonlinear sliding mode function is first designed by hyperbolic sine function.By using Lyapunov stability theory,it is proven that the finite time stability and anti-unwinding performance when the system states of the resulted closed-loop system are restricted to the sliding surface.Then,a finite time sliding mode attitude tracking control law with dynamic parameters is designed to ensure that the states of the closed-loop system converge to the sliding surface in finite time.Moreover,the dynamic parameter of the proposed finite time sliding mode attitude tracking control law is designed to ensure the anti-unwinding performance of the closedloop system in the approaching phase.In order to deal with the chattering problem of the proposed controller,a boundary layer is introduced to improve the proposed control law,and the parameter of the sliding function is further designed to ensure the unwinding-free performance of the closed-loop system within the boundary layer.Moreover,the corresponding convergence regions of the two equilibrium points of the closed-loop system are given.The anti-unwinding attitude maneuver control for rigid spacecraft system described by modified Rodrigues parameters is considered.First,a novel switching function is constructed by a hyperbolic sine function,such that the closed-loop system possesses unwinding-free performance on the sliding surface.Then,an anti-unwinding attitude maneuver controller is developed to guarantee that the system states converge to the sliding surface in a finite time.Moreover,the unwinding-free performance of the system on the reaching phase is achieved by designing the dynamic parameter of the proposed controller.Further,a boundary layer is introduced for the presented controller to avoid the chattering phenomenon.It is also proven that the convergence property and unwindingfree performance are achieved within the boundary layer.The attitude maneuver control without unwinding for rigid spacecraft based on the modified Rodrigues parameters(MRPs)is considered.First of all,an attitude control system model for rigid spacecraft is constructed by designing a selection logic for the MRP set and its shadow set.To guarantee the asymptotic stability in the large and antiunwinding performance of the closed-loop system on the sliding phase,a sliding function is presented.Then,a sliding mode control law is presented to ensure that the system states are driven to the sliding surface.Moreover,a dynamic parameter is designed for the proposed control scheme,such that the unwinding phenomenon is avoided when the system states are outside the sliding surface.Further,a boundary layer is introduced for the presented controller to avoid the chattering phenomenon.It is also proven that the convergence property and anti-unwinding performance are ensured when the system states are within the boundary layer.