Research On Attitude Control Of Underactuated Spacecraft With Two Reaction Wheels

If the number of degrees-of-freedom is greater than the number of degrees-ofactuation,spacecraft may be viewed as underactuated.This is a large concern for spacecraft systems in particular,as being underactuated because of design or failure of actuators can shorten its operational life and reduce its capabilities while on orbit.So the research of underactuated spacecraft is useful to improve the reliability of the spacecraft.Moreover,as one of the typical nonholonomic system,the exploration of control algorithm of underactuated spacecraft is helpful to the nonholonomic system.Focusing on the attitude control system of underactuated spacecraft with two reaction wheels which is uncontrollable,and there is not time-invariant smooth control law for it,this dissertation intensively investigates the nonholonomic control algorithm of the line-of-sight inertia orientation.The main contents of the dissertation are as follows:The controllability of the attitude control system of underactuated spacecraft with two reaction wheels and the attitude accessible region are analyzed.There is not time-invariant smooth control law for the entire attitude control system that is uncontrollable and nonholonomic,meanwhile the attitude accessible region is constrained.Small time local controllability of the control system is proved based on differential geometry theory.Then provide the theoretical basis through choosing the line-of-sight inertia orientation as control task,and calculating the attitude accessible region.By choosing relative attitude between spin-axis coordinate frame and inertia coordinate frame,the kinematic is established.The spin stabilization control law is proposed based on explicit Lyapunov theory,which drive the line-of-sight move to the given inertia direction till they are coincidence,meanwhile the spacecraft spins around the line-of-sight and other two attitude and angular velocities converge to the equilibrium point.Considering the attitude control problem of underactuated spacecraft with two reaction wheels installed orthogonally along to the inertial principal axises,attitude stabilization control law and the line-of-sight inertia orientation control law are proposed.Firstly,choosing the total angular momentum of the spacecraft as zero,the dimension of attitude control system is reduced,then the stabilization control law is proposed to drive the state variable asymptotic convergence to the equilibrium point.Secondly,when the total angular momentum of the spacecraft is non-zero,the error kinematics between the body frame and the target frame is established.After that,the line-of-sight and the inertia direction are coincidence and error attitude and angular velocity converge to the equilibrium point under the control of a singular control law.Considering the attitude control problem of underactuated spacecraft with two reaction wheels installed arbitrarily,a robust stabilization control law is derived using general dynamics inverse and sliding mode algorithm.Firstly,based on the conclusion of controllability analyzing,the dimension reduced system including three angular velocity and two attitude parameters is established.After that,a singular robust control law is derived.Secondly,in order to improve the performance of the attitude control system involving unknown disturbances,an observer of unknown disturbance is proposed using homogeneity theory and sliding mode algorithm to lower the influence of disturbance.Then under the control of a second order sliding mode control law,the state variable converges to the equilibrium point in finite time.In order to overcome the difficulty caused by the unknown boundary disturbances,a parameters adaptive algorithm is used to modify the second order sliding mode control law.Most of adaptive algorithm makes the control parameters arise all the time,till they satisfy the stability condition.The propose novel adaptive algorithm is able to drive the control parameters increase and decrease repeatedly,through choosing the Lyapunov function and the minimal control parameters as criterion.In the end,the control parameters can reach to the ideal value.In order to improve the optimality of the robust control law,inverse optimal control algorithm is used to derive two stabilization control laws.The first one is able to balance the control effort and the convergence rate of the Lyapunov function,but it needs input information.Because of that,the second control law is proposed.Whatever the input information is known or not,the second control law can drive the state variable to the equilibrium point robustly.In addition,both of the inverse optimal control law achieve a disk margin.