Research On Boundary Vibration Control Of Flexible Spacecraft

Flexible structural materials（such as flexible solar panels and large antennas）are widely used in spacecraft due to their advantages of light weight,low energy consumption and great economy.Large-angle rapid rotational maneuvers of spacecraft are essential to complete the space mission.In the complex space environment,both the external distur-bances and attitude maneuver of spacecraft result in the vibration of flexible appendages.The vibration of flexible appendages is difficult to offset naturally in a short time since they are characterized by low damping.The undesired continuous and excessive vibration affectes the stability and control accuracy of flexible spacecraft system,and can even de-stroy flexible appendages,which lead to reduced service life.The rapid attitude maneuver of spacecraft results in the variation of system structural parameters.Mathematically,flexible spacecraft system is distributed parameter system with infinite dimensional state space.Hence,flexible spacecraft system is a complex system with rigid-flexible coupling,parameter uncertainties,infinite dimensional state space and external disturbance.In practice,the actuator of spacecraft usually possesses the nonsmooth nonlinear charac-teristics such as dead zone,saturation and so on.In addition,tracking error of attitude angle is usually restricted to ensure precise orientation,these limits result in that the active vibration control design of flexible spacecraft during attitude maneuver is difficult.Combined theoretical research with practical engineering,this paper investigates the problem of active vibration reduction for a flexible spacecraft during attitude maneuver.Main results and novelties of this paper are given as:Using Hamilton’s principle and variation principle,the dynamic model of flexible spacecraft is derived as a set of partial differential equations coupled with ordinary dif-ferential equations.Utilizing Lyapunov direct’s method,based on the original dynamic model,observer-based boundary control is proposed to reduce the vibration of flexible appendages and simultaneously complete the rapid attitude maneuver,and handle the impact of external disturbance effectively.Different from traditional modal control meth-ods,the proposed boundary control can control all system modes and avoid the spillover instability.It is worth to note that all input signals in the deigned control can be directly measured by sensors,where it does not require any algorithm to estimate input signal.Hence,the proposed control scheme can avoid the problem of noise amplification.In addi-tion,the designed control only needs sensors and actors at the system boundaries,which reduces the difficulty of implementation.Subsequently,well-posedness and exponential stability of the closed-loop system are proven strictly by employing Lyapunov stability theory and C₀semigroup theory.Then,numerical simulation results indicate that the proposed boundary control has great control performance to the flexible spacecraft system with external disturbance.To a flexible spacecraft system subject to parameter uncertainties and external dis-turbance,by applying adaptive technique and robust control strategy,adaptive boundary control is adopted to realize the vibration reduction and attitude maneuver simultane-ously.Subsequently,three parameter adaptive laws are constructed to attenuate the system parameter uncertainties.Besides,an auxiliary input signal and a disturbance adaptive law are designed to compensated for the effect of unknown time-varying exter-nal disturbance.The proposed disturbance rejection technique successfully relaxes the requirement for external disturbance,where it only requires to ensure that external distur-bance is bounded.Subsequently,the uniform boundedness stability and well-posedness of the closed-loop system are proven mathematically.Finally,simulation results show that the proposed adaptive boundary control has great capability of vibration reduction and attitude adjustment,and possess robust to external disturbance and system parameter uncertainties.To deal with the problems of vibration reduction and attitude control for a flexible spacecraft system in the presence of asymmetric input saturation,asymmetric output constraint,parameter uncertainties and external disturbance,adaptive boundary barrier-based control is developed.By incorporating an asymmetric barrier Lyapunov function in control design,the tracking error of attitude angle is restricted into a desired open interval.Besides,an auxiliary system is introduced to analyze and handle the effect of asymmetric input saturation.Subsequently,an adaptive law is developed to estimate the system parameter,and a disturbance observer is constructed to estimate the upper bound of external disturbance.Then,the effect of external disturbance is eliminated by combined the sign function and proposed disturbance observer.Both input saturation and the designed disturbance observer can reduce the input chattering.Finally,under the Lyapunove analysis,the uniform boundedness stability of the closed-loop system is proven.Simulation results verify the feasibility of the proposed control.For a flexible spacecraft system with unknown input dead-zone,parameter uncer-tainties and external disturbance,by using adaptive backstepping technique,adaptive neural network boundary control is designed to ensure the uniform boundedness stability of the closed-loop system.Subsequently,the radial basis function neural networks are employed to handle the effect of input dead-zone and approximate the unknown system parameters.Besides,a disturbance observer is proposed to attenuate the effect of exter-nal disturbance.The proposed disturbance observer has a simple structure and can avoid the problem of input chattering.Finally,using lyapunov stability theory,it is proved that the designed control can stabilize the flexible appendages into a neighborhood of their original position and can enable the attitude angle to reach the around of the desired position.Simulation results illustrate the effectiveness of the proposed control scheme.