Dynamics Modeling And Attitude Control Of Flexible Satellite With Fuel Slosh In Orbital Plane

In order to meet the increasing needs of space missions,modern satellites generally consist of a central rigid body and flexible appendages including antennas,solar panels and mechanical cantilevers.The performance requirements of spacecraft are increasing,and the structure of spacecraft is becoming more and more complex.Spacecrafts need to carry more liquid fuel to complete long-term and more complex missions.In order to reduce the load,the rigidity and mass of flexible appendages on spacecraft are very small,which increases the flexibility of spacecraft structure.Sloshing of liquid fuel and vibration of flexible appendages coupling with rigid body motion of spacecraft may affect the stability and orientation accuracy of satellites.Therefore,how to effectively suppress the sloshing of liquid fuel and the vibration of flexible appendages has become an important topic in the field of aerospace technology.In this thesis,the dynamics modeling and attitude control of flexible liquid-filled satellite maneuvering in orbit plane are studied.In chapter 2,several basic coordinate systems and describing parameters of spacecraft attitude and motion are introduced.Then,Newton-Euler method and Lagrange method are introduced and compared.In Chapter 3,the dynamics model of satellite with fuel slosh is studied.Firstly,the dynamics model of liquid fuel sloshing is respectively equivalent to the pendulum model and the spring-mass model.The differential equations of dynamics of the system is established by Lagrange method.The system is transformed into a typical underactuated system.Then,a state observer is designed to estimate the liquid sloshing state.The sliding mode control method is used to design the controller,so that each state can quickly enter the equilibrium state and effectively suppress the liquid sloshing.In Chapter 4,the dynamics modeling and attitude control of a flexible liquid-filled satellite are studied.The coupling of vibration of flexible appendages with translational and rotational motions of spacecraft is considered in dynamics modeling.The dynamics equations of flexible liquid-filled satellite based on mixed coordinates are established by Lagrange method.Then,by decoupling the dynamic equations into a typical underactuated system,an underactuated sliding mode controller is designed,which can effectively suppress the liquid sloshing and the vibration of flexible appendages.In Chapter 5,the nonlinear optimal control law of flexible liquid-filled satellite and theactive vibration suppression method of flexible appendages with limited input are studied.Firstly,the State-Dependent Riccati Equation method is used to obtain the nonlinear state matrix,and the optimal control law is obtained by solving the corresponding Riccati Equation of spacecraft state at each time by MATLAB.Then,active vibration suppression of flexible appendages is studied to reduce the influence of flexible appendages vibration on satellite attitude angle and liquid sloshing.Lastly,in view of the saturation of the control inputs,the optimal control law designed can make the controlled variables reach the equilibrium state more smoothly and effectively suppress the sloshing of liquid fuel and the vibration of flexible appendages.