Dynamics Of The Space Tethered System And Attitude Control Of The Solar Panel

The space tethered system is a new type of spacecraft which contains multiple satellites connected by tethers.It has important applications in space research and deep space exploration with its unique structure.With the development of the space technology,various new application concepts about it have been proposed.The structure and the function of the space tethered satellite system become more and more complicated,and it is a hot research topic due to the complexity of tethers and the space environments.In this paper,based on the summary of researches about the tethered satellite system,the dynamics and control researches are carried out for a rotating triangular tethered satellite and a space tethered solar power station system.Main contents of this paper are as follows:(1)Based on Hill's constrained three body problem approximation and considering the coupling between the orbital motion and the configuration changes of the tethered satellite system,the dynamical formulation of a closed-loop rotating triangular tethered system near libration points in reconfiguration stage is developed.Through reasonable assumption,the tether is treated as a variable length and uniaxial stretching spring.The elasticity and the slack of the tethers,the change of the closed-loop configuration can be shown.The dynamical formulation can reveal the interaction between the configuration change and the orbital movement during deployment and retrieval stages.(2)For the rotating triangular tethered satellite system in Lyapunov periodic orbital near libration points L2,simulations are carried out utilizing time varying nonlinear dynamical formulations of the system.The dynamical stability of the system in reconfiguration stage is analyzed by comparing different reconfiguration processes in which the parameters of the system are various.The influences of the rotation speed,the tether length rate and the tether length on the dynamical stability of the system are studied.After the linear deployment stage of the tether,attitude errors of the system will arise due to the sudden change of the tether' s release rate.In order to reduce this attitude error,a tether release scheme including braking stage is designed.(3)A new complicated dynamical model is proposed for the space tethered solar power station in geosynchronous orbit.In this dynamical model,orbital movements of the bus system and the panel,the spatial attitude motion of the panel,the deployment and the retrieval of the tether are included.The continuous tether model is adopted.Tether's viscoelasticity and the inability to resist compression are taken into consideration,hence the flexibility and elasticity of tethers are involved.Tether's slacking,axial and the transverse vibrations can be presented.The geometric nonlinearity of the tether in large displacement movement is also included.Hermite interpolation is used to build the shape function for the discrete tether function.A freedom of degree adjustment strategy is designed in numerical simulations for the deployment and retrieval of the tethers.(4)Dynamical stability analyses are carried out for the space tethered solar power station.Numerical simulations are performed in the cases both initial state errors exist or not.The influences of the initial state errors on the orbital and attitude motion of system are analyzed by several simulations.The initial state errors include the initial panel attitude error in different directions,the axial and the transverse vibrations of the tether.(5)According to the dynamical characteristics of the space tethered solar power station,a new control method for solar panel is designed.When the bus system and the panel are at their equilibrium positions,a PD controller is designed.The pointing accuracy of the panel can be controlled by adjusting the lengths of the four tethers without leading to the orbital deviation.The simulation results demonstrate the feasibility of this control method.