Research On Characteristic Parameters Design And Dynamics Of Tethered Space Elevator System

As a kind of tethered system for the cost-conscious space transportation,space elevator system has good application prospects.The theories of dynamics and control on space elevator system have been well studied in western countries since 2000.This paper analyzes the influence of the characteristic parameters on the structure and performance of space elevator system as well as studies the dynamic characteristics of the system,for laying the foundation for our research in this field.In this paper,we investigate the relation between the system deployment latitude,the stability and mode of the space elevator,the effects of the dynamic response and the oscillation suppression in or out of the equatorial plane by controlling the elevator movement,which is conducted in the method of system modeling,theoretical analysis,and numerical simulation.Here as follows are the main contents and achievements of the paper.First,the feasibility of the equatorial space elevator system is justified theoretically,and the designs for the system structure are summarized with the regular influence of kernel parameters on the system size captured in details.As well,the calculation for the system load capacity is elaborated.Then,the paper proceeds to the design of the non-equatorial space elevator system on the basis of the discrete model.The validity and accuracy of the design method is demonstrated through comparative analysis,which shows that the deployment scope and load capacity of the non-equatorial space elevator system can be calculated with accuracy in this method.Next,a rigid tether dynamic model of equatorial space elevator system with atmospheric damping is established by Lagrange method,and the stability of the topological equivalent linear equation of the original nonlinear system near the equilibrium point is analyzed by using the linear stability theorem.The results show that the original nonlinear system is asymptotically stable at the equilibrium point.A general high-dimensional discrete non-linear dynamic model suitable for arbitrary deployment latitude is established by Newton-Euler method to fully describe the coupling oscillation between the climber and the tether.The linearization method of high-dimensional nonlinear dynamic equation is proposed by using binomial theorem and cosine theorem based upon the static equilibrium configuration of the system,and the modal of the system is analyzed.The simulation results show that all the other modes are insensitive to the latitude of system deployment except the first and fifth modes.Then,the nonlinear dynamic response of the space elevator system in the process of the climber climbing has been researched by numerical simulation based on the climber trajectory prediction scheme and the PI controller.The results show that the dynamic response of the system is mainly based on the first two modes of the tethers.The magnitude of the limit residual oscillatory angle amplitude is less than 10^-1 degree.For the non-equatorial elevator system vertical response is one order of magnitude smaller than the horizontal response.The amplitude of residual oscillation angle increases with the increase of deployment latitude,climber load and cruising speed.In addition,the influence of the solar-lunar perturbation gravitation on the system is analyzed briefly.It is found that the perturbation gravitation mainly excite the out-of-plane oscillation of the tether.The influence of solar perturbation gravitation on tether is almost the same as that of climbers,whereas the influence of lunar perturbation gravitation on tether is about two orders of magnitude larger than that of climbers on tether.The results of modal analysis are verified by extracting the response spectrum of the counterweight.At last,a passive control method based on the approximate time ratio is improved considering the adverse effects of tether residual oscillation.It is found that the amplitude of residual oscillation angle can be reduced to 10^-33 metric levels by increasing the deceleration time of the climber at the expense of the climbing time.In order to improve the efficiency of climber operation,a seven-stage climber speed loading scheme is proposed.Sequential quadratic programming（SQP）method is applied to optimize the reverse motion time of the climber.The results show that this method can make the residual oscillation response of the system zero,and greatly improve the efficiency of the climber.On this basis,the launch windows and cruise speed constraints are added to avoid the collision between climbers during operation.