Coupling Dynamic Characteristic And Attitude Control Of Super Large Space Structures On Orbit

With the development of the space technology,the super large space structures are widely concerned.The solar power satellite,which is one kind of super large space structures,is designed to collect solar energy on orbit and then transmit the energy to the ground.The solar power satellites usually are as large as several kilometers,due to the requirement of the sunlight collection on orbit.Meanwhile,the solar power satellites are highly flexible in order to reduce the cost of the construction in space,and the structural fundamental frequency could be as low as 10-3Hz.The dynamic coupling of this kind of the super large space structure is strengthened among the orbital motion,attitude motion and structural vibration.The effect of the space environment on the dynamics of the much larger space structure is also more obviously,and leads to the further enhancement of the dynamic coupling,especially the effect of the gravity gradient.Besides,the inertial moment of the super large space structure,like the solar power satellites,is usually much larger,and the electric propulsions are selected as the actuators of the attitude control for such space structures.Because the fuel of the attitude control system would be continuously consumed to maintain the normal operation,the fuel amount of the attitude control system becomes one of the key factors of the limitation of the operation life.It is thus very important to reduce the fuel consumption of the attitude control system for the long-life operation of the super large space structure.In addition,it is very necessary to consider the isolators among components of the solar power satellite to improve the high-accuracy pointing performance.There are the disturbances with the quite low frequency on the super large space structure during the attitude control.Taking the limitation of the frequency which the isolators could deal with into consideration,the isolators which are usually used for the spacecraft could be unsatisfying and a new one with very low stiffness is quite demanded for the solar power satellite.The specific researches in this paper are as follows:The dynamic coupling models of the super large space structure are established among the orbital motion,attitude motion and structural vibration with the effect of the space environment in the Earth orbit.The modeling of the dumbbell and the flexible beam which are moving in the orbital plane in the presence of the gravity gradient are derived,based on the Hamilton canonical equations.The generalized forces due to the solar radiation pressure exerted on the super large space structure are formulated with the effect of the Earth’s shadow.The equations of the thermal analysis on orbit of the dumbbell and the flexible beam with the effect of the space thermal radiation are derived,as well as the equations of the thermal-structural vibration.The effects of the space environment on the dynamic coupling of the super large space structure are investigated.The coupling phenomena between the attitude motion and the structural vibration of the super large space structure are discovered especially and the coupling principles are discussed.Firstly,the effect of the gravity gradient on the orbit motion,attitude motion and structural vibration is discussed in a circular orbit by comparing the simulation results with different parameters,and the dynamic coupling due to the gravity gradient between the attitude motion and the structural vibration is illustrated.Based on the Linzted-Poincare perturbation analysis method,the structural parametric excitation of the super large space structure,which is raised by the attitude motion,is investigated aiming at the unstable phenomenon for the increased size scale.Besides,the effects of the solar radiation pressure on the orbital motion of the super large space structure are discussed,and the effect on the attitude motion is compared with that of the gravity gradient when there is some deviation of the mass center.In addition,the temperature change and the thermal structural vibration of the super large space structure due to the thermal radiation is investigated,and the effect of the Earth’s shadow is considered.The integrated attitude control system of the super large space structure is designed based on the moving mass system and the electric propulsions.The moment of the solar radiation pressure is utilized as the partial attitude control moment actively,and then the reduction of the fuel consumption of the attitude control system is achieved.Firstly,according to the result in Chapter 3 that the effect of the moment due to the solar radiation pressure is significant,the integrated attitude control method is designed based on the moving mass system.The flexible beam with a moving mass is considered based on the dynamic model established in Chapter 2.The changes of the dynamics due to the motion of the moving mass are investigated.The results preliminarily imply the feasibility of the proposed attitude control method.Then the double-loop control system consisting of the attitude stabilization of the solar power satellite and the trajectory tracking of the moving mass is designed.The stability of the integrated attitude control system is proven based on the Lyapunov’s stability theory by constructing the Lyapunov’s function.The control moment allocation strategy is proposed aiming to maximize the moment provided by the moving mass system.Furthermore,the reduction of the fuel consumption of the attitude control system is achieved by the proposed attitude control method through the simulation results.The relationship between the efficiency of the fuel saving is discussed with the mass of the moving mass.The isolation system with quasi-zero stiffness is designed to suppress the disturbance of the low-frequency vibration of the main structure of the super large space structure on the pointing accuracy of the payload,such as the energy transmitting antenna of the solar power satellite.The structural vibration of the main structure would influence the pointing accuracy of the payload.The isolation strategy is proposed with the quasi-zero-stiffness isolators in the cam-roller-spring form on this issue.Then the relationship between the force and the displacement in the quasi-zero stiffness system is derived.The force and moment transmissibility of the isolation system are derived respectively based on the method of harmonic balance,which implies that the proposed isolation system is effective for excitation with lower frequencies.Meanwhile,the effects of the design parameters on the isolation system are explored.Moreover,the dynamic model of the super large space structure with the isolation system is established.The system parameters are determined due to the effect of these parameters on the isolation system.The suppression of the structural vibration with the low frequency is achieved by the proposed isolation system.In addition,combined with the integrated attitude control proposed in the Chapter 4,the attitude control strategy of the solar power satellite with the moving mass system and the isolation system is investigated.The effect of the moving mass system is strengthened with the help of the isolation system,and thus the fuel consumption of the attitude control is further reduced.In this work,the dynamic coupling phenomena of the super large space structure during the long-term operation on orbit are discussed,and the attitude control method which is proper to the super large space structure is explored.The aim of this work is to provide the principle support of the research of the on-orbit dynamics and control technology.