Gravity Compensation Method Of Deployable Space Cable-Net Antennas

Cable-net antennas are widely used in the aerospace field.There are differences of gravity field between the ground and space environment.At the same time,the the cable-net structures have the characteristics of large diameter,large flexibility and high nonlinearity.Therefore,how to perform the gravity compensation of deployable space cable-net antennas becomes a key technology in the ground-based verification process.In orger to solve this problem,this paper has carried out three aspects of work,as follows:(1)The nonlinear stiffness of cable-net structures in the gravity environment is studied.Firstly,the force density method is used to pre-tension the cable-net structure in the gravity-free environment to ensure that the cable-net structure has certain stiffness.Secondly,based on the static equilibrium equations in the gravity-free environment,the static equilibrium equation of the cable-net structure in the gravity environment is derived.The analysis proves that the stiffness of the cable-net structure in the gravity environment is nonlinear.Further,the pre-tension level,material properties,geometric topology and other factors have a great influence on the nonlinearity of the cable-net structures in the gravity environment.Finally,the effects of parameters such as pre-tension,density and antenna aperture on the surface accuracy of different cable-net structures in the gravity environment are studied.It is concluded that when the material density and the the diameter are larger in the gravity environment,increasing the pre-tension within a certain level makes the surface accuracy less affected by gravity.(2)The shape analysis method of the cable-net structures in the gravity environment is studied.Firstly,based on the characteristic analysis of catenary cable elements,the formulas for solving the nodal force of catenary cable elements are derived.Secondly,according to the force of vertical cable,the calculation method of nodal force of vertical cable is given.Aiming at the shape analysis of cable-net structure in the gravity environment,a mathematical solution model based on dynamic relaxation method is proposed.Finally,the computational accuracy and efficiency of the above method are analyzed with two-catenary clues structure,a planar catenary clue structure and a spatial catenary clue structure.The results show that the method has high computational precision and few iteration steps,which can effectively solve the problem of shape analysis of cable-net structure in the gravity environment,and has a good versatility.(3)The gravity compensation method of cable-net structures is studied.Firstly,this paper compares the difference between the gravity compensation and the shape adjustment of the antenna reflection surface,and clarifies the principle of gravity compensation the reflection surface of the cable-net antenna.Secondly,considering the size,shape and working state of the antenna reflection surface,the balloon suspension method is used to perform gravity compensation on the reflective surface of the space cable-network antenna.A comprehensive compensation method and a sensitive compensation method are proposed to determine the distribution of the compensation point and the magnitude of the eompensation force in the proeess of balloon suspension compensation.Simultaneously,a case study is carried out.It is found that the compensation effect of the comprehensive compensation method and the sensitivity-based compensation method are similar.However,increasing compensation points will lead to larger calculation amount and longer optimization time,which makes it difficult to get the optimal solution with the comprehensive compensation metihod.As for the sensitivity compensation method,the umifonnity of compensation point distribution and compensation force is good,and the internal structure of the cable-net structure is not changed.Besides,the compensation effect is relatively stable.