Research On Docking Technology For On-orbit Assembled Modular Optical Primary Mirror

Because space telescope is not affected by gravity distortion and atmospheric turbulence compared with ground observation,it can realize the observation of diffraction limit by its own aperture,which is a difficult target for ground telescope with the same aperture.With the increasing demand of resolution,the aperture of space telescope is increasing.The technical difficulty and manufacturing cost of one-single mirror have become the bottleneck of large aperture optical system.Compared with the traditional optical system,the on-orbit assembled space telescope is characterized by a complete mirror with a certain mechanical error assembled from a number of segmented mirrors on the orbit,which meets the optical technical indicators through active optics and wavefront sensing and control technology.It has the advantages of breaking through the size limitation of the vehicle fairing,high resolution,light weight and modularity.As one of the future space telescope technology routes,it has been paid more and more attention by the research groups of various countries.The calibration process of the optical mirror of the space telescope assembled in orbit includes initial assembly,rough calibration and fine calibration,among which,after the locking of the segmented mirror is completed,the clearance error of micron level should be guaranteed,which is convenient for the fine adjustment of the actuator of the optical mirror.On the basis of systematical arrangement of relevant domestic and foreign literatures and research projects,this paper summarized the key technologies involved in the initial on-orbit assembly process,including the prediction of contact points between the segmented mirrors,collision buffering system and the influence of locking precision on the optical system.The specific research work is shown as follows:In this paper,a technical solution is proposed for the assembly of the main mirror in space,which adopts the pin-hole capture system of isomorphism,the design of dual-channel positioning,the passive axial locking system,the integration design of the single-degree-of-freedom adjustment and the release mechanism.Under the requirement of the optical accuracy index of the main mirror,a reasonable error distribution model of the optical system is established,and the influence of the mechanical clearance error of the segmented mirror 2 microns on the optical performance is studied and analyzed.At the beginning of docking,it is necessary to ensure the capture accuracy to reach the submillimeter level after the capture completed.For this reason,compared with the configuration form of traditional small on-orbit capture system,the allogeneic isomorphic pin-hole type capture scheme suitable for the space on-orbit assembled mirrors is established.Applying the geometric mapping theory of cartesian coordinate system,the prediction model of "double-contact" collision model is established.The model fully takes the existence of two sets of contact variables into account,obtains the initial captured kinematics conditions successfully,and theoretically obtains the predicted position distribution of collision points under different poses.The physical simulation docking dynamics test is established,and the contact analysis is carried out for the typical working conditions of the allogeneic pin-hole docking mechanism.Finally,the displacement curve is shown to obtain the capture accuracy within the range of ±0.015 mm,meeting the design requirements of the capture accuracy.The impact in microgravity can not be ignored,the "double-elastic" passive buffering model is established.The flexible design of protruding pin head and chamfered hole is made according to the characteristics of pin-hole collision.Using Newton-Euler dynamic equation,the buffer energy needed in the capture phase is analyzed.According to the superposition method of the normal concentrated force on the surface of the semi-infinite body,the maximum deformation and the maximum contact compressive stress of the model in the process of contact collision are analyzed.Through the comparison with the traditional rigid pin-hole mechanism,the results show that the "double-elastic" passive buffering model can absorb the impact energy by increasing the deformation of the wall and pin head.The deformation value can be increased by 3 times with the impact force,and the maximum impact force can be reduced by 58%.After the completion of docking,the assembly of the segmented mirror needs to maintain a certain locking strength.A passive axial locking system is proposed,which utilizes the principle of energy self-recovery to complete the locking by engagement between the locking teeth and the protruding pin.Based on the method of variable decomposition of elastic potential energy under complex boundary conditions,the stress and strain represented by cartesian tensor are selected to transform the problem of definite solution of the basic equation of elastic potential energy into the problem of extreme value of potential energy functional,and the theoretical model of flexible locking system is established.According to the contact conditions in different stages,the force boundary conditions and equilibrium differential equations are obtained.The kinematics curves of flexible locking teeth under large deformation are obtained through geometric nonlinear analysis and combining with the dynamic environment of the locking process,and the validity of the proposed theoretical model is verified.