Design And Dynamics Of An Orbital Net-capture System

As the rapid development of space technology and application, on-orbit refueling, maintenance, rescue and space debris handling has become the top issues in space domain, leading the transformation of space systems architecture and space infrastructures development direction. The autonomous and safe capture of a non-cooperative target is an important foundation to solve the above problems and bottlenecks of the key technologies; and is the indication of the development of space technologies. An orbit net capture concept for non-cooperative space target was proposed and related issues were investigated, and dynamic simulations were performed along with a series of ground tests of prototype systems.Firstly, based on the analysis of the concept of space capture, different space capture methods were compared to show the features and advantages of the net-capture system. Through the analysis of the process of the net capture mission, a net capture system design was derived. The net-shotting scheme with four weights, an undirected graph method to design net structures of flexible cables, the division of planar net structures and 3D net structures, and mechanical automating net-closing devices, were proposed. Three net capture scenarios were given as a V-bar, an R-bar and an H-bar net capture, with which were some performances indexes of net-capture systems.Secondly, the dynamics of net capture systems was divided into the dynamics of rigid bodies and the dynamics of flexible cable structures. A dumped-mass method was utilized to derive a particle system model of the flexible cable structure, which was coupled with the connected rigid bodies to compose the coupling dynamics of the net capture system. A set of algorithms, which form the base of a computer-aid dynamic analysis software of net structures, were given to compute the coupling equations of motion of the systems automatically, with any given structure of net capture systems. Based on the algorithms, object-oriented simulation software was implemented. A primary investigation of the dynamics of impact and contact during the net capture were performed.Thirdly, dynamic aspects of planar nets and 3D nets were investigated by simulations. The process of casting of a planar net was concluded as spreading, flying and collapsing. Different mission scenarios, as V-bar, R-bar and H-bar capture, were considered as feasible as the simulations showed. Two design parameters, casting angle and damping ratio, were considered to be crucial to the net capture mission, further simulations and analysis showed opportunities of optimization. The simulation of casting of a 3D net showed that extra control was needed to keep the net structure in an advantageous shape for capturing; a simple control scheme was proved to be effective with simulations. Fourthly, the dynamics of ideal cable under impact was investigated to attempt to reveal the cable dynamics behind the collapsing of net structure when casting. The equations of motion for a flexible cable with snatch load acting at its ends are derived from the one-dimension continuum model, which are integrated with the finite difference method to investigate the processes of stress-waves propagating in cables and reflecting at a fixed end or a free end. The stress-waves propagation can reveal the underlying process when the cable changes between slack and tense. The results of stress-waves and energy analysis show the non-linear aspects of stress wave's propagation due to the physical and geometrical non-linearity of the cable.Finally, schemes of net casting ground test and net castings on an aero ship were proposed. The results obtained in ground test and casting on an aero ship show the feasibility of the concept and design of the net capture system, especially the casting device and the net closing device. Dynamic models and simulations are verified with the data collected in ground test.To sum up, a systematic investigation of a net capture system was performed, in which the coupling dynamics of flexible cable structure and rigid bodies were modeled and simulated, and which provides a theory framework of the design of net capture systems. Ground tests of the net capture system prototype are important complement of the analysis and the investigation, which build a base to implement the orbit net capture system.