Dynamic Behaviors Of Hierarchical-Tethered Towing System For Debris Removal

With-the increasing frequency of human launch activities,space debris has escalated from a danger to the space environment to a serious hazard to hum an space activities.To prevent collisions with space debris,the International Space Station,the Space Shuttle and many satellites often require orbital manoeuvres.In addition,at the altitude with tiny atmospheric drag,the orbits decay of the space debris is very slow,which implies that many of these objects may remain in their orbits for hundreds or even thousands of years.This required us to take active measure to remove these debris.The debris-tether-tug(DTT)system,has been considered as one of the most promising techniques for the space debris removal.In order to decrease the control difficulty of the DTT system,the DTT system was usually designed with a single tether.However,when the target owns the complex attitude motion,the removal efficiency of the classic DTT system(towing the target by a single tether)is limited.A modified DTT model with the hierarchical-tethered architecture is proposed to improve the removal efficiency in this paper.Compare with the classic DTT model,the hierarchical-tethered structure is introduced in the grabbing mechanism of our modified DTT system.This structure can enhance the catching ability while reducing the overall mass of the DTT system.In addition,we also improve the analysis method by introducing the sign function,in order to simulate the condition that the system is not constrained when the tethers are in relaxed state.Based on the Hamiltonian variational principle,the coupling non-smooth dynamic model for the hierarchical-tethered towing system is established,in which,four tethers are divided into two groups to describe the asymmetry of the DTT model well.The symplectic Runge-Kutta method is employed to simulate the evolution of the orbit radius of the target,the length of the tethers,the position of the tethers’ mass center and the target attitude angle.The numerical results reported show that,the competition relationship between the attitude stability of the target and the stability of the variation of the sub-tethers is affected by the relative stiffness of the tethers.In addition,the capture ability of the modified DTT system for the space target with a certain spinning speed is illustrated,which provides a theoretical basis for the design of the DTT system in future.We also study the influence of influence on system dynamics behavior cause by the variation of the towing force.The result verifies the ability of the proposed system to resist external interference.