Research On The Kinetic Penetrating Effects In The Main-belt Comet Rubble Pile Structure

The main-belt comet is a special type of celestial body discovered in recent years.Its orbit locates in the asteroid belt between Jupiter and Mars and normally shows periodic volatilization charateristics near perihelion.In order to find out the volatilization mechanisim of the main-belt comet and the relationship between local volatile and water on the earth,China has developed an exploration mission targeted at 133 P and the subsurface detection will be an important part of the mission.A kinetic penetrator project will be accepted to implement the subsurface exploration task.Considering the difficulty of uncertain rubble pile structure under low-gravity environment,the thesis mainly works with the design of the penentrator structure.The change of penentration characteristics in the rubble pile structure is predicted using theoretical and simulation methods and an optimization structure is selected according to comprehensive evaluating indexes.Taking the characteristics of the main-belt comet rubble pile structure into account,this thesis designs ogive and truncated two different noses for the penetrator.Based on Mohr-Coulomb yield criterion and linear compressible model,the stress distribution function on the nose is analysed when penentrating in the rubble pile.Then the axial resistive force which changes with the penetrator velovity is obtained using infinitesimal method.Finally,penetration depth is derived for different noses under corresponding initial velovity according to Newton’s second law.Based on the impact model,the penentrator is transformed to an equivalent spherical projectile and the crater volum is then derived.The relationship between material coefficient μ and particle ejection angle is established through Z model and modified Z model.In addition,the physical model between ejecta curtain angle and particle ejection angle is developed by analysing the motion of the ejected particle.Consequnently,the strength of the rubble pile structure is evaluated in combination of the penetration cratering model,particle ejection model and the actual crater diameter.The discrete element method of LS-DYNA software is used to simulate the rubble pile structure of the main-belt comet and rubble pile penetration parameters are obtained through the analysis of former penetration experiments.Based on these parameters,the penetration process can be simulated for different penetrator structures and a proper nose shape for rubble pile penetration can be selected according to comprehensive evaluation indexes.On the other hand,the accuracy of the ejecta curtain angle model is verified by applying results in other references to the model.This thesis mainly studies the change of penetration charactristics and particle ejection phenomenon in the rubble pile structure.The results will provide theoretical basis for the structure design and optimization of China’s penentrator project,and enrich the scientific value of the main-belt comet exploration mission on the other hand.