Load Characteristics Of Drilling And Coring In Lunar Regolith Simulant And Drilling Control Investigation

Lunar regolith refers to the 4–15 m thick layer of granular materials covering the underlying bedrock of the moon.The successful extraterrestrial sampling missions demonstrated that Drilling and coring is known to be an effective way to acquire regolith samples.The Chang'e-5 lunar exploration project aims to sample lunar regolith through an automated drilling and coring device and return it to Earth.The drill and lunar regolith have a complex physical interaction that may determine whether the device can obtain a desired sample.In the background of the third phase of the Chang'e project,this paper proposed a lunar regolith preparation method,observed the mechanism of the drill-regolith interaction,presented an automated control method for drilling and coring,and can serve a theoretical foundation for the lunar regolith drilling and coring mission of China.To facilitate the modeling and simulation of lunar drilling,ground verification experiments for drilling and coring should be performed using lunar regolith simulant.The simulant should mimic actual lunar regolith,and the distribution of its mechanical properties should vary along the longitudinal direction.Furthermore,an appropriate preparation method is required to ensure that the simulant has consistent mechanical properties so that the experimental results can be repeatable.Vibratory compaction actively changes the relative density of a raw material,making it suitable for building a multilayered drilling simulant.It is necessary to determine the relation between the preparation parameters and the expected mechanical properties of the drilling simulant.A vibratory compaction model based on the ideal elastoplastic theory is built to represent the dynamica l properties of the simulant during compaction.A simulant preparation method is presented to obtain drilling simulant with the desired mechanical property distribution along the depth direction.The modeling of drill-regolith interaction can provide a fundamental reference for the drill tool design and development of drilling strategy.In much previous work,the drill-soil interaction was divided into the screw conveyance and the soil cutting processes.The boundary conditions and soil mechanical property difference between these two processes were ignored in the modeling of drill-soil interaction.The simulant rupture is accompanied by simulant chip flow during simulant drilling,which may significantly influence the drilling load,and is required to consideration.In this paper,the interaction between the drill tool and lunar regolith simulant was divided into four parts: cuttings screw conveyance,cuttings extruding,cuttings bulldozing and in-situ simulant cutting.Considering the boundary conditions and simulant mechanical property difference between the four parts,a drill-simulant interaction model based on the passive earth pressure theory was developed to predict the drilling load.Drilling experiments indicate that the drilling loads calculated by the proposed model match the experimental results well.Because there is no relative sliding between the lunar regolith and the flexible tube,using the flexible tube coring method can acquire high coring rate and keep the stratification of regolith samples.A proper understanding of the coring process is necessary to develop the drilling strategy and verify whether the designed drill tool is appropriate.Based on the Walters analysis method and the Terzaghi bearing theory,two models are developed to analyze stress distribution in lunar regolith simulant during coring.Based on the developed models,a prediction method of coring rate is developed to analyze the influence of the drilling parameters on the coring rate.Comparison of the model calculation results with data of drilling and coring experiments obtains the suitable drilling parameters.The drilling media on the Moon contains loose granular lunar regolith and massive lunar rocks.Lunar regolith and lunar rock may be encountered randomly along the longitudinal direction.Due to the indeterminable drilling environments for the sampling device,the automated control becomes very crucial in the drilling process.This paper proposed an adaptive neuro-fuzzy inference system(ANFIS)based control strategy to tackle the complex drilling media beneath lunar surface.A multi-layered drilling medium is built with lunar regolith simulant and lunar rock simulant for drilling experimental test.Experiments are conducted to validate whether the ANFIS based control strategy can adapt to the complex environment.