Research Of Stratification-Keeping Oriented Lunar Subsurface Soil Sampling Technology

The stratification information of lunar subsurface soil covers the morphological characteristics of the lunar soil profile,records the meteorite impact history of the lunar surface,contains abundant spatial environmental information.It is the main source of studying the lunar soil components,mineral resources,lunar history,space environment of earth and moon and solar activity.The United States and the Soviet Union have successfully acquired the lunar subsurface soil through different methods in the 1970 s and carried out a lot of analytical and research work.With the steady implementation of China's lunar exploration project,it has become an urgent demand for current scientific research through the unmanned method to obtain a certain depth of samples containing the stratification information of lunar subsurface soil.It is also the important way for China to independently analyze the lunar soil and the distribution of lunar resources.Typical sampling methods that can preserve stratification information include direct push sampling method and follow-up boundary sampling method.The former is suitable for shallow lunar soil sampling,while the latter is suitable for deep lunar soil sampling.In this paper,the sampling ratio and stratification information of two sampling methods are analyzed and studied,which provides theoretical basis and technical support for engineering transformation.On the basis of fully reviewing the sampling methods of extraterrestrial objects of the domestic and foreign research,in this paper,the direct push sampling method which can preserve stratification information in the sampling process of shallow lunar soil is taken as the research object,the description method of the sampling tube parameters and the evaluation method of sampling ratio are established.The soil plug model of the sample in the sampling tube is established by using the silo theory,and the key parameters such as the stress steering coefficient in the model are theoretically and experimentally analyzed.According to the soil plug model,combined with the relationship between the bearing capacity of lunar subsurface soil and its depth,the equilibrium equation of lunar soil sampling is established.The influence of sampling tube diameter,friction coefficient between the tube wall and lunar soil and the mechanical parameters of lunar soil on sampling ratio and its mechanism are studied.In the aspect of preserving the stratification information of lunar soil samples,the numerical model of the sampling process of the direct push sampling method is established by using the discrete element method,and the meso-parameters in the discrete element model are matched with the macro-parameters.The numerical simulation of the internal stress state,force chain distribution,injection history,particle flow line,void ratio and bulk strain,and structural disturbance of the lunar soil samples obtained by the direct push sampling method are analyzed.The vortex characteristics of the particle flowing in the sampling tube are demonstrated.The disturbance mechanism of the lunar soil samples in the sampling tube is explained and the parameters that affect the disturbing degree of the lunar soil samples are given.Based on the analysis of the influence parameters of sampling ratio and stratification preservation ability of direct push sampling method,a flexible followup boundary sampling method for deep lunar soil sampling and preserving stratification information is proposed.By changing the contact mode between lunar soil sample and sampling tube boundary,the scope and mechanism of boundary influence zone are reduced,and the sampling ratio and soil sample quality represented by stratification information are improved.Based on this sampling method,a nonslip flexible sampling mechanism is designed.The mechanical properties and environmental adaptability of the flexible sampling tube in the mechanism are studied experimentally.The key structural parameters of the mechanism are optimized with the objective of reducing the lift force.The mechanism can realize the follow-up between sampling boundary and lunar soil samples.Finally,a test platform for evaluating disturbance characteristics of a lunar subsurface soil sampler is developed,which can be used for performance and functional test of the lunar subsurface soil sampler under various typical lunar soil and environmental conditions.A series of sampling verification tests are carried out by using this test platform,including sampling verification test under ground conditions,sampling verification test in high and low temperature environment and the preserving stratification information test.The experimental results support the capability of non-slip flexible sampling mechanism in sampling ratio,the stratification information preservation of the sample and extreme environmental adaptability of the moon.