Analysis On Maintaining Stratification Retention Characteristics In The Entire Sampling Process For Deep Lunal Regolith

With the successful launch of Chang-e III lunar probe, the accomplished soft landing on the moon and lunar rover patrolling on the lunar surface, China’s lunar exploration project has been stepping up the pace into the third stage: sample return. Collection and returning the storage of lunar soil is the core problem of engineering tasks at this stage, for deep regolith sampling task, as the lunar soil sample obtained has a certain depth, the lunar regolith samples are desired not only to have sufficient quantities, but also to maintain quality information of the real lunar soil as much as possible, which means keeping the stratification characteristics of lunar soil. Therefore, a research on lunar regolith samples stratification retention characteristics in the whole process for deep sampling(drilling process, shaping process) has been made and focuses have been put on the influencing factors of lunar regolith samples stratification characteristics in the shaping process.A three-dimensional lunar soil particle contact model has been built using the discrete element method. This model is based on the traditional Hertz contact model, besides the basic spring-damper interaction, the bending and twisting moment between lunar soil particles are taking into account, an equivalent gravity is also introduced to represent the field force like electrostatic forces and Van der Waals forces between lunar soil particles, an effect scope has been set to the equivalent gravity, the normal and tangential contact force, bending and twisting moment can be calculated according to the model. The discrete element simulation tri-axial test has been used to calibrate the microscopic parameters of the lunar soil discrete element model. Nine microscopic parameters are set as impact factors of the particle contact model. The single variable method is adopted to analyze the influence of each parameter on the macroscopic mechanical properties of the lunar soil discrete element model. A group of microscopic parameters are finally determined by the analysis and the macroscopic mechanical properties: cohesion and internal friction angle can be calculated, they are 0.90 k Pa and 42.25° respectively.A simulation for the whole process of deep sampling has been done, the "stratified probability method" is applied to analyze the lunar regolith samples stratification retention characteristics, results show that: at the end of the drilling process, all the layers of lunar regolith samples stratification retention characteristics are subject to certain destruction, but deep regolith are better than shallow regolith. At the end of the shaping process, further damage of all the layers of lunar regolith samples stratification retention characteristics occurs. Based on the phenomenon above, a separate simulation for the shaping process has been done, the factors that may affect the lunar regolith samples stratification retention characteristics are analyzed, the results show that: the change of sample filling rate only affects first floor of lunar regolith samples, the greater sample filling rate, the better first floor of lunar regolith samples stratification retention characteristics; the increase of sample bag winding radius will make all layers of lunar regolith sample stratification retention characteristics better, same as the winding radius, the increase of winding speed will also do good to all layers of lunar regolith sample stratification retention characteristics.