Research On The Compression Property Of The Lunar Soil Simulant In Low Gravity Environment And The Relationship Between The Lunar Soil Simulant And The Lunar Rover

The lunar rover will be landed safely onto the lunar surface and further explore the lunarenvironment in the great lunar exploration project “Chang’e program” of china. Thegravitational acceleration of the lunar surface is about1/6of the earth’s. The lunar surface iscovered with thick and soft lunar soil which is composed in form of powder. Because thelunar soil rover is light and small, it is easy to subsidence, slip or even cannot move whenworking on the lunar surface. So it has great significance to study the effect of the lowgravity environment to the simulant lunar soil, and to compare the situation under the earthgravity environment, to explore the mechanics characteristic under different gravityacceleration, and the relation between the rut depth and the lunar soil characteristics, throughthis analysis we can develop the lunar vehicle of high accessibility.The Lunar is divided into Maria and Highland. The Maria is the wide plains and most ofthem located in the northern hemisphere of the lunar positive, accounting for17%of thesurface area of Lunar. The United States Apollo11,Apollo12and the former Soviet UnionLunar24manned spacecraft are landed in this region, the Rainbow Bay area, the preferredlanding of China’s lunar exploration program, also belong to the Maria area, the averagethickness of lunar soil in this region is4⁵m; most of the particle diameter of30μm¹mm. The median diameter between40μm¹30μm, an average of70μm, the main strip ofthe particle form is sub-angular and angular; Lunar soil shear and bulk density and void ratiohave a close relationship. The compaction state of the lunar soil void ratio range of0.7¹.0and the loose state void ratio range of1.2to2.4. In addition, different locations and differentdepths of lunar soil porosity are also different.The development of JLU lunar soil simulant can be divided into as dehydrating, grindingand ratio, dehydrating is to remove the water content, grinding is to grind the raw materialinto a mesh of semi-finished products, and finally mixed by a certain percentage ratio, andthe pressure and shear characteristics of the lunar soil simulant is studied, the measured shearparameters c ranged from0.03⁰.06N/cm², φ is30³7°, the pressure parameters n rangedfrom1.1¹.4, k_cis0⁵.8N/cmn+1, k_φis3.1⁴.9N/cmⁿ⁺², compared with the real lunar soil,the measured parameters of the JLU lunar soil simulant are in line with the correspondingparameter range of the real lunar soil, the penetration resistance test are done to the simulant using different cone, and obtained the CI value of JLU-1is the biggest, followed by theJLU-3and the JLU-2is the smallest. The measuring effect of number d cone comes better.The pressure characteristic test of the JLU series of lunar soil simulant is done using thelow-gravity equipment. The principle of eliminating the invalid number is: under the samepressure, at the same tilt angle, speed, lunar soil and the lunar soil state, the subsidence of thelarge area of the plate is smaller than the plate with small area; The settlement amount-pressure curves of the three simulant lunar soil test data on the overall analysis shows that,When the settlement amount of JLU-1is20mm or even10mm, the pressure showing rapidgrowth. When the settlement amount of JLU-2is20mm or even50mm, the pressure showingrapid growth. The pressure of JLU-3is generally at30mm the settlement shows rapid growth,and at0²0mm shows the slow growth. The above low existed in different tilt angle, plate,lunar soil simulant and the state, it shows that JLU-2is relatively soft and easy to settle,followed by JLU-3,and JLU-2is the hardest of all, not easy to settle and bearing strongly.Using the lunar soil simulant plate test data processing software we can get the n、k_cand k_φwith different methods, the results show that the gravity acceleration affect the pressureparameters of the lunar soil simulant. The three lunar soil simulant generally show thefollowing law: the smaller the acceleration is the n and k_φis smaller, thought k_cchangesinsignificantly, it show the trend that it decrease with the acceleration of the gravity, testedon the7th plate, the results showed that the smaller angle of the inclination the less slope ofthe settlement amount-pressure curve, that is, the lunar soil simulant is solid and produce thesame amount of the settlement need greater pressure, while the larger angle of the inclinationthe bigger slope of the settlement amount-pressure curve. That is, the lunar soil simulant issoft and produce the same amount of the settlement need smaller pressure.Using the software of PFC3D, take the JLU-2lunar soil simulant at loose state and the6th,7th plant for example, the simulated plate test were taken at1/6g、2/6g、3/6g、4/6g、5/6g and1g condition. The test data analysis shows that the conclusion of the simulatedtest and the real test are same, that is the three pressure characteristic parameters of the lunarsoil simulant has the rising trend with the rising of the gravity acceleration on the overall.That is because the smaller of the gravity acceleration the bigger mobility of the particlesunder the action of the platen pressure, so resistance platen pressure deformation capacity ofthe lunar soil is smaller, that is the smaller of the gravity acceleration the smaller of the nvalue. Oppositely the larger the gravity acceleration the bigger the n is and the same to the k_c and k_φ, though the trend of rising is same for the k_cand k_φ, the law does not same underdifferent gravity acceleration.The relationship of the wheel and the lunar soil is researched based on test and simulation.The shape of the rut, the settlement and the resistant force of moving the soil is collected, theresults showed that the18round thorns driving wheel role in the JLU-2is best; The briefanalysis is taken to the destruction of the lunar soil under different structure of the wheelsand different slip rates. The wheel with thorn and the without makes different rut, the soilunder the wheel without thorn cause the backward destruction to the lunar soil, and formscaly rut morphology; While the rut of the wheel with thorn is formed by the thorn; The rutbecoming insignificantly with the increase of the slip rate, and the extent of the destruction isgrowing, this is because with the increase of the slip rate, the time the wheel work on aposition of the lunar soil become long, assume a fixed speed, the simulated lunar is disturbedfrequently; The shape and the formation of the driving wheel rut is analyzed. The process ofthe formation of rut is: while the driving wheel rotating forward, a certain thorn contact andcompress the soil, the soil in the neighbor of the thorn undertake the compress force, whilethe thorn is at its vertical position, the process of compressing the soil ended, the process thethorn insert into the lunar soil simulant belongs to the resist-settle period, before the verticalposition, it is belongs to friction force function period, these two period will help to promotethe accessibility of the lunar vehicle. After the vertical position it belongs to the no-powerperiod, in the design of the wheel thorn structure, the effect of the two period beforehandshould be enhanced and the last period should be decreased; Using the PFC software to takethe discrete element simulation results show that the relationship between test result and thesimulated results are same. With the rise of the height of the thorn the settlement increase,with the increase of the number of the thorn the frequency of the settlement increase, thethorn rut not only has the relationship with the structure of the wheel but also with slip rateand the load of the wheel.