Effect of gravity on the mechanical properties of lunar regolith tested using a low gravity simulation device

Simulations of the bearing capacity and shear strength of regolith under Earth’s gravity produce different results from those under low gravity. A low-gravity simulation device was developed in this study, and an internal stress model of regolith simulant was established to correct the errors. The model revealed additional force on both shear plane in the shear test and the press plate area in the pressure–sinkage test. The sinkage and shear test results showed that low gravity decreased the deformable index n, frictional modulus k_φ and cohesion c, whereas there were no obvious changes to the cohesive modulus k_c and internal friction angle φ. The sinkage generally increased as the gravity decreased under a consistent normal load larger than 50 N, but when the wheel load was lower than 50 N, the sinkage of the TYII-1 simulant was larger under 1 G than 1/6 G. Gravity had little effect on the shear strength of the regolith. However, the tractive thrust of the TYII-1 simulant was lower under 1/6 G than 1 G. The smaller difference was due to differences in the way the soils responded to changes in the gravity level for the TYII-2 simulant.     

基于XRD-Rietveld全谱拟合技术定量分析花岗岩风化壳中矿物组成

XRD-Rietveld全谱拟合方法突破了传统XRD定量分析的众多技术局限,在解决复杂多相混合物的定量问题方面具有显著优势。将XRD-Rietveld全谱拟合方法引入风化壳矿物学研究,有助于解决长期以来地学界对风化壳中矿物组分缺乏准确定量认知的技术瓶颈。在制定专门针对风化样品的全谱拟合精修策略基础上,以广西玉林大容山地区的花岗岩风化壳为研究对象,对发育在两组不同岩性之上的风化剖面(剖面A和剖面B)进行了对比研究。结果表明,风化剖面A(母岩为粗粒黑云母花岗岩)的矿物组合及含量变化范围为：高岭石(6.05%～44.67%)+伊利石(15.85%～49.59%)+石英(29.72%～46.15%)+钾长石(12.04%～22.85%)+斜长石(24.33%～32.70%);风化剖面B(母岩为细粒黑云母花岗岩)的矿物组合及含量变化范围为：高岭石(3.12%～11.47%)+伊利石(13.95%～31.94%)+石英(26.60%～58.05%)+钾长石(13.70%～43.47%)+斜长石(17.95%～23.47%)。两组剖面的全谱拟合修正因子R_wp值<15且gof值<5,计算谱与原始谱拟合效果好,指示矿物定量数据可靠,且能与地质规律较好匹配。在地质意义上,本研究通过母岩原生矿物与次生矿物的含量同步变化,深入揭示了研究区内花岗岩的化学风化过程,厘定了长石类矿物在亚热带气候环境下所经历的长石→伊利石→高岭石演变序列。基于剖面A与剖面B中粘土矿物总量和矿物构成出现显著差异,研究认为在研究区内粗粒黑云母花岗岩比细粒黑云母花岗岩更易遭受强烈的化学风化作用。     

Electrostatic transport of regolith particles for sample return mission from asteroids

To achieve reliable and autonomous regolith sampling from asteroids in space, the authors have developed a new sampling system that utilizes electrostatic force. This system consists of electrostatic capture and transport subsystems. Regolith particles on an asteroid are captured through parallel screen electrodes activated by the application of an alternating high voltage. The captured particles are then transported to a collection capsule from side to side basically along the electric flux lines in a zigzag path where an alternating electrostatic field is applied. It has been demonstrated that glass and sand particles can be transported in the horizontal direction that imitates micro-gravity on asteroids. The transport rate was increased by applying a high voltage of appropriate frequency. The demonstrated transport rate was approximately 3 g/min. The configuration of the path was improved to increase the transport performance. Numerical calculation using the discrete element method predicted that the transport of particles is successful if the gravity is less than 0.02-G. The process of sampling particles on asteroids will be easier than that on the Earth, because gravity is extremely low on small asteroids, particles are assumed to be highly charged because of cosmic rays, no air drag is exerted on the particles, and high voltage can be applied in vacuum where no gas discharge occurs.     

Vibration transport system for lunar and Martian regolith using dielectric elastomer actuator

An electrostatic transport system for lunar and Martian regolith particles was developed to realize In-Situ Resource Utilization for the successful long-term exploration of the Moon and Mars. The new system utilizes the dielectric elastomer actuator (DEA), which consists of a dielectric elastomer film sandwiched between elastic plate electrodes. When a high AC voltage is applied to the electrodes, the dielectric elastomer is driven by Maxwell stress and the resultant vibration is utilized to transport the regolith. The system has no mechanical drives and does not need complicated controls or high power consumption; thus, it is highly reliable for space application. In this study, the motions of regolith particles on a vibrating plate in the Earth and Moon environments were firstly investigated using a simple model calculation. Then, two types of vibration transport systems using DEA were developed based on the calculation results, and the basic characteristics of vibration transport for regolith were experimentally determined. The calculation result shows that the acceleration of the vibrating plate is the key factor for the success of vibration transport, and the lunar regolith simulant FJS-1 could be experimentally transported at a feed rate of approximately 1.95 g/s on the Earth using one of the developed system types when the plate acceleration exceeded 14.7 m/s². It is expected that the transport performance of the system will be improved in the Moon environment owing to the absence of air drag and the small gravitational force.     

Model of light scattering by dust particles in the solar system: Applications to cometary comae and planetary regoliths

We analyze both the intensity and linear polarization of cosmic dust particles by using the physically exact superposition T-matrix method in a fixed orientation for various aggregates of spheres and DDA for the aggregates of Gaussian random spheres. We study both the spherical geometry (in cometary comae) and cylindrical slabs (for regoliths) up to 2000 monomers with size parameters less than ∼3. It is straightforward to produce the observed linear polarization in both geometries while the typically convex and strong opposition spike seems to require wide regolith geometries. The dependence of various parameters on light scattering has also been studied in a rather detailed form. In applications to the cometary polarization we can fit the data in six colors from UV to the J band at a very good accuracy. We, however, emphasize that we do not claim our model to be unique. The most important parameters here are the refractive index and the size distribution of submicron particles. Rest of the parameters has only a minor role. We also found that it is critically important to use several realizations from any assumed particle geometry model because corresponding scattering characteristics can vary quite a lot.     

Light scattering by aggregates of varying porosity and the opposition phenomena observed in the low-albedo particulate media

The rule that the opposition phenomena in brightness and linear polarization observed in many regolith surfaces usually accompany each other is violated in the cases of very dark asteroids and particulate samples: practically no nonlinear surge of brightness to opposition is observed while the branch of negative polarization at small phase angles exists. To explain this fact, we model the light scattering by particulate media with ensembles of spherical particles (with size comparable to the wavelength) of varying packing density and refractive index. The superposition T-matrix method is used. The increase in the absorption and/or packing density diminishes the amplitude of the brightness opposition peak, and its profile becomes wider. The influence on the branch of negative polarization is more complex and depends on the relation between the size parameters of the constituents, the refractive index, and the porosity. However, the feature common to all considered cases is that the negative branch changes its shape and the polarization minimum moves to the inversion point. This behavior radically differs from that observed in nonabsorbing ensembles of particles and reflects the fact that the efficiency of the coherent backscattering, which mainly determines these characteristics in nonabsorbing ensembles (to the packing density of about 30%), decreases. Moreover, since the angular profiles are not simply damped, but the polarization minimum changes its angular position, we may conclude that the near-field interaction of the constituents becomes important: the shielding of particles by each other eliminates many constituents from the scattering and the near-field effects promote the negative polarization and smooth the backscattering brightness surge. Due to this, when the packing density exceeds 10-20%, the opposition phenomena in absorbing ensembles are caused not only by the coherent backscattering, and situations, when the opposition brightness surge is practically suppressed, but the negative branch of polarization still survives, are possible. This may explain the fact that the dark regolith surfaces show no brightness opposition effect, but produce the branch of negative polarization with the minimum shifted from opposition.     

Particle-size sorting system of lunar regolith using electrostatic traveling wave

A particle-size sorting system of lunar regolith using an electrostatic traveling wave is developed for In-Situ Resource Utilization on the Moon to extract indispensable resources from the regolith and realize long-term exploration. The regolith is sorted by utilizing a balance between the electrostatic and gravitational forces, which are determined depending on particle size, in vacuum conditions where the particles are not subjected to air drag. In this study, the effect of particle charge on the particle motion is confirmed by conducting model experiments and numerical calculations based on the distinct element method. In addition, it was experimentally demonstrated that particles less than approximately 20 μm in diameter were efficiently separated from the bulk of a lunar regolith simulant FJS-1 in a vacuum condition (∼1.5 × 10⁻² Pa), and the performance of the size sorting system on the Moon was predicted by the numerical calculations. The system utilizes only the electrostatic force, and it does not require any gas, liquid, or mechanical moving parts.     

Soft X-ray fluorescence from particulate media: Numerical simulations

We introduce a Monte Carlo ray tracing code for soft X-ray fluorescence in particulate media. We use the code to investigate the observation geometry dependent effects on absolute fluorescence line intensities and relative line ratios due to the medium porosity, incident spectrum, and particle size distribution. In particular, we assess the differences between the results given by the simulations and by the analytical fundamental parameters equation of X-ray fluorescence.