Characterization of Lunar Dust for Toxicological Studies. I: Particle Size Distribution

The particle size distribution (PSD) of lunar dust, the <20?μm portion of the regolith, was determined as an initial step in the study of the possible toxicological effects it may have on the human respiratory and pulmonary systems. Utilizing scanning electron microscopy, PSDs were determined for Apollo 11 (10084) and 17 (70051) dust samples, as well as lunar dust simulant JSC-1Avf. The novel methodology employed is described in detail. All measured PSDs feature a log-normal distribution having a single mode in a range 100–300?nm for lunar dust samples, but the lunar simulant has a mode at ～ 600?nm.     

Geotechnical Behavior of JSC-1 Lunar Soil Simulant

To facilitate the modeling and simulation of lunar activities and natural processes, various lunar soil simulants have been created. In particular, Johnson Space Center Number One lunar soil simulant (JSC-1) has come into wide use by a variety of investigators. In any physical experiment, the behavioral properties of this simulant will have a profound impact on the results. To better understand these soil properties, a variety of conventional and unconventional experiments were conducted on JSC-1 to determine its friction angle and appropriate low strain elastic constants. These experiments were conducted on JSC-1 at a variety of relative densities to quantify the response of the soil over the range of possible conditions. Further, the samples were prepared through vibratory densification, allowing for a better simulation of probable lunar surface packing arrangements.     

Engineering Properties of Lunar Soil Simulant JSC-1A

This study was carried out to assess the tensile and shear strength in lunar soil, and to examine the variation as a function of density and confinement. Geotechnical engineering properties of the lunar soil simulant designated Johnson Space Center Number One-A lunar soil simulant (JSC-1A) have been investigated experimentally. To better understand these soil properties, a variety of conventional and unconventional experiments were conducted on JSC-1A to determine its grain-size distribution, cohesion, friction angle, dilatancy angle, tensile strength, and appropriate low strain elastic constants. These experiments were conducted on JSC-1A at a variety of densities prepared through tamping densification to quantify the response of the soil over a range of conditions. To simulate lunar conditions, the samples were prepared at medium to very high relative densities. Grain-size distribution, shear strength, tensile strength, dilatancy angles, and elasticity modulus of the JSC-1A were compared with lunar soil and other simulants.     

Discrete Element Modeling of Strength Properties of Johnson Space Center (JSC-1A) Lunar Regolith Simulant

This paper simulates the three-dimensional axisymmetric triaxial compression of JSC-1A lunar regolith simulant under lunar and terrestrial gravity environments under a wide range of confining pressures and relative densities. To accomplish this, the discrete element method (DEM), using Particle Flow Code In Three-Dimensional (PFC3D) software, was employed. The paper focuses on the peak and the critical state (CS) friction angles, which were predicted in the ranges of 35.4°–82.7° and 31.2°–79.8°, respectively, depending on the specimen density and confining pressure. A significant increase in peak and CS friction angles was predicted at near-zero confining pressure. The DEM results validated an empirical model that relates the peak friction angle with the CS friction angle, relative density, and mean effective stress at the CS. Comparison of DEM results with lunar in situ measurements of friction angle, from Apollo missions and other extraterrestrial laboratory experiments under a microgravity environment, shows a favorable agreement.     

Lunar Dust Levitation

Observations of a lunar “horizon glow” by several Surveyor spacecraft on the lunar surface in the 1960s and detections of dust particle impacts by the Apollo 17 Lunar Ejecta and Meteoroid Experiment have been explained as the result of micron-sized charged particles lifting off the surface. The surface of the Moon is exposed to the solar wind and solar UV radiation causing photoemission, so it develops a surface charge and an electric field near the surface. Dust particles injected into this plasma from the lunar regolith, whether from human and mechanical activity or from meteoroid impacts or electrostatic forces, may be stably levitated above the surface and may undergo preferential deposition onto areas of the lunar surface (or equipment) with different electrical properties. This can lead to a net transport as well as contamination of sensitive equipment. This paper reports on new experimental measurements and numerical simulations of the plasma environment above the lunar surface and the related behavior of charged dust.     

Microwave Sintering of Lunar Soil: Properties, Theory, and Practice

The unique properties of lunar regolith make for the extreme coupling of the soil to microwave radiation. Space weathering of lunar regolith has produced myriads of nanophase-sized Fe0 grains set within silicate glass, especially on the surfaces of grains, but also within the abundant agglutinitic glass of the soil. It is possible to melt lunar soil (i.e., 1,200–1,500°C) in minutes in a normal kitchen-type 2.45?GHz microwave, almost as fast as your tea-water is heated. No lunar simulants exist to study these microwave effects; in fact, previous studies of the effects of microwave radiation on lunar simulants, MLS-1 and JSC-1, have been misleading. Using real Apollo 17 soil has demonstrated the uniqueness of the interaction of microwave radiation with the soil. The applications that can be made of the microwave treatment of lunar soil for in situ resource utilization on the Moon are unlimited.     

Geotechnical Properties of JSC-1A Lunar Soil Simulant

For the success of planned missions to the moon in the near future, it is essential to have a thorough understanding of the geotechnical behavior of lunar soil. However, only a limited amount of information is available about geotechnical properties of lunar soils. In addition, the amount of lunar soils brought back to Earth is small. To help the development of new regolith moving machines and vehicles that will be used in future missions, a new lunar soil similant JSC-1A has been developed. A group of conventional geotechnical laboratory tests was conducted to characterize the geotechnical properties of the simulant, such as particle size distribution, maximum and minimum bulk densities, compaction characteristics, shear strength parameters, and compressibility.     

Martian and Lunar Cold Region Soil Mechanics Considerations

Robotic missions to Mars are listed and significant results of each past mission related to soil engineering are noted. What is known of the Mars environment and surface features that may be of interest to the engineer is summarized. The presumptive engineering properties of soils on the Martian surface are postulated based on expected soil forming mechanisms, the thermal environment found on Mars, and experience from cold region engineering on Earth. The discussion also extends to likely soil characteristics in craters found in the polar regions of the Moon. Experimental results from triaxial testing inert silt (JSC-1 lunar soil simulant) at and near freezing temperatures, with and without water, are also presented. Areas for future investigation and research are suggested.     

Direct Shear Tests on JSC-1A Lunar Regolith Simulant

A series of direct shear tests were conducted on the JSC-1A lunar regolith simulant in a 101.6-mm- (4-in.-) diameter container. The direct shear test provides a unique mode of failure that aids the development of excavation tools for the Moon. Relative density and normal load were varied to study the strength behavior of such granular material at peak and critical state conditions. The values of the internal friction angle ranged from 30 to 70°. A relationship between the internal friction angle of the direct shear and the published triaxial compression test results is presented. Additionally, the measured dilatancy angle is related to the difference in peak and critical state stress friction angles.     

NAO-1: Lunar Highland Soil Simulant Developed in China

A new lunar highland soil simulant, NAO-1, has been created in National Astronomical Observatories (NAO), Chinese Academy of Sciences. This simulant was produced by gabbro, which includes large quantity of feldspar (An>90). The simulant’s chemical composition, mineralogy, particle-size distribution, density, angle of internal friction, and cohesion have been analyzed and results demonstrated that most characteristics of NAO-1 are similar with lunar highland soil samples. NAO-1 will benefit the scientific and engineering research of lunar soil.     

Modeling Effects of Chemical Explosives for Excavation on Moon

Twelve model tests of chemical explosives (1 g and 0.25 g) of PETN were conducted at 1 g (? = ?6?g [moon]) and 10 g (? = ?60?g [moon]) using the geotechnical centrifuge to determine the effect of chemical explosives on cratering and loosening a compacted lunar simulant prior to excavation. Even small depths of burial of the explosives were found to increase markedly the volume and lip of resulting apparent craters; optimum depths of burial were not pinpointed. Volumes of craters from PETN charges of different weights but equal depths of burial, were related as V? = ?kW084 when charges were fully buried, but not for surface tangent charges. Tests conducted at 1 g and 10 g showed no detectable difference in crater volumes for the depths of burial tested. Constraints to extrapolating the research to the lunar surface (using simulant rather than actual lunar soil; working in earth′s atmosphere rather than in a vacuum; and working at greater than 1 g [moon]) are acknowledged.     

Use of Explosives on The Moon

The utilization of explosives for excavation on the lunar surface is under serious consideration as a part of the design for construction of temporary and permanent bases. An excavation research program has shown that small‐scale explosives blasting in a lunar‐soil simulant will greatly reduce the digging forces required for scoop and dragline excavators. Some crater‐blasting parameters were determined for the lunar soil simulant at one Earth gravity and at 10 Earth gravities using a centrifuge. The size of the craters produced at 10 Earth gs matched those formed at one earth g by scaling according to the weight of the explosive. These data can be applied to explosive‐excavation problems such as habitat construction, burial of nuclear power sources, and the rapid construction of shelters remote from the main base to shield against solar‐flare activity.     

Surface Cleanliness Effect on Lunar Soil Shear Strength

Lunar soil consists of dry silty sand. Observations and measurements conducted during Surveyor, Apollo, and Luna missions indicated that the lunar soil is unusually cohesive. This is attributable to the fact that thick layers of adsorbed gases, which coat and lubricate soil particles on Earth, are absent in the ultrahigh vacuum on the Moon. “Surface cleanliness” is introduced as a new parameter for describing soils in different planetary environments. It is defined as the dimensionless inverse of adsorbate thickness on solid surfaces. By this definition, the ultrahigh vacuum on the Moon is associated with high surface cleanliness, while Earth's atmosphere is associated with low surface cleanliness. A model is developed to calculate surface cleanliness and its effect on shear strength in any planetary environment. Results obtained from the model compare well with data from previous ultrahigh vacuum and variable temperature laboratory experiments on Earth soils. It is shown that surface cleanliness is an important parameter with respect to lunar soil shear strength.     

Geotechnical Properties of NT-LHT-2M Lunar Highland Simulant

Future lunar explorations require a thorough understanding of the geotechnical properties of lunar soils. However, the small amount of lunar soil that was brought back to earth cannot satisfy the needs. A new lunar soil simulant, NU-LHT-2M, has been developed to simulate lunar regolith in the lunar highlands region. It is characterized to help the development of regolith-moving machines and vehicles that will be used in future missions to the moon. The simulant’s particle size distribution, specific gravity, maximum and minimum densities, compaction characteristics, shear strength parameters and compressibility have been studied; and the results are compared with the information about lunar regolith provided in the Lunar Sourcebook.     

Electrostatic Cleaning System for Removing Lunar Dust Adhering to Space Suits

Removing lunar dust adhering to astronaut space suits is critically important for long-term lunar exploration. We are developing an automatic cleaning system that uses electrostatic force. It employs an alternating electrostatic field that forms a barrier on the surface of fabrics. In this study, we applied single-phase rectangular voltage to parallel wire electrodes stitched into the insulating fabric of space suits. By applying mechanical vibration and operating the system in a vacuum, we realized high performance: the cleaning rate exceeded 80%. Flicking out particles smaller than 10?μm in diameter that were trapped between fibers was difficult, but this system can perform preliminary space suit cleaning and save precious time for astronauts on the moon.     

3D Shape Characterization and Image-Based DEM Simulation of the Lunar Soil Simulant FJS-1

This paper describes a procedure used to characterize the three-dimensional (3D) grain shape of lunar soil and undertake simulations of lunar soil by image-based discrete element method (DEM). Given that detailed 3D grain-shape information is unavailable for real lunar soil, a simulant material, FJS-1, is used in this study. We use the high-resolution micro X-ray CT system at SPring-8, a synchrotron radiation facility in Japan, to visualize precise 3D images of the granular assembly of FJS-1. A newly developed image-analysis procedure is then applied to identify individual grains. Using the obtained grain-shape data, a sufficient number of FJS-1 grains are directly modeled for DEM simulation using an efficient modeling scheme. A series of particle flow simulations are then performed with the modeled grains. The resulting slope angles are in good agreement with experimental results. We discuss the effect on the slope angle of grain parameters such as contact stiffness, restitution coefficient, and interparticle friction.     

Thermodynamic Analysis on Lunar Soil Reduced by Hydrogen

Although many experiments have been performed to reduce the lunar soil by hydrogen, no systematic thermodynamic analysis has been developed to design and optimize these experiments. Applying a thermodynamic model to the system of simulant lunar soil and hydrogen, this study analyzes and discusses the thermodynamic behavior of the system in detail. The calculations demonstrate that iron is the only metal that can be extracted significantly from the lunar soil. The amount of hydrogen in the system drastically affects the processes of iron extraction and water production. However, the effect of system pressure can be neglected in the process. The yields of metallic iron and water from the lunar soil as functions of temperature and hydrogen content are investigated in this study. Additionally, the calculations explain the metallic iron on the surface of the moon from the thermodynamic point of view.     

Evolution of the vertebrate H1 histone class: evidence for the functional differentiation of the subtypes

BACKGROUND: Indoor suspended particulate matter (SPM) consists of many different types of particles, the vast majority of which are less than 2.5 microm in diameter. The question arises how these particles may contribute to asthma and respiratory symptoms. One possibility is that airborne dust particles act as carriers of allergens into the airways, as several allergens have been found to be associated with inhalable airborne dust particles. OBJECTIVE: We studied the presence of three different allergens on the surface of SPM, i.e. Can f 1 (dog), Bet v 1 (birch pollen) and Der p 1 (house dust mite). We also examined the ability of diesel exhaust particulates (DEP) to attach these allergens and Fel d I (cat) in vitro. METHODS: SPM was collected on polycarbonate filters and an immunogold labelling technique was used to detect the allergens on the particles. The specimens were examined in the backscatter mode of a scanning electron microscope. The same technique was used to examine the binding of the allergens to DEP, after exposing DEP to either crude allergen extracts or partly purified allergens. RESULTS: Both Can f 1 and Bet v 1 allergens were detected on the surface of the soot particles in SPM mixtures, although to a lesser degree than previously found with Fel d 1. Der p 1 (house dust mite), however, did not show any significant binding to SPM particles. Furthermore, DEP had the ability to adsorb all four allergens in vitro, although to a varying extent. CONCLUSION: Soot particles in airborne house dust may act as carriers of several allergens in indoor air. Furthermore, DEP has the ability to bind all the four allergens investigated under aqueous conditions in vitro.     

Characterization of Microstructure, Texture, and Microtexture in Near-Alpha Titanium Mill Products

Microstructure, texture, and microtexture in Ti-6Al-2Sn-4Zr-2Mo-0.1Si billet/bar of three different diameters (57, 152, and 209 mm) were quantified using backscattered electron imaging and electron backscatter diffraction. All three billets exhibited a microstructure comprising a large fraction (≥70 pct) of primary alpha particles, the average size of which decreased and aspect ratio increased with increasing reduction/decreasing billet diameter, or trends suggestive of low final hot working temperatures and/or slow cooling rates after deformation. Appreciable radial variations in the volume fraction and aspect ratio of alpha particles were noticeable only for the smallest-diameter billet. Alpha-phase textures were typical of axisymmetric deformation, but were relatively weak (~3× random) for all billet diameters. By contrast, bands of microtexture, which were multiple millimeters in length along the axial direction, were relatively strong for all of the materials. The intensity and radial thickness of the bands tended to decrease with decreasing billet diameter, thus indicating the important influence of imposed strain on the elimination of microtexture and the possible influence of surface preform microstructure following the beta quench on the evolution of microstructure and microtexture.