Percussive Penetration of Unconsolidated Granular Media in a Laboratory Setting

This controlled study examined the feasibility of a simple percussive approach to drilling through unconsolidated regolith deposits on Mars. The experiments showed that the approach is feasible at the low power levels and low confining pressures used, and that the rate of impact is more important to the penetration rate than is the mass of the impactor (hammer). More massive impactors tend to lower energy efficiency, as they do in terrestrial pile-driving. Unexpectedly, penetration plotted against applied energy tends to cluster into parallel linear trends. Within a given cluster, penetration is very sensitive to applied energy, while between clusters, the same penetration requires different energy levels. The clusters are separated by gaps whose widths may be related to the average grain size of the material being penetrated. The layered nature of natural sedimentary deposits is reflected in the cumulative energy-penetration plots, which could thus serve to record bedding thickness and frequency during Mars exploration. This study has shown that percussive drilling using a down-the-hole hammer design may be feasible in unconsolidated fine regolith near the ground surface

Effect of Water Ice Content on Excavatability of Lunar Regolith

The amount of water ice contained within prepared samples of JSC-1 lunar regolith simulant strongly affects the excavatability of the material. As part of a NASA Phase I SBIR project, load-penetration testing of JSC-1 lunar regolith simulant was performed at water ice concentrations ranging from zero to 11% by mass (approximately saturated), after compaction and cooling to simulate probable lunar conditions. After mixing dry JSC-1 simulant with the appropriate amount of water, the samples were individually compressed into containment rings under 48 MPa of pressure. Thermocouples embedded in the samples monitored internal temperature while they were cooled in a bath of liquid nitrogen. At temperatures corresponding to the lunar polar cold traps, a 19mm-diameter hemispherical indenter was forced into the center of each sample while the required force and the resulting penetration were recorded. The results show strong sensitivity to water content. Regolith containing up to 0.3% water ice is very easy to excavate and behaves like weak coal. Regolith with 0.6 to 1.5% ice is readily excavatable and acts like weak shale or mudstone. Regolith with ~8.4% ice would be excavated with mechanical excavators, much like moderate-strength limestones, sandstones, and shales. The highest strength mix (~10.6% ice) behaves like strong limestone or sandstone, which require massive excavators. These results show that realistically compacted ice-regolith mixtures may be harder to excavate than previously believed, and that mixture variability must be well-understood to design effective excavators

Review of Lunar Regolith Properties for Design of Low Power Lunar Excavators

Lunar regolith is the product of the intermittent comminution of rocks over extremely long durations, and as such is very different from familiar terrestrial soils. A limited amount of information on lunar regolith was collected by the Apollo space program for a few locations. Additional data is required to design effective excavators to prepare outpost sites and to mine the feedstock for production of the material required for a self-sustaining crewed base on the moon. On-site manufacturing would reduce significantly the mass of material that must be launched from Earth. This paper discusses what is known and what is yet unknown about the characteristics and anticipated behavior of lunar regolith as they pertain to efficient excavation operations on the moon. It also discusses the results of tests performed on lunar simulant in dry and frozen conditions and the effects of moisture content as well as temperature on the strength of the frozen material. The results of indentation tests will be presented along with discussion of the cutting forces required for mechanical excavation of the frozen regolith. Implications of material behavior on the design of the cutterhead of excavation systems will also be reviewed

Asteroid Redirect Mission (ARM) Formulation Assessment and Support Team (FAST) Final Report

The Asteroid Redirect Mission (ARM) Formulation Assessment and Support Team (FAST) was a two-month effort, chartered by NASA, to provide timely inputs for mission requirement formulation in support of the Asteroid Redirect Robotic Mission (ARRM) Requirements Closure Technical Interchange Meeting held December 15-16, 2015, to assist in developing an initial list of potential mission investigations, and to provide input on potential hosted payloads and partnerships. The FAST explored several aspects of potential science benefits and knowledge gain from the ARM. Expertise from the science, engineering, and technology communities was represented in exploring lines of inquiry related to key characteristics of the ARRM reference target asteroid (2008 EV5) for engineering design purposes. Specific areas of interest included target origin, spatial distribution and size of boulders, surface geotechnical properties, boulder physical properties, and considerations for boulder handling, crew safety, and containment. In order to increase knowledge gain potential from the mission, opportunities for partnerships and accompanying payloads were also investigated. Potential investigations could be conducted to reduce mission risks and increase knowledge return in the areas of science, planetary defense, asteroid resources and in-situ resource utilization, and capability and technology demonstrations. This report represents the FAST"TM"s final product for the ARM

Coupled Deformation and Fluid-flow Behavior of a Natural Fracture in the CSM In Situ Test Block

The primary goal was the evaluation of an in situ block test as a data source for modeling the coupled flow and mechanical behavior of natural rock fractures. The experiments were conducted with the Colorado School of Mines in situ test block, an 8 m3 (280 ft3) gneiss cube which has been the focus of several previous studies. A single continuous fracture within the block was surrounded with instruments to measure stresses, deformations, and gas conductivity. The setup was subjected to combinations of normal and shear stress by pressurizing the block sides differentially with hydraulic flatjacks. The induced fracture deformation, as measured by two separate sensor systems, did not correlate closely with the fracture conductivity changes or with each other. The test fracture is more complicated physically than two parallel rock faces. Many joints which were not detected by mapping intersect the test fracture and strongly influence its behavior. These invisible joints create sub-blocks which react complexly to changes in applied load. The flow tests reflected the aggregate sub-block dislocations in the flow path. The deformation readings, however, were the movements of discrete points sparsely located among the sub-blocks. High-confidence extrapolation of block test results to large volumes, such as required for nuclear waste repository design, is not feasible currently. Present instrumentation does not sample rock mass behavior in situ at the proper scales. More basically, however, a fundamental gap exists between the nature of jointed rock and our conception of it. Therefore, the near-field rock mass must be discounted as an easily controllable barrier to groundwater flow, until radically different approaches to rock mass testing and modeling are develope

Economic Analysis Tools for Mineral Projects in Space

The charge to the workshop was to propose projects of commercial potential utilizing resources available in space. Many of the proposed projects involved resources that will have to be mined, either to supply a primary product or as raw feedstocks for products manufactured in space or for construction projects in space. Mining engineers are accustomed to dealing with all aspects of commercial projects, from initial planning through financing to final closedown. The economic analysis tools presented here comprise an overview of the tools provided to mining engineers, and are offered here as tools that can be applied effectively to space ventures. Space and mining projects share fundamental similarities: high risk, long lead times, and high capital cost. The analysis starts with the definition of ore, which is purely economic: ore is a geologic material that can be extracted from the ground at a profit. For profit to occur, sales must exceed costs, or: Sales-Costs = Profi

Surface Mine Design and Planning for Lunar Regolith Production

Terrestrial surface mine design and planning techniques are applied to the production of lunar regolith for manufacturing makeup gases for the life-support system of a lunar base. Two scenarios are examined, due to the uncertainty of whether bound hydrogen sensed near the lunar poles is from cometary ice deposited in cold traps (#1), or to hydrogen implanted within regolith grains by the solar wind (#2). Scenario #1, with a total production requirement of 44 tonne/day of regolith, could be handled with four groups of four 6-m3 capacity slushers (drag scrapers), each group extending 100 m around a single processing module. Scenario #2 (4.382 tonne/day) could be accomplished with three powered bowl-type scrapers (capacity 24 m3) gathering the regolith into long windrows feeding a large processor. The present orebody model is extremely thin (1 m), although broad in extent: this prevents usage of high production-rate systems such as large draglines