Special Issue on In Situ Resource Utilization

“Progress Made in Lunar In Situ Resource Utilization under NASA's Exploration Technology and Development Program,” by Sanders and Larson reviews the work performed by, and the accomplishments of, the National Aeronautics and Space Administration (NASA) ISRU project in the Exploration Technology and Development Program, created in 2005. The purpose of this project was to (1) develop technologies, hardware, and systems to technology readiness Level (TRL) 6; (2) mitigate the risk of using ISRU in future robotic and human missions to the Moon, Mars, and beyond; (3) coordinate development of ISRU technologies and systems with other exploration systems; and (4) coordinate insertion of ISRU capabilities into architecture and mission plans.

“Affordable, Rapid Bootstrapping of the Space Industry and Solar System Civilization” by Metzger et al. points to advances in robotics and additive manufacturing as game changing for the prospects of space industry, making it feasible to bootstrap a self-sustaining, self-expanding industry at reasonably low cost. Simple modeling was developed to identify the main parameters of successful bootstrapping. This indicates that bootstrapping can be achieved with as little as 12 t landed on the Moon during a period of about 20 years. The equipment will be teleoperated and then transitioned to full autonomy so the industry can spread to the asteroid belt and beyond. The mass of industrial assets at the end of bootstrapping will be 156 t with 60 humanoid robots or as high as 40,000 t with as many as 100,000 humanoid robots, if faster manufacturing is supported by launching a total of 41 t to the Moon. Within another few decades with no further investment, it can have millions of times the industrial capacity of the United States. This industry promises to revolutionize the human condition.

“Electrostatic Beneficiation of Lunar Regolith: Applications in In Situ Resource Utilization” by Trigwell et al. suggests that before processing the regolith, it would be cost effective if the regolith could be enriched in the mineral(s) of interest. This can be achieved by electrostatic beneficiation in which tribocharged mineral particles are separated out, and the feedstock enriched or depleted as required. The results of electrostatic beneficiation of lunar simulants and actual Apollo regolith in lunar high vacuum are reported in which various degrees of efficient particle separation and mineral enrichment up to a few hundred percent were achieved.

“Evaluation of Tribocharged Electrostatic Beneficiation of Lunar Simulant in Lunar Gravity” by Quinn et al. reports on the electrostatic beneficiation of a lunar simulant at 1/6g, as run on reduced gravity flights (RGFs). Enrichment of the target mineral ilmenite was achieved as high as 65 and 106% in the two RGF flights undertaken, showing that tribocharged electrostatic beneficiation is a viable process in the lunar environment. It was also shown that the efficiency of the separation was a factor of the orientation of the apparatus in the aircraft because of the fact that the force of gravity was not perpendicular to the plane of the apparatus during the flight parabolas.

“Integrated Mars In Situ Propellant Production System” by Zubrin et al. discusses the work of Pioneer Astronautics in the development of a system that harvests CO₂ from a simulated Martian atmosphere and reacts it with H₂ into rocket propellant at a rate of 1 kg/day. A prototype system operated autonomously for 5 consecutive days, during which it maintained a 100% conversion rate (to detectable limits) of CO₂ and H₂ into products, maintaining a constant O₂:CH₄ ratio in the product stream with only minor adjustments.

“Prototype Development of an Integrated Mars Atmosphere and Soil-Processing System” by Interbartolo et al. addresses the resistance in putting ISRU capabilities in the critical path of mission success. To this end, NASA ISRU developers have adopted the approach of designing and building hardware into end-to-end systems at representative mission scales and testing these systems under mission-relevant conditions at analog field test sites. Previous ISRU field demonstrations have been standalone lunar ISRU modules running on alternating current power with nonoptimal integration. The primary goal of the Mars atmosphere and regolith collector/processor for lander operations (MARCO POLO) project is to design, build, and test an end-to-end first-generation Mars ISRU atmospheric and soil processing system powered by mission relevant direct current power while also demonstrating closed-loop power production via the combination of a fuel cell and electrolyzer. This paper outlines the overall design, technologies used, and concept of operations for the MARCO POLO project and its upcoming field demonstration. A secondary goal is to perform remote and autonomous operations with this integrated system on a $3\times 3\text{-}\text{m}$ octagon lander and transfer oxygen and methane produced to a cryocart for use with a thruster to demonstrate an end-to-end Mars resource-to-thrust concept.

“The ROxygen Project: Outpost-Scale Lunar Oxygen Production System Development at Johnson Space Center” by Lee et al. presents an overview of the NASA Johnson Space Center design, fabrication, and testing of two hydrogen reduction reactors, accomplished as part of the ROxygen project. Engineers built and extensively tested a small-scale reactor that provided key design parametrics for the second reactor: a large-scale vessel consistent with the scale required to produce 1,000 kg (2,205 lb) of oxygen per year. Once designed and fabricated, this large-scale reactor was tested in the laboratory, in the 2008 ISRU field test on the slopes of Mauna Kea, Hawaii, and in the laboratory at the Johnson Space Center.

“LunarVader: Development and Testing of Lunar Drill in Vacuum Chamber and in Lunar Analog Site of Antarctica” by Zacny et al. discusses the accessing of water-ice and mineral reserves for ISRU purposes using the LunarVader drill, which is a 1-m class drill and cuttings acquisition system enabling subsurface exploration of the Moon. The drill uses rotary-percussive action, which reduces the weight on bit (WOB) and energy consumption. This drilling approach has been successfully used by previous lunar missions such as Soviet Luna 16, 20, and 24, and U.S. Apollo 15, 16, and 17. The drill was tested in a vacuum chamber and penetrated various formations such as water-saturated lunar soil simulant (JSC-1A) at −80°C, water-ice, and rocks to a depth of 1 m. The system was also field tested in the lunar analog site on Ross Island, Antarctica, where it successfully penetrated to 1-m depth and acquired icy samples into a sample cup. During the chamber and field testing, the LunarVader demonstrated drilling at the 1-1-100-100 level; that is, it penetrated 1 m in approximately 1 h with roughly 100 W power and less than 100 N WOB. This corresponds to a total drilling energy of approximately 100 Wh. The drill system achieved high enough technology readiness to be considered as a viable option for future lunar missions such as the South Pole-Aitken Basin Sample Return and Geophysical Network missions recently recommended by the Decadal Survey of the National Research Council and commercial missions such as Google Lunar X-Prize missions.

“Investigating the Effects of Percussion on Excavation Forces” by Green et al. presents research on percussive excavation as a viable technology to reduce the shear strength of dry lunar soil simulant, JSC-1A. Experimental tests were conducted in a percussive and quasi-static test bed that used a replica Surveyor scoop as the excavation tool. The effects of percussion, relative to measured excavation baseline draft forces, are presented in the context of six different variables. The test variables include percussive frequency, percussive impact energy, excavation speed, excavation depth, angle of attack, and relative soil density. It is concluded that percussion reduces the shear strength of dry JSC-1A by removing the effects of soil dilatancy from the internal friction angle along the shear failure boundary layer.

“Excavation of Lunar Regolith with Large Grains by Rippers for Improved Excavation Efficiency” by Iai and Gertsch discusses a study of the excavation of lunar regolith simulant by blading with and without preripping (mechanical raking) and points out the need to consider the relative proportion of coarse grains in regolith when dealing with excavation force and energy. The coarse-grain content of the lunar regolith, estimated from 11 Apollo cores, can reach 30% by mass. Prior ripping of vibrationally compacted beds of a standard fine regolith simulant can decrease total excavation resistance (when subsequent blading is included) by up to 20% for relative regolith densities greater than 60%. The effect of coarse grains on the response of compacted regolith to excavation was more significant than would be expected in most terrestrial practice. In conclusion, it is suggested that careful matching of excavator design to local coarse-grain content of the lunar regolith needs to be considered in designing a planetary surface engineering architecture.

“Laboratory-Scale Distributed Pressure Measurements of Blade Interaction with JSC-1A Lunar Simulant” by King and Brewer presents three-dimensional finite-element and discrete-element models for the precision designs of extraterrestrial excavator blades. These models require that the pressure distribution across the blade be known; however, this information is not available in the literature. To provide the information, this project measured the pressure distribution on a suite of laboratory-scale blades. The project constructed a suite of laboratory-scale model blades, designed and implemented distributed pressure and total load measurements, developed soil preparation techniques, measured pressure distributions and errors, and created empirical pressure distribution models. The models include an array of point pressures, a quadratic function, and an exponential function. The work concluded that a V-shaped blade with a tapered curve is the best configuration, and multiple passes of small-depth cuts is the best excavation operating procedure.

“Lunar Excavation Experiments in Simulant Soil Test Beds: Revisiting the Surveyor Geotechnical Data” by Agui et al. discusses the importance of understanding the geotechnical properties of planetary surfaces and considers how the interaction of surface materials with tools and implements will be essential in addressing the challenges of material-handling equipment for infrastructure development during surface missions. With this aim, a replica of the soil mechanics surface sampler, an extendable scoop with a bearing plate attachment that operated on some of the lunar Surveyor missions in the 1960s, was fabricated and used in a series of simulated bearing and excavation tests. Initially, a set of tests was performed on a small laboratory test stand using an acrylic soil bin with a $30.5\times 33.0\text{-}\text{cm}$ footprint. Subsequent tests were performed in a new large-scale soil bin facility ($2.27\times 5.94\times 0.76\text{m}$) to minimize wall effects. Both test setups involved the use of JSC-1A lunar simulant soil beds and motorized actuators to drive the scoop into the simulant. Emphasis was placed on methods of repeatable soil bin preparation. The scoop was attached to a commercial six-axis load cell that provided well-resolved measurements of the three-dimensional forces and torques. In addition, simultaneous video provided detailed imaging of the flow behavior and surcharge formation of the regolith during excavation. A surface-profiling technique was developed to resolve the surface deformation as the scoop penetrated and trenched the simulant. Bearing test data in loose bed preparations in both bins compared well with the Surveyor flight data. The data also included the soil response under compacted soil conditions.

“Building a Lunar or Martian Launch Pad with In Situ Materials: Recent Laboratory and Field Studies” by Hintze and Quintana discusses the building of launch pads on extraterrestrial surfaces to improve landing safety and mitigate dust problems caused by launch and landing. There have been many proposed surface stabilization technologies, and evaluation of the technologies requires the use of regolith simulants and terrestrial analog sites. Recent work on the lunar simulants used in sintering studies and results from recent field demonstrations are presented. Laboratory studies on simulants focused on determining how the composition of the simulant affected sintering. The glass content of the lunar simulant was found to be a key parameter in determining when a simulant sintered. Field demonstrations of a solar concentrator and a resistive heating sintering system are described. Field demonstrations factor in not only the simulant but also larger-scale thermal effects that are not present in laboratory tests.

“Computational Modeling and Experimental Microwave Processing of JSC-1A Lunar Simulant” by Allan et al. presents a computational model that predicts the heating behavior of a lunar simulant, JSC-1A, using various methods for applying microwave energy. Microwave heating is a potential method for mitigating dust issues and creating solid regolith structures, such as landing pads on the Moon, Mars, and other extraterrestrial bodies. The advantage of using microwaves is that regolith has the potential to be directly heated in situ. The efficiency of microwave heating is materials dependent. Dielectric properties are used to characterize a material’s microwave behavior, which is temperature and frequency dependent. Obtaining a variety of actual regolith samples for dielectric characterization can be challenging, which is why simulants and computational models were developed. This work used lunar simulant JSC-1A for dielectric characterization, microwave processing studies, and computational modeling, as the simulant is available in large quantities and has been extensively studied. JSC-1AC (a coarse sizing of JSC-1A) dielectric properties were previously measured at 2.45 GHz as a function of temperature up to the melting point. Only room temperature measurements were available for actual lunar regolith, which were comparable with JSC-1AC at low temperatures. An experimental design and a computational model were developed to study surface-only heating using microwave on a deep bed of powder. Heating was performed in a 2.45-GHz, 6-kW microwave chamber in argon atmosphere to avoid oxidative changes to the simulant powder on heating. The use of microwave for surface-only heating on deep beds of simulant powder was demonstrated. Modeling used finite-element and finite-difference methods to calculate the electromagnetic and thermal heat development, using the dielectric properties of JSC-1A. The heating patterns obtained from the computer model were compared with microwave heating experiments. The model was adjusted to achieve close approximations of JSC-1A microwave heating using different heating scenarios. The geometry of heating patterns and range of temperature agreement between the model and experimental methods demonstrated a good representation of JSC-1A microwave surface heating.

“Magnesium as an ISRU-Derived Resource for Lunar Structures” by Benaroya et al. proposes the use of magnesium, one of the most pervasive metals in lunar soil with many characteristics that make it applicable for in situ refining and production. This somewhat overlooked alkaline earth metal is easily cast, used, and recycled, characteristics that are required in the Moon's harsh environment. Moreover, alloys of this element have several properties fine-tuned for building shelters in a lunar environment, including several advantages over aluminum alloys. Magnesium alloys may prove to be the optimal choices for reinforcing lunar structures or manufacturing components as needed on the Moon. As such, further research on the ISRU of magnesium is imperative for the development of a self-sufficient lunar base. This paper brings together key properties of magnesium within the context of it being used as an in situ resource once the Moon, again, becomes a goal for permanent habitation, and we require the ability to live there in perpetuity.

“Power Requirements for the Construction and Operation of a Lunar Oxygen Plant” by Kanamori et al. specifies construction work and machinery required to build lunar facilities including an oxygen plant and estimated power requirements for the construction and operation of these facilities based on a proposed evolutional scenario. Individual components of lunar facilities such as habitat/laboratory modules, corridor modules, and connection/evacuation modules were designed, and specifications of lunar construction machines were determined. A realistic oxygen plant was also designed by referring to the experimental and analytical results of hydrogen reduction of ilmenite processes. The energy required for soil processing is estimated to exceed the energy for the construction facility, and covering of facilities with regolith is expected to be the most energy-consuming work. Estimated power demands for construction in evolutional Phases 1, 2, and 3 were 75, 75, and 155kW, whereas those for operation of the oxygen plant were 2.3, 31, and 761 kW, respectively.

“Planetary Regolith Delivery Systems for ISRU” by Mantovani and Townsend describes pneumatic and auger regolith transfer systems that have already been field tested for ISRU and discusses other systems that await future field testing. The challenges associated with collecting regolith on a planetary surface and delivering it to an ISRU system differ significantly from similar activities conducted on Earth. Because system maintenance on a planetary body can be difficult or impossible to do, high reliability and service life are expected of a regolith delivery system. Mission costs impose upper limits on power and mass. The regolith delivery system must provide a leak-tight interface between the near-vacuum planetary surface and the pressurized ISRU system. Regolith delivery in amounts ranging from a few grams to tens of kilograms may be required. Finally, the spent regolith must be removed from the ISRU chamber and returned to the planetary environment via dust-tolerant valves capable of operating and sealing over a large temperature range.

“Functional Comparison of Lunar Regoliths and Their Simulants” by Rickman et al. develops figures of merit (FOM) to quantify the similarities and differences between simulants. Lunar regolith simulants are essential to the development of technology for human exploration of the Moon. Any equipment that will interact with the surface environment must be tested with simulant to mitigate various risks, such as unexpected mechanical abrasion, chemical interactions, or thermal failures. To reduce the greatest amount of risk, the simulant must replicate the lunar surface as well as possible. The FOM software compares the simulants and regolith by particle size, particle shape, density, and the relative abundance of minerals, rocks, and glass; these four properties dictate the majority of the remaining characteristics of a geologic material. As a result, not only is the risk made quantifiable, but a conceptual framework is established for the evaluation of simulants. There are important limitations in our knowledge and technology pertaining to simulants. Specific examples include a surprising lack of specific, important measurements on lunar samples, the unavoidable presence of nonlunar phases in the stimulants, and the limited nature of the FOM.

“Mauna Kea, Hawaii, as an Analog Site for Future Planetary Resource Exploration: Results from the 2010 ILSO-ISRU Field-Testing Campaign” by ten Kate et al. discusses a suite of scientific instruments developed for in situ lunar research that was field tested and calibrated on the Mauna Kea volcano in Hawaii on January 27–February 11, 2010. This site may be used as one of the future standard test sites to calibrate instruments for in situ lunar research. Major advances in our knowledge of extraterrestrial bodies come from in situ measurements on robotized measuring devices deployed on the Moon and Mars by international space missions. It is essential to test these instruments in environments on Earth that bear a close resemblance to these planetary conditions. In 2010, a total of eight scientific teams tested instrument capabilities at the test site. In this paper, a geological setting for this new field test site, a description of the instruments that were tested during the 2010 ILSO-ISRU field campaign, and a short discussion for each instrument about the validity and use of the results obtained during the test are provided. These results will serve as reference for future test campaigns.