Journal of Aerospace Engineering

Incorporation of in situ resource utilization (ISRU) and the production of mission-critical consumables for propulsion, power, and life support into mission architectures can greatly reduce the mass, cost, and risk of missions, leading to a sustainable and affordable approach to human exploration beyond Earth. ISRU and its products can also greatly affect how other exploration systems are developed, including determining which technologies are important or enabling. Although the concept of lunar ISRU has existed for more than 40 years, the technologies and systems had not progressed much past simple laboratory proof-of-concept tests. With the release of the Vision for Space Exploration in 2004 with the goal of harnessing the Moon’s resources, the National Aeronautics and Space Administration (NASA) initiated the ISRU project in the Exploration Technology Development Program (ETDP) to develop the technologies and systems needed to meet this goal. In the 5 years of work in the ISRU Project, significant advancements and accomplishments occurred in several important areas of lunar ISRU. Also, two analog field tests held in Hawaii in 2008 and 2010 demonstrated all the steps in ISRU capabilities required, along with the integration of ISRU products and hardware with propulsion, power, and cryogenic storage systems. This paper will review the scope of the ISRU Project in the ETDP, ISRU incorporation, development strategies used by the ISRU project, and ISRU development and test accomplishments over the 5 years of funded project activity.

Advances in robotics and additive manufacturing have become game-changing for the prospects of space industry. It has become 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 strategy begins with a subreplicating system and evolves toward full self-sustainability (full closure) via an in situ technology spiral. The industry grows exponentially because of the free real estate, energy, and material resources of space. 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. Modeling over wide parameter ranges indicates this is reasonable, but further analysis is needed. This industry promises to revolutionize the human condition.

Returning to the Moon, or going further afield such as to Mars, presents enormous challenges in sustaining life for extended periods of time far beyond the few days the astronauts experienced on the Moon during the Apollo missions. A stay on Mars is envisioned to last several months, and it would be cost prohibitive to take all the requirements for such a stay from Earth. Therefore, future exploration missions will be required to be self-sufficient and use the resources available at the mission site to sustain human occupation. Such an exercise is currently the focus of intense research at National Aeronautics and Space Administration under the in situ resource utilization program. As well as the oxygen and water necessary for human life, resources for providing building materials for habitats, radiation protection, and landing/launch pads are required. All these materials can be provided by the regolith present on the surface because it contains sufficient minerals and metals oxides to meet the requirements. However, before processing, 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 is enriched or depleted as required. The results of electrostatic beneficiation of lunar simulants and actual Apollo regolith in a high lunar vacuum are reported, in which various degrees of efficient particle separation and mineral enrichment up to a few hundred percent were achieved.

Tribocharged electrostatic beneficiation of a lunar simulant and actual Apollo regolith has been shown to be successful under a high lunar vacuum in which various degrees of efficient particle separation and mineral enrichment of up to a few hundred percent were achieved. In this paper, electrostatic beneficiation of a lunar simulant at $\text{1/6}g$, as run on reduced gravity flights (RGFs), is reported. 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 in the orientation of the apparatus in the aircraft because the force of gravity was not perpendicular to the plane of the apparatus during the flight parabolas.

Pioneer Astronautics has developed 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. The integrated Mars in situ propellant production system (IMISPPS) uses a mixed catalyst bed to conduct the Sabatier methanation reaction and the reverse water gas shift in a single reactor. A recycle loop makes performance resistant to operational changes, with product ratios stable regardless of reactor temperature changes of as much as 100°C. An optimized IMISPPS is projected to produce 1 kg/day of O₂:CH₄ propellant and have a mass of 50 kg with a methane purity of 98+% while consuming 700 W of electrical power. With hydrogen from Earth, the system demonstrates a mass leverage of 18:1 in useful rocket propellant produced on Mars compared with imported feedstock.

The concept of living off the land by using the indigenous resources of the Moon, Mars, or other potential sites of robotic and human exploration has been termed in situ resource utilization (ISRU) and will be an enabling technology to open up the solar system. Although the most recent National Aeronautics and Space Administration (NASA) human Mars mission study (Design Reference Architecture 5.0) showed that production of propellants and life support consumables was a mission-enabling capability, mission planners were hesitant to select the newly proposed water extraction from Mars soil option because of the perceived high risk associated with this approach. To overcome resistance in putting ISRU capabilities in the critical path of mission success, 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. A secondary goal is to perform remote and autonomous operations with this integrated system on a $3\times 3\text{-}\text{m}\left(\sim \text{9}\times \text{9}\text{-ft}\right)$ 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. This paper will outline the overall design, technologies used, and concept of operations for the MARCO POLO project and its upcoming field demonstration.

In 2009; the Augustine report reinforced the importance of in situ oxygen production as a critical technology for sustainable exploration. Engineers at the National Aeronautics and Space Administration’s Johnson Space Center have been working on making this critical technology a reality through the 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 and in the 2008 in situ research utilization field test on the slopes of Mauna Kea, Hawaii, and in the laboratory at Johnson Space Center. This paper presents an overview of the approach taken, the high-level design information required, and the typical test data accrued for both the small-scale and large-scale reactors.

Future exploration of the Moon will require access to the subsurface and acquisition of samples for scientific analysis and ground truthing of water-ice and mineral reserves for in situ resource utilization purposes. The LunarVader drill described in this paper is a 1-m class drill and cuttings acquisition system enabling subsurface exploration of the Moon. The drill employs rotary-percussive action, which reduces the weight on bit and energy consumption. This drilling approach has been successfully used by previous lunar missions, such as the Soviet Luna 16, 20, and 24, and United States Apollo 15, 16, and 17. These missions and drilling systems are described in detail. The passive sample acquisition system of the LunarVader drill delivers cuttings directly into a sample cup or an instrument inlet port. The drill was tested in a vacuum chamber and penetrated various formations, such as a 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 weight on bit. This corresponds to a total drilling energy of approximately 100 Whr. 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.

Percussive excavation is researched as a viable technology to reduce the shear strength of the dry lunar soil simulant JSC-1A. Experimental tests were conducted in a percussive and quasi-static test bed, which 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.

As human activities expand to the Moon, Mars, and other extraterrestrial bodies, it will be necessary to use local resources rather than bringing everything from Earth. In situ resource utilization (ISRU), or planetary surface engineering, starts with excavation and dirt-moving. The current study focuses on excavation of lunar regolith simulant by blading with and without preripping (mechanical raking) and points out the need for considering 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.

Because of the requirement for high reliability and very low weight, extraterrestrial excavator blade design for in situ resource utilization (ISRU) must be more precise than for current terrestrial practice. Three-dimensional finite-element and discrete-element models should be employed to enhance the precision of designs. 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.

The establishment of permanent bases on planetary surfaces is an important long-term goal of the space community. Understanding the geotechnical properties of planetary surfaces and their interaction 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, 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 $30.5\text{×}33.0\text{-}\text{cm}$ footprint. Subsequent tests were performed in a new large-scale soil bin facility ($2.27\text{×}5.94\text{×}0.76 \text{m}$) 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 time-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 launch pads on extraterrestrial surfaces has gained interest as a way to improve landing safety and mitigate dust problems caused by launch and landing. On Mars, a landing pad may be a necessity for the safe landing of a large human-carrying vehicle. There have been many proposed surface stabilization technologies, and evaluation of the technologies uses regolith simulants and terrestrial analogue sites. Recent work on the lunar simulants used in sintering studies and results from recent field demonstrations are presented here. 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.

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 microwave heating is that regolith has the potential to be directly heated in situ. A computational model was developed that predicts the heating behavior of a lunar simulant, JSC-1A, using various methods for applying microwave energy. The efficiency of microwave heating depends on the properties of the materials. 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, inasmuch as this simulant is available in large quantities and has been extensively studied. The dielectric properties of JSC-1AC (a coarse sizing of JSC-1A) 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 microwaves on a deep bed of powder. Heating was performed in a 2.45-GHz, 6-kW microwave chamber, in an argon atmosphere to avoid oxidative changes to the simulant powder on heating. The use of microwaves 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 is one of the most pervasive metals in lunar soil and has many characteristics that make it applicable to 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 in situ resource utilization (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.

Construction work and machines required to build lunar facilities including an oxygen plant were specified, and power requirements for the construction and operation of these facilities were estimated 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 work is estimated to exceed the energy for a construction facility, and the covering of facilities with regolith is expected to be the most energy-consuming work. Estimated power demands for construction in the evolutional Phases 1, 2, and 3 were 75, 75, and 155 kW, whereas those for operation of the oxygen plant were 2.3, 31, and 761 kW, respectively.

This paper describes tests conducted since 2008 at the National Aeronautics and Space Administration (NASA) Kennedy Space Center (KSC) to address engineering challenges associated with delivering planetary regolith to in situ resource utilization (ISRU) systems. The need to excavate regolith under reduced-gravity conditions on a planetary surface and then deliver it to systems for material analysis and/or processing constrains the possible engineering approaches that can be used in space. Mission costs may further limit the mass and available power of a regolith delivery system. Mechanical systems operating in a planetary environment require high reliability with respect to system service life because it is usually difficult or impossible to perform maintenance robotically on a planetary surface. The regolith delivery system for most ISRU systems must have a leak-tight interface between the near-vacuum found on a planetary surface and the pressurized atmosphere within the ISRU reactor. Depending on the mission, the amount of regolith that must be delivered may range from a few grams (e.g., for analysis) to tens of kilograms (e.g., for oxygen production). Hot, spent regolith from an ISRU reactor must eventually be returned to the planetary environment by means of an interface that is capable of operating and sealing over a potentially large temperature range. In this paper, we will describe pneumatic and auger methods of conveying large amounts of regolith that have been studied and demonstrated at NASA KSC and at ISRU field tests and discuss other regolith delivery systems that are being designed for future field tests.

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. To quantify the similarities and differences between simulants, the figure of merit (FOM) was developed. The Figure of Merit 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 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 simulants, and the limited nature of the FOM.

The major advances in knowledge of extraterrestrial bodies come from in situ measurements on robotized measuring devices deployed by international space missions, for example, on the Moon and Mars. It is essential to test these instruments in environments on Earth that bear a close resemblance to planetary conditions. Within the framework of the 2010 International Lunar Surface Operation In Situ Resource Utilization (2010 ILSO-ISRU) Analog Test, a suite of scientific instruments developed for in situ lunar research was field tested and calibrated on the Mauna Kea volcano in Hawaii on January 27 to February 11, 2010. This site will be used as one of the future standard test sites to calibrate instruments for in situ lunar research. 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 of 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.