Lunar Resources

An artificially colored mosaic constructed from a series of 53 images taken through three spectral filters by ''Galileo's'' imaging system as the spacecraft flew over the northern regions of the Moon on 7 December 1992. The colors indicate different materials.
A lunar anorthosite rock collected by the Apollo 16 crew from near the crater Descartes

The Moon bears substantial natural resources which could be exploited in the future. Potential lunar resources may encompass processable materials such as volatiles and minerals, along with geologic structures such as lava tubes that, together, might enable lunar habitation. The use of resources on the Moon may provide a means of reducing the cost and risk of lunar exploration and beyond.M. Anand, I. A. Crawford, M. Balat-Pichelin, S. Abanades, W. van Westrenen, G. Péraudeau, R. Jaumann, W. Seboldt. "Moon and likely initial in situ resource utilization (ISRU) applications." ''Planetary and Space Science''; volume 74; issue 1; December 2012, pp: 42—48. .

Insights about lunar resources gained from orbit and sample-return missions have greatly enhanced the understanding of the potential for in situ resource utilization (ISRU) at the Moon, but that knowledge is not yet sufficient to fully justify the commitment of large financial resources to implement an ISRU-based campaign. The determination of resource availability will drive the selection of sites for human settlement.

Overview

Lunar materials could facilitate continued exploration of the Moon, facilitate scientific and economic activity in the vicinity of both Earth and Moon (so-called cislunar space), or they could be imported to the Earth's surface where they would contribute directly to the global economy. Regolith (lunar soil) is the easiest product to obtain; it can provide radiation and micrometeoroid protection as well as construction and paving material by melting. Oxygen from lunar regolith oxides can be a source for metabolic oxygen and rocket propellant oxidizer. Water ice can provide water for radiation shielding, life-support, oxygen and rocket propellant feedstock. Volatiles from permanently shadowed craters may provide methane (), ammonia (), carbon dioxide () and carbon monoxide (CO). Metals and other elements for local industry may be obtained from the various minerals found in regolith.

The Moon is known to be poor in carbon and nitrogen, and rich in metals and in atomic oxygen, but their distribution and concentrations are still unknown. Further lunar exploration will reveal additional concentrations of economically useful materials, and whether or not these will be economically exploitable will depend on the value placed on them and on the energy and infrastructure available to support their extraction. For in situ resource utilization (ISRU) to be applied successfully on the Moon, landing site selection is imperative, as well as identifying suitable surface operations and technologies.

Scouting from lunar orbit by a few space agencies is ongoing, and landers and rovers are scouting resources and concentrations ''in situ'' (see: List of missions to the Moon).

Resources

Solar power, oxygen, and metals are abundant resources on the Moon. Elements known to be present on the lunar surface include, among others, hydrogen (H), oxygen (O), silicon (Si), iron (Fe), magnesium (Mg), calcium (Ca), aluminium (Al), manganese (Mn) and titanium (Ti). Among the more abundant are oxygen, iron and silicon. The atomic oxygen content in the regolith is estimated at 45% by weight.Laurent Sibille, William Larson
Oxygen from Regolith.
. NASA. 3 July 2012.Gregory Bennett
The Artemis Project – How to Get Oxygen from the Moon
. ''Artemis Society International''. June 17, 2001.

Studies from Apollo 17's Lunar Atmospheric Composition Experiment (LACE) show that the lunar exosphere contains trace amounts of hydrogen (H₂), helium (He), argon (Ar), and possibly ammonia (NH₃), carbon dioxide (CO₂), and methane (CH₄). Several processes can explain the presence of trace gases on the Moon: high energy photons or solar winds reacting with materials on the lunar surface, evaporation of lunar regolith, material deposits from comets and meteoroids, and out-gassing from inside the Moon. However, these are trace gases in very low concentration. The total mass of the Moon's exosphere is roughly with a surface pressure of 3×10^−15 bar (2×10^−12 torr). Trace gas amounts are unlikely to be useful for in situ resource utilization.

Solar power

Daylight on the Moon lasts approximately two weeks, followed by approximately two weeks of night, while both lunar poles are illuminated almost constantly.Gläser, P., Oberst, J., Neumann, G. A., Mazarico, E., Speyerer, E. J., Robinson, M. S. (2017). "Illumination conditions at the lunar poles: Implications for future exploration. ''Planetary and Space Science'', vol. 162, p. 170–178. The lunar south pole features a region with crater rims exposed to near constant solar illumination, yet the interior of the craters are permanently shaded from sunlight.

Solar cells could be fabricated directly on the lunar soil by a medium-size (~200 kg) rover with the capabilities for heating the regolith, evaporation of the appropriate semiconductor materials for the solar cell structure directly on the regolith substrate, and deposition of metallic contacts and interconnects to finish off a complete solar cell array directly on the ground. This process however requires the importation of potassium fluoride from Earth to purify the necessary materials from regolith.

Nuclear power

The Kilopower nuclear fission system is being developed for reliable electric power generation that could enable long-duration crewed bases on the Moon, Mars and destinations beyond. This system is ideal for locations on the Moon and Mars where power generation from sunlight is intermittent. Uranium and thorium are both present on the Moon, but due to the high energy density of nuclear fuels, it could be more economical to import suitable fuels from Earth rather than producing them ''in situ''.

Radioisotope thermoelectric generators (RTGs) are another form of nuclear power which use the natural decay of radioisotopes rather than their induced fission. They have been used in space—including on the Moon—for decades. The usual process is to source the suitable substances from Earth, but plutonium-238 or strontium-90 could be produced on the Moon if feedstocks such as spent nuclear fuel are present (either delivered from Earth for processing or produced by local fission reactors). RTGs could be used to deliver power independent of available sunlight, for both lunar and non-lunar applications. RTGs do contain harmful toxic and radioactive materials, which leads to concerns of unintentional distribution of those materials in the event of an accident. Protests by the general public therefore often focus on the phaseout of RTGs (instead recommending alternative power sources), due to an overestimation of the dangers of radiation.

A more theoretical lunar resource are potential fuels for nuclear fusion. Helium-3 has received particular media attention as its abundance in lunar regolith is higher than on Earth. However, thus far nuclear fusion has not been employed by humans in a controlled fashion releasing net usable energy (devices like the fusor are net energy consumers while the hydrogen bomb is not a ''controlled'' fusion reaction). Furthermore, while helium-3 is required for one possible pathway of nuclear fusion, others instead rely on nuclides which are more easily obtained on Earth, such as tritium, lithium or deuterium.

Oxygen

The elemental oxygen content in the regolith is estimated at 45% by weight. Oxygen is often found in iron-rich lunar minerals and glasses as iron oxide. Such lunar minerals and glass include ilmenite, olivine, pyroxene, impact glass, and volcanic glass. Various isotopes of oxygen are present on the Moon in the form of ¹⁶O, ¹⁷O, and ¹⁸O.

At least twenty different possible processes for extracting oxygen from lunar regolith have been described, and all require high energy input: between 2–4 megawatt-years of energy (i.e. ) to produce 1,000 tons of oxygen. While oxygen extraction from metal oxides also produces useful metals, using water as a feedstock does not. One possible method of producing oxygen from lunar soil requires two steps. The first step involves the reduction of iron oxide with hydrogen gas (H₂) to form elemental iron (Fe) and water (H₂O). Water can then be electrolyzed to produce oxygen which can be liquified at low temperatures and stored. The amount of oxygen released depends on the iron oxide abundance in lunar minerals and glass. Oxygen production from lunar soil is a relatively fast process, occurring in a few tens of minutes. In contrast, oxygen extraction from lunar glass requires several hours.

Human oxygen consumption depends on physical activity and is affected by diet and also gravity. A commonly assumed round number for -production of humans of low to moderate physical activity assumes being exhaled per person per day. In the microgravity-environment of the International Space Station this value can be as low as per person per day. If one conservatively assumes that one mole of oxygen is consumed per mole of carbon dioxide produced (this ratio holds true for glucose but less oxygen is consumed per unit of carbon dioxide produced if fat or protein are the source of metabolic energy) 2.2 kg of carbon dioxide produced are equivalent to of oxygen consumed. The yearly oxygen need of a human would thus be roughly and per the above-mentioned energy requirements about 1.3-2.6 kilowatts would be constantly required per person to produce this amount of oxygen from lunar rocks. For comparison the average per person electricity consumption in the US in 2022 was or about 1,462 Watts.

Water

Cumulative evidence from several orbiters strongly indicate that water ice is present on the surface at the Moon poles, but mostly on the south pole region. However, results from these datasets are not always correlated.J. E. Gruener. "The Lunar Northwest Nearside: The Price Is Right Before Your Eyes." Lunar ISRU 2019: Developing a New Space Economy Through Lunar Resources and Their Utilization. July 15–17, 2019, Columbia, Maryland. It has been determined that the cumulative area of permanently shadowed lunar surface is 13,361 km² in the northern hemisphere and 17,698 km² in the southern hemisphere, giving a total area of 31,059 km². The extent to which any or all of these permanently shadowed areas contain water ice and other volatiles is not currently known, so more data is needed about lunar ice deposits, its distribution, concentration, quantity, disposition, depth, geotechnical properties and any other characteristics necessary to design and develop extraction and processing systems. The intentional impact of the LCROSS orbiter into the crater Cabeus was monitored to analyze the resulting debris plume, and it was concluded that the water ice must be in the form of small (< ~10 cm), discrete pieces of ice distributed throughout the regolith, or as a thin coating on ice grains.L. M. Jozwiak, G. W. Patterson, R. Perkins. "Mini-RF Monostatic Radar Observations of Permanently Shadowed Crater Floors." Lunar ISRU 2019: Developing a New Space Economy Through Lunar Resources and Their Utilization. July 15–17, 2019, Columbia, Maryland. This, coupled with monostatic radar observations, suggest that the water ice present in the permanently shadowed regions of lunar polar craters is unlikely to be present in the form of thick, pure ice deposits.

Water may have been delivered to the Moon over geological timescales by the regular bombardment of water-bearing comets, asteroids and meteoroids or continuously produced ''in situ'' by the hydrogen ions (protons) of the solar wind impacting oxygen-bearing minerals.

The lunar south pole features a region with crater rims exposed to near constant solar illumination, where the craters' interior are permanently shaded from sunlight, allowing for natural trapping and collection of water ice that could be mined in the future.

Water molecules () can be broken down to form molecular hydrogen () and molecular oxygen () to be used as rocket bi-propellant or produce compounds for metallurgic and chemical production processes. Just the production of propellant, was estimated by a joint panel of industry, government and academic experts, identified a near-term annual demand of 450 metric tons of lunar-derived propellant equating to 2,450 metric tons of processed lunar water, generating US$2.4 billion of revenue annually.

Hydrogen

Slopes on the lunar surface that face the Moon's poles show a higher concentration of hydrogen. This is because pole facing slopes have less exposure to sunlight that will cause vaporization of hydrogen. Additionally, slopes closer to the Moon's poles show a higher concentration of hydrogen of about 45 ppmw. There are various theories to explain the presence of hydrogen on the Moon. Water, which contains hydrogen, could have been deposited on the Moon by comets and asteroids. Additionally, solar winds interacting with compounds on the lunar surface may have led to the formation of hydrogen-bearing compounds such as hydroxyl and water. The solar wind implants protons on the regolith, forming a protonated atom, which is a chemical compound of hydrogen (H). Although bound hydrogen is plentiful, questions remain about how much of it diffuses into the subsurface, escapes into space or diffuses into cold traps. Hydrogen would be needed for propellant production, and it has a multitude of industrial uses. For example, hydrogen can be used for the production of oxygen by hydrogen reduction of ilmenite.

Metals

Iron

Iron (Fe) is abundant in all mare basalts (~14–17% per weight) but is mostly locked into silicate minerals (i.e. pyroxene and olivine) and into the oxide mineral ilmenite in the lowlands.Mark Prado
Major Lunar Minerals.
. ''Projects to Employ Resources of the Moon and Asteroids Near Earth in the Near Term'' (PERMANENT). Accessed on 1 August 2019. Extraction would be quite energy-demanding, but some prominent lunar magnetic anomalies are suspected as being due to surviving Fe-rich meteoritic debris. Only further exploration ''in situ'' will determine whether or not this interpretation is correct, and how exploitable such meteoritic debris may be. Hematite, a mineral composed of ferric oxide (Fe₂O₃), has been found on the Moon. This mineral is a product of a reaction between iron, oxygen, and liquid water. Oxygen from the Earth's atmosphere may cause this reaction as indicated by there being more hematite on the side of the Moon facing the Earth.

Free iron also exists in the regolith (0.5% by weight) naturally alloyed with nickel and cobalt and it can easily be extracted by simple magnets after grinding. This iron dust can be processed to make parts using powder metallurgy techniques, such as additive manufacturing, 3D printing, selective laser sintering (SLS), selective laser melting (SLM), and electron beam melting (EBM).

Titanium

Titanium (Ti) can be alloyed with iron, aluminium, vanadium, and molybdenum, among other elements, to produce strong, lightweight alloys for aerospace use. It exists almost exclusively in the mineral ilmenite (FeTiO₃) in the range of 5–8% by weight. Ilmenite is the main source of titanium on earth and processes like the chloride process to extract titanium from ilmenite are well established at industrial scale. Ilmenite minerals on the moon also trap hydrogen (protons) from the solar wind, so that processing of ilmenite will also produce hydrogen, a valuable element on the Moon. The vast flood basalts on the northwest nearside (Mare Tranquillitatis) possess some of the highest titanium contents on the Moon, with 10 times as much titanium as rocks on Earth.

Aluminum

Aluminum (Al) is found with a concentration in the range of 10–18% by weight, present in the mineral anorthite