The next era of space exploration, spearheaded by programs like Artemis, aims to establish a sustained human and robotic presence on the Moon. This long-term goal relies on utilizing materials found on the lunar surface, a concept known as In-Situ Resource Utilization (ISRU). Launching resources from Earth is immensely expensive. By processing local lunar materials, future missions can achieve self-sufficiency, drastically lowering the logistical and financial hurdles of deep space travel.
ISRU is foundational to creating a permanent lunar base and using the Moon as a stepping stone for missions to Mars and beyond. Lunar resources range from common bulk materials for construction to high-value elements needed for advanced technology and energy production. Identifying and developing technologies to extract these resources is a primary objective for international space agencies and commercial ventures.
Water Ice and Other Volatile Compounds
Water ice is the most valuable resource on the Moon for immediate utilization by human outposts. This ice is predominantly sequestered in Permanently Shadowed Regions (PSRs), which are deep craters near the lunar poles where sunlight never reaches. Orbital missions indicate the south pole may hold hundreds of millions to a billion metric tons of water ice, though concentrations vary locally within the regolith.
The utility of lunar water addresses the most significant needs of a space habitat. It can be melted and purified for direct life support, including drinking and growing food. Water molecules can be split into breathable oxygen and hydrogen through electrolysis. The resulting liquid hydrogen and liquid oxygen are components of highly efficient rocket propellant. Creating propellant on the Moon would transform the satellite into an interplanetary fuel depot, making onward travel to Mars or other destinations feasible.
Lunar regolith also contains other volatile compounds, which vaporize easily at low temperatures. Trace amounts of hydrogen, nitrogen, and carbon have been detected in the fine dust that blankets the surface. These elements were implanted into the lunar soil by the solar wind over billions of years. Though less abundant than water ice, these volatiles are valuable building blocks for life support systems, needed for pressurized atmospheres and agriculture.
Industrial Elements in Lunar Regolith
The Moon’s surface material, known as regolith, is a rich source of elements for manufacturing and construction. Oxygen is the most abundant element, making up an estimated 40 to 45 percent of the lunar soil by weight. This oxygen is not freely available as a gas but is chemically bound within mineral oxides, such as silicates and the iron-titanium mineral ilmenite.
Extracting this bound oxygen is an energy-intensive process requiring sophisticated technology. Several methods are currently under development.
Molten Salt Electrolysis
One promising technique is molten salt electrolysis, where regolith simulant is submerged in a bath of molten salt and heated to around 950°C. An electrical current is then applied, which draws the oxygen out of the minerals to be collected at an electrode.
Hydrogen Reduction
Another technique, hydrogen reduction, uses hydrogen gas at high temperatures (800-1000°C) to react with iron oxides. This process produces water vapor that is then electrolyzed to yield oxygen and regenerate the hydrogen.
The oxygen extraction process leaves behind a metallic residue that is an invaluable resource for lunar infrastructure. This residue is a mixture of various metal alloys, including Silicon, Aluminum, Iron, and Titanium. Silicon, which makes up about 20 percent of the lunar dust, is usable for manufacturing solar panels and electronics. Aluminum and Iron are suitable for structural components, while Titanium is a lightweight and strong metal for constructing habitats and machinery. Fabricating these bulk materials in place allows for the construction of permanent bases, reducing the need to ship massive components from Earth.
High-Value Energy Resources
The Moon holds specialized, high-value resources that could impact both lunar and terrestrial economies. The most discussed is Helium-3, a light, stable isotope of helium that is exceptionally rare on Earth. Because the Moon lacks an atmosphere, it has been exposed to the solar wind for billions of years, allowing solar particles, including Helium-3, to become trapped in the upper regolith.
While the concentration of Helium-3 is low (1.4 to 15 parts per billion in the regolith), the sheer volume of lunar soil suggests a massive overall quantity. Scientists propose its use as a fuel for second-generation nuclear fusion reactors. Its fusion reaction with deuterium produces fewer high-energy neutrons, potentially leading to a cleaner energy source with less radioactive waste. Extracting Helium-3 involves heating large amounts of regolith to release the trapped gas, which is collected along with other solar wind-implanted volatiles.
Another category of specialized materials is Rare Earth Elements (REEs), a group of 17 chemically similar metals used in modern electronics and high-tech applications. Concentrations of these elements are found in a rock type nicknamed KREEP, which is enriched in Potassium (K), REEs, and Phosphorus (P). The largest known deposits of KREEP are concentrated in the Procellarum KREEP Terrain on the Moon’s near side. Their presence offers the potential for the Moon to become a source for these economically valuable materials, though commercial mining viability is still being assessed.