Lead Image: Aristarchus Crater on the moon. Credit: NASA/GSFC/Arizona State University
When it comes to the future of space exploration, a handful of practices are essential for mission planners. Foremost among them is the concept of In-Situ Resource Utilization (ISRU), providing food, water, construction materials, and other vital elements using local resources. And when it comes to missions destined for the Moon and Mars in the coming years, the ability to harvest ice, regolith, and other elements are crucial to mission success.
In preparation for the Artemis missions, NASA planners are focused on finding the optimal way to produce oxygen gas (O2) from all of the elemental oxygen locked up in the Moon’s surface dust (aka. lunar regolith). In fact, current estimates indicate that there is enough elemental oxygen contained in the top ten meters (33 feet) of lunar regolith to create enough O2 for every person on Earth for the next 100,000 years – more than enough for a lunar settlement!
While the Moon does have a very tenuous atmosphere that contains elemental oxygen, it is so thin that scientists characterize the Moon as an “airless body.” But within the lunar regolith, the fine powder and rocks that cover the surface, there are abundant amounts of oxygen in lunar rocks and regolith. Also known as “Moondust,” this fine dust permeates the lunar surface and is the result of billions of years of impacts by meteors and comets.
According to John Grant, a lecturer in soil science at Southern Cross University, Australia, the Moon’s regolith is approximately 45% oxygen by content. However, this oxygen is bound up in oxidized minerals – particularly silica, aluminum, iron, and magnesium. The isoptic composition of these minerals is almost identical to minerals on Earth, which led to theories that the Earth-Moon system formed together billions of years ago (aka. the Giant Impact Hypothesis).
However, for that oxygen to be usable by future astronauts and lunar inhabitants, it needs to be extracted from all that regolith, which requires a significant amount of energy to break the chemical bonds. On Earth, this process (known as electrolysis) is commonly used to manufacture metals, where melted-down oxides are subjected to electrical current to separate the minerals from the oxygen.
In this case, the oxygen gas is produced as a byproduct so that metals can be produced for the sake of construction and fabrication. But on the Moon, oxygen would be the main product while the metals would be set aside as a potentially useful byproduct – most likely for habitat construction. As Grant explained in a recent article in The Conservation, the process is straightforward but suffers from two major roadblocks when adapted for space:
“[I]t’s very energy hungry. To be sustainable, it would need to be supported by solar energy or other energy sources available on the Moon. Extracting oxygen from regolith would also require substantial industrial equipment. We’d need to first convert solid metal oxide into liquid form, either by applying heat, or heat combined with solvents or electrolytes. We have the technology to do this on Earth, but moving this apparatus to the Moon – and generating enough energy to run it – will be a mighty challenge.”
In short, the process needs to be much more energy-efficient to be considered sustainable, which could be accomplished through solar power. Around the South-Pole Aitken Basin, solar arrays could be positioned around the rim of the permanently-shadowed craters to provide an uninterrupted flow of energy. But getting the industrial equipment there would still present a monumental challenge.
But if and when we did establish the infrastructure, there’s still the question of how much oxygen we could extract. As Grant indicates, if we consider just the regolith that is easily accessible on the surface and factor in data provided by NASA and the Lunar Planetary Institute (LPI), some estimates are possible:
“Each cubic metre of lunar regolith contains 1.4 tonnes of minerals on average, including about 630 kilograms of oxygen. NASA says humans need to breathe about 800 grams of oxygen a day to survive. So 630kg oxygen would keep a person alive for about two years (or just over).
“Now let’s assume the average depth of regolith on the Moon is about ten metres, and that we can extract all of the oxygen from this. That means the top ten metres of the Moon’s surface would provide enough oxygen to support all eight billion people on Earth for somewhere around 100,000 years.”
In many ways, estimating how an astronomical body will present opportunities for ISRU is like mineral prospecting. For example, NASA recently announced that the metallic asteroid Psyche II might contain as much as $10,000 quadrillion worth of precious metals and ores. In 2022, the Psyche orbiter will rendezvous with this asteroid, which could be the core remnant of a planetoid that lost its outer layers, to study it closely.
Naturally, some disagree with this assessment, citing that Pysche II’s composition and density are not particularly well-constrained. For others, estimates of this nature ignore the sheer cost of extracting that wealth, which would require that extensive infrastructure be built beforehand. And even then, hauling that kind of mass from the Asteroid Belt to Earth presents numerous logistical issues.
The same goes for asteroid mining, a potentially-lucrative venture that could result in trillions being mined from Near-Earth Asteroids (NEAs) in the near future. However, this is also contingent on creating a robust space-mining infrastructure that is still very much in the conceptual stage. Luckily, when it comes to establishing ISRU-related infrastructure on the Moon, proposed methods and pathways have been in place since the 1960s.
In the coming years, multiple missions will be sent to the Moon to investigate these possibilities further, two of which Grant cites in his article. In early October, NASA signed a deal with the Australian Space Agency to develop a small lunar rover that could be sent to the Moon as early as 2026. The purpose of this rover will be to collect samples of lunar regolith and transfer them to a NASA-operation ISRU system on a commercial lunar lander.
Also, the Belgium-based startup Space Applications Systems (SAS) announced this past summer that it was building three experimental reactors for on the Moon. They were one of four finalists contracted by the European Space Agency (ESA) to develop a compact technology demonstrator that can harvest oxygen to manufacture propellant for spacecraft, air for astronauts, and metallic raw materials for equipment.
The company hopes to send the technology to the Moon as part of a planned ESA ISRU Demonstration mission, which is currently scheduled to go to the Moon by 2025. These and other technologies are being pursued to ensure that humanity’s long-awaited return to the Moon will be to say.
Originally published on Universe Today.