One of the most commonly discussed challenges in embarking on our species’ journey of space exploration is how to obtain the resources necessary for life from Earth. It is usually thought of as two things—water and oxygen, but, fortunately, oxygen can be supplied by splitting a water molecule, so the most critical resource we find in space is water.
Commonly referred to as “volatile” in the language of space resources, water has been central to many plans for in-situ resource use on the moon, Mars, and elsewhere. Some of the plans were well thought out, some were not. One in particular showed some promise when it was selected as part of NASA’s Institute for Advanced Concepts (NIAC) funding back in 2019, and here we take a closer look at it.
The concept, published in a report titled “Thermal Mining of Ices on Cold Solar System Bodies” but hereafter referred to as “thermal mining,” is the brainchild of George Sowers, an expert in space resources and Professor of Mechanical Engineering at the Colorado School of Mines (CSM). The underlying concept is surprisingly simple and familiar to anyone who played with a magnifying glass as a child.
If you direct sunlight to a particular area using a giant mirror or other technology, that area will heat up. If you heat an area with ice, and it is in a vacuum, that ice will sublimate into water vapor and begin to release from the heated surface. That water vapor can then be captured using a cold trap or similar mechanism, and the water can be harvested for use in exploratory activities, such as drinking, breathing, or even burning. of rockets.
So the basic architectural system of the idea of thermal mining is simple and consists of three main components. First is a large mirror (known as a heliostat) to direct sunlight to a particular spot on another world. The second is a giant tent that captures the sublimated water, and the third is a cold trap/transport system that captures the water as it emerges from the surface.
None of this is a giant leap in technology—we don’t need to develop fancy technologies to make these three components. However, they have never been put to this use before, so it’s worth teasing them. That’s what Dr. Sowers and his team as part of their report to NIAC.
First, they looked at potential areas where the system could be useful. Four different bodies came to the surface—Mars, where the presence of water ice has been repeatedly proven; Ceres, where water vapor is emitted from its surface; and two main belt asteroids—24 Themis and 65 Cybele, both of which are thought to be ice-covered due to their reflectivity. All are in the inner solar system, making them easy targets for exploration and resource exploitation missions using this technique.
But the place that holds the greatest promise for starting to use human resources in space is the moon. Dr. Sower and his team’s second task is to develop an architecture for use in the Permanently Shaded Regions of the moon which are believed to contain a large percentage of the 600 billion kilos of water in our nearest neighbor.
The moon has some advantages over asteroids like 24 Themis for this thermal mining technique. One is that there is enough gravity to use standard rovers to get the ice where it needs to be. Another is the lack of atmosphere that reduces the efficiency of transferring solar thermal energy to the mine. But again, it’s very close.
Its proximity does not change the overall architecture, however—the three main components are still required wherever the mining site is located. Thus, the third task for the group of Dr.
They collected the lunar regolith simulant and manually scraped the pieces of ice that they made into balls and mixed with the regolith. They placed a version of this mixture, with different concentrations of ice, in a vacuum chamber cooled by a liquid nitrogen bath. Next, they applied a heat source from a lamp meant to mimic redirected sunlight and measured the resulting weight loss of the sample, and used that to calculate how much water had sublimated.
While conducting these experiments, they encountered two interesting problems—one related to their test setup, but the other would prevent actual use on the moon.
The CSM test setup is relatively small, with the liquid nitrogen cooling system relatively close to the sample that needs to sublimate. As such, most of the heat from the lamp that should be heating the sample is heating the liquid nitrogen, which acts like a heat sink. On the moon, this cannot happen, because the whole body is very cold and there is no thermally conductive material under your sample to absorb most of the energy intended to heat the water. And so, CSM built a bigger test chamber to try to limit the impact of this issue in their experiments.
Another problem is thorny though-after a relatively short time, the thermal method of mining creates a desiccated layer on top of the regolith that acts as a thermal barrier to the water that can be trapped further. Not only does little heat reach the lower level of the regolith, the dried layer essentially melts into a vapor barrier, making it nearly impossible for water to sublimate in the tent and collect in cold traps. .
Such difficulties are by no means insurmountable, and perhaps one of the most important aspects of the report shows why they think they are indeed surmountable — the business case. Estimated by the group of Dr. Sower that the total development cost for a reasonably sized PSR thermal mining operation on the moon is around $800M, with an additional $613M in product costs. It will also include operational costs of around $80M per year.
Those costs come with some hefty benefits—especially if it saves the cost of shipping water from Earth to any early lunar output. According to the report’s calculations, the Internal Rate of Return (IRR—a measure of how profitable a project is) would be approximately 8% if the system operators sold only commercial sources (for example, the trying to do other economic activities. of the month). That’s a little lower than many financiers would consider investment grade, especially for a risky project. However, suppose NASA or other national space agencies become customers to support their lunar operations. In that case, the IRR jumps to ~16%, closer to where financiers might be interested.
Admitted by Dr. Sowers that the business case is one of the riskiest parts of the overall proposal, because it requires demand, which currently does not exist because there is little or no operation on the moon that requires water. With NASA’s Artemis missions, that should change in the next decade, but it’s unclear if that will provide enough demand to make the technology economically feasible.
There are also many other risks, including uncertainty about the total amount and location of the moon’s water. Undoubtedly there are some of the PSR, but there may not be enough close to the surface, where it can be collected by thermal mining, to support long-term human habitation, and the water and other “volatiles ” should be sent. from Ceres or elsewhere in the asteroid belt. If that’s the case, there’s still an argument that the underlying thermal mining method could be profitable—it just might not be profitable.
Currently, the entire system is only in the planning stage, and it does not appear that the technology has received a Phase II NIAC, and it is not clear what progress has been made in the last few years. However, the technology is patented, and CSM offers it for licensing on their technology transfer website. And as technology generally advances, the idea of mining the moon becomes more appealing. So there’s a good chance this technology will eventually arrive, even if it takes a while.
Thermal Mining of Ices in Cold Solar System Bodies. space.mines.edu/wp-content/upl … eI-final-report.pdf
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