This is the first of a series of posts where I intend to explore the technical hurdles of mining on the Moon. It is also a living document, like a ball of clay that might need to be reworked until it is just the right consistency to begin pottery. As such, I ultimately want to get this collection of posts into a form that could be published as a whitepaper for lunar mining. It might not be the only solution, but I would like this to be thorough enough to work if implemented.
I met a guy at a party in California during my intern years at Ames Research Center in the summer of 2003. This guy had kind of long shaggy graying hair and sort of dirty clothes and smelled strongly of coffee and cigarettes from a full arms length away. I remember wondering at the time what he was doing there and if he had just wandered in to the gathering from off the street. When I introduced myself he reciprocated and told me he was working on first principles analysis of going back to the Moon. He told me it was his goal to develop an entirely new way of looking at both traveling to and staying at the Moon and that involved retasking and reusing equipment, getting creative with ways to travel on the surface and ways to exploit the Moon's resources once we got there. There are going to be rovers built from spare parts that roll over any obstacle on the Moon’s surface and they will be modular so they fit together to make a habitable base. We will mine the surface not just for the helium-3 that can be shipped back to earth to pay for the operation, but the regolith will also be processed for all the building materials and life-giving elements that a colony needs. This vision of colonization of the Moon was entirely unlike anything that happened during the Apollo mission. It was a vision of sustainably living on the Moon’s surface with a minimum amount of resupply or support from Earth.
This chance meeting has stuck with me ever since largely because it was surprising that this crazy, homeless man had a good enough story to fit in with the rest of us at the party but also because he was right. The next time the human race goes to the Moon, it should be to stay and it should look dramatically different than the first time - the next effort should not be “flags and footprints” so much as dust, sweat and tears.
Living off the land is the Zubrinian mantra (from The Case for Mars) for how to make sustainable exploration work. In long term economic exploration of the Moon mining is going to be an important part of making the effort worthwhile. One of the previous topics I have mentioned is using a unique formulation of concrete for construction on the Moon. This would require developing a way to mine and purify sulfur before any construction can begin. A different, more popular idea is paying for the missions by mining for helium-3, an isotope that is rare on the Earth, but relatively abundant on the Moon’s surface and can be used to dramatically improve nuclear power production using fusion. I have also heard arguments for mining metal from a thin layer of cosmogenically altered rock on the surface, oxygen bound in the minerals that compose the surface rocks, and silica in that same rock for solar panel production. Mining will also probably be required to extract and purify cometary water from the ever-dark craters that have preserved the ice on the north and south poles. I am going to discuss mining on the surface of the Moon in general terms because it encompasses all of these options. Going down into the depths of the Moon is a different story for a different day.
There are a few key questions that must be answered before going forward. First, is mining possible on the Moon’s surface? Second, if so, is it more economical than shipping every pound of oxygen, water, food, and construction materials required to sustain life from the Earth? There are likely a wide range of viewpoints that exist varying from yes to no for each question. I think the task of mining on the Moon’s surface is possible, but that it is a much more complicated task than any NASA scientist has ever considered and that could mean that mining and processing is not an economical alternative to flying every piece of a habitable base to the Moon…at least for the forseeable future.
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Mining is a process
In the old days it was drill, blast, muck, haul. Over and over again, as fast as possible. In recent times, the process is basically the same, but with a few extra steps along the way. And I am convinced that the process is the same here as it would be anywhere else materials must be extracted. The big differences are in the details of the individual steps of the process.
Today mining has two essential tracks, operations and engineering. Operations could occur without engineering but at the risk of long term disaster and failure of the mining operation itself. Each track has tasks that begin with defining an ore body during exploration and go through the steps of mining and processing that ore until it can be milled and a final product is produced. In this case operations includes both the mining and the milling staff. As the mine progresses the engineering and operations groups work together to optimize the mining operation. This is true for precious metal mines, coal mines, iron mines, and aggregate mines. Below I have a rough diagram that outlines the critical steps for a mine process that would result in, say, sulfur production.
Today mining has two essential tracks, operations and engineering. Operations could occur without engineering but at the risk of long term disaster and failure of the mining operation itself. Each track has tasks that begin with defining an ore body during exploration and go through the steps of mining and processing that ore until it can be milled and a final product is produced. In this case operations includes both the mining and the milling staff. As the mine progresses the engineering and operations groups work together to optimize the mining operation. This is true for precious metal mines, coal mines, iron mines, and aggregate mines. Below I have a rough diagram that outlines the critical steps for a mine process that would result in, say, sulfur production.
This is a lot of steps and there are very specific pieces of equipment that are used for each step. For example, a medium sized gold mine might have thirty large dump trucks and three or four pieces of loading equipment to extract enough ore to feed a mill and haul waste to dumps. The mill for a mine that size will have a footprint of several acres and be many stories tall with an electrical consumption equivalent to a moderately large neighborhood. The total gold production that might come from such an operation after a full year of production could be shipped out in one armored van.
How does this analogy transfer to the Moon? Does each step require a crew and equipment or can they be combined into one super miner/miller machine that does the job with an operator or a robot at the controls?
In the movie Moon, Sam Bell, played by Sam Rockwell, is a one-man crew living on a lunar base outpost mining helium-3. His mining equipment are house sized rovers that traverse the surface scooping up regolith and milling it onboard. The shipments of helium-3 are rocketed back to Earth in small containers that are easily manhandled by a single person, surprisingly similar to the gold mine scenario discussed above.
There is video of this miner in operation at IMDB here http://www.imdb.com/video/imdb/vi1306264089/ Moon 2009 is definitely worth watching, I highly recommend it. You can catch the full show on Netflix streaming or buy it on Amazon.com.
I love this vision of mining. It is the right idea for surface mining in loose, fine grained material that is rich in ore close to the surface. Instead of taking a block of material by scooping it into trucks that haul it to a mill, it shaves off the upper foot or so, separating the big rocks and hurling them away while processing the good stuff on the inside and dumping all the waste rock out the back.
A scenario like this might actually work for mining helium-3 or water from the regolith. There are plenty of designs for continuous mining equipment that can slowly move across a flat, ripped surface and load the dirt via conveyor to a waiting truck.
It is not difficult to imagine adding a module that heats up the ore regolith to a temperature high enough to drive off a significant fraction of the helium-3 or water and collect it in some kind of a condenser. The remaining waste rock is simply cast aside. This idea works because helium and water are relatively volatile and simply warming up the rock is enough to collect it.
But what about sulfur, or metals, or silica that are bound much more tightly to the rock and require significantly greater temperatures to be liberated? Sulfur is more volatile than the others. If the grains of sulfides (the class of mineral that sulfur would exist in basalt type rocks on the moon) could be exposed in the ore by crushing the rock to the grain-size of its constituent minerals, then the sulfides could be concentrated and heated up and exposed to a reducing agent to react with the metal in the sulfide. On Earth, carbon in the form of coal is added to the fiery mix to drive off the sulfur as a sulfur oxide gas. I am not sure what chemistry could be done using the materials on the moon to make that reaction go – it is unclear if heat alone is enough to drive the reaction.
That is it for today. We looked at the mine as a process and speculated a little about the validity of some recent science fiction that seems closest to the mark. The next post is going to focus on the first stages of exploration and sampling that will be required in order to define an area that can be mined.
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