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Friday, 26 June 2015

What's the Moon made of? A Review of Lunar Resources

Greetings! Welcome back to Embrace Space! Today, we are going to take a closer look at the Moon, our closet celestial neighbour, in order to better understand what it's made of and how that may help us further space exploration. 

First things first: no, the Moon is not made of green cheese. This myth, fable, metaphor seems to spring up all over the world; Google Moon even used a Swiss cheese image as its highest resolution, and you can learn more about it here.

I recently read an excellently-written article entitled, Lunar Resources: A Review, by Ian A. Crawford, from the University of London, and I found it really interesting. The paper, recommended to me by colleague Diego Urbina, not only discusses what resources exist on the Moon, but analyses how best we may extract them, and where the resources may be best used. While I highly recommend reading the paper yourself, I have taken it upon myself to create a chart, summarizing the findings.

If you're well-versed in lunar geology and/or space exploration, the chart may be sufficient, but in order to help bridge the gap, I thought I would explain a few things. The resources include solar wind particles, water, oxygen, iron, titanium, aluminum, silicon, rare Earth elements, thorium/uranium, and a few others. The chart breaks down the source of each resource (where on the Moon you can find it), the uses (either on the Moon, in space, back on Earth), the quantity, extraction methods, and final recommendations based on availability and "ease" of each resource.

Basically, the Moon is covered in dust and rock. The dust, broken down over time by solar wind, is called regolith. There are two main geological areas on the Moon and these include the highlands (lighter in colour), and the mare basins (referred to as cold traps, craters, darker in colour).

As you can see from the chart above, most of the resources can be found and extracted from anywhere on the Moon, but water (and by extension, oxygen) is more likely found and concentrated in the high-latitude mare, the crater basins kept in permanent shadow on the Moon. While there has been evidence that pyroclastic deposits (ancient volcanic glass, basically) contain water, the qualities retrieved from the Apollo 15 and 17 samples are too low to be considered for resource utilization. The two main difficulties involved with extracting resources from the Moon are the low-quantities, and the infrastructure required. 

Along with learning more specifics regarding the resources and their quantities on the Moon, I learned a few other interesting things.

The first deals with He-3 collection. It has been a long-standing debate over whether there is enough He-3 (helium-3) on the Moon to bother mining it for nuclear power generation. Simplistically, you can combine He-3 with deuterium from the Earth's oceans to make nuclear power. However, the current estimates regarding He-3, deposited on the Moon by solar wind, are so low, that any area of solar panels would provide just as much energy/year, as all the regolith under it, to a depth of 3m. And, while the equator receives sunlight > 90% of the time and is essentially "limitless", once the regolith was mined, there would be no He-3 left to use.

The next point concerns rare Earth elements. Two really interesting points were discussed in the paper. The first deals with enabling a hydrogen fuel-cell market. Apparently, a lack of the proper elements is one factor impeding the advance of this technology, and these elements do exist in abundance on the Moon. Perhaps returning these elements to Earth could drive that industry. Secondly, while there are ample quantities of REE on the Earth, (in spite of its name, and I was happy that the author made the same joke), the environmental impact of mining for them may become too costly. If one considers the environmental costs of mining on Earth, perhaps mining on the lifeless Moon may start to look more favourable.

This leads me to the next point. It is incredibly unlikely that we would ever mine anything from the Moon and bring it back to Earth, since Earth is such a lush planet. However, lunar resources could be used to supplement space exploration activities on the Moon, in Earth's orbit, or beyond. Not an entirely new idea for me, still, I was glad to see that the author had taken the time to analyze the energy requirements for launching from the Moon to several locations. 

Space is expensive, and one of the main reasons is that it takes a lot of fuel and energy to get off the Earth. However, if an infrastructure were already in place on the Moon, it may be less expensive and easier to send fuel and supplies to orbiting stations and satellites from the Moon. Of course, having an existing infrastructure and having the yield produced be worthy of resupplying anything are big "ifs".

And that's it for today. As I said, I recommend the paper as it examines the sources of this information, and discusses some of the advantages and obstacles in lunar resource utilization, but it may be a bit too scientific for recreational reading.

I will likely address the topics of lunar and martian exploration in subsequent posts so, if you find this interesting, be sure to come back!

Thanks for reading!

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