Mar 30 2020

Building Moon Bases Using Urine

This is an interesting idea that will probably not be actually implemented (although not impossible) but does raise some important points. A paper explores the viability of using urea from human urine as an agent in lunar concrete. Why is something like this even being considered?

The overwhelmingly dominant factor of building anything on the Moon is that it costs about $10,000 to put one pound of anything into Earth orbit, and more to take it to the Moon (although most of the energy would be used just getting into orbit). This is why it is a high priority for NASA to reduce the cost of getting stuff into space. Elon Musk has also made this a priority and SpaceX is geared mainly toward this purpose. Even if they reach their goal of reducing the cost by 10 fold, to about $1000 per pound, that still adds up when you are trying to build an entire Moon base. One solution is to use as much native material as possible.

Let’s talk a bit about the lunar regolith. The term regolith just refers to any loose material on top of the rocks on a world’s surface. The Earth has regolith, we call it dirt, sand, or soil. The lunar regolith is the result of micrometeors pulverizing the lunar surface for billions of years. In most locations the regolith extends down 4-5 meters, but can be as deep as 15 meters in places. Because of the absence of natural erosion from wind, water, or biological activity, the lunar regolith remains sharp and pointy. So the Moon is basically covered with a deep blanket of fine but jagged dust.

Lunar colonists are going to find the regolith more annoying that Anakin Skywalker finds sand – it gets everywhere, it ruins equipment, electronics, and spacesuits, and it’s irritating to the eyes, lungs, and anything exposed. Keeping living spaces relatively free of regolith is going to be a major engineering problem for a lunar colony. One proposed solution is use some process to solidify the surface in the region of the colony, to turn the regolith into some king of concrete so that there is no loose dust. You can also build your colony underground, away from any regolith.

Here is what the lunar regolith is made from:

Major Elements – In lunar rocks and soils 99% of the mass consists of the following 7 chemical elements.

Oxygen (41-45%) | Silicon (Si) | Aluminum (Al) | Calcium (Ca) | Iron (Fe) | Magnesium (Mg) | Titanium (Ti)

Minor Elements – Nearly all of the remaining 1% consists to these 4 chemical elements.

Manganese (Mn) | Sodium (Na) | Potassium (K) | Phosphorous (P)

Much of what we might need is right there. (The big thing that is not in the regolith is water, but there actually is more than we at first thought, especially at the poles.) Aluminum, iron and titanium could be refined into strong building materials. Oxygen is obviously critical for life support, but also as fuel and propellant. The entire regolith can be sintered (partially melted so that it sticks together) into solid blocks, which can then be used as building blocks. Silicon can be used to make glass. But also – the regolith might be usable as cement in the making of concrete. There is a lot of research looking into this, somewhat limited by the fact that we don’t have tons of lunar regolith available for study. Some scientists are using volcanic ash as a close approximation.

One thing that needs to be added to cement is some kind of binding agent or plasticiser. That is where the new study comes in – they explored the possibility of using urea from urine as a plasticiser agent for lunar concrete.

The team took a regolith simulant developed by ESA and mixed it with urea, then 3D printed the mud-like material into cylinders. A series of experiments carried out at Østfold University College in Norway revealed that samples carrying urea supported heavy weights and remained largely stable. The resistance of the structures was also tested at 80°C and was actually found to have increased after eight freeze-thaw cycles like those experienced on the Moon’s surface.

They also explored ways of separating the urea from the urine. However, you don’t necessarily need to do this. You can just use the raw urine, which then includes the water necessary to make concrete. I am not sure what “largely stable” means in practical terms. That seems like one of those details that need to be sorted out. I also did not see any discussion of how much urea would be needed for construction, and how many colonist days of urine would be necessary. The scale may simply not work.

The paper was mainly a proof-of-concept, showing that urea from urine can likely be used as a plasticiser in making “lunarcrete”. Whether or not this turns out to be a practical idea remains to be seen, and of course most such ideas do not turn out to be practical, because there are so many things that can go wrong.

But the big picture here is that we are going to have to be creative if we are going to build and maintain a successful lunar colony. Every ounce of material is going to be precious on the Moon, and we are going to have to think very creatively about how to use material at hand, repurpose material, and recycle as much as possible. I wonder what culture would emerge from such a reality. It reminds me of the Fremen on Dune, where water was the most precious substance and respect for water ultimately dominated their culture.

But for now building a lunar colony is a problem to be solved, and the culture at NASA is optimized for solving problems.

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