Lunar Construction Calls for a Personal Touch

By Mike Howie

As NASA prepares to send humans back to the Moon and eventually Mars, its scientists are putting on their creative hats. They’re tasked with providing tools that astronauts will need to live and work in space. To do that, they’re looking at all the possible resources at their disposal, and nothing is off the table. Not even pee.

Once the astronauts reach the moon, they’ll need a place to live. Traditional building materials, however, are far too heavy to send into space. According to NASA, it costs about $10,000 to send a pound of material into Earth’s orbit — rocket fuel is expensive.

So researchers considered what resources astronauts could gather from the Moon’s surface. Lunar soil, they suggest, could be used to make a cement that the astronauts could put through a 3D printer to make small buildings. The only problem is water — it’s heavy, and you need a lot of it to make cement. Sending a mere gallon of water into orbit would cost about $80,000.

Enter Anna-Lena Kjøniksen, an engineering professor at Østfold University College in Halden, Norway. She and her colleagues were working on this problem when she asked herself two questions: “What’s available on the Moon? If you add humans, then what do you have available?”

You have human waste. Gross, sure, but a little science can do wonders, and this wouldn’t be the first time our leavings would be put to good use either on Earth or in space. For example, keeping the International Space Station stocked with fresh water from Earth would be prohibitively expensive, so NASA installed a water system that collects and treats moisture. Everything from sink and shower runoff to breath, sweat, and — you guessed it — urine is collected, distilled, and reused for cleaning, making food, and drinking.

Kjøniksen was especially interested in the urea present in urine. Urea breaks hydrogen bonds between molecules, which reduces friction, and she had previously used it to thin out plastic mixtures. She thought it might be useful as a type of super-plasticizer that could reduce the amount of water needed to make the Moon cement.

Kjøniksen’s team couldn’t get real lunar soil to test their idea, so they used a silica and aluminum oxide powder as a substitute — it’s similar to the primary ingredient in many cement mixes but has larger and more crystalline grains. They then added powdered urea and mixed it all together with water to make cement.

They found that the urea worked well. The team was able to extrude the cement into layers to make a small wall that supported light weight and withstood temperature changes. The Moon, of course, is a much harsher environment than a lab here on Earth, so the team still has more work to do. Namely, they’ll need to test the cement at extreme temperatures and in a vacuum. But their work is an exciting proof of concept.

The team will also need to detail the process astronauts would use to make the cement on the Moon. Do they need to distill the urine? Can it be used directly? Questions remain, but this we know to be true: humans sure are crafty.