Transporting building materials to the Moon is expensive. Urine, however, is easily and inexpensively produced, and there is a potential of solving this critical problem using – er – “astronaut byproducts”.

The suggestion originally came from a study published in March in the Journal of Cleaner Production. In cooperation with the European Space Agency (ESA), a team of European researchers have conducted an experiment wherein urea was mixed with various materials, including Moon rocks, to see if we could one day use astronaut pee to build a lunar base.

“To make geopolymer concrete that will be used on the moon, the idea is to use what is already there: regolith and the water from the ice present in some areas,” Ramón Pamies, a professor at the Polytechnic University of Cartagena, Spain, and co-author of the study said in a statement.

It mostly worked. The urea itself acted as a “plasticizer” — stuff that allows us to shape other harder materials into different forms. In their unusual experiment, the team used an analog of lunar regolith, or loose Moon rock, and mixed it with the urea. Using a 3D printer, the team squeezed out Playdough-like shapes out of the urine concrete. 3D printing has become one of the most promising ways to build structures on distant planets including the Moon and Mars.

The big advantage: using local materials is a lot easier — and dramatically cheaper — than lugging heavy construction supplies from Earth.

After heating them up to a temperature of 80 degrees C (176 Fahrenheit), they found that the resulting structures could support heavy weights — even after eight freeze-thaw cycles that simulated several day and night cycles on the lunar surface.

The idea of humans visiting the Moon has been around at least since Jules Verne’s 1865 novel De la terre à la lune (“From the Earth to the Moon”). The notion of a lunar colony originated in 1638, so far as we know, when Bishop John Wilkins wrote A Discourse Concerning a New World and Another Planet, in which he predicted a human colony on the Moon. Now that we’ve actually been there a few times (the Apollo missions, between 1969 and 1972) and sent countless unmanned probes, we know a lot more about what we’ll be working with if we try to set up a permanent base. In particular, we know there’s water on the moon at the poles, hiding in the craters where sunlight never goes – and the poles offer the opportunity for an endless energy supply because at the poles, if you’re on a high spot, the sun never sets. With the proper location for a moon base generally picked out, we can turn our attention to what such a moon base might be made from.

Professor Ramón Pamies of Spain’s Polytechnic University of Cartagena suggested “To make the geopolymer concrete that will be used on the moon, the idea is to use what is there: regolith, or loose material from the moon’s surface and the water from the ice present in some areas.”

Although the idea sounds like the topic of schoolboy jokes, it’s not impossible that when (if) we return to the Moon, the astronauts could produce their own building materials. Urea is the principal component of urine after water, described as “a colorless crystalline compound which is the main nitrogenous breakdown product of protein metabolism in mammals and is excreted in urine.” There is, in fact, an entire branch of plastics called urethanes (urea-formaldehyde), practically ubiquitous in modern technology, so the idea of using it to make a sort of lunar concrete isn’t all that alien or far-fetched.

From the report:

“Urea can break hydrogen bonds, and therefore reduces the viscosities of many aqueous mixtures. Since urea is the second most abundant component in urine (after water), it is readily available anywhere there are humans. We have therefore explored the possibility of utilizing urea as a chemical admixture for lunar geopolymers. Addition of urea has been compared with polycarboxylate and naphthalene based superplasticizers, and with a control mixture without superplasticizer. When curing the sample containing urea at 80°C, the initial setting time became longer. The samples containing urea or naphthalene-based superplasticizers could bear heavy weights shortly after mixing, while keeping an almost stable shape. Samples without superplasticizer or containing the polycarboxylate-based admixture were too stiff for mold-shaped formation after casting. Samples containing urea and naphthalene-based admixtures could be used to build up a structure without any noticeable deformation. Initial compressive strength of the samples with urea was higher than for the two other specimens containing superplasticizers, and it continued to rise even after 8 freeze-thaw cycles. Microstructural studies revealed that superplasticizers can influence the formation of additional air voids within the samples.”

The layman’s translation of the above is that urea takes the normally uncooperative materials available in the lunar regolith and plasticizes them to the point where they can be effectively molded into a load-bearing material. That’s perfect if what you’re trying to make is habitable structures.

The environment on the Moon is almost exactly as hostile as open space is, but it has the bare essentials – a bit of water, a lot of sunshine, free unlimited electrical power, and with this new idea of combining materials from the Moon’s crust with something the astronauts can literally produce themselves, the establishment of a permanent lunar colony is now perhaps a step closer.

The obvious question that comes to mind is, how much astronaut pee will it take to make a moon shelter? While the answer to that one is up to the scientists and engineers, there’s no denying that in terms of the ongoing history of space exploration, this is definitely a “gee whiz” moment.

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