On the Moon, Astronaut Pee Will Be a Hot Commodity - WIRED

It’s too expensive to ship everything from Earth, which means they’ll have to get creative with the limited resources on the lunar surface.

Moon dirt is a great building material and there’s water in the form of ice at the south pole that can be turned into rocket fuel.

Earlier this year, a team of European researchers demonstrated that urea, the second most common compound in human urine after water, can be mixed with moon dirt and used for construction.

The resulting material is a geopolymer, which has similar properties to concrete and could potentially be used to build landing pads, habitats, and other structures on the moon.

When this is mixed with water and certain reactive compounds, it creates a putty-like material that can be cast into desired shapes before it’s left to dry.

Lunar regolith has chemical similarities to fly ash, which makes geopolymers an attractive option for building stuff on the moon.

Superplasticizers are materials that are used to reduce the water content of concrete and geopolymers while maintaining their flowability.

To test the idea, the researchers mixed synthetic urea powder with lunar regolith simulant to make cylindrical structures the size of a fist and let them dry under a weight.

The team’s pee-powered polymer may also help create shelters that shield astronauts from dangerous ionizing radiation on the lunar surface.

The moon doesn’t have an atmosphere or a strong magnetic field to deflect the radiation streaming from the sun, which means astronauts have an increased risk of cancer from long stays on the lunar surface.

Geopolymers have emerged as a promising candidate for containing nuclear waste on Earth, and Arnhof says the same principle could protect astronauts on the moon.

It’s easier to scale polymer-based construction, but Metzger is skeptical that urine will end up being the superplasticizer of choice on the moon.

Even if humans do end up drinking moon water instead of recycled pee, using astronaut urine for geopolymers may still not be the best choice.

This means that it could be used in a closed-loop life support system where the water from urine is recycled and the urea is used as feedstock for vegetable fertilizer.

So whether it's used as a building material, a fertilizer, or life support, it looks like pee is going to have a big role to play as humans venture out into the solar system.