Ever since the president Donald Trump has directed NASA to get boots on the moon by 2024, the agency and its partners are working hard to do so. Late last month, NASA awarded contracts to three lunar crew development companies, but reaching the moon is just the beginning. The agency also plans to build a permanent lunar base before the end of the decade and use it as a step towards Mars.
If astronauts spend weeks on the moon, they will have to figure out how to live offshore – er, regolith. It is too expensive to transport everything from Earth, which means they will have to be creative with the limited resources of the lunar surface. Moon dirt is a great building material and there is ice at the South Pole, which can be turned into rocket fuel. But the hottest commodity of them all may be a powerful astronaut.
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 lunar dirt and used for construction. The resulting material is a geopolymer that has similar properties to concrete and could potentially be used to build landing sites, habitats and other structures on the moon.
Geopolymers are regularly used on Earth as an environmentally friendly alternative to conventional concrete. One of the main ingredients in concrete is cement, which requires a high temperature 22a production process that releases a lot of CO2But the geopolymer does not need much energy at all. Instead of cement used powdered rocks or fly ash, the waste product of coal combustion. When this is mixed with water and some reactive compounds, it creates a screed-like material that can be cast into desired shapes before it remains dry.
On the moon, the infrastructure will most likely be built by industrial 3D printers. Brick construction would be too inefficient and would limit the types of structures that could be made. But robotic 3D printers could autonomously build more complex habitats. Lunar regolith has chemical similarities to fly ash, which makes geopolymers an attractive option for building things on the moon. The downside is that geopolymers require a lot of water to pass through the nozzle of a 3D printer.
“Water is very, very valuable on the lunar surface,”
Superplasticizers are materials used to reduce the water content of concrete and geopolymers while maintaining their flowability. On Earth, superplasticizers are usually difficult to pronounce, such as naphthalene and polycarboxylate. But as Arnhoff and her colleagues found, urea works just as well and can easily supply the moon. Instead of filtering contaminants into the astronaut’s urine and recycling the wastewater, the peak can be stored in a tank and collected for urea.
To test the idea, the researchers mixed synthetic urea powder with a lunar regolith simulator to make fist-sized cylindrical structures and let them dry under weight. They then simulate using the material in a 3D printer, extruding it in layers using a syringe. They compare the results with conventional geopolymers. “She performed quite well,” said Anna-Lena Koenicsen, a materials scientist at Østfold University College and co-author of the study. “It seems to give the best overall results, especially when it comes to avoiding cracking.”