A mixture of moondust and astronaut urine. This is how future astronauts could build buildings with the aim of easily establishing a colony on our satellite. That is the suggestion of chemist Anna-Lena Kjøniksen and her colleagues, who made a urea cement, and whose work they publish in the Journal of Cleaner Production and which has been supported by the European Space Research and Technology Center (ESTEC). of the ESA.
We cannot ignore that, in the coming decades, NASA, the European Space Agency (ESA), China and Russia plan to create outposts on the surface of the Moon that will allow a permanent human presence. These proposals seek to take advantage of advances in 3D printing with in situ resource utilization (ISRU) to address the challenges of living and working on the Moon.
When humans settle for the long term on other planets, or sooner on the Moon, they will need to carry as little as possible, since shipping materials from Earth to the Moon is expensive. The economic viability of lunar missions depends on getting as much of what we need as possible right there. Not surprisingly, NASA has estimated that each kilogram of material sent into orbit around the Earth costs around $ 20,000 (about 18,000 euros).
In this way, if it is possible to take advantage of local resources it would help to keep the cost of the mission low. Although the use of lunar soil to make concrete or cement to 3D print homes for astronauts has been previously suggested, most cement recipes require a lot of water, something that is in short supply on our satellite and an element too heavy for be transported from the Earth to the Moon.
But what if astronaut urine could be used as a component?
Scientists from all over Europe have collaborated to find a way to sculpt the lunar surface into something that will hold the shape they want without having to drill caves in solid rock.
Scientists have been working on lunar regolith combined with a binding agent to create a building material, and it turns out that urine is an excellent ingredient. Specifically, the chemical urea, which is an organic compound found in the urine of animals (it is the component in greater quantity after water) and that could turn the upper layer of the Moon into something that research teams or even the settlers can use it as a refuge.
The urea molecule “allows hydrogen bonds to break and thus reduces the viscosities of many aqueous mixtures.” In other words, it makes water-based fluids flow better, but won’t stop them from hardening as the brutal sunlight of the long lunar day dries them out.
Remember that without an atmosphere, the surface of the Moon is subject to a lot of radiation; And, without an atmosphere, there is also no protection against space rocks. With an estimated 44,000 kilograms of meteoric material hitting the Earth every day, there are many potential bombardments on the Moon as well and to guard against. And there is also the problem of temperature : lunar temperatures vary, from 120 degrees Celsius during the day to -130 ° C at night, so the building material must be able to withstand a significant thermal temperature change to the time to insulate the interior.
Thus, using a 3D printer, the researchers built cylinders of the mixture named ” lunacrete” (a silica and aluminum oxide powder, a substitute for moondust and undistilled urea powder from real urine and a little water) to determine how well urea works as a plasticizer.
Compared to two other superplasticizers used in construction on Earth, “urea worked very well,” says Kjøniksen. The mixture kept its shape under light weight and withstood changes in temperature. They even built a small wall with the 3D printer.
Kjøniksen plans to test the cement at more extreme temperatures and in a vacuum chamber that mimics the moon’s lack of atmosphere; so the next step would be to build a life-size wall. It will also be necessary to investigate if future astronauts would need to purify the urine, or if they could use it on the cement directly.
Referencia: S. Pilehvar et al. Utilization of urea as an accessible superplasticizer on the moon for lunar geopolymer mixtures. Journal of Cleaner Production. Vol. 247, February 20, 2020. doi: 10.1016/j.jclepro.2019.119177.
