Human excrement brings a possible solution to the problem of transporting heavy loads to the Moon, a new study suggests.
Space agencies in the United States, Europe and China have already expressed interest in building lunar bases in the coming decades. The plan is quite challenging: to begin with, transporting just 450 grams of material from Earth to its natural satellite costs about $10,000. However, according to a new study released in the Journal of Cleaner Production, part of this problem can be solved using the urine of astronauts.
Research conducted by experts from Norway, Spain, the Netherlands and Italy in collaboration with the European Space Agency (ESA) raises the possibility that the substance excreted by humans can serve as a plasticizer, a type of additive that softens building materials.
“To make the geopolymer concrete that will be used on the Moon, the idea is to use what is there: regolith (loose material from the Moon’s surface) and the water from the ice present in some areas,” explains Ramón Pamies, a professor from the Polytechnic University of Cartagena (Spain) and co-author of the study, in a statement. “But in this study, we have seen that a waste product, such as the urine of the personnel who occupy the Moon bases, could also be used.”
Additionally, according to the expert, human excrement is mostly composed of water and urea, and this second molecule allows the breakdown of hydrogen bonds – which reduces the viscosities of various aqueous mixtures.
To test this idea, scientists mixed a material similar to lunar regolith with urea and different plasticizers, and then used a 3D printer to create cylinders of “mud”. What they found, then, is that the samples with urea in their composition supported heavy weights and maintained their very stable shapes, in addition to becoming even more resistant after being heated to 80°C and going through freeze-thaw cycles, as they would on the Moon.
The results of the experiments bring new light to the difficulties of building a lunar base – a challenge that, in addition to the high cost of transporting materials, also includes problems such as high levels of radiation, extreme temperatures and meteorite shocks. However, the study’s authors reinforce that more tests are still needed to find the best materials for these constructions.
“We have not yet investigated how the urea would be extracted from the urine, as we are assessing whether this would really be necessary, because perhaps its other components could also be used to form the geopolymer concrete,” points out Anna-Lena Kjøniksen, a researcher at Østfold University (Norway) and co-author of the study.