The rockets that will take us back to the Moon are on hold while we cope with Earthly problems but planning goes on. Scientists seeking building materials to construct lunar bases have hit upon urine as a key ingredient, one that can turn the Moon's upper layer into something in which research teams or even colonists could shelter.
If you think excess luggage is expensive, try the cost of getting even a few additional grams into space, let alone all the way to the Moon. The economic viability of lunar missions depends on sourcing as much of what we need as possible on location. Having found we can probably access water there, at least if we base ourselves near the poles, the question has turned to other necessities.
The absence of an atmosphere means a shelter must keep out extreme temperatures and high radiation while being large enough to grow food beneath. Scientists from across 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 caverns into solid rock.
"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," said Professor Ramón Pamies of the University of Cartagena in a statement.
Unfortunately, the samples brought back by the Apollo missions lack anything obviously suitable as a plasticizer, something that softens concrete enough to allow it to be shaped before it hardens. In the Journal of Cleaner Production, Pamies and co-authors propose the astronauts make their own, not through advanced chemical processing but using their own urine.
The authors are apparently not taking the piss, they genuinely want future lunar explorers to do just that. Urea, the largest component of urine after water, “allows the hydrogen bonds to be broken and therefore reduces the viscosities of many aqueous mixtures.” In other words, it makes water-based fluids flow better but won't prevent them from setting rock hard as the long lunar day's brutal sunlight dries them out.
A mixture resembling lunar regolith combined with urea and modest amounts of water proved capable of being 3D printed before setting at just 80ºC (176ºF). Exposure to repeated freeze-thaw cycles similar to those on the lunar surface also didn't prevent the dried material from holding heavy weights, as the base of a dome would need to do, even in low gravity.
The team did not test whether the urea and water would need to be separated from less common components in urine or if the astronauts could just piss in the same pot until they had enough to start building their golden city.