Finding suitable building materials presents a major obstacle to plans to colonize space, but a solution may lie in the blood of astronauts. No one is planning to sacrifice brave explorers to build cities on other worlds, but it still sounds a lot like space vampires.
Transporting heavy materials into Earth's orbit is horrendously expensive, let alone longer journeys. One estimate puts the cost of getting a brick to Mars at $2 million. Prices will presumably fall, but the motivation to use locally sourced materials is obvious.
Mars has plenty of regolith (loose rocks and soil) that could provide the bulk of future building materials but lacks an obvious binding agent. A paper in Materials Today Bio explores the possibility of getting what is needed from astronauts' own bodies, noting that while “you can't get blood from a stone,” you can get its proteins into one.
First author Dr Aled Roberts of the University of Manchester and colleagues combined human serum albumin (HSA) with the closest Earth counterparts to Martian and lunar dust. The result is a material they called AstroCrete. AstroCrete can resist 25 megapascals of compression, right in the middle of the range of concretes used on Earth, and easily sufficient for low Martian gravity.
Following on from ideas of using urine to build golden cities on the Moon, the team found they could go further by adding urea, increasing the compression strength to 40 MPa. Astronauts may not be entirely comfortable with donating their blood serum to build their new homes, but urea, which gets its name from the urine (and sweat and tears) in which it's excreted, should be in plentiful supply.
Roberts assures us he is not taking the p**s. "Scientists have been trying to develop viable technologies to produce concrete-like materials on the surface of Mars, but we never stopped to think that the answer might be inside us all along," he said in a statement.
The human body produces 12-25 grams (0.4-0.8 ounces) of HSA a day and can be safely extracted several times a week using medical technology that would be taken to a new world anyway. The authors calculate a crew of six astronauts on a 72-week Mars mission could produce 250 kilograms (550 pounds) of AstroCrete without getting anemic. If the entire structure was made of AstroCrete that wouldn't be much of a legacy, but the authors propose using AstroCrete as mortar, perhaps for regolith bricks fused with heat. As such, each mission could build housing sufficient for one subsequent visitor.
The authors did not come up with the idea from scratch, instead noting blood has been used for mortar before, although it was usually acquired from animals. "It is exciting that a major challenge of the space age may have found its solution based on inspirations from medieval technology," Roberts said. The paper notes we still use horses' hooves to make things sticky today.
The team considered various alternatives but some were ruled out through the great heat required for processing, while one reliant on bovine serum albumin was rejected because “Bringing cows to Mars [is] not feasible with current technology.”
By the end of such a mission astronauts would probably be heartily sick of certain jokes. Roberts has started already, noting “The concept is literally blood-curdling.”