Printing Houses on the Moon

Later this month, an unusual device is headed for the International Space Station. The U.S. National Aeronautics and Space Administration (NASA) is sending up a specialized 3D printer, a machine that manufactures objects from the bottom up, building them layer by layer. The printer, developed by Made in Space, Inc., has been through rigorous testing at NASA’s Marshall Space Flight Center. The next question is whether it is going to work in zero gravity.

NASA envisions 3D printers serving as miniature on-site manufacturing plants creating replacement parts and tools, but the upcoming experiment is also an early test of a far grander idea. NASA and the European Space Agency (ESA) are both exploring the possibility of printing entire buildings on the Moon, or even on Mars.

Building habitats on the Moon using lunar soil as the raw material may prove less expensive than shipping ready-made structures from Earth. "You must learn to apply the local material, and the easiest approach is to use 3D printing," says Amit Bandyopadhyay, a Washington State University biomedical engineer.

Of course, printing a building is no simple task, even with gravity. The Dutch firm DUS Architects estimates it will take three years to complete its 3D-printed Canal House in Amsterdam. A Chinese company reportedly printed a number of concrete houses recently, but Behrokh Khoshnevis, a 3D printing pioneer at the University of Southern California (USC), inspected the technology last year, and he suspects the structures were created in sections, cured over time, and assembled later, rather than being printed whole.

Khoshnevis has been working in the field for a decade, and his goal is to build a machine capable of printing an entire home, on site, in one day. In his process, called contour crafting, a large, scaffold-like rig would sit over the site, gradually moving a nozzle back and forth, ejecting concrete or another material to create the floors, then the walls, layer by layer. Many problems can arise—he had to develop a proprietary technology to prevent the concrete from clogging in the nozzle, for example—yet the technology has to work perfectly for it to be a viable alternative to traditional construction. "If you’re printing on paper, and in the middle you notice that the ink is fading, you scrap the paper and change the cartridge and print from the beginning," Khoshnevis says. "If you’re building a house and you’re two-thirds up and a problem happens, are you going to throw the rest of the house away? You cannot. It’s much like a NASA project. Failure is catastrophic."

Khoshnevis has been collaborating with NASA, applying his contour crafting technique to plans for printing outposts on the Moon and Mars.

Bandyopadhyay, the Washington State University engineer, and his colleague Susmita Bose, performed related experiments for the agency. The pair are experts in using high-powered lasers to transform certain powders into viscous materials that can be used to print artificial bones. The Moon does not come with its own supply of cement or bricks; the space agencies would have to find a way to transform the loose lunar soil, regolith, into something that could be printed and, when in place, remain structurally strong. NASA asked the pair to use their technique with simulated regolith (surface dust/soil), and they succeeded in printing a few basic objects. Bandyopadhyay envisions a robotic system that gathers soil, heats it with a laser, adds a binding material shipped from Earth, then prints the resulting concrete-like substance into structures.

The ESA has a similar vision. The agency worked with architecture firm Foster + Partners, along with several other collaborators, to conceptualize a two-story inflatable lunar habitat shielded from the rigors of space by a 3D-printed dome. The dome would be printed from modified regolith, but it would have a cellular structure, complete with gaps. Foster + Partners architect Xavier De Kestelier says this inner cellular structure, inspired by bird bones, would maintain strength while limiting the amount of binding material required. The gaps could be filled with loose lunar soil, allowing the dome to further protect the inhabitants from harsh radiation and micrometeorites.

The head of ESA’s project, Laurent Pambaguian, adds that it would also be possible to build much larger structures with 3D printing, yet he says there is only one way to find out if these techniques will actually work. "The only way to know is to go to the Moon," he says.

Gregory Mone is a Boston-based science and technology writer.