The surface of the Moon is a dangerous place. There’s no large magnetic field to deflect charged particles, and it’s covered with a fine layer of abrasive dust known as the regolith—mainly silicon dioxide crystals that are the consistency of flour. In the low lunar gravity, the dust is easily kicked into suspension, especially as lunar rovers move across it. And when Apollo astronauts walked on it a half century ago, it scratched their visors and made their throats sore. According to recent research, prolonged exposure can damage the DNA in lung cells. (See the Quick Study by Larry Townsend, Physics Today, March 2020, page 66.)
Infrastructure, such as roads, would mitigate those problems. But it’s prohibitively expensive to transport construction materials from Earth: Shipping a single brick’s worth of material into low Earth orbit costs $5000 (see the Quick Study by Aled Roberts, Physics Today, March 2023, page 62). To avoid the expense of delivering material to the Moon, nascent colonies will have to rely on resources already there.
A group of engineers and materials scientists led by Juan-Carlos Ginés-Palomares (Technical University of Berlin), Miranda Fateri (Aalen University in Germany), and Jens Günster (Federal Institute for Materials Research and Testing in Berlin) now propose an approach to create paved roads and landing pads on the Moon. The idea: Focus sunlight through an optical lens to melt the lunar regolith into a molten liquid that cools into a solid, layered composite. The researchers’ laboratory experiments were designed as part of the European Space Agency’s Project PAVER—paving the road for large area sintering of regolith. They used carbon dioxide laser light as a proxy for concentrated sunlight and a powdery material (EAC-1A) as a proxy for the regolith.
The researchers explored the effects of different beam strengths and widths—up to 12 W and 100 mm, respectively—and demonstrated that the molten liquid cools into a hard solid. But overlapping the beam with already condensed patches thermally shocked the composite and cracked it. To avoid overlapping the laser spot with already irradiated areas, the researchers adopted an approach in which they scanned a smaller, 45-mm-diameter beam over the artificial regolith to create repeated, triangular shapes about 250 mm in size. Those shapes, the researchers showed, could interlock to form a solid surface across large areas of lunar ground as part of the first roads.
On the Moon, colonists would need an optical lens in place of the laser, and it would have to be shipped from Earth. Given a solar flux of 1400 W/m on the Moon, Ginés-Palomares and colleagues calculated that the lens would need to be 2.37 m2 in size to melt the regolith. (J.-C. Ginés-Palomares et al., Sci. Rep. 13, 15593, 2023.)
