With the development of civilization comes roads, and this will be especially true on the moon. To do this, the dust must be kept away. In the Apollo era, dust blocked equipment and worn space suits.
When the astronauts return before the moon, they will probably drive more than walk - but to keep flying moon dust away they will need roads. A European Space Agency ESA project reported in Nature Scientific Reports tested the possibility of creating roadworthy surfaces by melting simulated moon dust using a powerful laser.
With the development of civilization comes roads, and this will be especially true on the moon, you just need to keep the dust away first. Moon dust is extremely fine, abrasive and sticky. In the Apollo era, dust blocked equipment and worn space suits.
The Survivor 3 lander was swept up in dust when the Apollo 12 lunar module landed about 180 meters away. Current NASA models indicate that when lunar landers land, their engine jets can move tons of dust, which could stick to the lander's surfaces and cover the entire area around a landing.
The most practical response is to keep dust away by paving activity areas on the moon, including roads and landing pads. The idea of melting sand to create roads was first proposed to Earth, back in 1933.
ESA's PAVER project - Paving the way for a large area sinter of Regolith - investigated the feasibility of the same approach to paving roads on the Moon, led by the BAM Institute for Materials Research in Germany together with the Aalen University in Germany, the LIQUIFER Systems Group in Austria and Germany and the Klausthal University of Technology in Germany, with the support of the Institute for Materials Physics in Space of the German space agency DLR.
The consortium used a 12-kilowatt carbon dioxide laser to melt simulated lunar dust into a glassy solid, as a way to build paved surfaces on the moon's surface.
As ESA's materials engineer, Advonite Makaya, explains, the project actually goes back to the original concept from 1933: "In practice, we will not bring a carbon dioxide laser to the moon. Instead, the current laser is used as a light source for our experiments, to replace lunar sunlight that can be focused using a Fresnel lens several meters in diameter to produce parallel melting on the lunar surface.
"In previous on-site resource utilization projects - including building bricks using solar heat concentrated in mirrors - we looked at surface melting limited to relatively small melting points, from a few millimeters to several centimeters in diameter. To build roads or airstrips, a much wider focal point is required, to scan a very wide area in a practical amount of time."
In facilities installed at the Klausthal University of Technology, the consortium achieved a focus point of 5-10 cm.
Through trial and error, they developed a strategy to use a 4.5 cm laser beam to create hollow-centered geometric shapes about 20 cm in diameter that could be joined together to form large solid surfaces that could be used as roads or runways.
Advonite adds: "It turned out that it was actually easier to work with regolith at a larger focal point, because on a scale of millimeters, heating creates molten spheres whose surface tension makes it difficult for them to aggregate to the surface. A wider beam produces a stable layer of molten regolith that is easier to control.
"The resulting material is glassy and brittle, but it will mainly be under downward compressive forces. Even if it breaks, we can continue to use it, and repair it as needed."
A single melting layer is about 1.8 cm deep
The team found that reheating a cooled paved road could cause it to crack, so they switched to geometries that included minimal crossings. A single melting layer is about 1.8 cm deep; Built buildings and roads may consist of several layers, depending on the required load forces.
Jens Ginster, head of the multi-material manufacturing process department at BAM, explains: "Such a high melting depth to create massive structures can only be achieved by large laser spots."
The team estimates that a landing pad of 100 square meters with a thickness of 2 cm of fastened material can be built in 115 days.
This project originated from a call for ideas from the Discovery Foundation in ESA's Fundamental Activities through the Open Innovation Platform OSIP. The calling voice asked for research ideas related to extraterrestrial manufacturing and construction.
The call was answered no less than 69 times. Of these, 23 ideas were implemented - based on an assessment carried out by a panel of ESA experts, who scored the ideas according to their innovation.
"This initial call was an effective investment from our point of view", notes Adventit, "it opened up many promising research paths to follow".
The project is part of ESA's Terrae Novae exploration program, leading the European manned mission to the Solar System, with targets in low orbit around Earth, the Moon and Mars.