A Guide to Constructing Roads on the Moon

When astronauts return to the lunar surface, they will need more than just their moon boots – they will need roads. The ultra-fine, abrasive, and clingy lunar dust poses a significant challenge for future lunar missions. In the past, the dust has clogged equipment and eroded spacesuits, causing serious problems for the astronauts.

One notable incident occurred during the Apollo 17 mission when the lunar rover lost its rear fender. The vehicle became so coated in dust that it threatened to overheat. The astronauts improvised a fix using recycled lunar maps, but this incident highlighted the need for better solutions to deal with lunar dust.

The Soviet Union’s Lunokod 2 rover also faced a similar fate. Its radiator got covered in dust, leading to overheating and ultimately causing the rover’s demise. These examples demonstrate the importance of finding ways to keep dust at bay on the Moon.

To address this issue, an ESA project called PAVER (Paving the road for large area sintering of regolith) investigated the feasibility of creating roadworthy surfaces on the Moon by melting simulated moondust with a powerful laser. The project was led by Germany’s BAM Institute of Materials Research and Testing, with contributions from Aalen University, LIQUIFER Systems Group in Austria, and Germany’s Clausthal University of Technology, along with support from the Institute of Materials Physics in Space of the German Aerospace Center, DLR.

The project utilized a 12-kilowatt carbon dioxide laser to melt simulated moondust into a glassy solid surface, resembling paved roads. While it’s unlikely that a carbon dioxide laser would be brought to the Moon, the current laser serves as a light source for experiments. Lunar sunlight could be concentrated using a Fresnel lens to produce equivalent melting on the lunar surface.

In previous in-situ resource utilization projects, researchers have focused on small melt spots. However, for building roads or landing pads, a wider focal point is required to cover a large area in a practical timescale. The consortium achieved a spot size of 5-10 cm at Clausthal University of Technology.

Through trial and error, the researchers developed a strategy using a 4.5 cm diameter laser beam to create triangular, hollow-centered shapes approximately 20 cm across. These shapes could be interlocked to create solid surfaces across large areas of lunar soil, serving as roads or landing pads.

Working with regolith at a larger spot size proved to be easier because heating at the millimeter scale produces molten balls that are difficult to aggregate. The larger beam produces a stable layer of molten regolith this is easier to control. The resulting material is glasslike and brittle but can withstand downward compression forces. Even if it breaks, it can be repaired as necessary.

The team found that reheating a cooled track can cause it to crack, so they focused on geometries involving minimal crossovers. A single melt layer is approximately 1.8 cm deep, and built structures and roads may consist of several layers, depending on the load forces required.

The team estimates that a 100 sq. m landing pad with a thickness of 2 cm of dense material could be constructed in 115 days using this approach.

The PAVER project originated from a call for ideas run by the Discovery element of ESA’s Basic Activities through the Open Space Innovation Platform (OSIP). Out of the 69 ideas submitted, a total of 23 have been implemented based on their novelty and evaluation by a panel of ESA experts.

Overall, the PAVER project represents an important step towards enabling and supporting future lunar missions. By developing techniques to create roadworthy surfaces on the Moon, astronauts will be able to navigate the lunar surface more efficiently and effectively. This innovative approach to dealing with lunar dust discovers new possibilities for lunar exploration and paves the way for future human journeys into the Solar System.