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An autonomous robotic hydraulic excavator could build a dry stone wall to act as a blast shield around a launch pad on the moon, a team of Swiss researchers has suggested.
The excavator would use in situ materials (rather than the expensive practice of transporting building materials from World to the moon), collecting rocks on the lunar surface for use in a ring wall with a radius of 50 to 100 meters (164 to 328 feet).
“The robot would be used to collect the boulders as well as build the wall,” study lead author Jonas Walther told Space.com.
Walther did the research for his master’s thesis at ETH Zürich and now works at the Swiss company Venturi Lab, which works with other companies on the design of a lunar rover, specializing in wheels.
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If humans return to the moon permanently and set up a base then, this infrastructure will need to be protected from the exhaust and debris from rockets taking off and landing. Dust, small particles and gases from rocket exhaust can be hazardous, as demonstrated when the Apollo 12 the crew brought back the Surveyor 3 probe from Oceanus Procellarum and was found to have been damaged by dust blown off the Intrepid Lunar Module.
It is also expected that the rocket will be launched by the giant SpaceX Starship vehicle, which will be used on NASA Artemis 3 mission to return astronauts to the lunar surface, will affect the lunar environment over hundreds of meters, possibly extending into kilometers. A blast shield is therefore required to protect any future ground infrastructure.
Walther mentions a terrestrial prototype of his imagined lunar digger. As reported in a 2023 paper in the journal Science, a team led by Walther’s co-author Ryan Luke Johns of ETH Zürich designed an autonomous robot to dig up material and use it to assemble a dry stone wall here on Earth. Their new research takes this technology and applies it to a lunar environment.
Among the challenges this technology would face on the moon are the distance a vehicle would have to travel to collect enough raw materials to build a blast shield, the energy required to achieve this and the source of that energy.
However, the benefits, Walther and his team argue, far outweigh those of other construction techniques. For one thing, a dry stone wall that uses boulders plucked from the lunar surface does not require the energy-intensive methods of material processing that other techniques might use, such as heating to cement the material in place. What’s more, Walther points out that dry stone walls, as primitive as they sound, can have remarkable longevity.
“Some dry stone walls on Earth have survived for thousands of years,” Walther said. And while such structures built on the moon don’t necessarily last that long, the greatly reduced weathering on the moon (no air, no water, no wind, just space weathering from cosmic particles) means that they the forces alone. such a wall would have to resist the blasts of the rockets taking off or landing. Walther’s team estimates that the pressure on the blast shield from gases ejected by one of SpaceX’s Starship rockets would be 1,135 Pascals. This is very small compared to the normal atmospheric pressure on Earth of 101,000 Pascals.
The time and energy consuming part, however, is gathering the material. Walther’s team estimates the excavator’s payload capacity to be 10 cubic meters (353 cubic feet) of boulders; to build a blast shield ring with a radius of 50 meters, a circumference of 314 meters (1,030 feet) and a height of 3.3 meters (10.8 feet) would be required in full estimated of 1,000 cubic meters’ (35,314 cubic feet) lunar value. boulders (defined as stones larger than 25.6 centimeters, or about 10 inches).
The digger has to roll out all this material and find it on the moon itself. Walther’s team studied images of two possible locations where a lunar base could be located, namely the Shackleton-Henson Connecting Ridge which connects the Shackleton and Henson craters in the south polar region of the moon and is possible landing site for Artemis 3and the Aristarchus Plateau pyroclastic deposit near the prominent Aristarchus cline in Oceanus Procellarum.
Based on images of these two regions taken by NASA’s Narrow Angle Camera Lunar Exploration Orbit, which can detect boulders down to 2 meters (6.6 feet) wide, and by using boulder size frequency laws to estimate how many smaller boulders are not visible (there are more smaller boulders than larger ones), Walther’s team used an algorithm to calculate. the most efficient path the excavator could take to collect all the raw material and bring it back to the construction site, going back and forth several times. They reached a total distance traveled of between 776 and 880 kilometers (482 and 547 miles), although this figure will depend on factors such as payload capacity and ease of access to material (many are expected to be collected at the base of the slopes, ie for example).
“I agree that the distance is quite large to begin with,” said Walther, but he points out that driving such a distance is not unrealistic. “The IS Lunar Land Vehicle (LTV) being developed for Artemis, or NASA’s concept rover called Endurance, will be capable of similar distances.”
The excavator and the dry stone wall would use much less energy than other methods that would replace the cement wall. Walther’s team calculates that the digger would spend between 9 and 10 gigajoules of energy in building just a quarter of the blast shield. In comparison, cast regolith, whereby regolith (lunar material and rock) is heated until it melts and then poured into molds and left to cool to form molded parts, would use 1,250 gigajoules per quarter item. Microwave heating would be even more energy intensive, using between 6,440 and 17,500 gigajoules depending on the density of the material. Therefore the autonomous excavator that would build a dry stone wall would be at least two orders of magnitude less energy intensive.
This is important on the moon because an isolated lunar base would need to be energy aware, at least initially. The estimated total time to build the blast shield is about 63 Earth days, but that doesn’t include recharge times, and if solar power was used the digger would have to go into hibernation every two weeks for a moonlit night, so this would be double. the construction time to at least 126 days. Portable recharging stations, or equipping the excavator with nuclear power in the form of a radioisotope thermoelectric generator (RTG) of the type a Trainer Mars Curiosity and Persistence Could, but more powerful, mitigate some of these delays.
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There may be some gaps in a dry stone wall, and Walther admits that more study is needed to determine if these gaps would be a problem in weakening the structure or not providing enough protection for any moon base that is located behind the blast shield. However, his team predicts that the digger could be even more useful Marswhere there is a greater density of boulders across a smaller area, reducing driving time and energy use.
The land prototype shows that a lunar version could be developed within a relatively short timescale. However, much depends on NASA’s progress The free Artemis program,with Artemis 2 already delayed to September 2025 at the earliest, and Artemis 3, which would have made the first moon landing since then Apollo 17 in 1972, no definite timeline. It is currently unknown whether any further missions will be launched beyond Artemis 3, but if efforts are made to develop a base on the lunar surface, the autonomous excavator and its dry stone walls could be critical to building bulky structures in a hurry.
The assessment of the excavator by the Walther team was published on June 6 in the journal Frontiers in Space Technologies.