Work continues on designs for robots that can help assist the first human explorers on the Moon in over half a century. One of the most important aspects of that future trip will be utilizing the resources available on the Moon’s surface, known as in-situ resource utilization (ISRU). This would give the explorers access to materials like water, structural metals, and propellant, but only if they can recover it from the rock and regolith that make up the Moon’s surface. A new paper from researchers mainly affiliated with Tohoku University describes the design and testing of a type of robot excavator that could one day assist lunar explorers in unlocking the world’s potential.
One of the primary problems with using conventional mining equipment on the Moon is gravity. Equipment like bulldozers and bucket excavators use their heavy weight to their advantage by using it to apply force to the material they are excavating, allowing them to move large chunks at a time. That technique isn’t feasible on the Moon, where low gravity would cause even “heavy” mining equipment to simply push itself around rather than extract any resources.
Engineers at both Tohoku University as well as NASA have therefore turned their attention to a “bucket excavator” design. In this use case, a bucket drum design has two major advantages over traditional mining equipment on the Moon. First, it can extract only a small amount of material with each pass, which requires much less force than a single large scoop or bucket. However, the passes can come quickly and continuously, allowing it to still effectively excavate a large amount in a relatively short amount of time. Second, it can perform three key processes for material manipulation - excavation, material loading, and haulage - all without the need for a conveyor belt, which are prone to failure in the abrasive lunar dust environment.
Fraser discusses how to live off the land on the Moon.NASA’s Regolith Advanced Surface Systems Operations Robot (RASSOR) is currently the gold standard for these types of excavators, having been through several rounds of testing already itself. However, JAXA, Japan’s space agency, has been supporting development of a “Moonshot Program” with the goal of providing robots that won’t require constant supervision from Earth to support lunar explorers by 2050. The recent paper describes an attachment of the program’s Moonbot, a modular platform originally developed at the University.
Engineers designed a type of “spiral bucket” that solves one of the main problems of traditional bucket drum designs - material falling out while the drum is rotating. This improvement ensures the inlet for the drum is always engaged with the soil while the outlet is always at least slightly above the collected material level, stopping material from spilling out.
To prove its effectiveness, the authors built a prototype system and performed some tests with it, both with and without attaching it to a Moonbot chassis. Two drums on either side of a robotic arm (which provides the interface to the Moonbot platform) are made largely of 3D printed PLA, with some carbon fiber reinforcements in some of the gears. The attachment itself only weighs 4.8 kg, while it is able to carry around 21L of material when fully loaded.
Isaac Arthur discusses how much usefulness we can get out of lunar material. Credit - Isaac Arthur YouTube ChannelThe test results for the stand-alone arm were impressive. On its own it could excavate about 777 kg/h, while only consuming .022Wh/kg, and impressively low power consumption for large excavation amounts. Even when attached to a “Dragon” rover (i.e. a Moonbot chassis configured as a rover), the rate of excavation actually increased to 839 kg./h.
However, to simulate a real mission scenario, the team then implemented a protocol where the robot would excavate material until it was full, drive 10 m to a “dump site”, deposit the material it had collected, return to the worksite and begin working again. In that scenario the efficiency drops to only 172 kg/h with a power consumption of .86 Wh/kg - significantly worse than its specialized mining role, but comparable to other systems like RASSOR.
There’s always room for improvement though, and in this case there’s room both in the mission design and the design of the robot itself. Since Moonbot is a modular platform, mission designers could provide a separate, specialized rover/hauler that could move the material to the dump site, allowing the excavating arm to simply focus on the thing its best at - digging material. And to make it even better at doing that, the designers want to implement additional sensor and control features for the next iteration. They also plan to engineer it to withstand the harsh environment on the Moon, which would be critical for its actual use case.
For now, the paper represents another steps towards the development of helpful robots on the lunar surface, with bucket drums seeming to be a favorite choice of engineers for this use case. It might be a bit before we see one in action on the Moon itself, but at some point in the future a spinning bucket will begin churning away at lunar material that has been undisturbed for billions of years.
Learn More:
S. Giel et al - Design and Development of a Modular Bucket Drum Excavator for Lunar ISRU
UT - A Single Robot Could Provide a Mission To Mars With Enough Water and Oxygen
UT - Modeling Lunar ISRU Extraction Can Help Plan Future Prototypes
