Particle-Size Classification of Lunar Regolith through Inclined Vibrating Tube

The Moon has been the focus of several space exploration programs worldwide because it has valuable materials that could be mined and is suitable for a relay station to Mars. To realize long-term and large-scale crewed lunar exploration, a particle-size classification technology should be developed to achieve efficient in situ resource utilization. As conventional classification technologies that use airflow are not suitable for operations on the Moon, the authors have developed a new technology utilizing the Brazil nut effect in an inclined vibrating tube. Large particles included in the lunar regolith were susceptible to a downward fall in the inclined vibrating tube, and small particles were transported upward; thus, large and small particles were separated. It was demonstrated that particles with a diameter larger than 100 μm were separated from the bulk of the regolith and transported downward when the tube inclination angle was 20°. Conversely, small particles were selectively transported upward when the tube inclination angle was 30°. When the inclination angle was less than 20°, almost all particles were transported upward, and when it exceeded 30°, almost no particles were collected at the upper outlet, and almost all particles fell downward. This system is potentially efficient and reliable for lunar exploration because it is simple and does not require consumables, such as air and water.