Angle of Repose of Lunar Regolith on the Farside of the Moon: A Micro–Macro Mechanical Study Based on Chang’e-6 Samples

Understanding the mechanical properties of the farside lunar regolith is vital for reconstructing the geological history of the Moon and supporting future surface engineering and resource utilization; however, these data were unavailable prior to the Chang’e-6 (CE-6) mission. This study presents a multiscale framework linking the particle-scale Young’s modulus, shape, and surface roughness to the angle of repose (AoR), which is a key parameter that dictates slope stability, flowability, and geomorphological evolution in low-gravity environments. Using nondestructive X-ray micro-computed tomography, nanoindentation, and white light interferometry, the three-dimensional morphology, nanomechanical properties, and nanometer–micrometer-scale roughness were quantified for breccia, agglutinate, and other particle types. These descriptors parameterized the discrete element method (DEM) simulations calibrated against six AoR experiments on 1742 coarse grains, yielding a terrestrial AoR of 45.56° (range 43.03°–48.09°). The best-fit model (interparticle friction coefficient μ p = 0.55) reproduced this value within 1% and predicted an AoR of 49.73° under lunar gravity. Both the coarse- and full-grain-size tests exceeded the theoretical spherical-grain predictions by ∼15°, reflecting enhanced friction from elevated roughness and rolling/torsional resistance from irregular geometries. By providing a validated mapping from measurable grain descriptors to DEM contact parameters and AoR, this study established a first mechanical baseline for farside regolith, together with quantitative constraints for slope/berm design, stockpiling grades, and regolith handling systems in lunar missions.