Characterisation of planetary simulants using a rotating drum experiment

Many celestial bodies in our Solar System, such as the Moon, Mars and small bodies, are covered with a layer of regolith. Numerous current and upcoming space missions aim to interact with these surfaces such as the IDEFIX rover of the Martian Moons eXploration (MMX) mission [1] and the Hera mission [2]. Some instruments, such as the instrument InSight HP³ mole, have even failed to perform as expected [3], highlighting the importance of understanding the geotechnical behavior of regolith surfaces. Due to the limited accessibility and high cost of in situ missions, laboratory experiments using regolith simulants are crucial for the preparation of surface operations like landing, mobility, and sampling. Different extraterrestrials simulants have been developed and characterized regarding the mineralogical, granulometric and some geotechnical properties [e.g., 4-7]. Here we present the results of additional characterisation experiments focussing on the dynamic angle of repose and the cohesive properties of the simulants. A rotating drum experiment has been developed to measure bulk properties of different planetary simulants in low consolidation conditions. The setup is presented in Figure 1. The simulant is placed in a cylinder container of  4 cm diameter and 5 cm depth so that the container is half full with the granular material. Two PMMA windows are mounted on the front and back of the container, to be able to see through the system. The sample container is attached to a drive shaft which allows it to rotate around its axis. A CCD camera (mvBlueFox-120aG) is fixed facing the front window to image the granular material. An LED panel illuminates the experiment from behind allowing a shadometry image analysis to be performed. The rotational speed of the motor is controlled by an Arduino card. The gear ratio between the motor and the container allows it to rotate between 10 and 70 rotations per minute (RPM).Figure 1: The rotating drum experiment at ISAE-SUPAERO.The motor rotational speed is varied and 10 images are taken for each speed with a frame rate of 20 Hz. A binarization of the image is performed followed by an edge detection which automatically detects the surface of the material. This process is shown in Figure 2 for glass beads at two different rotational speeds. It is performed on the 10 images, and for each rotational speed, as illustrated in Figure 3.Figure 2: Surface detection for glass beads at two different rotational speeds.Figure 3: Surface profiles for 10 images at different rotational speeds for glass beads.By measuring the surface slope close to the center of the drum, the dynamic angle of repose for each rotational speed can be determined. This result is presented in Figure 4 for three different granular materials: quartz sand with a mean particle diameter of 500 µm, glass beads with a diameter between 90 and 150 µm and Mars Global (MGS-1) High-Fidelity Martian Regolith Simulant. Figure 4: Dynamic angle of repose as a function of the rotational speed. The error bars represent the standard deviation of the angle of repose measured in 10 different images at each rotation speed.This experimental set-up also allows for a characterisation of the cohesive properties of the granular material. The rugosity of the surface at each rotational speed can be used to compute the cohesive index, an adimensional number directly linked to the total cohesive force [8]. This gives a comparative measurement of the cohesion of the different simulants.In summary, we have developed a rotating drum experiment to characterise different planetary simulants. Two main material parameters can be extracted: a cohesive index, which is an adimensional number directly linked to the total cohesive forces, and the dynamic angle of repose. The set-up has already been tested with three different materials (glass beads, quartz sand and Mars Global (MGS-1) High-Fidelity Martian Regolith Simulant). The results of the rotating drum characterisation of the Exolith planetary simulants - Lunar Highlands (LHS-1) High-Fidelity Regolith Simulant, Lunar Mare (LMS-1) High-Fidelity Regolith Simulant, Carbonaceous Chondrite (CI-E) High-Fidelity Asteroid Regolith Simulant and Carbonaceous Chondrite (CM-E) High-Fidelity Asteroid Regolith Simulant - will be presented during the conference.References:[1] Michel, Patrick, et al. "The MMX rover: performing in situ surface investigations on Phobos." earth, planets and space 74 (2022): 1-14.[2] Michel, Patrick et al. (2022). The ESA Hera mission: Detailed Characterization of the DART Impact Outcome and the Binary Asteroid (65803) Didymos. The Planetary Science Journal, 3:160.[3] Spohn, Tilman, et al. "The InSight-HP3 mole on Mars: Lessons learned from attempts to penetrate to depth in the Martian soil." Advances in Space Research 69.8 (2022): 3140-3163.[4] Long-Fox, Jared M., et al. "Geomechanical properties of lunar regolith simulants LHS-1 and LMS-1." Advances in Space Research 71.12 (2023): 5400-5412[5] Cannon, Kevin M., et al. "Mars global simulant MGS-1: A Rocknest-based open standard for basaltic martian regolith simulants." Icarus 317 (2019): 470-478[6] Yin et al., “Shear Properties of LHS-1 and LMS-1 Lunar Regolith Simulants”. Planetary and Space Science 2023, 226, 105630. https://doi.org/10.1016/j.pss.2022.105630.[7] Just, G. H.et al., “Geotechnical Characterisation of Two New Low-Fidelity Lunar Regolith Analogues (UoM-B and UoM-W) for Use in Large-Scale Engineering Experiments”. Acta Astronautica 2020, 173, 414–424. https://doi.org/10.1016/j.actaastro.2020.04.025.[8] Neveu, A., F. Francqui, and Geoffroy Lumay. "Measuring powder flow properties in a rotating drum." Measurement 200 (2022): 111548AcknowledgementsThis project is carried out with the support of the European Research Council (ERC) GRAVITE project (Grant Agreement N°1087060), and from CNES in the context of the Hera mission and the MMX rover/wheelcams.