Investigating the Minerals and Laboratory-Scale Property of Planetary Rocks Using AGBM
Authors: Zhang Yiheng , Tang Xuhai , Xu Jingjing , Liu Quansheng 
Published: September 2023

ABSTRACT
The physical properties and mechanical behaviour of planetary rocks are critical parameters in the design of asteroid mining. Rock samples obtained by sample-return missions via spacecraft and meteorites collected in the earth are usually rare, fragmented and arbitrarily shaped. These samples are difficult to be processed into standard cylinders required by traditionally macroscale rock mechanics testing methods (e.g., MTS tests), leading to the use of microscale rock mechanics experiments to derive the macroscale Young's modulus of these samples. These microscale experiments have to then be upscaled to obtain macroscale values. The performances of three upscaling methods are considered, two are based on effective medium theory and the third is the computational method of accurate grain-based modeling (AGBM). These methods are compared in the context of granitic samples, and the errors these three methodologies are quantified. The AGBM is found to be the most accurate, and is subsequently extended to measure the mechanical properties of unconventional rock samples, Hammadah al Hamra 346 (HaH 346) asteroid meteorites. The microstructure, mineral composition and mechanical properties of rock-forming minerals and interphase in HaH 346 meteorites are measured using microscale rock mechanics experiment (micro-RME). Then, the macroscale Young's modulus of HaH 346 meteorites is upscaled and estimated using the validated AGBM method. The work is helpful for the characterization of the unconventional rock samples during asteroid mining.

INTRODUCTION
Asteroid mining involves the hypothetical exploration of materials from asteroids and other minor planets, including near-Earth objects. Metal-rich near-Earth asteroids provide the intriguing possibility that ferrum (Fe), nickel (Ni) and cobalt (Co) could someday be mined for use on Earth or in space (Hiroi et al., 1993). Therefore, understanding the deformation and failure properties of planetary rocks is critical to optimize construction activities beyond Earth (Gibney, 2018).
The properties of asteroid rocks, such as composition, thermal parameters and magnetic properties, have been measured and are available in the literature (Flynn et al., 2018; Gattacceca et al., 2014; Krot et al., 2009; Ostrowski and Bryson, 2019). However, the strength measurements of asteroid rocks are scarce, mainly due to the destructive nature of traditional macroscale rock mechanics experiments (macro-RME). The physical properties of stony meteorites, including mechanical properties such as strength, provide important clues to understand the formation and physical evolution of material in the solar protoplanetary disk (Flynn et al., 2018; Pohl and Britt, 2020). However, asteroid samples (e.g. meteorites) are usually arbitrarily-shaped making it difficult to produce standard specimens (Shao et al., 2020) that are required by macro-RME. Recently, the microscale Rock Mechanics Experiment (micro-RME) and Accurate Grain-Based Models (AGBM) have been developed to investigate the mechanical properties of rock-forming minerals of arbitrarily-shaped rocks and their macroscale mechanical properties (Xu et al., 2020; Tang et al. 2022).