Contact dynamics investigation towards microgravity experiment for asteroid-related scenarios

Most asteroids are now considered gravitational aggregates of loosely consolidated material, and their granular nature suggests that their dynamics can be effectively simulated using N-body codes, such as GRAINS, whose contact dynamics engine is based on the open source code Chrono. Currently, contact parameters in N-body codes are usually tuned to reproduce the macroscopic behavior of large-scale scenarios. Recent in-situ measurements revealed unexpected behavior of granular media on asteroid surfaces, exposing the limitations of current scaling models. Accurately modeling the interactions at particle scale is key to enhance the realism of the models and simulations necessary to support future asteroid exploration missions. This work presents the set-up of an experimental campaign for investigating contact physics in asteroid-related scenarios. The outcome of the campaign can be then used for fine tuning and calibration of contact parameters in multi-body codes. The high-level goal of the experiment is to observe the collision between two asteroid simulant cobbles in micro-gravity and vacuum conditions. Then, a digital twin of the experiment will be calibrated to reproduce their 6-dof trajectory to the best accuracy possible. This work describes the experiment's design and preliminary testing, including requirements and constraints identified for each component of the experimental set up, focusing on the benchmark model of the digital twin and on the strategy designed to estimate the cobbles' states and contact parameters. The estimation results from preliminary numerical simulations show good performance in all the scenarios tested, providing important guidelines for the next phases of the experiment development.