Soil Cohesion Effects on Cratering and Transport of Regolith due to Plume-Surface Interaction

The plume-induced environment from propulsive landing of robotic and human-rated vehicles is one of the top unresolved critical risks for extraterrestrial missions. Primary risks of plume-surface interaction (PSI) are the creation of large craters and high-speed ejecta that can impact and damage the vehicle or surrounding infrastructure. NASA analysts use advanced modeling and simulation capabilities to predict the PSI-induced environment, but a critical gap in these tools is soil cohesion. Cohesion, or the ability of soil grains to adhere to one another, dominates in low-pressure, reduced-gravity environments and is a primary driver in the initiation and resistance to motion and suspension and resettlement of soil. Without accounting for cohesion, predictions of soil behavior in a PSI-induced environment fail to accurately capture erosion onset, the evolution of crater formation, and soil berming as seen from Apollo and other missions. Experiments targeting cohesion processes in the low-pressure, reduced-gravity environment are minimal, so validation of models is difficult. In this effort, CFD Research and University of Central Florida’s (UCF) Center for Microgravity Research (CMR) Lab will implement, validate, and improve existing cohesion models for the PSI-induced environment. Cohesion and bulk cohesion models will be implemented into CFD Research’s Gas-Granular Flow Solver, Loci/GGFS, and validated against existing terrestrial cohesion data sets from UCF. UCF will perform additional cohesion-focused experiments in the low-pressure, reduced gravity regime, which will also enable the identification of critical gaps in current models in the PSI-induced regime for further improvement. The resulting experimental data and predictive simulation tool will be delivered to NASA, dramatically improving the PSI simulations and enabling further pathways for model development and validation for any existing simulation tool.