Numerical estimations of lunar regolith trajectories and damage potential due to rocket plumes

This study presents a numerical investigation of rocket plumes carrying regolith particles in the context of the lunar environment (gravity and vacuum conditions). We investigated two lander masses with a single rocket hovering at 5 different low altitudes perpendicular to a flat surface. For the regolith, we considered 9 particle sizes, with diameters from 1 mu m to 1 cm. The initial condition of all particles was a null velocity at 0.3 m above the ground. The particles started at 19 different radial positions from the centerline of the rocket jet, 1 m to 10 m. We used a DSMC method to solve the rocket plume cases, considering the combustion product molecules from the propellant N2O4+Aerozine 50. Steady-state plume flow solutions are one-way coupled with discrete particles, considering drag and weight forces. The results showed that particle angle is nearly constant for small (d(p) < 100 mu m) particles varying with initial radial position and lander altitude. Particle velocity is related to particle diameter as a power-law function and a Gaussian function of the initial particle position. Lander altitude and mass modulate the magnitude of particle velocity. Using the numerical solution data, we derived a numerical correlation for particle velocity that provides insight to avoid regolith abrasive blasting into the lunar lander, surrounding structures, and orbital satellites.