Effective Diffusivity in Porous Media Under Rarefied Gas Conditions

Abstract

For future space missions in which soft landings on extra-terrestrial bodies will be required, it is important to understand the interaction of the propulsion system with the surface of the body. During the landing phase, the porous surface regolith can become contaminated with the exhaust products of the rocket plume, and this contamination must be minimised if sample return from the landing site is the goal of the mission. How far in-depth the exhaust products can reach depends on the effective diffusivity of the gas in the porous surface regolith material. The purpose of this work is to study the influence of temperature, gas number density, and adsorption parameters on the effective diffusivity in highly porous media under rarefied conditions. The procedure to recover the effective diffusivity, using direct simulation Monte Carlo, from a real sample is presented, along with trends as parameters are being varied, which will prove informative for later use of simplified engineering methodologies that assume a homogeneous porous structure