A data assimilation framework to derive surface erosion quantities from sparse ejecta measurements during plume surface interactions

The impingement of thruster plumes on regolith surfaces during propulsive landings on the Moon and planetary bodies creates a dense ejecta cloud that obscures the surface and poses risks to surface assets. The opacity of the ejecta cloud challenges a complete characterization of ejecta velocity and concentration, and impedes direct access to surface erosion, during flight or in laboratory scale experiments. A data assimilation framework is presented that combines temporally resolved but spatially sparse measurements of radial concentration distributions, and particle velocity measurements in dilute regions, to provide erosion quantities of interest at the surface. The data was obtained from sub-scale experiments using a Mach 5 jet impinging on a bed of glass microspheres under sub-atmospheric pressures. Millimeter-wave interferometry and particle-tracking velocimetry provided concentration and particle velocities in different regions within the cloud. An inverse particle trajectory function is used to obtain the initial conditions for particle velocity and angle distributions, and particle flux that best match the measured concentration and ejecta velocity. The proposed framework provides a tool to derive erosion parameters, as well as the complete reconstruction of the evolving particle field, from sparse data. The framework can be enriched with other sources of data and the outputs are key to inform predictive models.