Modeling Plume-Surface Interactions for Landing Pads and Untreated Ground

Outward Technologies with support from its subcontractor Astrobotic Technology proposes to continue developing Free Open-Source Software (FOSS) for simulating Plume-Surface Interactions (PSI) relevant to lunar and Martian landing conditions. These software tools include 1) a two-way coupled Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) numerical modeling framework for simulating regolith-plume interactions; 2) a grain-based DEM model of lunar regolith ejecta with accurate distributions of grain types, sizes, and shapes capable of receiving input from the plume model to predict erosion physics and ejecta dynamics; 3) a damage calculator for identifying the location and extent of pitting and fracturing produced by soil ejecta impacting near- and far-field surfaces; 4) a calibrated and validated set of model input parameters to fit the soil mechanics response of ground obtained from PSI experimental data, to include time-dependent crater geometry and ejecta trajectories and velocities; and 5) a demonstration model incorporating the full capabilities of this developed software to simulate PSI during a landing event at large-scale, deployed in a massively parallel cloud computing environment. These combined tools and calibrated model inputs will enable high-fidelity PSI models to be run in a reasonable time to aid Commercial Lunar Payload Services (CLPS) lander companies such as project partner Astrobotic in planning for near-term missions, while also enabling design studies of lunar Human Landing Systems (HLS). Test performance will be documented to demonstrate agreement with analytical and experimental predictions of PSI across a range of conditions. The results of these proposed Phase II efforts represent a robust engineering and analysis tool for NASA and its commercial partners in the design and evaluation of landers in support of the Moon-to-Mars program and missions to other planetary bodies. Plume-surface interactions (PSI) are a hazard to propulsive landers due to the erosion of ground and its effects on lander stability, sensing capabilities, deep cratering, and ejecta. Damage to or loss of landers by PSI is a risk which is difficult to mitigate due to an inability to test full-scale lander systems in a relevant environment. PSI simulation software is required to supplement current needs and help reduce risks to lander missions. The SOA for PSI simulation software are CFD tools which treat regolith as an input in purely fluid models. This simplification does not capture realistic cratering physics and requires empirically derived relationships which lead to accumulated errors. A validated two-way coupled CFD-Discrete Element Method (DEM) is being proposed in a massively parallelized two-way coupled solid-fluid PSI simulation framework incorporating an ejecta damage estimator. Following validation in Phase II, these tools may be used for PSI simulations of time-evolving cratering physics, ejecta transport, and damage by ejecta to evaluate landers and reduce current risks. 1. Compile existing experimental training and validation data capturing time-evolving cratering, surface erosion, and ejecta transport of PSI in low-pressure and rarefied environments 2. Implement CFD fluid solvers in the coupled software for simulating transonic/supersonic flow in a reduced pressure environment and verify their performance against theoretical models 3. Calibrate the two-way coupled CFD-DEM numerical framework to fit the time-evolving cratering behavior and ejecta transport observed in the experimental training data 4. Validate performance of the calibrated CFD-DEM models by comparing simulated results against physical experimental data which were not used in the training of those models, and calculate residual error between the model and experiment for time-evolving crater geometry and ejecta particle velocities and trajectories 5. Integrate the ejecta damage estimator module directly into the coupled CFD-DEM modeling framework to estimate damage to surfaces with assumed brittle and ductile failure modes and material properties representative of lander hardware 6. Deploy the developed PSI simulation software with integrated damage estimator on a massively parallel cloud computing network in a large-scale demonstration model of a landing event on the lunar surface and document computational speed and performance  

NASA applications include the design and validation of lander systems and hardware to facilitate safe touchdown of spacecraft on planetary surfaces while not causing unacceptable risk from rocket plume impingement. This proposed work will provide multi-disciplinary coupled analysis tools, plume-surface interaction models, and multi-scale simulation tools under TX09.4.5 Modeling and Simulation for EDL for configuration definition and design verification and validation for landing systems that cannot be tested in an operational environment. Potential non-NASA applications include sale of engineering support services to Commercial Lunar Payload Services (CLPS) providers for evaluating lunar lander systems, landing sites, and lander control strategies using high-fidelity PSI simulation software. Additional applications include the evaluation of sensor and payload design, and their placement on a lander to reduce risks posed by ejecta.

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