Evolution of the Mars 2020 Organic Carbon Model to a Predictive Tool for Mars Sample Return Science

The Mars 2020 Total Organic Carbon (TOC) Model tracks organic carbon generation, transport, and accumulation throughout the Mars 2020 Perseverance Rover sampling system across the mission life.[1] This TOC model was the culmination of a several-year, multi-disciplinary effort to ensure the sample tubes aboard the Mars Perseverance Rover would be amongst the cleanest hardware ever launched and enable the detection of traces of past life on Mars.[2] The analysis tools used and assumptions made in the final pre-launch analysis were tailored to be flight project verification and validation (V&V) tools, with many conservative choices made to ensure margin against uncertainty in model inputs and flight conditions.[1,3] Now that Perseverance is successfully operating on Mars and has begun to collect samples, it is important to evolve the TOC model to provide realistic predictions for each individual tube so that the Mars Sample Return Science Team can calibrate their models accordingly. Primary areas of model evolution have included expanding from a 1-dimensional to a 2-dimensional axisymmetric analysis domain, incorporating multiple surface materials and associated surface properties in the model system, incorporating flight data rather than using flight predictions, and performing the analysis in a single tool (COMSOL) that tracks accumulation in the sample tubes throughout their lifespan in a physically and temporally-consistent manner. To first demonstrate equivalence between the original and updated TOC models, a set of simplified analysis cases have been performed in which model parameters were varied to identify differences and inconsistencies between the models. Parameters studied in these equivalence cases have included system temperature, diffusion coefficients, contamination densities, and model geometries. This work documents the formulation of the TOC model and its updates, results of the model equivalency study including general lessons-learned about system sensitivities, and additional analysis cases incorporating the next model evolution steps toward fully-integrated mission life simulations for organic carbon accumulation within the Mars 2020 sample tubes. The decision to implement Mars Sample Return will not be finalized until NASA’s completion of the National Environmental Policy Act (NEPA) process. This document is being made available for information purposes only.