In order to more accurately predict loads subjected to the EEV (Earth Entry Vehicle) upon impact with a variety of materials, finite element simulations of soil/EEV impact were created using the program LS-DYNA. Various modeling techniques were analyzed for accuracy through comparison with physical test data when available. Through variation of numerical methods, mesh density, and material definition, an accurate and numerically efficient representation of physical data has been created. The numerical methods, Lagrangian, arbitrary Lagrangian-Eulerian (ALE), and spherical particle hydrodynamics (SPH) are compared to determine their relative accuracy in modeling soil deformation and EEV acceleration. Experimentally validated soil material parameters and element formulations were then used in parametric studies to gain a perspective on effects of EEV mass and geometry on its maximum acceleration across varying soil moisture content. Additionally, the effects of EEV orientation, velocity, and impact material were explored. Multi-material arbitrary Lagrangian-Eulerian (MMALE) formulation possess the most effective compromise between its ability to: accurately display qualitative soil behavior, accurately recreate empirical test data, be easily utilized in parametric studies, and to maintain simulation stability. EEV acceleration can be minimized through increase of EEV mass (with constant geometry), allowing for maximum penetration depth, and longest deceleration time. A critical orientation was discovered at 30⁰ from normal, such that maximum EEV surface area impacts the soil surface instantaneously, resulting in maximum acceleration. Off-nominal impact with concrete is predicted to increase acceleration by up to 630% from impact with soil. / MS / As part of a larger effort to return Martian soil samples to Earth, the creation of a vehicle (Earth Entry Vehicle, EEV) to carry those samples from Mars, to the surface of Earth is underway. The EEV is designed to enter Earth’s atmosphere and decelerate using its geometry to slow itself during descent, and the crushing of the soil to absorb impact energy upon collision with Earth. Paramount in concern is the containment of the soil samples during the EEV’s impact. As part of the design process with respect to this concern, computer simulations are built in this work which are compared to collected physical test data, and used to predict impact forces on the EEV under various impact conditions. Impact conditions considered are the variation of the mass, orientation relative to vertical, geometry of the EEV, the moisture content of the soil, and the impact material. Through the testing of a variety of different numerical techniques, the optimal method for each case is determined based on the ability of each technique to accurately predict EEV acceleration, its ability to maintain computational stability during simulation, and its ease of use between various testing scenarios. It was determined through this process that more massive EEVs show a lower peak acceleration during impact due to their ability to penetrate the surface of the soil, extending the time of impact, and lowering the force applied by the soil per unit time. There was found to be a critical EEV orientation at 30⁰ from vertical such that the largest possible surface area of the EEV impacts the soil at one instant, resulting in a large spike in acceleration upon impact. Additionally, it was predicted that more massive EEVs be made into smaller, more sharply pointed geometries and less massive EEVs use larger geometries in order to minimize peak acceleration. Impact with concrete was estimated to increase acceleration by up to 650% when compared to soil impact acceleration. This work is intended to serve as an exploratory study into the validity of various impact simulation techniques, to be used in future in higher fidelity impact models.

abstract: The search for life on Mars is a major NASA priority. A Mars Sample Return (MSR) mission, Mars 2020, will be NASA's next step towards this goal, carrying an instrument suite that can identify samples containing potential biosignatures. Those samples will be later returned to Earth for detailed analysis. This dissertation is intended to inform strategies for fossil biosignature detection in Mars analog samples targeted for their high biosignature preservation potential (BPP) using in situ rover-based instruments. In chapter 2, I assessed the diagenesis and BPP of one relevant analog habitable Martian environment: a playa evaporite sequence within the Verde Formation, Arizona. Coupling outcrop-scale observations with laboratory analyses, results revealed four diagenetic pathways, each with distinct impacts on BPP. When MSR occurs, the sample mass returned will be restricted, highlighting the importance of developing instruments that can select the most promising samples for MSR. Raman spectroscopy is one favored technique for this purpose. Three Raman instruments will be sent onboard two upcoming Mars rover missions for the first time. In chapters 3-4, I investigated the challenges of Raman to identify samples for MSR. I examined two Raman systems, each optimized in a different way to mitigate a major problem commonly suffered by Raman instruments: background fluorescence. In Chapter 3, I focused on visible laser excitation wavelength (532 nm) gated (or time-resolved Raman, TRR) spectroscopy. Results showed occasional improvement over conventional Raman for mitigating fluorescence in samples. It was hypothesized that results were wavelength-dependent and that greater fluorescence reduction was possible with UV laser excitation. In Chapter 4, I tested this hypothesis with a time-resolved UV (266 nm) gated Raman and UV fluorescence spectroscopy capability. I acquired Raman and fluorescence data sets on samples and showed that the UV system enabled identifications of minerals and biosignatures in samples with high confidence. The results obtained in this dissertation may inform approaches for MSR by: (1) refining models for biosignature preservation in habitable Mars environments; (2) improving sample selection and caching strategies, which may increase the success of Earth-based biogenicity studies; and (3) informing the development of Raman instruments for upcoming rover-based missions. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2016

<p dir="ltr">Modern space missions like Mars Sample Return and Artemis involve multiple systems that serve different functions. The individual failure modes of the constituent systems coupled with the complex interdependencies among them can result in various combinations of failures or disruptions that may have an unpredictable impact on the mission. Existing methods of risk assessment are unable to adequately represent the interactions between systems and the progressive consequences of total or partial disruptions for these complex missions. Therefore, a state-based framework has been developed for the probabilistic risk assessment of multi-system uncrewed space exploration missions. This hierarchical framework leverages Harel statecharts to model the operations and failure modes of individual systems. Each failure mode can be characterized by its probability of occurrence and primary consequence (delay in operations, additional cost, fatal failure, etc.). The system-level statecharts are contained within a mission-level model that connects them through logical and temporal operators to simulate functional dependencies among the systems. The double-layer (system-level and mission-level) model can be used for stochastic analysis through Monte Carlo simulations. By defining mission-level performance metrics and observing them for various mission profiles, the system-level operational risks can be related to the mission outcomes, and the mission-level impact of each failure mode can be assessed. Overall, this framework can provide deeper and richer insights by enabling sensitivity analysis, risk quantification/ranking, and comparison of various operational concepts and mission architectures. The framework has been demonstrated for three types of analyses within the Mars Sample Return Campaign.</p>