Investigation of particle effects on a hypersonic Mars entry

Abstract

Large dust storms periodically form in the Martian atmosphere and pose a threat to future NASA missions. This threat arises from the current lack of understanding of how a Martian dust storm will affect the Thermal Protection System (TPS) of a planetary entry vehicle. While these storms occur infrequently, the long travel-times associated with Martian missions make avoiding these events nearly impossible and therefore the impact of a dust storm on the TPS must be estimated conservatively. However, excessive TPS margins increase the overall entry mass and diminish the allowable mass allocation for mission payload. The overall goal of this thesis is to identify, investigate, and improve underlying computational modeling assumptions relevant to dusty hypersonic Martian entries in order to reduce the conservative margins associated with TPS sizing. The first portion of this thesis covers a recently developed generalized drag coefficient for spherical particles, relevant for Martian dust particles interacting with a hypersonic flow. The proposed model incorporates simple physics-based scaling laws and is valid for a large range of Mach and Knudsen numbers. Additionally, the model retains an explicit dependence on gas type, which is useful for understanding the effect of the Martian atmosphere on particle drag. Next, several studies are performed that utilize Lagrangian particle-tracking to characterize atmospheric particles impacting the surface of high-speed flight vehicles. Two of the studies investigate the effect of Mars entry missions flying through a severe dust storm. The first involves determining the sensitivity of particle-induced surface erosion to underlying particle modeling for the Mars 2020 mission and the second targets an inflatable design that could potentially be used to support human missions to Mars. An additional study is performed in order to understand the impact characteristics of stratospheric particles in Earth's atmosphere on a representative hypersonic flight vehicle. Lastly, a comparison of several numerical strategies for colliding hard-sphere particles is performed. While particle-particle collisions are not likely to play an important role for atmospheric particles because of their low concentrations, particle collisions can play a more important role in characterizing ground experiments that typically have higher particle mass loadings. Specifically, a collision procedure based on the direct-simulation Monte Carlo (DSMC) method is compared to event-driven and time-driven methods for two numerical setups, where the DSMC-inspired collision method is found to be preferable to the other approaches considered because of its improved accuracy and efficiency.