Olivia Schroeder
University of Minnesota
One of the greatest challenges for Mars Sample Return Earth Entry Vehicle is certifying high thermal protection system reliability. This is because the modes by which thermal protection system materials fail are not well understood. Of particular concern for risk assessment is micro-meteoroid and orbital debris (MMOD) impact on thermal protection systems. Some studies of impact and hole growth on various materials have been conducted through arc-jet tests, however these ground facilities are not yet capable of fully recreating the harsh environments of planetary entry. Furthermore, the number of tests required to provide statistically significant data for establishing reliability is too high for the cost and difficulty of ground tests. Therefore, there is a need for numerical models that can help understand the thermal and structural response of TPS that has been impacted or damaged by MMOD. The proposed research aims at developing these models by studying the effect of a cavity in TPS material. Firstly, the aerothermal environment will be characterized and the heating augmentation factors due to surface roughness elements will be quantified. Secondly, the thermal response of various TPS materials will be evaluated and the effect of the environment on the cavity growth will be determined. This will involve studies primarily related to pyrolysis gas transport and gas surface interaction. Next, a thermo-mechanical analysis of the materials will be conducted. Because impact damage can also cause micro-cracks in the substructure near the cavity, an estimation of the mechanical property variation near a cavity will be required. Furthermore, how the internal stresses impact the thermal properties such as thermal conductivity will affect the thermal material response and subsequently the ablation rates of the surface of a vehicle.
The objective of this work is to quantify all of the effects mentioned above and develop a model for predicting TPS response under a wide range of impact conditions. The research will require the use and development of hypersonic computational fluid dynamics, material response and thermo-mechanical response solvers. This project aligns with the NASA Space Technology Roadmaps under TA9:Entry, Descent and Landing, section 9.4.5 Modeling and Simulation.