This thesis examines the modeling of the shock-layer radiative heating associated with hypersonic vehicles entering the atmospheres of Earth and Titan. For Earth entry, flight conditions characteristic of lunar-return are considered, while for Titan entry, the Huygens probe trajectory is considered. For both cases, the stagnation region flowfield is modeled using a two-temperature chemical nonequilibrium viscous shock layer (VSL) approach. This model is shown to provide results that are in agreement with the more computationally expensive Navier-Stokes solutions. A new radiation model is developed that applies the most up-to-date atomic and molecular data for both the spectrum and non-Boltzmann modeling. This model includes a new set of atomic-lines, which are shown to provide a significant increase in the radiation (relative to previous models) resulting from the 1 - 2 eV spectral range. A new set of electronic-impact excitation rates was compiled for the non-Boltzmann modeling of the atomic and molecular electronic states. Based on these new rates, a novel approach of curve-fitting the non-Boltzmann population of the radiating atomic and molecular states was developed. This new approach provides a simple and accurate method for calculating the atomic and molecular non-Boltzmann populations. The newly-developed nonequilibrium VSL flowfield and nonequilibrium radiation models were applied to the Fire II and Apollo 4 cases, and the resulting radiation predictions were compared with the flight data. For the Fire II case, the present radiation-coupled flowfield model provides intensity values at the wall that predicted the flight data better than any other previous study, on average, throughout the trajectory for the both the 0.2 - 6.0 eV and 2.2 - 4.1 eV spectral ranges. The present results over-predicted the calorimeter measurements of total heat flux over most of the trajectory. This was shown to possibly be a result of the super-catalytic assumption for the wall boundary condition, which caused the predicted convective heating to be too high. For the Apollo 4 case, over most of the trajectory the present model over-predicted the flight data for the wall radiative intensity values between 0.2 - 6.2 eV. For the analysis of Huygens entry into Titan, the focus of the radiation model was the CN violet band. An efficient and accurate method of modeling the radiation from this band system was developed based on a simple modification to the smeared rotational band (SRB) model. This modified approach, labeled herein as SRBC, was compared with a detailed line-by-line (LBL) calculation and shown to compare within 5% in all cases. The SRBC method requires many orders-of-magnitude less computational time than the LBL method, which makes it ideal for coupling to the flowfield. The non-Boltzmann modeling of the CN electronic states, which govern the radiation for Huygens entry, is discussed and applied. The radiation prediction resulting from the non-Boltzmann model is up to 70% lower than the Boltzmann result. A new method for treating the escape factor in detail, rather than assuming a value equal to one, was developed. This treatment is shown to increase the radiation from the non-Boltzmann model by about 10%. / Ph. D.

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.