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Author ORCID Identifier

https://orcid.org/0000-0002-6115-5917

Date Available

6-2-2028

Year of Publication

2026

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy (PhD)

College

Engineering

Department/School/Program

Mechanical Engineering

Faculty

Savio J. Poovathingal

Faculty

Jonathan Wenk

Abstract

High entry speeds and exotic planetary gases can result in significant radiative heat loads on space capsules. The mechanism of radiative transport is fundamentally different from that of conductive energy transport, and the penetration of radiative signatures depends on the radiative properties of the thermal protection system (TPS) material protecting the space capsule. The radiative coefficients of carbon-based and silica-based fibrous materials have been computed as a function of wavelength using the photon-path-length Monte Carlo method, explicitly accounting for the materials microstructure. To model the material, synthetic and real microstructures have been generated. Micro-CT has been utilized to scan a material and reconstruct the surface files. Further characterization of the materials has been performed, including porosity, surface area, fiber diameter, and orientation. Significant variations in the radiative coefficients are observed at wavelengths relevant to shock-layer emissions. Although carbon-based fibrous materials exhibit higher absorption coefficients in comparison to silica-based systems, the absorption coefficients of carbon-based material drops by two orders of magnitude in the range of 100-200 nm. The radiative coefficients of carbon-based fibrous material are dominated by scattering and absorption, with minimal transmission. However, the transmission coefficients for the silica system dominated the radiative coefficients over 100-2000 nm, which corresponds to most shock-layer emissions. The radiative coefficients also vary with the change in porosity and length scale. At the same length scale, because of changes in porosity distribution, the radiative coefficients differ, which in turn affects the in-depth heating profiles. The radiative coefficients are used to solve the radiative transfer equation using the P-1 approximation to obtain the in-depth radiative heat flux. The total energy equation for decomposing porous TPS materials is solved with the radiative heat flux from the P-1 approximation and the conductive heat flux using Fourier’s law. It is observed that peak temperatures inside the material are higher when radiative transport is explicitly accounted for through the P-1 approximation. Small variations in the absorption coefficient of the silica-based materials also affected the in-depth temperature profiles. Additionally, a broader temperature distribution is observed within the material with a low absorption coefficient, and the charring density profiles are also influenced by the radiative heat flux. At the same time, because of the change in porosity distribution across the material, the radiative coefficients change, which influence the local in-depth temperatures. This study demonstrates the importance of including radiative transport in material response solvers, and that the variation in radiative coefficients must be accurately computed by accounting not only for the material’s microstructure but also for changes in porosity.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2026.314

Archival?

Archival

Funding Information

The work is supported by the NASA Entry Systems Modeling Project under grant number 80NSSC20K1072, NASA Space Technology Research Institute (STRI), Advanced Computational Center for Entry System Simulation (ACCESS) under grant number 80NSSC21K1117, and NASA Kentucky Established Program to Stimulate Competitive Research (EPSCoR) under NASA grant number 80NSSC19M0052. 

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Available for download on Friday, June 02, 2028

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