Assessment of the effect of designed-in features on thermal protection systems with application to vascular self-healing

Thermal protection systems (TPS) are a mission critical component of atmospheric entry vehicles. TPS are sensitive to damage from micrometeoroid and orbital debris, which may cause damage severe enough to result in TPS failure and subsequent loss of vehicle and mission. The density of objects in low-Earth orbit (LEO) may increase by nearly 6 times over the course of the next 100 years, and in mid-Earth orbit (MEO) by 3 times over the course of the next 100 years. Including a self-healing mechanism in the TPS is one potential approach to reducing risk of vehicle failure due to impact damage. The TPS self-healing concept studied in this work integrates a vascular network (as described in White et al. and Blaiszik et al.) into ceramic TPS materials. The self-healing system activates if MMOD impacts expose the vascular network to space; the vessels deliver healing agent to the impact damage location. A vascular system was chosen due to the ability to provide a higher volume of healing agent to fill the damage, as compared to alternative concepts in the literature. The vascular system implemented in TPS would be composed of a system of “designed-in features,” or large, non-homogeneous components placed below the surface of the TPS. To study the potential effect of a self-healing system on TPS performance, computational analysis is performed to determine of the effect of generalized designed-in features on the thermal response of the TPS. Feature placement, size, and number are examined to determine their influence on the thermal response of the TPS, including bondline temperature and temperature inside the features. Results indicate the addition of these features does have a significant impact. The deeper the features are in the material, the lower the peak bondline temperature will be. Increasing the diameter of features as well as increasing the number of features magnifies the effect that changing the depth has on the thermal response. The primary TPS material choice and boundary conditions are also important in determining the impact the features have on the thermal response. While the trends are similar across TPS materials and boundary conditions, the magnitude of the effect changes. Experimental analysis of the effect of designed-in features on the thermal response of thermal protection materials is also conducted to verify and anchor computational predictions. Samples of LI-2200 tile with high emissivity RCG coating and a variety of designed-in features were tested in a radiant heater apparatus and inverse parameter estimation was used to match the data accurately while adjusting the material properties and boundary conditions. Using this method, computational results match experimental results within 0.35 K for a solid sample and within 1.74 K for a sample with a designed-in feature. Experimental results also confirmed the general trends seen in the computational study. Increasing the number of features increased the peak bondline temperature, decreasing the size decreased the peak bondline temperature, and increasing the depth decreased the peak bondline temperature. Finally, models and data are used to assess the feasibility of including a self-healing capability on a relevant atmospheric entry system. Utilizing boundary condition and material data from the STS-1 Space Shuttle mission, the aerothermal environment is used to examine the thermal response of a TPS tile with an integrated vascular network. Geometric and thermal requirements are defined and tested to determine the feasibility of a self-healing thermal protection system. Two self-healing architectures are investigated; a reservoir architecture which holds healing agent in a central location to be delivered when damage is detected and a discrete architecture in which each TPS tile contains a set amount of the self-healing agent. Results indicate the discrete architecture is likely infeasible. However, depending on specific TPS materials, vehicle configuration, and mission profile, the reservoir mechanism may be feasible.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Aerospace Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2022

Author dc:creator

• Skolnik, Nathaniel L.

Contributors dc:contributor

• Putnam, Zachary
• Panera, Francesco
• Geubelle, Philippe H
• Jacobi, Tony
• Stackpoole, Mairead

• Thermal Protection Systems

Statement dc:rights

• Copyright 2022 Nathaniel Skolnik

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/115337

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F115337