23-NSTGRO24-0085 - Investigation of Spallation in Low Permeability TPS Materials

Investigation of Spallation in Low Permeability TPS Materials Ablative thermal protection systems are used to shield space vehicles from intense heating during atmospheric entry. Although these materials are designed to burn away during descent, recent missions have experienced unexpectedly high levels of surface recession, particularly in the Orion heat shield during the Artemis mission. A major contributor to this undesired mass loss is spallation, a process where particles are ejected from the bulk material into the surrounding flow. AVCOAT was the selected material for the Orion TPS, and it is suspected the decreased permeability compared to materials such as Phenolic Impregnated Carbon Ablators (PICA) could cause increased spallation during atmospheric entry due to an increase in pyrolysis gas buildup. Data analysis from recently conducted arc-jet tests on PICA will be used for the validation and integration of a spallation model into a previously developed Lagrangian particle trajectory code. The proposed research seeks to investigate the differences in material response of PICA and AVCOAT as well as make predictions regarding coking reactions and their impact on permeability.