Quantification of spacecraft heatshield contaminants seen in reentry shock layer emissions using calibration-free LIBS

Shock layer thermochemistry during atmospheric reentry of spacecraft is strongly influenced by the composition of thermal protection system (TPS) materials. In this study, we implement calibration-free laser-induced breakdown spectroscopy (CF-LIBS) to profile cross-sections of phenolic impregnated carbon ablator (PICA) and room temperature vulcanizing (RTV) silicone from the heatshield of a commercial reentry capsule. CF-LIBS measurements determine that these materials contain alkali and alkaline earth contaminants (e.g., Na, Ca) at levels up to 10 parts-per-million (ppm) and heavier metals like Fe at 103 ppm. Contaminant concentrations are linked to observed strong atomic radiators identified from in situ shock layer emissions taken during reentry, demonstrating the value of CF-LIBS for interpreting complex shock-layer emission data from reentry spacecraft.