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

Abstract

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.