Dual-Component Sensor Design for In Situ Ablation Measurement

In this study, a novel ablation sensor capable of measuring surface recession and thermal decomposition in an ablative heat shield was developed by implementing two measurement principles into a single sensor unit. The proposed dual-component ablation sensor includes a surface-recession sensor and char sensor. The surface-recession sensor was designed using an ablative rod with embedded optical fibers, and the char sensor was designed using polyimide tubes and resistive wire with a low-temperature coefficient. In application, the surface-recession sensor detects thermal-emission transitions from the ablative material to shock layer, and the char sensor acts as an electric circuit that changes its resistance as the polyimide tubes carbonize. In this study, the proposed ablation sensor was miniaturized for possible flight-measurement application. To test the operational principles of the proposed design, a prototype ablation sensor was embedded in a polyimide-impregnated carbon-based ablative material, and tested in an arcjet wind tunnel. Results demonstrated that both surface-recession and thermal-decomposition rates can be simultaneously measured using the proposed sensor.