Heat shield technology is a critical component of manned spaceflight. In particular, the new Crew Exploration Vehicle (CEV) requires thermal protection systems (TPS) beyond the current state of the art. While new TPS shields are under development, a key difficulty is the ability to diagnose TPS performance. In Phase-I SBIR research carried out by EDA and Penn State, we developed a low intrusive fiber optic plug insert for TPS materials that will enable spectrographic measurements of the reentry environment surrounding an ablating TPS. We propose to develop a ruggedized compact spectrometer suitable for coupling with this low-intrusive fiber optic insert. This resulting fiber-coupled spectrometer system plug enables the collection of benchmark data for fundamental flow, radiation, and materials modeling as well as operational correlations between vehicle reentry drag and radiation if implemented in a TPS flight test. The program proposed here will take the concept, originally encouraged at the request of researchers at NASA Ames, from concept to demonstration, through prototype, to a technology readiness level suitable for inclusion in the design of an ablation shield flight demonstrator mission.