NASA is in the process of improving heat shield design either through the use of new heat shield materials or by reducing the thickness of existing heat shields using conventional materials. Currently, NASA heat shield predictive models are not reliably consistent with observed measurements. The proposed concept will provide time-resolved recession measurements that can be used for model validation (both during arc jet test and flight tests). With validated predictive models, NASA can optimize the heat shield design for expected reentry conditions. Additionally, reliable onboard real-time recession measurements could possibly be used to identify localized excessive recession. This diagnostic could be integrated with capsule flight control system to orient the vehicle such as to reduce heating loads in the damaged area. Furthermore, this technology could be used to monitor re-entry events of planetary and lunar landers/probes whose heat shields cannot be physically inspected post-entry. Commercial and DoD applications also exist. For instance, SpaceX and Blue Origin are pursuing capsule reentry capabilities. Currently, SpaceX is focusing on reentries from low earth orbits where heating rates are low. However, SpaceX is also investigating Mars missions where heat rates will require a much different heat shield design. SpaceX will likely conduct Mars-like entry conditions using Earth reentry missions. The use of non-intrusive heat shield recession diagnostics could be utilized to provide time-resolved heat ablation during all phases of reentry. This will allow SpaceX to validate their heat shield recession models under higher heating rates.