Although significant advances have been made in ground-based testing and simulations, it is still impossible to precisely replicate the diversity of in-flight conditions experienced by ablative thermal protection systems (TPS). This leads to uncertainty in the predictions of the magnitude and rate of TPS ablation. Because in-flight monitoring is difficult, the uncertainty in actual boundary conditions and models must be considered when designing a TPS. To reduce risk, designers must resort to trade-offs which often involve increasing heat shield mass. Direct ablator temperature, heat flux and recession measurements would allow engineers to reduce design uncertainty and improve modeling. These improvements will lead to decreased heat shield mass, enabling missions that are not otherwise feasible and directly increasing science payload and returns. Ultrasonic methods for real-time monitoring of ablator conditions including internal temperature distribution, heat flux and recession will be developed in this program. Internal localization methods of ultrasonic thermometry will be used to accurately measure temperature distribution to within close proximity of surface charring. Temperature compensation will be applied to ultrasonic thickness gauging techniques to estimate surface recession in real time. Heat flux can be extracted from the measured temperature distribution. Combined together, these ultrasonic techniques will form a sensor system capable of sensing and relating real-world ablator performance to computational models as well as qualifying ablator materials. When developed to maturation, such a sensor system even has applications for in-flight health monitoring.