Ablation

The focus of this effort is the development of a steady-state ablation model to understand and predict the response of the Thermal Protection System (TPS) of an Earth re-entry vehicle. The steady state ablation model developed includes a simplified description of the most important surface chemical reactions that promote ablation. Furthermore, approximations are made to account for the internal solid decomposition and pyrolysis processes. The calibration of the parameters in the model and validation of the underlying assumptions are the current focus of the ablation team.

To calibrate surface reaction model parameters, existing shock tube experiments can be used. However there are major difficulties in carefully controlling the experiment as well as obtaining the measured radiation intensities to get reaction probabilities.

The internal solid degradation and pyrolytic gas evolution processes are also poorly understood and, therefore, required strong assumptions in the model; these assumptions must be validated. In particular, we can separate the validation of the surface reactions and the in-depth processes, since the former occur at high temperatures and heat fluxes similar to the external environment that is encountered in atmospheric re-entry, while the latter take place internally within the solid at lower temperatures.

• Surface chemistry calibration using carbon nitridation and oxidation shock tube experiments
• Work with PECOS shock tube team to explore uncertainty in shock tube experiments and effect on calibration of ablation model
• Validation of internal solid degradation and pyrolytic gas evolution models
• Use of small-scale experiments involving Thermo-gravimetric analysis (TGA), Differential Scanning Calorimetry (DSC) and Fourier Transform Infra Red Spectroscopy (FTIR)
• Devise experiments to study the gas transport internal to the solid
• Develop calibration of ablation model within coupling scheme