Numerical thermal investigation of a space probe heat shield - Comparison with experimental results

Abstract: The objective of this internship was to study the physical properties of a thermal protection used for a space probe to be launched for a mission to Mars. The protection is composed of two main components. The topmost part is a cork derivative that deteriorates via ablation and pyrolysis in order to reduce the amount of heat transferred to the vehicle's main body. The junction between the ablative layer and the spaceship is ensured by a sandwich material composed of two carbon skins separated by a grid of Aluminium honeycomb cells. In a first part, numerical models of variable complexity were created to simulate the properties of the sandwich material (thermal conductivity, specific thermal capacity). The models' results were then compared to experimental measurements to upgrade Astrium's databases concerning similar products with new values for the physical properties of the studied materials. The results obtained by both the model and the experiments were found to be in accordance, which justies the validity of the simulation, and the choices made for the values of physical properties. In addition, a thorough consideration of the in　uence of phenomena neglected was performed to justify the stability of the numerical computations. In a second time, a staggered coupled simulation was developed to study the physical behaviour of the ablative protection. A thermal simulation considered the ablation, pyrolysis and thermal conduction. A mechanical simulation considered the swelling induced by the heating of the cork material. The results (temperature, swelling, density) from infra-red experiments and plasma jet testing were compared to the prediction of the coupled simulation. Although a substantial discrepancy remained between experimental and numerical results, the mere fact that a working program emulating at the same time ablation and swelling gave results physically coherent was already a positive advance in this domain.