Assessment of the impact on capsule stability when the outer line mold changes by the recession of the Thermal Protection System due to ablation.

The design of a re-entry vehicle and the analysis of its performance are extremely challenging tasks. The difficulties increase when the understanding of its transient behaviour is sought and grow even further if this transient is affected by uncontrolled phenomena such as the shape change caused by the ablation of the thermal protection material used as heat shield. An activity with the Von Karman Institute, Belgium activity aimed to join numerical, experimental and modelling expertise to shed light on the possible impact of the ablation-driven shape change of the heat shield on the capsule aerodynamic behaviour. The obtained results suggest that the developed techniques and the acquired knowledge may be used in the future to support more standard design approaches for re-entry missions. In addition, it is believed that the synergistic use of experimental, theoretical and numerical techniques used by the team represents a valuable example of how to properly tackle a complex multi-physical problem as the atmospheric entry.

Return exploration missions foresee capsules re-entering the earth atmosphere at high velocity without the usage of a (supersonic) parachute: capsule stability has then to be guaranteed from hypersonic conditions down to the subsonic regime at landing.During the re-entry, the capsule shape will change due to Thermal Protection System (TPS) recession and the CoG will shift backward due to TSP mass loss. In such a situation capsule stability might deteriorate becoming critical.The proposed study will focus on quantifying recession rates for a typical ablative material via wind tunnel tests. A special emphasis will be devoted to the wind tunnel measurement technique allowing shape recession.