The ESA ARC project: Ablation radiation coupling for hypervelocity re-entry with low density type ablators

The ARC project is an ESA funded project aiming to evaluate critical issues of abla-tion radiation coupling for hypervelocity (> 10km/s) return missions of capsules equipped with carbon phenolic type heat shields. The plasma environment of such return trajecto-ries strongly radiates, while the ablation of the heat shield ejects species into the bound-ary layer. These species, which can include strong radiators, interact with the near-wall plasma resulting in further reactions, diffusion, and radiation, producing ablation-radiation coupling and blocking effects. The only recent flight data for such missions with carbon phenolic ablators comes from the Hayabusa and Stardust missions, which were observed during re-entry. However, the high energy radiation (vacuum ultraviolet and beyond) could not be measured due to atmospheric absorption. Theoretical estimations and numerical modelling predict that a considerable proportion of the radiation is emitted at these wave-lengths. Hence the goal of the ARC project is to use ground-based facilities to perform radiation measurements with vacuum ultraviolet capabilities over ablating samples and as-sess radiation-ablation coupling at conditions that are relevant to such fast return mission conditions. Calibrated measurements of vacuum ultraviolet radiation with an ablating sur-face in hypervelocity entry conditions are presented from facilities in Australia, Germany and France.