Assessing the accuracy of Radar-Plasma signature simulations using hypersonic shock-tunnel data with variable freestream oxygen levels

The plasma generation in hypersonic flight is known to affect the radar signatures of flight vehicles as well as their communications and sensing (radio blackout). Although these effects have been known since the beginning of spaceflight in the 1950s, accurate prediction is still difficult. Today, the most promising approach is to combine Computational Fluid Dynamics (CFD) and Computational Electromagnetics (CEM) to solve the plasma distribution in the flow field and derive the respective microwave response based on the two major plasma parameters: plasma and collision frequency. But dedicated experimental reference data is extremely scarce, which renders the validation of the multi-model dependent CFD-CEM approach difficult. To improve the validation, this study provides new experimental shock-tunnel radar data of the stagnation-point plasma of a 15 c m diameter sphere. To vary plasma and collision frequency independently, both the flow enthalpy and the freestream oxygen level were varied. The measurements are compared with respective CFD-CEM simulations.