Analysis of Mars Entry Shock Wave Radiance in the T6 Stalker Hypersonic Wind Tunnel

Predictions and experimental simulations of the aerothermodynamic conditions experienced by spacecraft entering the Martian atmosphere have progressed modestly but consistently over several decades. This includes phenomenological work to validate computational predictive models, inform chemical kinetic reaction rates and improve experimental processes. During commissioning of the Aluminium Shock Tube by the University of Oxford the opportunity was taken to add to this body of data. The free piston driver was used to generate shock waves of between 6.5 to 7.8 Km/s in Mars atmospheric composition test gas (95.8 \% CO2, 4.2 \% N2). Freestream pressures between 6.6 Pa (0.05 Torr), 13.3 Pa (0.1 Torr), 32.3 Pa (0.25 Torr) and 133.3 Pa (1 Torr) were tested as representative of Mars entry trajectory points. Using optical emission spectroscopy techniques the absolute radiance in the shock waves was measured using spectrometers calibrated from UV to near Infrared (210 nm - 840 nm). Nine tests yielded good data for further analysis, the results of which are presented here. Strong CN Violet radiation in the UV dominate across all pressures and regions with C2-Swan dominant in the Vis/IR region. The shock waves generated in the lower pressure tests do not reach thermo-chemical equilibrium. In addition non-equilibrium metrics are presented, allowing direct comparison with other facilities. Further analytical comparison with predictive spectra from the NEQAIR software is also conducted. Further these findings are in agreement with those produced by other facilities validating the Aluminium Shock Tube as a credible experimental facility specifically designed for the investigation of atmospheric entry shock wave radiance.