Dragonfly backshell radiation measurements in the EAST facility

Abstract

A test series was performed in the Electric Arc Shock Tube (EAST) facility, with the aim of obtaining afterbody radiative heating validation data at Titan. The test campaign focused on reproducing conditions similar to those encountered on the backshell of the Dragonfly spacecraft during Titan entry. Measurements of shock-layer radiation from CN Violet, CN Red and C2 Swan bands are made in mixtures of 2.2% CH4 in N2 (by mole) heated by incident shock waves spanning from 3 to 7 km/s. This study focuses on the spectrally and spatially resolved measurement of absolute radiance made with four optical emission spectrometers covering 220-1400 nm. Comparison with CFD simulations and equilibrium conditions were made. The error in predicted radiation at the nonequilibrium peak increased nearly linearly with velocity, being about 40% lower at 3 km/s and up to 100% higher at 6 km/s. At 7 cm/150 μs from the shock front, the discrepancies appear to be larger, ranging from -50 to +200%. Comparison between measured and predicted temperatures and number densities of CN indicate shortcomings in both the CFD kinetic model and the non-Boltzmann model of CN.