Abstract
To enhance magnetohydrodynamic (MHD) aerobraking performance in low-enthalpy flight environments, this study observes the calcium supply behavior from a calcium oxide (CaO) seeded ablator using an arc-heated wind tunnel. First, flight-equivalent heat flux conditions (0.2–0.5 MW/m²) were established via laser absorption spectroscopy. Subsequent heating tests using two-dimensional emission spectroscopy confirmed strong Ca ion distribution throughout the shock layer. Although the surface temperature of 1800 K remained below the melting point of CaO, significant mass loss and carbonization were observed. The theoretical upper limit of the time-averaged Ca number density, estimated from this mass loss assuming complete vaporization without reaction losses, was 1.48×1018 m-3. Furthermore, the Ca II number density estimated from the emission intensity ratio under the assumption of local thermodynamic equilibrium (LTE) was 1.21×1018 m-3, corresponding to the Ca-derived electron number density. Although this value is approximately 1/80 of the background Argon electron number density, the strong non-equilibrium nature of the flow introduces significant uncertainties into the LTE-based estimation. Therefore, the actual electron density enhancement cannot be definitively concluded as limited based solely on these results. Consequently, while this study demonstrates the ablator's capability to supply ionization seedants, LTE-independent direct measurement techniques such as absorption spectroscopy are necessary to accurately evaluate the electron density enhancement.
https://ror.org/01w6wtk13 
