Solar-Thermal Testing of Ablator Materials in an Atomic Oxygen Plasma

The process by which chemically reactive gases interact with porous carbon surfaces is controlled by three competing rates: gas diffusion through the boundary layer, gas diffusion through the porous medium, and heterogeneous chemical kinetics. The ablation rate of a thermal protection system depends on which of these processes limits the overall oxidation rate. An investigation of these competing phenomena requires laboratory-scale experimental data to inform and validate chemical-kinetics models. A new apparatus has been developed at Sandia National Laboratories to achieve conditions representative of hypersonic flight. A radio-frequency generated oxygen plasma produces a reactive gas mixture containing atomic oxygen. This gas source is combined with the concentrated solar irradiation (up to 550 W/cm2) from a solar furnace. Temperature and mass loss of material samples are dynamically measured via pyrometery and a mass balance. Observations are compared to theoretical predictions of the regimes of porous ablation.