Comparative modeling study and experimental results of atomic oxygen recombination on silica-based surfaces at high temperature

Heat load on spacecraft during atmospheric re-entry is of crucial importance, not only because of the thermal shield design and payload improvement, but also because of the threat that it represents for the passengers. One major part of the heat flux is due to the catalytic heterogeneous atoms recombination over the whole Thermal Protection System (TPS). As there is some evidence in the literature that the recombination coefficient of oxygen and nitrogen atoms is a key parameter to predict heat flux on TPS, the four major factors (temperature, pressure, nature of the material and recombination mechanism) that could affect the recombination efficiency are evaluated. Then, comparisons for different experimental and modeling results follow this part. Using two kind of silica surfaces, β-cristobalite and quartz, experimental results dealing with oxygen atoms recombination coefficient are discussed and compared with literature data and modeling. The various catalytic models found in the literature are helpful for a phenomenological understanding of the recombination process but usually too many parameters have to be adjusted by fitting with experimental results. Then, Molecular Dynamics simulation is more relevant to obtain accurate recombination coefficients.