Surface characterization of metallic and ceramic TPS-materials for reusable space vehicles

The newly qualified IRS facility for the determination of total and spectral emissivities and its recent numerical optimization is described. Values of measured total emissivities of the ceramics HfO2, Al2O3, Yt2O3 and the metals/alloys tungsten, TZM and PM1000 in the temperature regime of 750–1800 K are given. The drastic influence of the oxidation state of PM1000 on the emissivity is discussed. Additionally, results of an investigation of the influence of surface roughness and surface topology on emissivity are presented. Therefore, three SSiC samples with surface roughness from Rq=0.05Rq=0.05 to 0.66 have been prepared using common finishing operations. The tests showed that the emissivity increased about 10% with an increase of the surface roughness even in the regime where RqRq values are in the same magnitude or much smaller than the maximum emitting wavelength.Recombination coefficients for the abovementioned materials have been determined in pure oxygen plasma. The methodology for the determination of recombination coefficients of ceramic and metallic thermal protection system (TPS) materials in single species gases used at IRS and its latest improvements is presented. Test results for the recombination coefficients in oxygen plasma are shown between 1469 and 2072 K.