Quantitative Comparison of Measured and Numerically Simulated Erosion Rates of SiC Based Heat Shield Materials Stefan L ¨ ohle, Markus Fertig, and Monika Auweter-Kurtz 1 Institut f¨ ur Raumfahrtsysteme, Pfaffenwaldring 31, 70550 Stuttgart, Germany WWW home page: http://www.irs.uni-stuttgart.de Summary The main mission critical part of planned reusable re-entry vehicles is its thermal protection system. The surface material has to withstand high heat loads and a chem- ically aggressive environment in the upper atmosphere. In case of re-usability the candidate material has to withstand these loads several times. Therefore, the mass loss during one re-entry mission has to be as small as possible. In order to predict the mass loss, the material is investigated in plasma wind tunnels and meanwhile nu- merical simulation of surface processes is possible at Institut f¨ ur Raumfahrtsysteme (IRS). This paper describes for the first time a quantitative comparison of the spe- cific mass loss estimated on the one hand by plasma wind tunnel experiments and on the other hand by numerical simulation. Results for pressureless sintered silicon carbide (SSiC) and realistic C/C-SiC material are presented. Finally, an attempt is made to interpret the occurring differences. 1 Introduction Thermal protection systems for future reusable re-entry vehicles have to withstand temperatures of about 2000 K . The up to date favored materials are silicon-based ceramics. The chemical reactions of SiC with oxygen lead to the formation of SiO, SiO 2 , CO and some other compounds that can be neglected at elevated tempera- tures [1]. Since SiO and CO are gaseous at those temperatures erosion and thus material loss is the consequence. SiO 2 in contrast is liquid or solid and forms a layer on top of the SiC so that it acts as a diffusion barrier. This effect is often named a self protection mechanism, because the oxygen flux to the surface is hin- dered and hence, the mass loss is lowered. The process is called passive oxidation. At higher temperatures and lower oxygen pressures, a possible protection layer will be removed and SiO formation becomes easily possible. This is called active oxida- tion and obviously is a state that has to be avoided. But, as can be seen in Fig. 1(a), on planned re-entry missions like EXPERT and X-38 active oxidation may occur. In Fig. 1(a), theoretically calculated reference trajectories are plotted together with a regime known as passive-to-active transition calculated by Lou and Heuer [ 2]. In