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In the present study, radiation emanating from the freestream and shock-layer ow over a 15.24-cmdiam, at-faced cylinder model was measured in the NASA Ames Research Center's 20-MW Arcjet Facility. The test gas was a mixture of argon and air. Spatially resolved emission spectra were obtained over a 200-to 890-nm wavelength range using a charged-coupled device camera (1024 3 256 array) attached to a spectrograph. The optical system was calibrated using tungsten and deuterium radiation sources. Analytical tools were used to determine the following line-of-sight-averaged thermodynamic properties from the calibrated spectra: 1) rotational temperature of the freestream and 2) rotational, vibrational, electronic temperatures, and species number densities within the shock layer. An analysis was performed to estimate the uncertainty bounds of the determined properties. Nomenclature C = constant I = atomic line intensity, W /cm 3 L = optical path length, cm m = magni cation n = number density, cm 2 3 P = peak value of a band system, W /cm 2 mm 2 sr T = temperature, K W = area under a spectra, W /cm 2 sr x = distance from the model surface, mm u = characteristic temperature, K s = standard deviation Subscripts e = electronic r = rotational v = vibrational

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High‐temperature aero‐thermal heating in a 30 kW inductively coupled plasma torch was used to replicate the effects of harsh oxidizing environments during hypersonic atmospheric entry on fracture behavior and microstructure of two‐dimensional woven SiC fibers. Hi‐Nicalon SiC woven cloths were exposed to surface temperatures over 1400°C with different high‐enthalpy dissociated oxygen and nitrogen plasma flows, and were subsequently deformed in pure tension at room temperature. Changes in fiber microstructure and surface chemistry after thermal exposure were examined by scanning electron microscopy. Pure nitrogen plasmas resulted in a 50% decrease of strength in woven SiC fibers with minimal effects on the fiber structure, except for highly localized surface pitting caused by partial decomposition of silicon oxycarbonitride phase at high temperature. In contrast, exposure to dissociated oxygen and air plasmas led to severe strength reduction and embrittlement over significantly short time scales, corresponding to degradation rates up to 200 times higher than those reported with static heating at equivalent temperatures. The origin of accelerated embrittlement at microscopic scale was found related to complex gas‐surface interactions and high‐temperature oxidizing processes involving the formation of SiO2 bubbles and microcracks on the surface. These findings are important for the development of outer fabric materials for new flexible thermal protection systems in space applications.

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