Abstract
The present work reports on the use of emission spectroscopy as a diagnostic tool in arc-heated thermal protection system (TPS) testing. Absolute radiance measurements by emission spectroscopy from candidate TPS materials were performed concurrently with two-wavelength optical pyrometry in both a split tube furnace and the 30 kW mini-Arc Jet (mARC) at NASA Ames. In doing so, the emissivity values of certain common TPS materials were characterized as they vary with wavelength in the 685 to 925 nm spectral range. Preliminary measurements on carbon FiberForm, PICA, and TUFROC have yielded emissivity values between 0.84 and 0.96 at maximum survivability surface temperatures ranging from 1980-2860 K, depending on material. These measurements lay the foundation for more precise TPS surface temperature diagnostics by obtaining improved material emissivity estimates, while providing independent validation of surface temperature measurements via optical pyrometry. Because these specific material emissivity estimates are solely dependent on measured radiation intensity at a given wavelength and temperature, such results can be readily transferred to similar experiments on TPS material within larger arc jet systems, ultimately improving the understanding of surface temperature as it relates to TPS material recession.
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