Characterization of Ablation Product Radiation Signatures of PICA and FiberForm

Abstract

Emission spectroscopy measurements in the post-shock layer in front of low density ablative material samples of different shapes were obtained in the NASA Langley HYMETS arcjet facility. A horizontal line of measurement positions was imaged on the entrance slit of the spectrometer allowing detection of the entire stagnation line in front of the samples. The stagnation line measurements were used to compare the post-shock layer emission signatures in front of PICA and FiberForm. The emission signatures of H, NH, and OH are characteristic for pyrolysis gases and consequently were only observed in front of the PICA samples. CN and C were found in front of both materials and are mainly due to interactions of the carbon fibers with the plasma. In all tests with instrumented samples, the emission of Mn, Cr, and Ni was observed when the thermocouple temperatures reached or exceeded ~1,500 K, strongly indicating erosion of the molten thermocouple tips. Temperatures in the post-shock layer were estimated from comparing the CN band emission to spectral simulation. The resulting rotational and vibrational temperatures were on the order of 7,000 to 9,000 K and close to each other indicating a plasma condition close to equilibrium. In addition to the stagnation line configurations, off-axis lines of observation were investigated to gather information about spalled particles in the flow. From a comparison of measured continuum emission with simulated Planck radiation, average particle temperatures along the measured line of observation were determined for two cases. Particle temperatures between 3,500 and 2,000 K were found. A comprehensive investigation of the entire amount of data set is ongoing.

Infrared spectroscopic measurements of carbon monoxide within a high temperature ablative boundary layer

“…Additional work has looked at air and nitrogen flows, and the ablative species introduced within the boundary layer and post shock regions. [4,5,6,7,8] Much of this work has focused on, or identified the presence of, both C and CN emission.…”

Development of a probe for in-situ radiative heat flux measurements at the surface of an ablator

“…Wernitz et al [2] used a plasma wind tunnel facility to model the atmosphere of Titan and looked at the formation of N 2 , N + 2 and C 2 species within an ablative boundary layer. Additional work has looked at air and nitrogen flows, and the ablative species introduced within the boundary layer and post shock regions [3,4,5,6,7]. Much of this work has focused on both C and CN emission.…”