Material response characterization of a low-density carbon composite ablator in high-enthalpy plasma flows

Future space exploration missions beyond Earth's orbit, such as sample returns from Mars, will use ablative
materials for the thermal protection system in order to shield the spacecraft from the severe heating during
reentry. In this paper, we present the results of an elaborate test campaign on a lightweight carbon composite
ablator with the aim of defining a procedure for material response characterization in a 1.2-MW inductively
heated Plasmatron facility, suitable to reproduce the hypersonic flight boundary layer environment. Three
different test gases were used, including air, nitrogen, and argon, at surface temperatures exceeding 3300 K.
A comprehensive experimental setup was developed including a nonintrusive technique to measure surface
recession by means of a high-speed camera. Surface degradation was strongly test gas dependent, while mass
loss was mainly driven by in-depth decomposition of phenolic resin. Emission spectroscopy helped us identify
C2 as a product of dissociating hydrocarbons, as well as cyanogen, suggesting surface nitridation. Melt flow
at the surface and silicon emission indicated degradation of the glass microspheres used as additional filler.
In air plasma, oxidation was inferred to be the main mechanism for ablation.

Publication year:2014

Keywords:composite materials, phase transformations, characterization methods