Plasma and material temperature/emissivity knowledge by applied physics technique based on compact VNIR emission spectroscopy in aerospace re-entry

Abstract

The following work presents a study based on spontaneous emission spectroscopy that evaluates the average temperatures of the plasma shock layer next to the solid surface and of the test article surfaces subject to the hypersonic jet determined by Scirocco Plasma Wind Tunnel (PWT) at CIRA. The SCIROCCO arcjet plasma tunnel, is the most powerful PWT in the world used to test the materials of TPS (Thermal Protection System) in the atmospheric entry phase. The methodology focuses on the radiation emitted by the test article in the VIS- NIR (i.e. Visible- Near Infrared) spectral ranges, from which the surface temperature and the emissivity values can be obtained. A UV nikkor camera connected to a compact spectrometer framed the lateral side of a C/SiC test article flap, subject to a known PWT fluid-dynamic flow condition expressed in terms of total pressure P0, total enthalpy H0 and air mass flow rate. A spectrometer with sizes of centimetres was used. It consisted of a commercially available Ocean Optics USB 2000, characterized by no moving parts and no cooling sensor with a 600 gr/mm diffraction grating.