Experimental Trends of Spectral Emissivity by Dual-Colour Pyrometers During the Development of Re-entry Tests in Ground Facilities

During the ascent and re-entry phase of a space vehicle in the Earth's atmosphere, it is well known that the surface of the thermal protection system covering the vehicle changes its physical properties due to the severe aerothermodynamic loads generated during the flight. Such phenomena are under investigation in the hypersonic plasma ground facilities with various techniques. At the CIRA-Plasma Wind Tunnel (PWT) the Test Engineer Team (INPP) has improved the new technique in the INPP laboratory for the investigation of the material surface spectral emissivity variation during the development of hot tests performed in the SCIROCCO and GHIBLI hypersonic plasma facilities. It is based on the use of one optical device of the dual-colour type, that now is able to measure the two and single-colour temperatures of the material surface simultaneously and to obtain the trends of the spectral emissivity at the operative wavelength of the device. The present paper will show the results obtained during the development of a test campaign, giving evidence of the kindness of the technique.