Optical subsystems calibration and derived radiometric instrument response of the PHEBUS spectrometer on board of the BepiColombo Mission

Probing of Hermean By Ultraviolet Spectroscopy (PHEBUS) is a double spectrometer that will fly onboard of the BepiColombo mission. It will investigate the composition and dynamic of Mercury's exosphere to better understand the coupled surface - exosphere - magnetosphere system of the planet. The radiometric calibration tests are ongoing and an approach based on the Mueller Matrix formalism has been adopted to determine the pure efficiency of the instrument. To our knowledge, this is the first time that a such complete method is applied to the calibration of space instrumentation.