Measurement of the fluidic resistance of the MicroMED optical particle counter

The Optical Particle Counter MicroMED will be part of the ExoMars 2022 mission in the Dust Complex Suite, a suite of sensors mounted on the Kazachok Surface Platform. One of the main goals of the ESA/Roscosmos ExoMars program is the study of the Martian surface environment characteristics through the analysis of the atmosphere and climate, and the MicroMED will perform within this framework the first-ever direct measurement at the Martian surface of the airborne dust. The flight model was delivered at Thales Alenia Space premises in the initial of 2020 to allow integration with the Dust Complex Suite, but accurate calibration of the instrument performances is still ongoing on different models, i.e. a flight spare, and mockups manufactured within the project framework. The present work describes the measurement of the fluidic resistance of an instrument mockup in low-pressure simulating operative conditions of the mission. The measured fluidic resistance is of primary importance to recover the flow rate through the instrument from the pressure drop measurement at the instrument optical head. The latter parameter will be available on the flight model as well, to derive an indirect measurement of the flow rate during the operative phases on Mars and thus measure the dust probability distribution during the instrument science campaigns.