The SERENA/Strofio Sensor Onboard BepiColombo

The sensor Strofio is a mass spectrometer, part of the SERENA plasma/neutral particles package for the BepiColombo mission to Mercury.All the calibrated responses of Strofio to external stimuli are compatible with the requirements necessary to characterize the tenuous exosphere of Mercury. In the measured particle sensitivity (0.14 (cts/sec)/(1/cm3)), resolution (m/dm>90), mass range (4-60 + 80-120) and capability of background rejection ( > 40) are well fitted to the expected conditions around the planet. We present the current understanding of composition and variability of the Hemean exosphere, the derived physical measurables, and show the relevant Strofio calibration results. On December 12, 2018 Strofio has been turned on in-flight and is performing as expected: examples of collected spectra show background composition and resolution capabilities.