In-Flight Diagnosis and Recovery Operations of the Strofio Mass Spectrometer Following the D5 Electrode Anomaly During BepiColombo Cruise Phase

During post-launch commissioning of ESA–JAXA's BepiColombo mission to Mercury, the Strofio neutral gas time-of-flight mass spectrometer aboard the Mercury Planetary Orbiter experienced an electrode voltage anomaly that threatened nominal science operations. One of the electrodes used to steer ion trajectories near the microchannel plate detector (the D5 electrode) became permanently shorted to ground, significantly altering the instrument’s ion optics and reducing performance. A comprehensive diagnostic approach combined Strofio in-flight data, engineering model laboratory testing, and SIMION ion-optics simulations to identify the anomalous electrode operating state and assess its operational impacts. Following this investigation, an alternative ion-optics configuration was identified and implemented using a dual-electrode approach, enabling recovery from the anomaly and allowing the instrument to meet its measurement requirements. This work demonstrates the value of targeted in-flight characterization during cruise operations and shows that the combined use of in-flight data, engineering model testing, and ion-optics simulations provides a transferable framework for diagnosing and mitigating anomalies in time-of-flight mass spectrometers and other planetary science instruments when flight testing opportunities are limited.