Strofio: A novel neutral mass spectrograph for sampling Mercury´s exosphere

Strofio is a scientific investigation to sample in-situ the neutral atoms in Mercury´s exosphere. Strofio is based on a novel mass spectrograph that determines the particle mass-per-charge (m/q) by a time-of-flight (TOF) technique. This novel technique achieves a mass resolution (m/Δm) at mass 18 of >;100, with a high sensitivity of 0.14 (counts/s)/(particles/cm³) and a mass of only 4kg. Strofio employs a rotating electric field to “stamp” the start time of the incoming ionized particles and a micro-channel plate (MCP) detector to record the stop time and position. This eliminates the need for foils or shutters, resulting in nearly 100% duty cycle and a low mass design. Strofio is funded by NASA to fly on the European Space Agency mission BepiColombo to the planet Mercury. It is part of the four instrument SERENA suite situated on the Mercury Planetary Orbiter (MPO), which will enter in a 400 × 1500km polar orbit. This paper describes the theory of operation, the instrument components, and focuses on the front end electronics and processing required to read and accumulate the particle data.