The Start from a Rotating FIeld mass spectrometer (STROFIO) is an instrument in the SERENA (Search for Exospheric Refilling and Emitted Natural Abundances) suite on the Mercury Planetary Orbiter on BepiColombo. STROFIO was developed and built at SwRI. The STROFIO instrument measures the neutral particle composition and particle density of Mercury’s exosphere at very low energies (up to only a few eV). STROFIO is a unique mass spectrometer that uses rotating electric fields to mark “start” times of a particle’s trajectory within the instrument. The main scientific objectives of STROFIO are to better our understanding of the relationship between the composition of the surface and the exosphere of Mercury, and understand the chemical composition, density, and variability of Mercury’s exosphere.