Plasma wakes from the Baffle Scanning Mechanism on a LEO mass spectrometer

The Modular Spectrometer for Atmosphere and Ionosphere Characterization (MoSAIC) is a quadrupole mass spectrometer (QMS), which will fly on NASA's Geospace Dynamics Constellation (GDC) mission in low Earth orbit, providing measurements of neutral and ionized gas density, temperature, composition, and wind/drift. MoSAIC includes a Baffle Scanning Mechanism (BSM), which periodically sweeps in front of the QMS aperture, enabling determination of the ion temperature and cross-track velocity. Accurate knowledge of the plasma wake formed by the BSM is critical for accurate determination of these quantities. We conduct particle-in-cell simulations modeling the interactions between the baffle and plasma across the full range of ion densities, temperatures, and flow speeds GDC is expected to encounter. We discuss the wake physics and present an empirical model, which can be implemented in the MoSAIC data analysis process to determine the relevant ion quantities.