First detection of field-aligned currents using engineering magnetometers from the OneWeb mega-constellation

Field-aligned currents are the main physical mechanism behind magnetosphere--ionosphere coupling, with these currents communicating environmental changes between the two regions of geospace. Field-aligned currents are thus a key factor in monitoring space weather, both from an operational and scientific perspective. While the AMPERE project has demonstrated that engineering fluxgate magnetometers on commercial satellite constellations can be assimilated to estimate the field-aligned currents across the entire polar cap, a limiting factor in the spatio-temporal resolution of this assimilation is the coverage of measurement points. However, in recent years much larger satellite mega-constellations have been launched into low Earth orbit which might offer unprecedented opportunities. Here we leverage engineering anisotropic magnetoresistive magnetometer data from the OneWeb constellation for the first time. A case study during the 12 May 2021 geomagnetic storm is presented. We show conclusive evidence that OneWeb engineering magnetometers were able to detect field-aligned current signatures present during this event by validating against AMPERE magnetic field and current maps from the same time. However, this result was despite significant challenges due to the OneWeb spacecraft instrumentation, data availability, and magnetic cleanliness, which we discuss in detail. Finally, we provide an outlook on the next steps required for OneWeb magnetic field data to provide valuable contributions to space weather science and operations.