ELFIN mission overview and first results.

The Electron Loss and Fields Investigation with a Spatio-Temporal Ambiguity-Resolving option (ELFIN-STAR, or ELFIN*) mission, comprised of two 3U CubeSats, was launched in September 2018 to explore the mechanisms responsible for relativistic electron loss during magnetic storms. It is currently in commissioning phase, with all instruments and spacecraft functioning nominally as verified by data collections that will be presented in this talk. Nominal science operations is expected to commence in June 2019, and is expected to yield at least one complete scan of the radiation belt L-shells once per orbit (90 min period) from each satellite (up to four possible, limited only by downlink capability). Pitch-angle resolved energy spectra of ions and electrons between 50-5000keV are routinely measured, as well as the local magnetic field and its variations in the electromagnetic ion cyclotron (EMIC) wave frequency range (at the equator), in order to determine the role of EMIC waves in causing relativistic electron precipitation. Survey mode allows after-the-fact selection for downlink of interesting periods, based on local activity and quality of conjunctions with THEMIS and other equatorial satellites, using on quick-look data. Satellite separations enable resolution of spatial from temporal variations to determine definitively the latitudinal extent and temporal evolution of the precipitation. We describe the technical mission implementation and show how the first results guarantee a rich dataset with high scientific potential to be collected over the ~6months of remaining mission lifetime.