Elfen: A mission to measure the heavy ion composition of the Earth’s magnetosphere

Abstract Elfen is a CubeSat mission concept designed to investigate the role of heavy ions in the Earth’s magnetosphere, focusing on both dayside and nightside dynamics. While the significance of heavy and molecular ions is well established in astrophysical contexts, their contribution to solar wind–magnetosphere–ionosphere coupling at Earth remains poorly quantified. On the nightside, the origin and transport mechanisms of ions within the low-latitude plasma sheet are still debated. The mission science questions are based around two overarching questions; What is the heavy ion influence at the dayside magnetosphere? and What is the heavy ion influence on the plasma sheet and on nightside reconnection? Elfen will contribute to this knowledge gap using two primary instruments; a plasma spectrometer for in situ heavy ion composition measurements, and a magnetometer for contextual plasma regime characterization. The payload will be hosted on a cost-effective 16U CubeSat, operating for at least one year. We present the baseline mission architecture developed through a Concurrent Design Facility study and further engineering analysis, designed in conjunction with industrial collaborators and consultants. The proposed orbit, a 12 Earth radii circular trajectory at low inclination with a 59.8-hour period, ensures sampling of both upstream and downstream magnetospheric regions, while offering high-science duty cycles and robust ground contact times. Alternative orbital configurations are considered to optimise science return within engineering constraints. Elfen is a timely mission, aligned with growing interest in space weather forecasting and near-Earth space exploration, and it will complement upcoming missions exploring solar-terrestrial interactions.