A 350-kilogram, spin-stabilized satellite developed by Japan’s Institute of Space and Astronautical Science. It is designed to repeatedly fly through Earth’s Van Allen belts—exposing its science package to plasma and particle flows in all directions as it spins—to study how chaotic geomagnetic storms form and evolve. The ERG satellite was launched successfully into Earth orbit by an Epsilon-2 booster on 20 December 2016 (JST) from the Uchinoura Space Center; Arase is named after a river running near that facility.