Probing Magnetospheric Wave–Particle Interactions Through Coordinated VLF Transmission and In-Situ Measurements

Earth’s magnetosphere provides a unique natural environment in which plasma processes unfold across broad temporal, spatial, and energy scales. A particularly important class of these processes is wave–particle interaction, which governs both the acceleration and loss of energetic particles and strongly influences radiation belt dynamics. Relativistic electrons in the radiation belts can exchange energy and momentum with plasma waves through resonant interactions, leading to pitch-angle scattering and, in some cases, precipitation into the upper atmosphere. Despite decades of theoretical and observational work, quantitatively characterizing wave–particle interactions remains an outstanding challenge in magnetospheric physics, largely due to the scarcity of co-located and simultaneous measurements of both energetic particles and electromagnetic waves at interaction sites.

The Leucippus mission is designed to address this limitation by combining controlled wave generation with coordinated in-situ observations. The mission concept consists of two 6U CubeSats operating in formation to enable active experiments on wave–particle interactions. One spacecraft acts as a transmitter, generating Very-Low-Frequency (VLF) electromagnetic waves, while the second spacecraft performs targeted measurements of the resulting plasma and particle response. This architecture enables direct observation of resonant scattering signatures under representative inner magnetospheric plasma conditions, providing an experimental capability that has not previously been available.

The transmitter CubeSat carries a rotating magnetic dipole antenna optimized for VLF wave emission in the 5–20 kHz frequency range, complemented by a Langmuir probe for measuring local plasma density and improving coupling to whistler-mode propagation. The receiver CubeSat is equipped with VLF electric and magnetic field sensors to characterize wave properties, as well as an energetic particle detector capable of resolving electron energy distributions. By exploiting magnetic conjunctions between the two spacecraft, Leucippus enables measurements along shared magnetic field lines where wave–particle interactions are expected to be strongest.

The primary scientific goals of the mission are to demonstrate efficient space-based VLF wave injection into the magnetosphere, to investigate wave propagation behavior across varying plasma conditions, and to directly quantify electron energy diffusion driven by injected wave fields. The resulting observations will place new constraints on long-standing theoretical models, including questions related to nonlinear effects, ducted versus oblique wave propagation, and the effectiveness of controlled VLF transmission as a tool for radiation belt modification. Leucippus is currently in the concept development phase, with subsystem design, antenna–plasma coupling simulations, and wave–particle interaction modeling actively underway.