PRELUDE

PRELUDE [Nihon University]

PRELUDE (Precursory Electric Field Observation CubeSat Demonstrator) is a Japanese 6U CubeSat developed to investigate ionospheric disturbances as potential precursors to earthquakes, with a focus on hybrid electric field and plasma sensing technologies.

The mission aims to elucidate the mechanisms behind earthquake precursor phenomena by observing ionospheric fluctuations from orbit. PRELUDE targets very low frequency (VLF) electromagnetic signals, which may be affected by seismic activity. In parallel, it measures total electron content (TEC) using an onboard GNSS receiver to detect variations in electron density, a phenomenon associated with ionospheric disturbances potentially linked to tectonic processes. The satellite is also intended as a pathfinder for future dense constellations enabling tighter spatial and temporal observation of such effects.

The spacecraft emphasizes miniaturization and specialization compared to earlier missions such as DEMETER and China’s Zhangheng (CSES), which exceed 100 kg in mass. PRELUDE focuses specifically on signal intensity analysis in the VLF band and ionospheric diagnostics, demonstrating a compact hybrid sensor system combining electric field and plasma measurements. This approach allows targeted scientific observation within the constraints of a CubeSat platform.

PRELUDE is a 6U CubeSat operating in a Sun-synchronous quasi-regression orbit at an altitude between approximately 500 and 700 km. Its payload includes instruments for measuring VLF signal intensity, electron density, and electron temperature. The observations are based on the principle that electromagnetic wave penetration can induce charge distribution deviations in plasma, generating electric fields. Differences in mass between electrons and ions can further lead to charge separation effects, which are detectable as variations in plasma parameters.