PRELUDE CubeSat mission: early operational results and multi-satellite perspectives on ionospheric earthquake precursors

Despite advances in satellite remote sensing, predicting large earthquakes remains a major challenge. Building on previous DEMETER observations of seismo-ionospheric disturbances (e.g., Němec et al., GRL, 2008), we investigate atmospheric and space-electrical variations as potential ionospheric earthquake precursors, with an emphasis on the D region. Such observations can improve our understanding of lithosphere–atmosphere–ionosphere coupling and support the development of short-term prediction approaches.

We present the PRELUDE CubeSat mission (Precursory electric field observation CubeSat Demonstrator), dedicated to detecting earthquake-related ionospheric signatures and clarifying their physical mechanisms. PRELUDE is scheduled for launch in Japanese Fiscal Year 2025 within JAXA’s 4th Innovative Satellite Technology Demonstration Program, on Rocket Lab’s Electron from New Zealand (Mahia Peninsula, Launch Complex 1). PRELUDE is a 6U CubeSat (8 kg) optimized for VLF electromagnetic-wave intensity measurements. To reduce onboard storage and downlink load, PRELUDE implements an event-focused “drive-recorder” concept that selectively downlinks data acquired around target earthquakes and their vicinity. A key payload innovation is a compact hybrid sensor that combines a Langmuir probe and an electric-field probe—functions typically flown on >100 kg-class satellites such as DEMETER—into a CubeSat-compatible unit. The sensor deploys two booms extending 1.5 m in opposite directions from the spacecraft body via a folding deployment mechanism, enabling plasma and electric-field measurements within CubeSat resource constraints.

This presentation highlights early operational (initial in-orbit) results from PRELUDE and discusses their implications in a multi-satellite context. After DEMETER (local time ~10:30), complementary observations are provided by the China–Italy CSES-1 (local time ~14:00) and CSES-2 (local time ~14:00, with an ~180° orbital phase offset relative to CSES-1), which are in operation in 2026. PRELUDE provides observations at local time ~15:30 and operates during the same period. Coordinated analyses among DEMETER, CSES-1/2, and PRELUDE enable multi-local-time sampling, offering a timely pathway to test local-time dependence of precursor candidates and to better constrain the underlying physical processes.