Planetary-Defense KCR Mesh: An Open-Source CubeSat Constellation for Sub-Millisecond CME Early Warning

We propose a low‑cost, open‑hardware constellation of smallsats positioned sunward of Earth (nominal heliocentric 0.7 AU ring with modest longitudinal spread) to measure CME‑related magnetic and plasma signatures upstream of Earth and provide extended warning for severe geomagnetic storms. Sub‑millisecond on‑board sampling and on‑edge burst classification are used; end‑to‑end alert latency is dominated by solar‑light‑time (minutes), not by telemetry/ground processing. For a radial separation of ~0.3 AU, lead‑time scales with CME speed and geometry as: with capturing arrival‑cone and flux‑rope orientation uncertainty (typ. 0.5–3 h; reduced by external heliospheric context). This yields ~6–25 h for . We add a plasma sensor to the baseline and specify a Radial‑First downlink/alert policy.