Earth's magnetic field traps energetic protons (inner belt, ~1,000–6,000 km altitude) and electrons (outer belt, ~13,000–60,000 km) into doughnut-shaped regions that bounce and gyrate between the poles for months to years, building intense flux.
A satellite only takes a dose hit while its instantaneous altitude sits inside a belt. Orbits that stay below the inner belt (LEO) or above the outer belt (GEO) largely avoid it; orbits that cross or linger inside a belt (slow-moving near apogee, per Kepler's second law) accumulate dose fast.
- Orange torus — inner proton belt.
- Purple torus — outer electron belt.
- Cyan trail — the satellite's orbit path, glowing where it currently crosses a belt.