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The South Atlantic Anomaly (or SAA) is the region where Earth's inner van Allen radiation belt makes its closest approach to the planet's surface. The result is that, for a given altitude, the radiation intensity is higher over this region than elsewhere. The SAA is produced by a "dip" in the Earth's magnetic field at that location, caused by the fact that the center of Earth's magnetic field is offset from its geographic center by 280 miles.
The South Atlantic Anomaly is of great significance to satellites and other spacecraft that orbit at several hundred miles' altitude and at orbital inclinations between 35° and 60°; these orbits take satellites through the Anomaly periodically, exposing them to several minutes of strong radiation each time. The International Space Station, orbiting with an inclination of 51.6°, required extra shielding to deal with this problem. The Hubble Space Telescope does not take observations while passing through the SAA.
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