The Van Allen Belts

A diagram of the Van Allen Belts that surround the Earth.

The Van Allen Belts are trapped protons and electrons surrounding the Earth, in radiation. These belts pose a threat to astronauts in orbiting missions, which most of the current space missions are. Space stations also fall in this category. These types of missions are affected by the area of the Van Allen Belts called the South Atlantic Anomaly, which is closer to the Earth than any other part of the Belts. An orbiting craft passes through this area several times per day. In an interplanetary mission (to the Moon or Mars, for example), the craft passes all the way through the Belts, once when leaving Earth, and once when returning. In this case, the South Atlantic Anomaly plays a small role; the radiation comes from the craft?s passage through the Belts.