Van Allen radiation belt "Impact on space travel"

http://en.wikipedia.org/wiki/Van_Allen_radiation_belt

Solar cells, integrated circuits, and sensors can be damaged by radiation. Geomagnetic storms occasionally damage electronic components on spacecraft. Miniaturization and digitization of electronics and logic circuits have made satellites more vulnerable to radiation, as incoming ions may be as large as the circuit's charge. Electronics on satellites must be hardened against radiation to operate reliably. The Hubble Space Telescope, among other satellites, often has its sensors turned off when passing through regions of intense radiation.[citation needed]

Missions beyond low earth orbit leave the protection of the geomagnetic field, and transit the Van Allen belts. Thus they may need to be shielded against exposure to cosmic rays, Van Allen radiation, or solar flares.
An astronaut shielded by 3 mm of aluminium in an elliptic orbit passing through the radiation belt will receive about 2,500 rem (25 Sv) per year.[6]