"In 2010, and again in 2011, the crew of the International Space Station (ISS) was forced to evacuate on shortnotice when a piece of space debris came perilously close to colliding with the space station. On both occasions, the object was detected too late for the crew to perform an avoidance maneuver.
The space station is in a LEO, an orbit around our planet just above the atmosphere (see diagram on page 10). At altitudes between 300 km and 2,000 km, the risk of collision is mostly due to man-made debris, particularly defunct satellites and decommissioned launch vehicles in upper LEO levels, which have not been deorbited. More than 12,000 debris objects measuring at least 10 cm across have been cataloged in this part of space.
The number of smaller items is even greater but they are too small to observe or track, making them all the more dangerous."
