Space debris or orbital debris, also called space junk and space waste, are the objects in orbit around Earth created by humans, and that no longer serve any useful purpose. They consist of everything from entire spent rocket stages and defunct satellites to explosion fragments, paint flakes, dust, and slag from solid rocket motors, coolant released by RORSAT nuclear powered satellites, deliberate insertion of small needles, and other small particles. Clouds of very small particles may cause erosive damage, like sandblasting. Space "junk" has become a growing concern in recent years, since collisions at orbital velocities can be highly damaging to functional satellites and can also produce even more space debris in the process. This is called the Kessler Syndrome. Some spacecraft, like the International Space Station, are now armored to mitigate damage from this hazard. Astronauts on space-walks are also vulnerable.
The first major space debris collision was on February 10, 2009 at 16:56 UTC. The deactivated Kosmos-2251 and an operational Iridium 33 collided 789 kilometres (490 mi) over northern Siberia. The relative speed of impact was about 11.7 kilometres per second (7.3 mi/s), or approximately 42,120 kilometres per hour (26,170 mph). Both satellites were destroyed. The collision scattered considerable debris, which poses an elevated risk to spacecraft.