Space debris is the collection of deceased man-made objects in Earth orbit, such as old satellites, rocket stages depleted and fragments of disintegration, erosion and collisions - including those caused by the space debris itself. As of December 2016, five satellite collisions have resulted in the generation of space debris.
As of July 5, 2016, the United States Strategic Command tracked a total of 17,852 artificial objects in orbit on Earth, including 1,419 operational satellites. However, these are just objects large enough to be tracked. As of July 2013, it is estimated that more than 170 million debris smaller than 1 cm (0.4 inches), about 670,000 remains 1-10 cm and about 29,000 larger debris are in orbit. Collisions with debris have become a danger to spacecraft; cause similar damage to sandblasting, especially to solar panels and optics such as telescopes or star trackers that can not be covered with a Whipple ballistic shield (unless it is transparent).
Below 2,000 km (1,200 miles), Earth-altitude wastes are denser than meteoroids; most of them are solid rocket motor dust, surface erosion remnants such as paint scales and frozen refrigerant from RORSAT nuclear satellites. For comparison, the international space station orbits in the range of 300-400 km (190-250 mi), and the 2009 satellite collision and the 2007 antisat test occurred at 800 to 900 kilometers (500 to 560 miles) altitude. The ISS has Whipple armor; however, known debris with a collision probability greater than 1 / 10,000 is avoided by maneuvering the station.
It has been hypothesised that Kessler syndrome, an unrestrained chain reaction of collisions that exponentially increase the amount of debris, goes beyond a critical density. This could affect useful bands in polar orbit, increase the cost of protection of space missions and destroy satellites live. It has already been debated whether Kessler syndrome is already under way. Some participants in the space industry perform measurement, mitigation, and potential removal of debris.