The scientific space community has long been aware that, as the Low Earth Orbit (between 60 and 600 miles up) fills with space garbage such as spent rocket stages, the likelihood of collisions would become ever more likely. In a 1978 paper, Don Kessler, who later became head of NASA’s Orbital Debris Office, predicted that by 2000 collisions would produce debris more dangerous than natural meteoroids in spaces. Collisions would cut big objects into small ones. The little objects — marble size and smaller — pose the danger, says Kessler. And at 600 miles up, debris takes about 1,000 years to decay.
Each of these little pieces of debris whizzes around in its own orbit at a speed of about 6 miles a second — more than six times faster than a speeding bullet. The kinetic energy at that speed is about 36 times that of an equivalent mass of TNT.
The Low Earth Orbit, where the space station and the Iridium satellite band operate, is the crowded part of space. By the 1990s, scientists at NASA realized that man-made environmental hazards in that shell already exceeded meteoroid hazards. They gave the space station a shield to protect it from collisions with these marble-sized missiles.
The prediction of a major collision came true in February 2009 when a defunct Russian Cosmos satellite collided with a working American Iridium satellite at about 500 miles up. That incident created 1.5 tons of shrapnel. These include approximately 100,000 fragments of 1 millimeter or greater, which are large enough to be dangerous, and about 2,000 that are at least baseball size. Each is whizzing around at six miles a second, or 21,600 miles a hour.
(Source, St Louis BEacon).
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