Space debris is any nonworking object made by people that remains in orbit around Earth. Space debris is sometimes called space junk. The objects that become space debris range from spent rocket stages (sections) of launch vehicles to tiny paint chips that have flaked off old satellites and rockets. Space debris does not include working bodies, such as functioning satellites. It also excludes naturally occurring chunks of matter called meteoroids. Scientists have identified more than 28,000 pieces of space debris. Space agencies track some 10,000 objects larger than about 4 inches (10 centimeters) using radar and telescopes. Space experts worry about space debris because collisions with it can damage spacecraft or injure astronauts.
Space debris results from routine or destructive events involving spacecraft. For example, many space missions leave such objects in orbit as nuts, bolts, and tools. The space environment causes paint chips to come off old spacecraft and rocket stages. Some satellites break apart. More destructive events, such as an old rocket stage with leftover fuel that exploded in 2007, can produce hundreds of pieces of debris. In addition, military tests of weapons that destroy satellites can add to space debris. One such incident occurred in 2007, when a Chinese satellite was destroyed in orbit by a Chinese ground-based missile. This event produced a large amount of debris close to the satellite’s original orbit.
The damage caused by a space debris impact depends on the size of the debris. An impact from a large piece of debris could destroy a satellite. But most collisions involve small pieces of debris that cause minor damage. For example, impacts with space debris as well as tiny natural objects created small pits in the windshields of the United States space shuttles, leading engineers to replace them frequently. In early 2009, the first incident of a working satellite being destroyed by space debris occurred when a non-functioning Russian satellite collided with an American satellite. The collision destroyed both craft.
Some space debris at high altitudes may remain in orbit indefinitely. At lower altitudes, friction with Earth’s thin upper atmosphere slows the debris, causing its orbit to lower. Eventually, the debris reenters Earth’s atmosphere. There it either burns up due to friction or crashes into the ground or the oceans. Only a few pieces of reentering space debris have ever been recovered. Reentering space debris has caused no reported injuries to people or damage to property.
Space agencies are exploring ideas to reduce the amount of space debris in orbit. But the most effective method for limiting space debris is to prevent the creation of additional debris.
See also Satellite, Artificial (Falling from orbit) .
