Space debris (also known as space junk, space pollution, space waste, space trash, or space garbage) is defunct artificial objects in space principally in Earth orbit which no longer serve a useful function. Some space junk results from collisions or anti-satellite tests in orbit. When two satellites collide, they can smash apart into thousands of new pieces, creating lots of new debris. This is rare, but several countries including the USA, China and India have used missiles to practice blowing up their own satellites. Such debris includes nonfunctional spacecraft, abandoned launch vehicle stages, mission-related debris, and fragmentation debris. There are approximately 23,000 pieces of debris larger than a softball orbiting the Earth. The accumulation of space junk poses a particularly catastrophic threat to humankind's future in space exploration, due to increased risk of collision with and damage to functioning satellites. It could also have detrimental effects on Earth's environment. There is no doubt that active orbital debris removal is technically challenging, Gorman says. “However, the big issue is that any successful technology that can remove an existing piece of debris can also be used as an antisatellite weapon,” she says. The satellite exploded into more than 3,500 pieces of debris, most of which are still orbiting. Many have now fallen into the ISS's orbital region. To avoid the collision, a Russian Progress supply spacecraft docked to the station fired its rockets for just over six minutes. Since atmospheric drag is low at that altitude, the debris is slow to return to Earth, and in June 2007 NASA's Terra environmental spacecraft maneuvered to avoid impact from the debris. Australia already holds the record in the category of “who can be hit by the biggest piece of space junk”. In 1979, the 77-tonne US space station SkyLab disintegrated over Western Australia, peppering the area around the southern coastal town of Esperance with fragments. How long a piece of space debris takes to fall back to Earth depends on its altitude. Objects below 600 km (375 miles) orbit several years before reentering Earth's atmosphere. Objects above 1,000 km (600 miles) will orbit for centuries. There are approximately 900,000 pieces from 1 to 10 cm. The current count of large debris (defined as 10 cm across or larger) is 34,000. The technical measurement cutoff is c. 3 mm (0.12 in). As of 2020 there is 8000 metric tons of debris in orbit with no signs of slowing down.

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