Snipfact:

  The USSR's Sputnik I was the first artificial satellite to enter Earth's orbit. This 83.6 kg (184 lb) metal sphere transmitted signals back to Earth for three weeks before its batteries failed. In 1958 the USA began to launch its own satellites. Five went into orbit. All of the earliest satellites have since crashed back to Earth, expect Vanguard 1 (USA, 1958) Which is still in space and likely to remain so for another 200 years.

  About 100-200 objects, each larger than a football, re-enter every year, but there are still many pieces of space junk in orbit. A survey carried out in June 2000 calculated that there are 90 space probes and 2,671 satellites still in space. There are as many as 100,000 objects larger than 10cm including parts of rockets: an Ariane rocket booster exploded in 1986, scattering 400 fragments large enough to be tracked. In 1991 space shuttle Discovery STS-48 narrowly avoided a discarded Soviet rocket.

  Thrust is the force required to lift a vehicle such as an aircraft or rocket off the ground. Rockets often have several stages. Each one provides a proportion of the thrust required to carry a satellite, space shuttle or other vehicle into orbit or into space, dropping away as their propellant has been used so their propellant has been used so that their weight no longer need to be carried.

  The 69 ton Skylab re-entered in 1979, scattering large chunks in the Australian desert, and Russia’s Mir space station, which weighed 120 tones, came down in the Pacific.

  When satellites reach the end of their useful life, they may be deliberately directed back in such a way that they burn up as they re-enter the Earth’s atmosphere or come down in the oceans or away from places where they could cause damage. So far, no one has been killed or seriously injured by space debris.