According to simulations, there are 750,000 particles in orbit that are bigger than one centimetre. Currently, approximately 18,000 pieces of space debris with a size of around 10 centimetres have been catalogued. Space debris refers to all man-made objects located in space and which no longer fulfil any function. Typical examples are used rocket upper stages and shut-down satellites. In terms of numbers, the majority consists of pieces of debris generated when space vehicles break up, because, for example, fuel residues have exploded or collisions between various pieces of space debris have taken place in orbit.