Space debris a growing problem

Millions of chunks of metal, plastic and glass are whirling round Earth, the garbage left from 4,600 launches in 54 years of space exploration.

The collision risk is low, but the junk travels at such high speed that even a tiny shard can cripple a satellite costing tens of millions of dollars.

Around 16,000 objects bigger than 10 centimetres (four inches) across are tracked by the US Space Surveillance Network, according to NASA's specialist newsletter (newsletter http://orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv15i1.pdf).

There are around 500,000 pieces between one and 10 cms (half and four inches), while the total of particles smaller than one centimetre (half an inch) "probably exceeds tens of millions," NASA says elsewhere on its website.

The rubbish comes mainly from old satellites and upper stages of rockets whose residual fuel or other fluids explode while they turn in orbit. As the junk bumps and grinds, more debris results.