Discarded items are crowding the heavens, and could seed a catastrophic "cascade" effect, where litter collides and smashes into small pieces forming a whirling junkyard destroying everything in its path.
With speeds of thousands of miles per hour, a pea-sized piece of junk could destroy millions of dollars' worth of space equipment. "Our great concern is that the proposal to launch 1,000 satellites for telephone communications by the end of the century will provide a concentration of mass which [could] prompt a cascade," said Richard Crowther of the Defence Research Agency.
In July last year the first documented space collision occurred between the French Cerise microsatellite and a piece of an Ariane rocket, destroying the satellite's functions.
"There are 8,500 objects that Nasa can track up there, and only 6 per cent of them are operational, which means 94 per cent is space junk," said Dr Crowther.
"They vary from satellites left in orbit, to breakups from the old days, when the Soviets used to blow up their surveillance satellites, and a screw driver dropped by an astronaut."
Though many items of space debris are eventually dragged down into the atmosphere where they burn up harmlessly, a huge number remain in orbit.
Experts say that in future, space travel will still be possible, but will be more expensive, as rockets and astronauts will need extra shielding against the possibility of debris impact.