Since the US abandoned its Vanguard 1 satellite half a century ago, space has been filling up with litter almost as rapidly as our city streets. And no one has made any effort to clear it away.
Discarded rocket stages, dropped spanners, even chunks of deep-frozen astronaut urine whizz around the globe at up to 25,000 miles per hour, in what Newsweek calls the "debris cloud" of some 750,000 objects larger than a marble, and even more smaller ones.
Last February, two satellites crashed into each other, producing another 100,000 bits of debris. Even the smallest pieces endanger satellites, valued at £10 billion. A fragment a millimetre across has the impact of a bullet; one the size of a tennis ball is equivalent to 25 sticks of dynamite.