ORBITAL COLLISION Satellites crash 485 miles above Russian Arctic

Last Tuesday at 4.56pm a defunct Russian military satellite that was falling out of its orbit collided with Iridium 33, a privately owned American communications satellite, 485 miles above Siberia. Both were destroyed, producing debris that scientists say could circle the Earth for tens of thousands of years. Iridium, which was travelling at about 17,000mph, was one of a network of 66 satellites positioned in near-polar orbit that circle the globe every 100 minutes. The Russian Kosmos 2251 satellite was launched in 1993 but has been out of operation since 1995, and has been gradually falling out of its original orbit about 490 miles above the Earth. It was only the fourth orbital collision on record but the first between two intact satellites.

MILLIONS OF PIECES Satellite explosions have left Earth ringed

There are an estimated 300,000 objects of more than 1cm in diameter orbiting the Earth, including about 12,000 satellites, of which only 6% are still functioning. US Space Command monitors about 18,000 objects that it considers to be dangerous. Among the oddities in orbit are a glove, which was lost by an American astronaut doing repairs on the International Space Station (which is itself orbiting 135 miles up). If you include debris that is less than 1cm in diameter, the total rises to tens of millions of items. These are added to by the shooting-down of satellites that have outlived their usefulness with ballistic missiles. China destroyed a satellite by this means in 2007, as did the United States last year.

DEBRIS DANGERS Astronauts and craft could be jeopardised

Scientists warn that collisions will become more of a risk as the number of satellites and amount of debris increases. Indeed, last week’s incident sent two large clouds of debris into the orbits of numerous satellites. The number of satellites has increased rapidly with the growth in mobile phone networks and the use of sat nav systems in cars. A future collision could be crippling for these services. From an astronaut’s perspective, debris can make life on spacecraft perilous. Space shuttles have had to avoid debris once a year on average. On a space walk the effects could be catastrophic: an object the size of a speck of paint hitting a spacesuit at 17,000mph would have the same effect as a bullet. The Pentagon is known to be concerned.

HOW TO SOLVE IT? Satellites should self-destruct after use

This week the issue will be raised at the United Nations Committee on the Peaceful Uses of Outer Space conference in Vienna. Professor Richard Crowther of the Science and Technology Facilities Council, who will represent Britain at the meeting, says that countries and companies should develop satellites that will have a mechanism that automatically sends them back towards Earth once they have finished their work so that they burn up in the planet’s atmosphere. Some satellites and the International Space Station already have boosters and fuel to allow them to dodge space debris. Last week’s collision also raises the issue of who is liable for crashes in space.

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