044_G17 Arena

Global_17

Arena Science Counting the cost of cosmic clutter The amount of junk orbiting the Earth is growing, as bits of old satellites and other man-made objects remain in space long after they have ceased to be functional. They bring with them an increasing risk that there will be a serious collision with the satellites that we have come to depend on Rosamund West and Katie Silvester There are 17,000 man-made objects currently orbiting in the zone closest to the Earth – and that’s just the hardware that is big enough to monitor. But most of it is junk, nothing more than a giant scrap metal yard in the sky. Only seven per cent of these orbiting items are functioning satellites, the rest is debris from old satellites and the remains of rocket engines or propulsion systems left floating in orbit long after their mission was launched. It doesn’t take a genius to work out that there is a growing risk of the satellites we rely on – for everything from weather warning systems to satellite TV – being seriously damaged as a result of a collision with cosmic debris. Since Sputnik was launched by the Russians in 1957, there have been more than 6,000 successful satellite launches. Twenty-first Only seven per cent of orbiting items are functioning satellites, the rest are debris from old satellites and rocket engines century life has come to rely, almost unthinkingly, on satellites. We use them for navigation systems, environmental monitoring, military defence systems, credit card authorisation, radio and television broadcasting, and mobile phone calls, to name but a few things. But what goes up doesn’t always come down. Scientists are becoming increasingly worried about the growing amount of space debris in low Earth orbit. This orbit zone stretches 2,000 km above the earth’s atmosphere and is the most important area for communications and observation satellites. It is also home to the Hubble Space Telescope and the International Space Station, which are equally at risk of taking a direct hit. There are an estimated 20,000 to 30,000 objects in orbit over 10 cm in diameter that can be monitored from Earth – a mixture of man-made items and natural objects like meteoroids – and an almost incalculable number of smaller fragments that are undetectable by surveillance systems but that still pose a significant threat. Donald J. Kessler, a NASA scientist, predicted in 1978 that at some point there would be so much debris in space that the resulting congestion would produce an uncontrollable and exponential growth in collisions and debris. If the so-called Kessler syndrome becomes a reality, operational satellites in low Earth orbit will almost certainly be damaged and their services disrupted. Some predict that the Kessler effect will mean that we are unable to use satellites in the lower echelons of space at all and that, as a result, drastic changes in the technology we use to communicate globally will have to be made. Hugh Griffiths, president of the IEEE Aerospace and Electronic Systems Society, says that the problem is a “ticking time bomb”. “A plot of the number of orbital space objects shows a steady rise since the mid-1960s, with two step changes,” he explains. “In January 2007 a Chinese missile destroyed a Chinese weather satellite in polar orbit, generating over 2,000 pieces of debris of the same order of size as a golf ball, and an estimated 150,000 Growth of orbital objects including debris 16,000 14,000 12,000 10,000 8,000 6,000 4,000 2,000 China anti-satellite test 0 1956 1960 1970 1980 1990 2000 Number of objects Source: Nasa Iridium/Kosmos collision Total objects Fragmentation debris Spacecraft Mission-related debris Rocket bodies 2010 44 l www.global -br ief ing.org f i rst quar ter 2014 global


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