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Pentagon officials have announced plans to shoot down a failing spy satellite orbiting over Ireland with a missile from a US navy warship to prevent debris from showering the Earth.

The dramatic operation will target the secret satellite identified as USA 193, which is expected to fall from orbit in the first week of March.

Amateur satellite trackers say that the craft, about the size of a small bus, travels an orbit of 58.5 degrees that takes it over most the Earth from Ireland and the tip of Scotland to Patagonia at the southern end of Latin America. It could crash almost anywhere.

John Locker, a British astronomer, photographed the satellite with sunlight glinting off it at an altitude of about 200 miles from his home in the Wirral, Cheshire, and posted the picture on the website Galaxypix.com.

Astronomy enthusiasts in Ireland say that debris could land anywhere from Co Cork to Co Donegal. The Australian Government has prepared contingency plans in case the craft falls on its territory.

US officials made the decision to shoot it down after predicting that about half the 5,000lb spacecraft would survive its blazing descent through the atmosphere.

The statistical risk of death or injury is considered small. Even when the space shuttle Columbia broke up over Texas and scattered debris over two states no one on the ground was hurt. Two thirds of the Earth’s surface is covered with water. In the past 50 years about 17,000 man-made objects have re-entered the atmosphere, including the 78-ton Skylab space station that fell into the Indian Ocean and across west Australia in 1979.

The USA 193 spy satellite is equipped with small rocket “thrusters” loaded with toxic hydrazine fuel. Contact with hydrazine can cause coughing, irritated throat and lungs, convulsions, tremors or seizures, and long-term exposure can damage the liver, kidney and reproductive organs. US officials say that the craft carries no nuclear material.

USA 193 was launched on December 14, 2006, from the Vandenberg US Air Force Base in California. Once it reached orbit it failed to communicate with its ground controllers, making it uncontrollable. Though its design is top-secret, it is reported to be a high-resolution radar satellite that would take images for the National Reconnaissance Office.

Defence analysts have suggested that the Pentagon may be reluctant to allow a large piece of its most sophisticated technology to fall into the hands of a rival such as Russia or China.

The operation will test the capability of Washington’s new missile defence system, a successor to the “Star Wars” missile interception system of the 1980s.

Pentagon officials said that a navy cruiser would shoot down the satellite using a special missile modified for the task. The operation is likely to prove controversial after the rumpus over China’s anti-satellite test last year. China drew criticism from the US and other nations for shooting down a defunct weather satellite.

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