How do cruise missiles work

A.� Cruise missiles are guided weapons. They look like small planes and fly like normal aircraft for much of their flight, but without a pilot.

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Q.� If no one is piloting them, how are they launched

A.� Sea-launched cruise missiles are launched using a booster, after which on-board systems

take over. Cruise missiles can also be air -aunched by US B-52 bombers.

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Q.� What happens once the missile is flying

A.� Once airborne, it releases its wings and switches on navigational and communication systems.

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Q.� Is it possible to stop one once launched

A.� Because they're small and fast they're hard to stop, especially if they're travelling in a group.

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Q.� Why are they so effective

A.� They're designed to fly low, hugging the terrain, allowing them to fly fast at low altitudes, below radar detection signals.

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Q.� How does it 'hug' the terrain

A.� By using TERCOM (terrain contour-matching software). This provides the missile with a 3D map of the ground it's flying over. The software compares what it 'sees' below with the map, allowing the missile to make adjustments that keep it on target.

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Q.� Where does the map come from

A.� From the US National Imagery and Mapping Authority.

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Q.� Does TERCOM take the missile to its target

A.� No, at this point a much more sophisticated system kicks in: DSMAC (Digital Scene Matching Area Correlation).

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Q.� How does DSMAC work

A.� As the missile nears its target, DSMAC compares what's on the ground with a digital image of its target.

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Q.� So, with TERCOM and DSMAC, cruise missiles are very accurate

A.� Well, only as accurate as the information and maps they're using. Cruise missiles can still hit abandoned military targets or new civilian buildings if the maps are out of date.

A�future version of the missile is intended to circle the target, sending back live images to the control centre Military personnel would then decide whether the target is the intended one before the missile hits it.

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Q.� What happens once the missile hits the target

A.� A 1,000lb bomb is detonated.

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Do you have a question about how something works

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by Lisa Cardy