A Navy heat-seeking missile is getting its first real-world use in an attempt to demolish a crippled US spy satellite before the orbiting craft falls back to Earth.

The targeting of the satellite which could come Wednesday night is not the mission for which this piece of the Pentagon’s missile defence network was intended, however.

The attempted shootdown, already approved by President Bush out of concern about toxic fuel on board the satellite, is seen by some as blurring the lines between defending against a weapon like a long-range missile and targeting satellites in orbit.

The government issued notices to aviators and mariners to remain clear of a section of the Pacific Ocean beginning at 10.30 pm (EST) on Wednesday, indicating the first window of opportunity to launch an SM-3 missile from a Navy cruiser, the USS Lake Erie, in an effort to hit the wayward satellite.

Adding to the difficulty of the shootdown mission, the missile will have to do better than just hit the bus-sized satellite, a Navy official said Tuesday. It needs to strike the relatively small fuel tank aboard the spacecraft in order to accomplish the main goal.

China and Russia have expressed concern at the planned shootdown, saying it could harm security in outer space.