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The military will try to shoot down a crippled spy satellite in the next two weeks, senior officials said Thursday. The officials laid out a high-tech plan to intercept the satellite over the Pacific just before it tumbles uncontrollably to earth carrying toxic fuel.

President Bush ordered the action to prevent any possible contamination from the hazardous rocket fuel on board, and not out of any concern that parts of the spacecraft might survive and reveal its secrets, the officials said.

The challenging mission to demolish the satellite on the fringes of space will rely on an unforeseen use of ship-based weapons developed to defend against ballistic missile attacks.

The effort will be a real-world test of the nation’s anti-ballistic missile systems and its anti-satellite abilities, even though the Pentagon said it was not using the effort to test its most exotic weapons or send a message to any adversaries.

The ramifications of the operation are diplomatic, as well as military and scientific, in part because the United States criticized China last year when Beijing tested an anti-satellite system with an old weather satellite as a target.

The three-ship convoy assigned to the new task will stalk the satellite’s orbital path across the northern Pacific, tracking the satellite as it circles the globe 16 times a day. The sensors and weapons in the operation, modified from anti-aircraft defenses for use as a shield against incoming missiles and installed on Navy cruisers, have been used just in carefully controlled tests.

This time, the target is not an incoming warhead or a dummy test target, but a doomed experimental satellite the size of a school bus and weighing 5,000 pounds. It died shortly after being launched in December 2006 and contains a half ton of hydrazine, a fuel that officials said could burn the lungs and even be deadly in extended doses.

The tank is believed to be sturdy enough to survive re-entry, based on studies of the tank that fell to earth after the Columbia shuttle disaster in 2003.

The military and NASA have calculated that the best opportunity to shoot down the satellite with an interceptor missile is just before it re-enters the atmosphere and starts to tumble and break apart on a random path, an opportunity that begins in three to four days and continues for eight days. At that point, the debris would be quickly dragged out of orbit.

In many ways, the task resembles shooting down an intercontinental nuclear missile, although this target is larger, its path is better known and, if a first shot misses, it will continue to circle the earth for long enough to allow a second or even a third try.

The weapon of choice, after modifications that are way, is the Standard Missile 3 on by Aegis cruisers. The missiles and supporting radar were being modified and tested to shoot down enemy warheads. So the software is being reprogrammed to home in on the radar and other signatures of a large satellite instead of a ballistic missile, officials said.