Washington - The US Navy has successfully hit a falling spy satellite with a missile fired late Wednesday by a warship in the Pacific Ocean, a Pentagon spokesman confirmed. The US targeted the satellite because it carries a toxic fuel that could be harmful if the spacecraft drifted back into Earth's atmosphere and the fuel tank fell into a populated area.
The USS Lake Erie near Hawaii fired an unarmed missile at 10:26 pm (0326 GMT) that collided at a speed of 27,000 kilometres per hour with the satellite at an altitude of 247 kilometres above the Pacific.
The successful hit will likely be viewed as a major success for the sea-based missile defence system, which was built to counter medium-range threats and in testing has been among the Pentagon's most reliable missile defence programmes.
The Pentagon said it should be able to confirm within 24 hours whether the interceptor missile ruptured the fuel tank, holding 453 kilogrammes of hydrazine. Officials expect most of the debris to burn up while re-entering the atmosphere.
The Pentagon wanted to avoid the possibility of the satellite's debris from returning to a high orbit and posing a threat to other objects in space.
"Nearly all of the debris will burn up on reentry within 24 to 48 hours, and the remaining debris should re-enter within 40 days," the Pentagon said.
The Pentagon was expected to provide more details about the operation Thursday morning.
The US military opened a window beginning Wednesday in hoping to launch a missile to shoot down the satellite, despite earlier concerns about poor weather that caused rough waters around the firing vessel.
The satellite lost communication shortly after it was launched in 2006 and has since wandered aimlessly in orbit. The National Reconnaissance Office (NRO), the secretive agency, which oversees the nation's spy satellites, said the spacecraft hit Wednesday was classified and refused to reveal its construction cost.
A senior defence official had said that once the satellite came within range, the launch window would narrow to "tens of seconds."
The Pentagon estimated that it would have until the end of February to shoot down the satellite but waited to fire until the return of the Space Shuttle Atlantis early Wednesday at Cape Canaveral, Florida.
The Pentagon was concerned that once the satellite fell into re- entry in March, would not be possible for the missile defence system to track it for a missile strike.
A senior defence official, briefing reporters on condition of anonymity, had cautioned earlier Wednesday that rough waters off Hawaii could have forced a delay in the launch.
President George W Bush's controversial decision to proceed with the intercept has prompted complaints from China and Russia, who argue it marks a step toward weaponization of space and a broader mission for the US missile-defence system. The sea-based Aegis version of missile defence is the system deployed by the Navy to strike the satellite.
Last year, China used a land-based missile to shoot down one of its old weather satellites, which was in much higher orbit than the US satellite, generating strong international criticism including from the United States.
Thousands of pieces of debris from the destroyed Chinese satellite remain in orbit and have to be monitored.
The mission to shoot down the satellite was seen as so crucial that the order to fire came from Defence Secretary Robert Gates, not a uniformed military commander.
The USS Lake Erie, a Ticonderoga-class cruiser, fired a Standard Missile-3, which used thermal image sensors to seek out the satellite and computer-guided thrusters to stay on course. When the satellite mission arose, the Navy quickly adjusted three of its missiles to hit a satellite target rather than an enemy missile; only one was needed.
The Standard Missile does not carry explosives, instead colliding with targets at high speeds.
Experts have suggested that the US military could have used the satellite to test the adaptability of its missile defence system for taking out satellites or to prevent sensitive technologies on the satellite from ending up in the wrong hands.
The United States had not tested an anti-satellite weapon since 1985.
