A US missile hit an out-of-control spy satellite orbiting 130 miles above the Earth's surface and officials have a "high degree of confidence" that its hazardous fuel tank was destroyed, the Pentagon said today.
In the first mission of its kind, the US Navy struck the satellite with its first attempt.
Marine General James Cartwright, vice chairman of the US Joint Chiefs of Staff, said he could not rule out that hazardous material would hit the Earth, but added he was 80% to 90% sure the unprecedented mission had been successful.
In a press conference at the Pentagon, he said trackers detected a fire ball and vapour cloud which, although not conclusive, both suggested the toxic hydrazine in the fuel tank had been destroyed.
"We're confident that we hit the satellite and we also have a high degree of confidence that we hit the tank," he said.
"The high-definition imagery that we have indicates that we hit the spacecraft right in the area of the tank."
He said the US military was tracking the debris as it falls over the Atlantic and Pacific oceans and said it would take 24 to 48 hours for the full picture to become clear.
"Thus far we've seen nothing larger than a football, which tells us we're in the right area," he said.
"We have seen nothing yet, in the way of reporting or re-entry, that has survived to the Earth."
But Chinese officials said China was on alert today for possible harmful fallout from the fuel tank and urged Washington to release data to allow the countries likely to be affected to take precautions.
Some observers said the US mission blurred the lines between defending against a hostile long-range missile and targeting satellites in orbit.
But US officials insisted it was different to when the Chinese intercepted a satellite in January last year, because that had not posed any risk to human life.
China's anti-satellite test was criticised for being dangerous. The targeted satellite was located about 500 miles (800km) above the Earth and the resulting debris threatened communication satellites and other kinds of orbiting space vehicles.
Gen Cartwright said the US satellite was shot down because it contained the toxic hydrazine - not because of its size, the fact it was out-of-control or that it contained sensitive information.
"The intent here was to preserve human life," he said.
"While the technicians are looking at what they did in their part and feeling very good about it, at the end of the day what's important to us is what debris is out there that could fall, where is it going to fall, and if it falls in some area that's populated, getting to it and making sure nobody gets hurt."
He continued: "This is a one-time type of event.
"You can imagine at the point of intercept there were a few cheers that went up at the operation centres and on that ship, but with the understanding that we still have some work to do."
The Pentagon said the USS Lake Erie, armed with an SM-3 missile designed to knock down incoming missiles - not orbiting satellites - launched the strike from the Pacific Ocean at around 10.26pm EST on Wednesday (3.26am GMT today).
It hit the satellite as the spacecraft travelled at more than 17,000mph.
President George Bush made the decision to shoot down the 5,000lb USA 193 satellite, which is about the size of a small bus, after predicting that about half the satellite would survive its descent through the atmosphere.
It was equipped with small rocket "thrusters" loaded with toxic hydrazine fuel, which can cause coughing, irritated throat and lungs, convulsions, seizures, and long-term exposure can damage the liver, kidney and reproductive organs.
The missile attempt was approved by the US President out of concern that the toxic fuel on board could crash to Earth.
Earlier, speaking at a news conference, Chinese Foreign Ministry spokesman Liu Jianchao said China was "continuously following closely the possible harm caused by the US action to outer space security and relevant countries".
He continued: "China requests the US to fulfil its international obligations in real earnest and provide to the international community necessary information and relevant data in a timely and prompt way so that relevant countries can take precautions."
The US government organised hazardous materials teams, under the codename Burnt Frost, to be flown to the site of any dangerous or otherwise sensitive debris that might land in the United States or elsewhere.Reuse content