Using radar, data from sensors and other technology, officials were studying smaller-than-expected pieces of the spacecraft that was hit Wednesday by an interceptor missile launched from a Navy cruiser in the Pacific, said Marine Gen. James Cartwright, vice chairman of the Joint Chiefs of Staff.
The main question was whether the high-speed collision of the missile and satellite had destroyed the satellite's hydrazine fuel tank and vented its toxic gas into space. Officials had said avoiding human exposure to the toxin was the primary reason for destroying the spacecraft, which lost power shortly after it reached orbit in late 2006 and was out of control and slowly descending toward Earth.
Cartwright said officials had a "high degree of confidence" that the tank had been destroyed, but would need a day or two to study debris before knowing for sure.
"We have a bunch of techies that are trying to work their way through the data," he told a Pentagon news conference.
"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 said.
Debris from the satellite had started re-entry over the Atlantic and Pacific oceans and re-entry was expected to continue into Friday, Cartwright said. He gave no further details about where the military had tracked fields of fragments from the satellite, which was described as the size of a school bus and weighing about 5,000 pounds. Amateur observers on Canada's west coast reported see seeing some two dozen trails of debris in the sky within minutes of the missile hit, while they were watching a lunar eclipse late Wednesday.
The military was counting the pieces of debris caused by the satellite shootdown, which was an unprecedented use of components of the Pentagon's missile defense system, but believed they were smaller than the Pentagon had forecast and that most of the satellite's intelligence value was likely destroyed, Cartwright said. Though pieces had been detected in the atmosphere, there were no reports any had survived the fiery heat of re-entry and hit Earth, he said, indicating he didn't think the debris would pose a problem.
"Thus far we've seen nothing larger than a football," Cartwright said.
Private defense analysts said they didn't expect many, if any, pieces of the debris to turn up.
"I wouldn't want to get hit by one, but the chances are pretty small," analyst John Pike said.
That point also was made last week by critics who said the shootdown was unnecessary because parts of rockets or satellites regularly fall from space, but usually burn up on re-entering the atmosphere. When they don't, they rarely fall where they do any harm.
Even before the missile launch, some international leaders and critics in the scientific community suggested it was a thinly disguised attempt to test an anti-satellite weapon
-- one that could take out other nations' orbiting communications and spy spacecraft.
They also said the U.S. was worried that allowing the errant satellite to fall itself would mean larger pieces might survive re-entry, opening the possibility that secret technology could wind up in the hands of the Chinese or others.
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Within hours of the reported hit, China said it was on the alert for possible harmful fallout from the shootdown and urged Washington to promptly release data on it.
"China is continuously following closely the possible harm caused by the U.S. action to outer space security and relevant countries," Foreign Ministry spokesman Liu Jianchao said at news conference in Beijing. "China requests the U.S. to fulfill 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."
Defense Secretary Robert Gates said the U.S. would share information.
"We provided a lot of information ... before it took place," Gates told reporters traveling with him Hawaii. But he also said that he's determined to be open about the U.S. operation and "we are prepared to share whatever appropriately we can."
Cartwright estimated there was an 80 percent to 90 percent chance that the missile struck the fuel tank, containing 1,000 pounds of hydrazine. He showed a video clip of the missile smashing into the satellite and producing a flash of light.
"We have a fireball, and given that there's no fuel (on the tip of the missile), that would indicate that that's a hydrazine fire," he said.
The video showed the three-stage SM-3 missile launching from the USS Lake Erie at 10:26 p.m. EST Wednesday northwest of Hawaii, and of the missile's small "kill vehicle"
-- a non-explosive device at the tip -- maneuvering into the path of the satellite and colliding spectacularly.
Cartwright said the satellite and the kill vehicle collided at a combined speed of 22,000 mph about 130 miles above Earth's surface, and that the collision was confirmed at a space operations center at 10:50 p.m. EST.
The satellite was described as the size of a school bus and weighing about 5,000 pounds.
On the Net:
Defense Department: http://www.defenselink.mil/
Press; By PAULINE JELINEK]
AP Military Writer Robert Burns contributed to this report from Washington.
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