The satellite, the size of a small bus, was speeding through space at 18,000 mph, about twice as fast as the test missiles previously targeted. "It's moving at roughly 300 miles a minute, and so you need to know where it's going to hit. And if you're off by just a minute on that, that's 300 miles off," said Ivan Oelrich, vice president for strategic security programs at the Federation of American Scientists.
Nor was the 40-pound missile equipped with explosives - it was to rely on its own kinetic energy to smash the 5,000-pound satellite to bits, experts say.
Had the Navy missed, it could have proved a highly visible failure for the Defense Department's $1 billion-a-year Aegis Ballistic Missile Defense System.
Then there are international politics. Some experts say the move is a U.S. attempt to counter actions by the Chinese last year. China blasted one of its own weather satellites on Jan. 11, 2007, prompting criticism that it had created thousands of new shards of hazardous space debris and escalated international tensions about conflicts in space.
The U.S. effort is not expected to create as much space debris because the point of impact is closer to Earth. But it might still spark international tensions, experts say. "It takes us further along that road of weapons in space and war in space," McDowell said.
Chinese and Russian officials recently proposed a ban on anti-satellite missile testing in space. The Bush administration has rejected the proposal as unverifiable.
"Yet again, we have a superpower testing what the world will perceive is a space weapon," said Phil Smith, assistant director of the Secure World Foundation, a nonprofit group organized to promote peace in space.
Others, too, are suspicious of the Pentagon's motives. "So far, in the entire history of the Space Age, no manmade object has badly injured anyone," said Michael Krepon, director of the Space Security Project at the Henry L. Stimson Center in Washington.
The Pentagon has never provided estimates on the risk attached to the demise of the satellite. But Krepon said other experts have put the risk that a single human being would be injured by the satellite at between 1 percent and 3.5 percent - not worth the "extreme measures" being undertaken.
Krepon offered two other explanations that he considers more plausible. The first is the protection of "state secrets" - a fear that key components of the satellite could fall into Russian or Chinese hands and divulge something about our spy technology.
