The operation marked the first time that the Aegis system, designed to intercept missiles, was used to strike a satellite. Such spacecraft always have a limited life span, but in most cases can be guided toward oceans -- and away from population centers -- as they plummet back to Earth.
Defense Secretary Robert M. Gates, who was on a flight from Washington to Hawaii when he gave the order for the missile shot, said afterward that the exercise showed the system had worked.
"I think the operation speaks for itself in that respect," Gates told reporters after touring a warship that served as a backup vessel Wednesday.
At the same time, Gates said the missile defense system had proved itself in past tests and needed only to be improved for larger and more sophisticated threats.
The unusual nature of the operation had prompted speculation that the United States was using the failed spacecraft as an excuse for testing a system ordinarily designed for missile defense, or demonstrating its capabilities to other countries.
Cartwright dismissed those suggestions, saying that the modifications necessary to target the satellite made the operation of little use as a test for hitting a missile. He also said that there was no need for such tests because the capabilities of the SM-3 missile had been demonstrated during exercises in the 1980s.
Even so, military experts said the operation was likely to rattle China and other countries, and showed the significant capabilities of America's sea-based defense system.
John Pike, who tracks weapons systems at GlobalSecurity.org, said the strike showed a capability that could be used to thwart ballistic-missile-carrying subs deployed by China.
He also said the success of the operation would strengthen the case that the sea-based system operated by the Navy should play a greater role in overall missile defense strategy. "It does suggest that the demands on the land-based systems could be reduced by putting this layer in first," Pike said.
Much of the missile defense effort in recent years has centered on the development of more expensive -- and, so far, less reliable -- land-based systems in Central California and Alaska.
Those systems are designed to intercept intercontinental ballistic missiles aimed at the U.S. mainland, while the Navy's Aegis system is designed for shorter-range threats, such as a possible missile strike by North Korea against Japan.
