HONOLULU — The Navy hit a failed intelligence satellite speeding 133 miles above the Earth with a three-stage missile on the first try Wednesday, a shot the Pentagon hopes destroyed the spacecraft's fuel tank filled with 1,000 pounds of potentially toxic gas.
The missile, shot from the cruiser Lake Erie as it sat in the Pacific Ocean west of Hawaii, came just as the window for the operation opened at 7:26 p.m. Pacific time. While the Pentagon said in a statement that it would take 24 hours to be certain the fuel tank was punctured, initial indications were that it had been hit.
The Navy waited until the space shuttle Atlantis landed Wednesday morning before moving into position to fire the missile. Planners determined that the best time to attempt the shot was late afternoon local time, when the satellite would have had maximum exposure to the sun, warming it up enough for the heat-seeking "kill vehicle" atop the missile to find the cold, tumbling satellite.
The interceptor was not armed with explosives, relying on the high-speed impact to do its work.
Even if the fuel tank of the spy satellite was not destroyed, officials said, any hit would reduce the risk of danger to humans. The 5,000-pound satellite is so big that only half of it was expected to burn up on reentry. But the missile strike probably broke it up into smaller pieces that will be destroyed before entering the Earth's atmosphere.
A senior defense official reported that observers monitoring the satellite saw what appeared to be an explosion, indicating the fuel tank was hit.
In a sign of how important the military viewed the shoot-down, Defense Secretary Robert M. Gates gave the final approval to fire the Standard Missile-3. According to Pentagon Press Secretary Geoff Morrell, Gates gave the go-ahead during a conference call with military commanders while flying from Washington to Hawaii.
Although weather reports earlier in the day had warned of choppy seas, the waters had calmed by the afternoon and "the secretary was told conditions were ripe for an attempt," Morrell said. "That is when the secretary gave the go-ahead to take the shot."
Gates landed in Hawaii for an overnight stop ahead of a weeklong trip to Asia less than two hours before the missile was fired and was informed of the successful hit just minutes after it occurred.
Morrell said Gates congratulated the commanders -- Air Force Gen. Kevin P. Chilton, head of U.S. Strategic Command, and Marine Gen. James E. Cartwright, vice chairman of the Joint Chiefs of Staff -- during a conference call in Honolulu and was "obviously very pleased."
Some experts with knowledge of military satellite programs have expressed skepticism about the danger posed by the spacecraft and its hydrazine jet fuel, arguing that the Pentagon was instead seeking to prove its ability to strike down a satellite just a year after China shot down one of its own aging weather satellites.
Military officials have denied any ulterior motive, and Navy Adm. Timothy J. Keating, commander of all U.S. forces in the Pacific, told reporters here that in multiple conversations with nations in the region, he had been told of no objections to the shoot-down.
The U.S. has repeatedly protested the Chinese test, particularly Beijing's failure to notify the international community that it was attempting the strike. But Keating said he did not believe the two operations were comparable.
"There are similarities, and there are significant differences between what we're doing and what the Chinese did," Keating said. "Even after the fact, they denied it in certain quarters, and when confronted at senior military levels initially said it was a scientific experiment, [that] there was no military connection."
According to the Pentagon statement, the missile fired from the Lake Erie hit the satellite as it was traveling more than 17,000 mph. Nearly all of the debris was expected to burn up within 48 hours, with the rest reentering the atmosphere within 40 days. Keating said that hazardous-materials teams had been organized in case any dangerous debris eventually hit the Earth.
The satellite mission is a significant boost to the Navy's missile defense system. All of the ships, Aegis radars and missiles used in the shoot-down are normally assigned the task of targeting short- and medium-range enemy missiles. The software on the missiles was modified so they could find the satellite as it passed overhead.
Unlike the high-profile ground-based missile defense system, the Navy has had a strong track record of testing its system over the last eight years, hitting 12 of 14 dummy missiles.
Officials said the major difference between the satellite shoot-down and a missile defense operation was the speed and coldness of the falling satellite. The satellite was traveling nearly twice the speed of an incoming missile and, having been dormant since just days after its launch in December 2006, was frozen from months in space.
The satellite was operated by the National Reconnaissance Office, the intelligence agency responsible for the nation's spy satellites. Officials would not comment on the satellite's mission.
The Navy had been prepared to take a shot at the satellite every day during the same two-hour afternoon window for much of the next week, and it had prepared three separate missiles -- each costing $10 million -- for the operation in case the first shot missed or malfunctioned.
The remaining two missiles will now have their software reconfigured so they can be used in their normal missile defense mission.
The destroyers Decatur and Russell were also on scene in case the Lake Erie's missiles missed or misfired.