A missile fired by the Japanese destroyer Chokai yesterday failed to intercept a ballistic missile target off Kaua'i in a second test of Japan's ship-based Aegis ballistic missile defense system.

The $55 million exercise paid for by Japan was intended to knock down a simulated ballistic missile in which the warhead separated from the booster.

But Rear Adm. Brad Hicks, the Aegis system program manager for the U.S. Missile Defense Agency, said an "anomaly" occurred in the fourth stage of flight by the Standard Missile-3 Block 1A seeker missile.

A kinetic warhead released by the missile found and tracked the simulated ballistic missile, but in the last few seconds it "lost track" of the target, Hicks said.

"The missile, until the very end of flight, had excellent performance," Hicks said.

Hicks said an investigation will determine "if it was just that individual missile, or something that we need to take a look at."

The Aegis ballistic missile defense system has been successful in 16 of 20 attempts.

Hicks said the same type of missile, fired by the Pearl Harbor cruiser Lake Erie, was used to successfully shoot down a failing U.S. spy satellite in February.

"This system works," said Hicks, adding the success rate is good compared to other U.S. missiles.

On Dec. 17 off Kaua'i, the Japanese destroyer Kongo shot down a ballistic missile target, marking the first time that an allied naval ship successfully intercepted a target with the sea-based Aegis weapons system.

That target was a nonseparating simulated ballistic missile. Officials said yesterday's target separated from a booster, making it harder to discriminate.

At 4:21 p.m., the ballistic missile target was launched from the Pacific Missile Range Facility. The Japanese destroyer Chokai detected and tracked the target using an advanced on-board radar, according to the Missile Defense Agency.

The Pearl Harbor-based destroyer Paul Hamilton also participated in the test.

The Aegis Weapon System developed a fire-control solution, and at 4:24 p.m., a single SM-3 Block IA was launched. The Chokai was about 250 miles off Barking Sands in Kaua'i, and the intercept was to occur about 100 nautical miles above earth in the mid-course phase of the ballistic missile's trajectory.

Approximately two minutes later, the SM-3 failed to intercept the target. The Chokai crew performance was "excellent" in executing the mission, according to the Missile Defense Agency.

The Japanese ship will stop in Pearl Harbor before returning to Japan with additional SM-3 Block 1A missiles.

Hicks said Aegis ballistic missile defense is a certified and deployed system in the U.S. Navy, and certified and operational in Japan's navy.

Eighteen U.S. cruisers and destroyers and four Japanese ships are being outfitted with the Aegis ballistic missile defense capability.

On Nov. 1, during the exercise "Pacific Blitz," the Hawai'i-based destroyers Hamilton and Hopper fired SM-3 missiles at separate targets launched from Kaua'i.

Hamilton scored a direct hit, while the missile fired by the Hopper missed its target, the Navy said.

Hicks yesterday said the missiles fired from the ships were older rounds going out of service, and the Navy took the opportunity to use them as training rounds "knowing that they carried a higher probability of failure."