A ballistic missile defense test off the Pacific Missile Range Facility on Kaua'i — which had been scheduled for yesterday afternoon — has been put off for a day, apparently because there was a vessel in the range safety area.

The test, which is designated Flight Test Mission-12, has been rescheduled for today.

"While conducting range safety surveillance, PMRF officials determined the range was not clear. For safety reasons, the test was postponed," the Missile Defense Agency said in a statement.

The Missile Defense Agency operates a series of different ballistic missile defense programs. The one being tested today involves the Aegis system, which is fitted aboard Navy ships. Previous tests have involved Navy cruisers, but today's test is the first to involve an Aegis-equipped Navy destroyer.

The scheduled test calls for a target missile to be fired from the missile range on the Mana plain of west Kaua'i. It is a medium-range target with a separating warhead.

Three ships at sea and two satellites are to track the missile. The destroyer USS Decatur is scheduled to launch an interceptor, a Standard Missile-3.

In addition to testing the ability of the interceptor to crash into the target in flight, the schedule includes data collection aboard other military vessels, and data interchange between the Navy's Aegis ballistic missile defense system and another U.S. ballistic missile defense program, the Army's THAAD, for Theater High Altitude Area Defense. The test will also involve tracking and communication by a Spanish navy frigate, the Mendez Nunez, which has a modified Aegis missile defense system.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.