Pentagon: Missile intercept test postponed

WASHINGTON (CNN) -- Inclement weather led defense officials to postpone the fifth test of the government's ground-based missile interceptor Saturday night, the Pentagon said.

"The planned intercept of a long-range ballistic missile target scheduled for tonight over the central Pacific Ocean has been postponed due to poor weather conditions at Vandenberg Air Force Base, California, and the site of the launch of the target missile for the interceptor," a Pentagon statement read. "The poor weather did not meet range safety requirements."

Officials rescheduled the test for Sunday, between 9 p.m. and 1 a.m. ET -- providing that weather conditions improve.

The Ballistic Missile Defense Organization will conduct the test, the statement said, in support of the Ground-based Midcourse Defense program, formerly known as the National Missile Defense system.

Two previous attempts to intercept an in-flight missile have failed and two have been successful.

The so-called "hit to kill" test will not involve any explosives on the "kill vehicle." Instead, the kinetic energy from one rocket hitting another will be counted on to destroy the target.

EXTRA INFORMATION How missile defense works

The test target will be launched from Vandenberg Air Force Base, home to the Air Force's 30th Space Wing, heading about 4,800 miles from the central Californian coast into the South Pacific.

Defense officials hope a ground-based interceptor missile will hit the test target some 144 miles above the earth, somewhere near the Kwajalein Islands.

The test will simulate a long-range intercontinental ballistic missile in midcourse -- in effect, "two small objects going in closing velocities of close to 15,000 miles per hour and trying to collide with one another," said Air Force Lt. Gen. Ronald Kadish, head of the missile defense program.

In a Friday news conference, Kadish insisted a test failure should not be interpreted as a failure of the entire program.

"We are learning about the system," he said. "We will make corrections as a result of any anomalies, and we continue to test to build our confidence and learn more until such time as we feel confident to do operational testing against more realistic targets and realistic scenarios."

The target area is "measured in centimeters, not meters or feet," he said. "So that's the challenge that we have tomorrow and it's the same one that we have been using since we started these Integrated Flight Test attempts." Some critics have questioned the Defense Department's classification of two previous tests as successful, citing "unrealistic condition."

If Sunday night's test proceeds as planned, the next test is expected to occur in February.