The agency made progress last year as it redesigned and tested components of the warhead, which costs $30 million apiece, "and established more stringent" requirements for parts and manufacturing, Michael Gilmore, the Pentagon's director of operational testing, said in his annual report.
Confirmation that the guidance system's flaw has been fixed would permit the first effort to intercept a test target since a failure in 2010. The $35 billion system of ground-based interceptors in Alaska and California hasn't successfully destroyed a target since 2008.
"Analysis and ground test results indicate" the causes of the December 2010 failure "have been identified and fixed, but a demonstration flight test is required" for verification, Gilmore wrote in the report sent to Congress last week.
The warhead's guidance flaw, the nature of which remains classified, caused the failure of the $300 million test in the final seconds before it was to intercept its target. The flaw hadn't been identified during ground testing, the agency said a year later.
The U.S. Government Accountability Office estimated last year that fixing the flaw and confirming it's resolved would cost more than $1.2 billion.
The "kill vehicle" made by Waltham, Massachusetts-based Raytheon is a 120-pound spacecraft about the length of a broomstick. It looks like a telescope mounted on a pack of propane cylinders. It is supposed to pick out a target amid decoys and debris and destroy it by smashing into it high speed. The warhead is launched off a missile made by Orbital Sciences Corp.
The Missile Defense Agency will seek to verify the interceptor's guidance problem has been repaired through a demonstration test in space by March, according to agency spokesman Rick Lehner.
The National Research Council said in a September report requested by Congress that the design of the ground-based missile defense system has fundamental weaknesses, including a vulnerability to counter-measures by a U.S. enemy.
Improvements in the costly system "'will take time, money and careful testing, but unless this is done" it "will not be able to work against any but the most primitive attacks," according to the Washington-based council, part of the National Academies.
Ten of the latest-model warheads already are in U.S. silos in Alaska as the key weapon in the ground-based missile defense system intended to intercept a small number of missiles if they were fired at the U.S. by North Korea or Iran.
"What is extraordinary" is that the missiles have been deployed even though they "have never successfully intercepted a test target," Kingston Reif, director of nuclear nonproliferation for the Council for a Living World, said in an e-mail. His group opposes the missile-defense system.
In January 2011, the Missile Defense Agency directed Raytheon's Tucson-based missile unit to halt final assembly of complete warheads pending resolution and verification that the guidance flaw has been fixed. Lehner said the halt will remain in place until the next scheduled intercept test is a success.
The Missile Defense Agency said without elaboration in October 2011 that the guidance system on the newest model had a fault "related to outer space-related dynamic environments."
"It was something that occurred only in space and was not identifiable during pre-flight ground testing," Lehner said.
The agency is responsible for developing, fielding and upgrading the nation's ground- and sea-based missile defense programs, working with Japan and Israel, among other nations.
Its top contractors are Boeing Co.; Lockheed Martin Corp., Raytheon, Northrop Grumman Corp.; and Dulles, Va.-based Orbital Sciences.
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