The test failure last month of the Bush administration's new missile defense system resulted from a "very minor" computer software glitch that can be easily corrected and will have no effect on the system's ability to defend the United States against attack, the general in charge of the Pentagon program said yesterday.
Lt. Gen. Henry "Trey" Obering III, who directs the Pentagon's Missile Defense Agency, said the flight test will be tried again in mid-February, and other tests scheduled for later this year will proceed as planned.
Last month's experiment was to have marked the first flight of the system's interceptor missile, which is designed to fly into space and release a "kill vehicle" that steers into enemy warheads. Previous flight tests had relied on a slower, less advanced interceptor.
During the Dec. 15 event, the interceptor never launched from its site at Kwajalein Atoll in the central Pacific Ocean after a target missile lifted off without incident from Kodiak Island in Alaska.
Providing the first detailed account of what went wrong, Obering told reporters that the countdown was automatically aborted when a routine system check of internal electronic signals detected a potential problem. The check showed that too many electronic messages had been missed in the signal flow between the flight computer and the unit that controls the interceptor's thrusters.
In retrospect, Obering said, designers of the interceptor had imposed too tight a limit on the number of allowable missed messages.
"It turns out we had overly constrained the system," he said.
Obering called the chances of such a glitch occurring "very rare." If it had happened during an actual crisis, with an enemy missile heading toward the United States, the system would have simply bypassed the faulty interceptor and launched another one, Obering said.
Nevertheless, to avoid a recurrence, Pentagon officials plan to raise the interceptor's tolerance level for missed messages -- something that can be done by changing one line of computer software code, Obering said.
"What we discovered was we could almost sustain twice as much -- in terms of dropout rates of the messages -- and still not affect the flight of the interceptor," the general said.
Critics in Congress, the scientific community and elsewhere have accused the Bush administration of rushing ahead with deployment of the antimissile system before testing it sufficiently under realistic conditions.
The first eight interceptors were installed last year -- six at Fort Greely, Alaska, and two at Vandenberg Air Force Base, Calif. -- with 10 more to go into silos in Alaska this year.
Obering said that if the antimissile system had been subjected to the Pentagon's "classic" development approach, the United States would still be several years away from installing interceptors. He defended the administration's effort, saying it has resulted already in some antimissile capability.
Just how much, though, remains in question.
Obering expressed confidence that the system "would work" if pressed into service against relatively simple enemy targets, meaning warheads without complex decoys or other measures for deceiving U.S. interceptors. But the Pentagon's chief weapons evaluator has yet to issue any public statement validating the system's probable effectiveness, and instead has cited the paucity of realistic flight testing.
Additionally, despite the installation of the first interceptors last autumn, Defense Secretary Donald H. Rumsfeld has delayed a decision to start operating the system full time. Pressed on when such a decision might come, Obering had no answer. "Whether or not that occurs -- and when that occurs -- is not my decision," he said.
He added that his agency had met its responsibility to field most of the system's initial components last year. Those components, which include tracking radars, communication links and control networks along with the interceptors, have been run through "shakedown" exercises in recent weeks and have been shown ready to go on alert if necessary, Obering said.
The official vagueness about when the system might begin round-the-clock operations may reflect a desire to keep the focus on further development.
Pentagon officials have argued that the fledgling system could be activated and still serve as a "test bed" for more development. But these dual missions can impose conflicting demands on military crews and facilities. In the absence of an immediate long-range missile threat to the United States, Rumsfeld has made clear his interest in giving priority to continued testing.