Air Force General Richard Myers, chairman of the Joint Chiefs of Staff, said Monday's failure was not due to anything wrong with the interceptor missile, which is intended to shoot down an incoming enemy missile before it reaches its target. Myers blamed hardware in the silo that did not move out of the way so the missile could launch from the central Pacific test site. "That'll have to be corrected," Myers told the Senate Armed Services Committee.
The system has experienced failures in five of its 10 major tests, and this week's test was actually a repeat of a failed December test that the Pentagon blamed on a "very minor software glitch." The previous test two years earlier also failed.
Rick Lehner, a spokesman for the Pentagon's Missile Defence Agency, said Myers was referring to lateral supports that hold a missile in place within the silo, mainly as seismic protection.
But Lehner said the investigation into the test failure has not been completed, and that the explanation offered by Myers was merely "one of the things we're focusing on."
"It's certainly not the final results of the investigation because there may be some other things that may have led to that," Lehner said.
The system, designed with potential enemies like North Korea in mind, is based on the concept of using one missile to bring down another after a network of radars detects an enemy ballistic missile launch.
At the Senate hearing, Democratic Sen. Hillary Rodham Clinton of New York told Rumsfeld it was important to have operationally realistic tests that demonstrate whether the system works.
Rumsfeld said the last two test failures "have clearly thus far inhibited us from conducting a system test for all its capabilities."
"The failure did not, according to people in the activity, undermine their confidence in the technology or the ability to integrate the geographically dispersed elements of the components," Rumsfeld said of this week's test.
"And we remain committed to produce and deploy a missile defence capability. And the program director has assured us that the key aspects of the program are on track," Rumsfeld added.
Supporters of the system have argued that deploying the system may deter adversaries from staging an attack.
Clinton told Rumsfeld, "It strikes me a little odd that we would deploy a system that hasn't succeeded and expect that to serve a deterrent value."
Rumsfeld responded, "I agree with that point, that there's no deterrent if something is known to not work."