The U.S. Missile Defense Agency (MDA) has attributed last December’s failed intercept test of its primary system for defending U.S. territory against missile attacks to a design flaw in the interceptor’s warhead, or kill vehicle, and said corrective actions are being implemented.

In a statement sent to selected media outlets Oct. 18, the MDA said quality control was not the issue in the test failure of the Ground-based Midcourse Defense (GMD) system. Instead, the statement said, the kill vehicle’s “guidance system had a fault related to outer space-related dynamic environments which caused it to fail” seconds before it was supposed to hit its target. 

During the test, the Raytheon-built Exoatmospheric Kill Vehicle released successfully from its booster rocket and locked onto the target warhead, but was unable to complete the intercept. The interceptor was launched from Vandenberg Air Force Base, Calif.; the target took off from the Reagan Test Center on the Kwajalein Atoll in the Pacific.

In the aftermath of the failure, the MDA halted deliveries of the kill vehicle pending the outcome of its investigation into the cause. Ground testing and modeling pointed to a design issue that only revealed itself in a space environment and not during ground testing, Richard Lehner, a spokesman for the MDA, said.

Raytheon Missile Systems of Tucson, Ariz., is making modifications to the kill vehicle design, and these changes will be verified in a flight test of the GMD scheduled for late this coming spring, the MDA said. That test will not involve an intercept; later next year the MDA will re-attempt the intercept test that failed.

Lehner said the issue identified as the culprit in the test failure is related to a new kill vehicle design and does not affect earlier-generation versions that tip the GMD interceptors already installed at Vandenberg and at Fort Greely, Alaska.

Riki Ellison, founder of the Missile Defense Advocacy Alliance in Alexandria, Va., said the failure was likely caused by vibration of the small rocket thrusters that propel and steer the kill vehicle toward its target. The problem can easily be fixed with software modifications that dampen the vibration, he said.