WASHINGTON — The U.S. Missile Defense Agency (MDA) hopes to resume flight testing late this year of the nation’s primary missile shield after a two-year hiatus following consecutive failures in early and late 2010.

The upcoming flight test of the Ground-based Midcourse Defense system is unusual in that it will not involve an attempt to intercept a target missile. Rather, it is intended to validate fixes to a key interceptor component cited in the most recent test failure, in December 2010.

The component, the Exoatmospheric Kill Vehicle (EKV) Capability Enhancement 2, is the business end of the missile shield, designed to home in on its target and destroy it via direct impact. It is an upgraded version of the EKV that tops the 20 U.S. missile interceptors deployed today at Vandenberg Air Force Base, Calif., and Fort Greely, Alaska.

The upcoming nonintercept test had been scheduled for this past spring but was postponed because of continuing technical concerns with the upgraded EKV, according to Wes Kremer, vice president of air and missile defense at Raytheon Missile Systems of Tucson, Ariz., which builds the kinetic warhead.

The guidance system problem that caused the failure and the necessary fix are well understood, Kremer said in a recent interview. “What delayed us was making the fix repeatable and producible,” he said.

The failure, Kremer said, was associated with a physics phenomenon that exists only in the space environment and previously was poorly understood. “This is not something that we would have anticipated and not something that we … could have found in ground testing and so it was the flight test that actually exposed this technical challenge and we worked through the process,” he said.

Assuming the upcoming validation test is successful, the MDA will attempt an intercept test during the first half of 2013. If that is successful, Raytheon will resume production of the upgraded EKV, which was halted in February 2011.

The Ground-based Midcourse Defense system is designed to protect U.S. territory against a missile strike by Iran and North Korea, although neither of those countries has demonstrated a missile with the necessary range to mount such an attack. The system, developed and maintained by Boeing Strategic Missile & Defense Systems of Huntsville, Ala., has not had a successful intercept test since December 2008.

According to the U.S. Government Accountability Office, the MDA has pursued a risky procurement strategy on the enhanced EKV involving concurrent development and production of the hardware. A total of 12 of the upgraded EKVs have been manufactured and delivered despite the fact that the hardware’s performance has not been verified in flight testing, the congressional watchdog agency said in a March report. The two failures, the first of which was attributed to a quality control issue, could cost the MDA more than $1.2 billion including the failure reviews, additional testing, redesigns and retrofits, the watchdog agency said.

Kremer has disputed the Government Accountability Office’s assessment, saying some level of development and production concurrency is unavoidable and even necessary to maintain the health of the missile defense industrial base. He also questioned the level of concurrency the agency has attributed to the EKV program since the hardware is not in full-rate production.

U.S. Army Lt. Gen. Patrick O’Reilly, the MDA’s outgoing director, told lawmakers in April that conducting a successful intercept test of the EKV Capability Enhancement 2 is the agency’s highest priority. In response to the findings of the review of the most recent failure, the MDA has redesigned critical components of the EKV hardware and adopted “stringent manufacturing and component test standards — standards previously not used anywhere in the U.S. aerospace industry.”

O’Reilly cited these programmatic changes as the primary reason for the delay in the Ground-based Midcourse Defense test program. “Flight testing as often as possible is our goal, but we risk further failure if we conduct [Ground-based Midcourse Defense] testing prior to verification that we resolved problems discovered in previous flight tests,” he said. “Also, conducting flight tests at a pace greater than once a year prohibits thorough analysis of pre-mission and post-mission flight test data and causes greater risk of further failure and setbacks to developing our homeland defense capability as rapidly as possible.