WASHINGTON — The U.S. Missile Defense Agency believes it has identified the problem behind the third consecutive intercept failure involving its primary U.S. missile shield and hopes to apply a fix to the interceptors currently deployed in California and Alaska before the end of the year, the agency’s director told lawmakers June 11.

Testifying before the Senate Appropriations defense subcommittee, Navy Vice Adm. James Syring did not identify the root cause of the July 2013 failure. During the test, the interceptor’s kinetic warhead, or Exoatmospheric Kill Vehicle (EKV), failed to separate from its booster rocket.

The EKV used in that test was an older variant known as Capability Enhancement 1, which is installed aboard Ground-based Midcourse Defense interceptors at Vandenberg Air Force Base, California, and Fort Greely, Alaska. The previous failure, which occurred in December 2010, involved a newer EKV variant known as Capability Enhancement 2.

Syring said he was confident that the MDA had fixed the problem that marred the December 2010 test — there were two failures that year — and that he looks forward to a repeat of that exercise, dubbed FTG-6b, in June. An MDA fact sheet attributed that failure to an error with the EKV’s guidance sensor in the last few seconds of flight.

“I’m also optimistic we have identified the cause of the intercept failure involving our first-generation EKV last July when the CE-1 failed to separate from the booster’s third stage,” Syring said. “We have accounted for this issue in the upcoming flight test and we are working toward a correction for the entire fleet before the end of the year.”

The first of the three consecutive intercept failures involving the Ground-based Midcourse Defense system occurred in January 2010. Syring did not address that incident during the hearing, but an MDA fact sheet cites “kill vehicle and system sensor performance issues” as the cause. Immediately after that failure occurred, the MDA noted in a press release that the agency’s Sea-based X-band Radar failed during the test.

Sen. Lisa Murkowski (R-Alaska) said the FTG-6b test would be conducted June 22 at Kwajalein Atoll in the Pacific. The interceptor would launch from Vandenberg, Syring said.

Sen. Richard Durbin (D-Ill.), a missile defense skeptic, noted the EKV’s poor track record in recent testing and asked Syring how the MDA would respond to another failure in the upcoming test.

Syring responded that a failure with the kill vehicle would allow the MDA to recoup contractor award fees.

Both variants of the EKV are built by Raytheon Missile Systems of Tucson, Arizona, while the interceptor booster is built by Orbital Sciences Corp. of Dulles, Virginia. Boeing Defense, Space & Security of St. Louis is overall prime contractor for the Ground-based Midcourse Defense system.

Also at the hearing, Syring said he was following a “very aggressive schedule” for the award of a long-range discrimination radar contract later this year.

The radar is part of Syring’s effort to “dramatically improve” the nation’s primary territorial shield, whose inability to reliably distinguish between incoming warheads and decoys has long been identified as a major weakness. MDA requested $79 million for the radar in the 2015 budget, including $50 million for research and development of the radar itself. MDA officials hope to have the radar operational in Alaska by 2020.

Murkowski said during the hearing she was disappointed by the recommendation in a House spending bill that trims $20 million from a $38.7 million MDA request for facilities construction, a portion of which was assigned to the discrimination radar program.

At an event here June 9, Jim Sheridan, director of Aegis Navy Programs for Lockheed Martin Mission Systems and Training of Moorestown, New Jersey, said the company would be interested in building the radar.

Raytheon Co. of Waltham, Massachusetts, a key supplier of missile defense radars, is among the companies that planned to respond to the request for information on the discrimination radar issued by the MDA March 14. Northrop Grumman Electronic Systems of Linthicum, Maryland, is also interested in the request and is evaluating its response.

Mike Gruss covers military space issues, including the U.S. Air Force and Missile Defense Agency, for SpaceNews. He is a graduate of Miami University in Oxford, Ohio.