WASHINGTON — After two test failures and a subsequent two-year hiatus, the United States’ primary missile defense system passed a key flight test Jan. 26 at Vandenberg Air Force Base, Calif., and is a step closer to attempting once again to intercept ballistic missiles.

The most recent test of the Ground-based Midcourse Defense system by the U.S. Missile Defense Agency focused on the Exoatmospheric Kill Vehicle (EKV) Capability Enhancement 2, a crucial component of the missile shield that has proved problematic in the past.

In December 2010, a guidance error led to the missile missing the intercept. Shortly thereafter, in February 2011, the flight test program was suspended.

In theory, the defense system is expected to protect the United States from a ballistic missile attack, particularly future threats from North Korea. When operating as expected, the kill vehicle is designed to launch, home in on its target, and then destroy an incoming warhead upon impact. The system tested Jan. 26 was an upgraded version of the Raytheon-built EKV that tops the 20 U.S. missile interceptors at Vandenberg and Fort Greely, Alaska.

But during this exercise, the system was not required to intercept a missile. Instead, it performed “a variety of pre-planned maneuvers to collect performance data in space,” according to a press release from the U.S. Defense |Department.

“Today’s test allowed us to challenge the EKV in a series of realistic outer-space environments, which gives us a broad range of data prior to moving toward an intercept scenario,” Wes Kremer, vice president of air and missile defense systems at Raytheon Missile Systems, Tucson, Ariz., said in a prepared statement.

The latest flight test cost about $170 million, said Rick Lehner, a spokesman for the Missile Defense Agency.

Lehner said the agency would study the test results and use those data to determine a date for the next step, which would likely be an intercept test.

The Ground-Based Midcourse system has not had a successful intercept test since December 2008.

Boeing Strategic Missile & Defense Systems of Huntsville, Ala., is the program’s prime contractor. Raytheon, Northrop Grumman Electronic Systems of Baltimore and Orbital Sciences Corp. of Dulles, Va., build parts of the system.

Mike Gruss is a senior staff writer for SpaceNews. He joined the publication in January 2013 to cover military space. Previously, he worked as a reporter and columnist for The Virginian-Pilot in Norfolk, Va. and The Journal Gazette in Fort Wayne, Ind. He...