HUNTSVILLE, Ala. — The U.S. Missile Defense Agency (MDA)’s planned Aug. 17 flight test of the Airborne Laser system was postponed when one of its cooling systems failed in preparation for the test, the agency’s top official said Aug. 18.

The Airborne Laser, a modified 747 aircraft designed to zap ballistic missiles with a high-power laser, was being prepared for its third intercept test at Edwards Air Force Base, Calif. A commercial-off-the-shelf cooling system for the aircraft’s tracking laser failed, and its replacement is now being installed, Army Lt. Gen. Patrick O’Reilly, the MDA’s director, told reporters at the Space and Missile Defense conference here. The agency is targeting Aug. 21 for the next attempt, he said.

The Airborne Laser was originally conceived to be an operational system for boost-phase missile defense, but has since been relegated to a technology development platform. In its first shoot-down test in February, the aircraft destroyed a boosting sounding rocket. Eight days later, it returned to the sky and destroyed its first threat-representative target missile but was then unable to destroy a second target.

For the upcoming flight test, the Airborne Laser will attempt to destroy a target missile from twice the distance of previous tests, MDA officials have said. The MDA does not disclose actual standoff distances for the flight tests.

Boeing Defense, Space & Security of St. Louis is the Airborne Laser prime contractor; Northrop Grumman Aerospace Systems of Los Angeles developed the high-power chemical laser; and Lockheed Martin developed the beam control/fire control system.