WASHINGTON — The Pentagon’s Airborne Laser (ABL) is being prepared for a late July test in which it will attempt to shoot down an ascending target missile from twice the distance of the aircraft’s previous intercept tests, the program’s top official said.

Originally conceived as an operational military system that would use a high-power chemical laser to destroy ballistic missiles in the early stages of flight, the ABL platform — only one has been built — has been relegated to the role of technology test-bed. The program is funded by the U.S. Missile Defense Agency (MDA) through September, but its future is uncertain beyond that.

Boeing Defense, Space & Security of St Louis is the ABL 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.

The modified Boeing 747-400 aircraft made its long-awaited debut in February. In one test flight, the ABL fired on and destroyed a boosting sounding rocket known as a MARTI. Eight days later, the aircraft succeeded in its first attempt to shoot down a threat-representative, liquid-fueled target missile. During the same flight test, it fired on a second liquid-fueled missile, but a problem caused the weapon system to shut itself down before the target was destroyed. The MDA will not reveal the aircraft’s distance from its target in any of those tests.

The most important lessons from the ABL’s first intercept tests were that it actually worked, and it was more efficient and lethal than expected, said U.S. Air Force Col. Robert McMurry, the MDA’s ABL program manager.

“What I think it’s proven is the beam control system and the atmospheric compensation and the power out of the laser are all working extraordinarily well to put power on target,” McMurry said in a June 16 interview.

The government-industry ABL team believes it has identified the cause of the anomaly that caused the automatic laser shutdown that occurred during the second February flight test, McMurry said. Some of the high-power laser’s hydrogen peroxide fuel is thought to have breached the lasing cavity, causing some of the beam’s energy to be deflected in another direction. When the system senses that not all of the energy is being directed through its aperture, it shuts itself down in about 25 milliseconds, McMurry said.

The ABL has flown several times since the February tests. On May 3, the aircraft conducted a simulated intercept test against a MARTI sounding rocket from twice the distance of the previous intercept tests, McMurry said. The ABL fired its high-power laser at an instrument board on a hardened section of the rocket body, which showed that the laser was delivering a beam accurate and powerful enough power to destroy the target.

There was no internal pressure on the part of the rocket body that was hit with the beam, “and because of that it didn’t create a lethal effect,” McMurry said. “If you fired at the engines where you have that pressure differential, that’s part of what helps destroy it.”

During that test, a piece of contaminant the size of a fingernail fell into the beam and then melted onto one of the optics. The optic was replaced, and engineers at the Air Force Research Laboratory are working to repair the damaged hardware. Other than that, the ABL has needed very few repairs, McMurry said. The aircraft is essentially ready to make its next intercept test and is waiting on range assets currently being used for another MDA test, he said.

In February, the Defense Department announced that ABL would be relegated to a research and development test-bed and transferred from MDA to the research-and-development arm within the office of the undersecretary of defense for acquisition, technology and logistics. The MDA eliminated ABL’s dedicated funding line but created a new line for directed energy programs, for which it requested $99 million for 2011.

The Pentagon is expected to complete a study this month on its entire portfolio of directed energy programs, which will likely determine ABL’s future role.