The comments by Air Force Lt. Gen. Trey Obering, the Missile Defense Agency director, come at a time when the Government Accountability Office is again raising questions about the ABL program, a multibillion-dollar effort to shoot down enemy ballistic missiles with a directed-energy laser aboard a Boeing 747. In a recent report, GAO said the program could experience a cost overrun of between $43.8 million and $231.7 million under the current contract with prime contractor Boeing.

Now well into its ninth year of development, the ABL program is focused on getting to a live test against a target missile planned for late 2008. Using a high-powered chemical laser placed on a 747-400 aircraft, the ABL is being designed to destroy ballistic missiles during their early boost phase of flight. Following a series of successful ground tests of the laser last year, Boeing will spend the next two years placing the device in the aircraft. The laser is composed of six modules, each the size of a large sport utility vehicle.

But even if the program achieves its technical goals, it may end up costing too much money to operate, according to the MDA director.

During a March 9 appearance before the House Armed Services strategic forces subcommittee, Obering said, “We may have tremendous success with airborne lasers all the way through to lethal shoot-down, but if we don't think it's an affordable capability, we won't pursue it.” Nearly a month later, he laid out the situation with ABL stating, “We may get to a point where it is very technologically achievable and it's very viable technically, but we may have trouble making it operational.”

On March 20, Obering discussed the matter further with reporters during MDA's fourth annual missile defense conference in Washington.

Explaining that agency officials do not know what ABL's operating costs may be, he then gave the following example: “Let's say we put an ABL together. We get it flying. It goes up and shoots down a boosting missile.

“But every time we come back and land we have to recalibrate and re-wicker and refine that laser. And we have to do it again and again,” he continued. “If it becomes labor-intensive like that it could not very well be made affordable or operational in that regard. So even though you may meet your technical goal, you want to make sure that you met supportability and operability goals as well.”

Exactly how the ABL will operate is an unanswered question. During a public discussion in January, ABL Program Director Air Force Col. John Daniels said it would operate similar to the Joint Surveillance Target Attack Radar System in that it will have fighter aircraft protection and will “stand off” a bit from hostile areas. “It is obviously a big airplane,” he said.

Daniels noted that when the Air Force was in charge of the program -- MDA took control in late 2001 -- the service's Air Combat Command drew up an ABL concept of operations.

“That document hasn't been updated probably as much as it could have been when we moved to the Missile Defense Agency, but under that old concept the Air Force envisioned a fleet of seven airplanes,” he said.

The idea was for those aircraft to be on a combat air patrol orbit “in some hot spot in the world,” he added.

In an Aug. 18, 2005, report, Christopher Bolkcom and Steven Hildreth of the Congressional Research Service raised questions about how much stress the ABL will place on the Air Force's already strained aerial refueling fleet.

“While based at some yet-to-be-determined U.S. base, ABLs will likely deploy to forward operating locations such as Guam, Diego Garcia, RAF Fairford England, and Elmendorf Air Force Base, AK, during crises,” the duo wrote. “Although these bases are likely closer to tomorrow's hot spots than the continental United States, they are still hours of flying time away from the Persian Gulf, the Korean peninsula, and Central Asia.”

The two analysts said the ABL fleet “will require refueling to get to the crisis theater, refueling to maintain combat air patrols in theater, and refueling to return to base.” The report notes though that “it is difficult to assess how the ABL might be employed because it is not currently clear what the ABL's capabilities will be, once fielded.”

Obering added a similar caveat when he spoke with reporters March 20. “To predict costs in a developmental area, especially missile defense, is very hard to do,” he said.

Because the ABL is a very large aircraft -- approximately 231 feet long with a a wingspan of 211 feet -- and will need a fighter escort, its use will be restricted to areas where it can be protected. In November 2004, then-ABL Program Manager Col. Ellen Pawlikowski told sister publication Inside Missile Defense the airplane would have limited use against countries with large land masses.

“You are hard-pressed to use ABL against an [intercontinental ballistic missile] launched in the middle of the European-Asian land mass,” she told IMD. “When we approach the design of the ABL and its application in the [Ballistic Missile Defense System] it is based on where can that system contribute. . . . ABL, like any other piece of BMDS, will have places it is applicable and places where it is not.”

Pawlikowski was promoted to brigadier general in June 2005.  

The most-often cited use for the ABL would be patrolling off the coast of Korea where the aircraft could target and destroy ballistic missiles launched by North Korea, if that were to happen.