No capability currently exists to destroy missiles in the boost phase. During that interval, the ABL is expected to detect, track, and destroy the missile, as shown in figure 1. ABL’s Operational Effectiveness Is Currently Unknown

A key factor in determining whether the ABL will be able to successfully destroy a missile in its boost phase is the Air Force’s ability to predict the levels of turbulence that the ABL is expected to encounter. To date, the Air Force has not shown that it can accurately predict the levels of turbulence the ABL is expected to encounter or that its technical requirements regarding turbulence is appropriate. Optical turbulence can be measured either optically on non-optically. The Air Force’s ABL program office has not determined whether non-optical measurements of turbulence can be mathematically correlated with optical measurements. Without demonstrating that such a correlation exists, the program office cannot ensure that the non-optical measurements of turbulence that it is collecting are useful in predicting the turbulence likely to be encountered by the ABL’s laser beam. Technical Requirements for Overcoming Turbulence May Be Understated

The ABL program office also has not shown that the turbulence levels in which the ABL is being designed to operate are realistic. Available optical data on optical turbulence indicate that the turbulence the ABL may encounter could be four times greater than the design specifications. These higher levels of optical turbulence would decrease the effective range of the ABL system. DOD officials also indicated that a more realistic design may not be achievable using current state-of-the-art technology. Developing and Integrating ABL Components Pose Many Technical Challenges

Developing and integrating a weapon-level laser, a beam control system, and the many associated components and software systems into an aircraft are unprecedented challenges for DOD. The Air Force must build the laser to be able to contend with size and weight restrictions, motion and vibrations, and other factors unique to an aircraft environment, yet be powerful enough to sustain a killing force over a range of at least  500 kilometers. Integrating the beam control system with the aircraft also poses a challenge for the Air Force. The Air Force must create a beam control system, consisting of complex software programs, moving telescopes, and sophisticated mirrors, that will compensate for the optical turbulence in which the system is operating and control the direction and size of the laser beam. In addition, the beam control system must be able to tolerate the various kinds of motions and vibrations that will be encountered in an aircraft environment. Conclusions and Recommendations

The ABL program is a revolutionary weapon system concept. Although DOD has a long history with laser technologies, the ABL is its first attempt to design, develop, and install a multimegawatt laser on an aircraft. A fundamental challenge is for the Air Force to accurately and reliably predict the level of optical turbulence that the ABL will encounter and then design the system to operate effectively in that turbulence.
Why GAO Did This Study

Pursuant to a congressional request, GAO reviewed the status of the Airborne Laser (ABL) program, focusing on: (1) the way in which the ABL is expected to change theater missile defense; (2) assurances that the ABL will be able to operate effectively in the levels of optical turbulence that may be encountered in the geographical areas in which the system might be used; and (3) the technical challenges in developing an ABL system that will be compatible with the unique environment of an aircraft.

What GAO Found

GAO noted that: (1) the ABL program is the Department of Defense's (DOD) first attempt to design, develop, and install a multimegawatt laser on an aircraft and is expected to be DOD's first system to intercept missiles during the boost phase; (2) a key factor in determining whether the ABL will be able to successfully destroy a missile in its boost phase is the Air Force's ability to predict the levels of turbulence that the ABL is expected to encounter; (3) the Air Force has not shown that it can accurately predict the levels of turbulence the ABL is expected to encounter or that its technical requirements regarding turbulence are appropriate; (4) because ABL is an optical weapons system, only optical measurements can measure the turbulence that will actually be encountered by the ABL laser beam; (5) the Air Force has no plans to take additional optical measurements and instead plans to take additional non-optical measurements to predict the severity of optical turbulence the ABL will encounter; (6) to ensure that the non-optical measurements can be validly applied to the ABL program, the Air Force must determine whether the non-optical measurements can be correlated to optical measurements; (7) until the Air Force can verify that its predicted levels of optical turbulence are valid, it will not be able to validate the ABL's design specifications for overcoming turbulence; (8) the Air Force has established a design specification for the ABL that is based on modelling techniques; (9) data collected by the program office indicate that the levels of turbulence that ABL may encounter could be four times greater than the levels in which the system is being designed to operate; (10) DOD officials indicated that a more realistic design may not be achievable using a current state-of-the-art technology; (11) in addition to the challenges posed by turbulence, developing and integrating a laser weapon system into an aircraft pose many technical challenges for the Air Force; (12) the Air Force must build a new laser that is able to contend with size and weight restriction, motion and vibrations, and other factors unique to an aircraft environment and yet be powerful enough to sustain a killing force over a range of at least 500 kilometers; (13) the Air Force must create a beam control system that must compensate for the optical turbulence in which the system is operating and control the direction and size of the laser beam; and (14) because these challenges will not be resolved for several years, it is too early to accurately predict whether the ABL program will evolve into a viable missile defense system.