Theater Missile Defense:

Significant Technical Challenges Face the Airborne Laser Program

NSIAD-98-37: Published: Oct 23, 1997. Publicly Released: Oct 23, 1997.

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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.

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.

Recommendations for Executive Action

  1. Status: Closed - Implemented

    Comments: The Air Force has stated that it has demonstrated that there is a correlation between optical and non-optical turbulence data. Other involved DOD activities have agreed that such a correlation exists. The correlation was established before the program went through the June 1998 authority to proceed milestone.

    Recommendation: The Secretary of Defense should direct the Secretary of the Air Force to demonstrate as quickly as possible, but no later than the time when DOD decides whether to grant the ABL program the authority to proceed (currently scheduled for June 1998), the existence of a correlation between the optical and non-optical data. If a correlation between optical and non-optical turbulence cannot be established, the Air Force should be required to gather additional optical data to accurately predict the turbulence levels the ABL may encounter, before being given the authority to proceed with the program as planned.

    Agency Affected: Department of Defense

  2. Status: Closed - Implemented

    Comments: DOD has indicated that it is satisfied that the Air Force has established a correlation between optical and non-optical turbulence data and has completed gathering a sizable amount of additional non-optical turbulence data. The Air Force used this data to validate the appropriateness of the design specifications for atmospheric turbulence.

    Recommendation: The Secretary of Defense should direct the Secretary of the Air Force to validate the appropriateness of the design specification for turbulence based on reliable data that are either derived from a correlation between optical and non-optical data or obtained through the collection of additional optical data.

    Agency Affected: Department of Defense

 

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