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Theater Missile Defense: Significant Technical Challenges Face the Airborne Laser Program (Letter Report, 10/23/97, GAO/NSIAD-98-37).

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.

--------------------------- Indexing Terms -----------------------------

 REPORTNUM:  NSIAD-98-37
     TITLE:  Theater Missile Defense: Significant Technical Challenges 
             Face the Airborne Laser Program
      DATE:  10/23/97
   SUBJECT:  Air defense systems
             Advanced weapons systems
             Military aircraft
             Weapons research
             Ballistic missiles
             Specifications
IDENTIFIER:  Boeing 747-400 Aircraft
             Chemical Oxygen Iodine Laser
             Airborne Laser
             
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Cover
================================================================ COVER

Report to the Ranking Minority Member, Committee on National
Security, House of Representatives

October 1997

THEATER MISSILE DEFENSE -
SIGNIFICANT TECHNICAL CHALLENGES
FACE THE AIRBORNE LASER PROGRAM

GAO/NSIAD-98-37

Theater Missile Defense

(707210)


Abbreviations
=============================================================== ABBREV

  ABL - Airborne Laser
  ABLEACE - Airborne Laser Extended Atmospheric Characterization
     Experiment
  COIL - Chemical Oxygen Iodine Laser
  DOD - Department of Defense
  OSD - Office of the Secretary of Defense

Letter
=============================================================== LETTER


B-275849

October 23, 1997

The Honorable Ronald V.  Dellums
Ranking Minority Member
Committee on National Security
House of Representatives

Dear Mr.  Dellums: 

As you requested, this report discusses our review of the status of
the Airborne Laser (ABL) program.  The Department of Defense (DOD)
plans to develop the ABL as its primary program for intercepting
theater ballistic missiles shortly after they have been
launched--also known as the boost phase.  The Air Force estimates the
life-cycle cost of the ABL program to be about $11 billion.  That
estimate includes $1.3 billion for the program definition and risk
reduction phase, $1.2 billion for the engineering and manufacturing
development phase, $3.8 billion for the production phase, and $4.9
billion for 20 years of operations and support. 

This report discusses (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. 


   BACKGROUND
------------------------------------------------------------ Letter :1

Operation Desert Storm demonstrated that the U.S.  military and other
allied forces have limited capability against theater ballistic
missiles.  In fact, U.S.  defensive capability is limited to weapons
that defend against missiles nearing the end of their flight, such as
the Patriot.  No capability currently exists to destroy missiles in
the boost phase.  Consequently, DOD is expending considerable
resources to develop the ABL's capability to intercept missiles in
their boost phase.  In simple terms, the ABL program will involve
placing various components, including a powerful multimegawatt laser,
a beam control system, and related equipment, in a Boeing 747-400
aircraft and ensuring that all the components work together to detect
and destroy enemy missiles in their boost phase. 

In November 1996, the Air Force awarded a 77-month program definition
and risk reduction contract to the team of Boeing, TRW, and Lockheed
Martin.  Under the contract, Boeing is to produce and modify the
747-400 aircraft and integrate the laser and the beam control system
with the aircraft, TRW will develop the multimegawatt Chemical Oxygen
Iodine Laser (COIL) and ground support systems, and Lockheed Martin
will develop the beam control system. 

The various program components are in the early phases of design and
testing.  One prototype ABL will be produced and used in 2002 to
shoot down a missile in its boost phase.  If this demonstration is
successful, the program will move into the engineering and
manufacturing development phase in 2003.  Production is scheduled to
begin about 2005.  Initial operational capability of three ABLs is
scheduled for 2006; full operational capability of seven ABLs is
scheduled for 2008. 


   RESULTS IN BRIEF
------------------------------------------------------------ Letter :2

Although DOD has a long history with laser technologies, the ABL
program is its first attempt to design, develop, and install a
multimegawatt laser on an aircraft.  The ABL is also expected to be
DOD's first system to intercept missiles during the boost phase.  To
successfully destroy a missile in its boost phase, the ABL system
would have to, within about 30 to 140 seconds, detect a missile
shortly after it has been launched several hundred kilometers away,
track the rising missile's path, and hold a concentrated laser beam
on the missile until the beam's heat causes the missile's pressurized
casing to fracture and then explode.  This explosion would then cause
a missile's warhead, along with any nuclear, chemical, or biological
agents it may contain, to fall short of the intended target and
possibly back on the aggressor's territory. 

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.  An accurate prediction of those turbulence levels is
needed to define the ABL's technical requirements for turbulence.  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 are appropriate. 

The turbulence that the ABL will encounter is referred to as optical
turbulence.  This type of turbulence can be measured either optically
or non-optically.  Optical measurements are taken by transmitting
laser beams from one aircraft to instruments on board another
aircraft at various altitudes and distances.  Non-optical
measurements of turbulence are taken by radar or by temperature
probes mounted on balloons or on an aircraft's exterior.  The Air
Force has taken both optical and non-optical measurements for the ABL
program.  However, because the ABL is an optical weapon system, only
optical measurements of turbulence can measure the turbulence that
will actually be encountered by the ABL laser beam along its path. 
The Air Force has no plans to take additional optical measurements. 
Instead, it plans to take additional non-optical measurements to
predict the severity of optical turbulence the ABL will encounter. 
Therefore, 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. 
A senior-level ABL oversight team has expressed concern about the
absence of such a correlation.  In response, the Air Force has
indicated that it plans to determine, in late 1997, whether a
correlation exists between optical and non-optical measurements. 

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 specification for overcoming turbulence.  The Air Force has
established a design specification for the ABL that is based on Air
Force modeling techniques.  However, data collected by the program
office indicate that the levels of turbulence the ABL may encounter
could be four times greater than the levels in which the system is
being designed to operate.  According to DOD officials, if the higher
levels of optical turbulence are encountered, the effective range of
the ABL system would decrease, and the risk that the ABL system would
be underdesigned for its intended mission would increase.  DOD
officials also indicated that a more realistic design may not be
achievable using current state-of-the-art technology. 

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.  The Air Force must build a
new laser that is able to contend with size and weight restrictions,
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.  Also, 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.  The beam control system will consist of
complex software programs, moving telescopes, and sophisticated
mirrors.  To date, the Air Force has not demonstrated how well a beam
control system of such complexity can operate on an aircraft. 
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. 


   THE ABL IS A NEW WEAPON CONCEPT
------------------------------------------------------------ Letter :3

The ABL is a complex laser weapon system that is expected to detect
an enemy missile shortly after its launch, track the missile's path,
and destroy the missile by holding a concentrated laser beam on it
until the beam's heat causes the pressurized missile casing to crack,
in turn causing the missile to explode and the warhead to fall to
earth well short of its intended target. 

The ABL's opportunity to shoot down a missile lasts only from the
time the missile has cleared the cloud tops until its booster burns
out.\1 That interval can range from 30 to 140 seconds, depending on
missile type.  During that interval, the ABL is expected to detect,
track, and destroy the missile, as shown in figure 1. 

   Figure 1:  ABL Missile
   Engagement

   (See figure in printed
   edition.)

The first step--detection--is to begin when the ABL's infrared search
sensor detects a burst of heat that could be fire from a missile's
booster.\2 Because clouds block the view of the infrared search
sensor, the sensor cannot detect this burst of heat until the missile
has broken through the cloud tops--assumed to be at about 38,500
feet.  The sensor detects the heat burst about 2 seconds after the
missile has cleared the cloud tops.  (In the absence of clouds,
detection can occur earlier.) The ABL would then use information from
the sensor to verify that the heat burst is the plume of a missile in
its boost phase and would then move the telescope located in the nose
of the aircraft toward the coordinates identified by the infrared
sensor. 

The second step--tracking--is to be performed sequentially and with
increasing precision by several ABL devices.  The first of these
tracking devices, the acquisition sensor, is to take control of the
telescope, center the plume in the telescope's field of view, and
hand off that information to the next device, the plume tracker. 

The plume tracker, having taken control of the telescope, is to track
and determine the shape of the missile plume and use this information
to estimate the location of the missile's body and project a beam
from the track illuminator laser to light up the nose cone of the
missile.  The plume tracker is then to hand its information, and
control of the telescope, to the final tracking device, the fine
tracker. 

The fine tracker is to measure the effects of turbulence and
determine the aimpoint for the beacon laser and, ultimately, for the
COIL laser.  The reflected light from the illuminator laser provides
information that is to be used to operate a sophisticated mirror
system (known as a fast-steering mirror) that helps to compensate for
optical turbulence by stabilizing the COIL beam on the target.  The
reflected light from the beacon laser provides information that is to
be used to operate deformable mirrors that will further compensate
for turbulence by shaping the COIL beam.\3 With the illuminator and
beacon lasers still operating, the fine tracker is to determine the
aimpoint for the COIL laser.  The COIL laser is to be brought to full
power and focused on the aimpoint. 

At this point, the final step in the sequence--missile
destruction--is to begin.  During this final step, a lethal laser
beam is held on the missile.  The length of time that the beam must
dwell on the missile will depend on turbulence levels and the missile
type, hardness, range, and altitude.  Throughout the lethal dwell,
the illuminator and beacon lasers are to continue to operate,
providing the information to operate the fast-steering and deformable
mirrors.  Under the intense heat of the laser beam, which is focused
on an area about the size of a basketball, the missile's pressurized
casing fractures, and then explodes, destroying the missile. 

The ABL is expected to operate from a central base in the United
States and be available to be deployed worldwide.  The program calls
for a seven-aircraft fleet, with five aircraft to be available for
operational duty at any given time.  The other two aircraft are to be
undergoing modifications or down for maintenance or repair.  When the
ABLs are deployed, two aircraft are to fly, in figure-eight patterns,
above the clouds at about 40,000 feet.  Through in-flight refueling, 
which is to occur between 25,000 and 35,000 feet, and rotation of 
aircraft, two ABLs will always be on patrol, thus ensuring 24-hour 
coverage of potential missile launch sites within the theater of 
operations.  The ABLs are intended to operate about 90 kilometers 
behind the front line of friendly troops but could move forward 
once air superiority has been established in the theater of
operations.  When on patrol, the ABLs are to be provided the same
sort of fighter and/or surface-to-air missile protection provided to
other high-value air assets, such as the Airborne Warning and Control
System and the Joint Surveillance Target Attack Radar System. 


--------------------
\1 The missile's booster is under pressure only while it is burning. 
This pressure causes the missile to explode after heat from the laser
fractures the casing. 

\2 Even though the ABL's surveillance system will be the primary
means for detecting missiles, the ABL will also have the capability
to accept missile detection information from other DOD sensor
systems. 

\3 A deformable mirror is a flexible reflective surface mounted to an
array of actuators, or pistons, that can rapidly (up to 1,000 times
per second) alter the shape of the mirror.  In effect, the mirror's
shape is altered to predistort an outgoing laser beam, which is then
refocused by the turbulence through which the beam travels on its way
to the target. 


   ABL'S OPERATIONAL EFFECTIVENESS
   IS CURRENTLY UNKNOWN
------------------------------------------------------------ Letter :4

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.  Those levels are needed to define the ABL's technical
requirements for turbulence.  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. 


      CORRELATION BETWEEN
      NON-OPTICAL AND OPTICAL
      TURBULENCE MEASUREMENTS IS
      NEEDED
---------------------------------------------------------- Letter :4.1

The type of turbulence that the ABL will encounter is referred to as
optical turbulence.  It is caused by temperature variations in the
atmosphere.  These variations distort and reduce the intensity of the
laser beam.  Optical turbulence can be measured either optically on
non-optically.  Optical measurements are taken by transmitting laser
beams from one aircraft to instruments on board another aircraft at
various altitudes and distances.  Non-optical measurements of
turbulence are taken by radar or by temperature probes mounted on
balloons or on an aircraft's exterior. 

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. 

Concern about turbulence measurements was expressed by a DOD
oversight office nearly 1 year ago.  In November 1996, during its
milestone 1 review of the ABL program,\4 the Defense Acquisition
Board directed the program office to develop a plan for gathering
additional data on optical turbulence and present that plan to a
senior-level ABL oversight team for approval.  The Board also asked
the program office to "demonstrate a quantifiable understanding of
the range and range variability due to optical turbulence and assess
operational implications." This requirement was one of several that
the Air Force has been asked to meet before being granted the
authority to proceed with development of the ABL.  That
authority-to-proceed decision is scheduled for June 1998. 

In February 1997, the program office presented to the oversight team
a plan for gathering only non-optical data.  The oversight team
accepted the plan but noted concern that the plan was based on a
"fundamental assumption" of a correlation between non-optical and
optical measurements.  If that assumption does not prove to be
accurate, according to the oversight team, the program office will
have to develop a new plan to gather more relevant (i.e., optical
rather than non-optical) measurements.  Accordingly, the oversight
team required that the program office include in its data-gathering
plan a statement agreeing to demonstrate the correlation between the
non-optical and optical measurements.  Program officials said they
plan to demonstrate that correlation in the summer of 1997. 

To establish that a correlation exists, the program office plans to
use optical and non-optical turbulence measurements taken during a
1995 Air Force project known as Airborne Laser Extended Atmospheric
Characterization Experiment (ABLEACE).  Optical measurements were
made by transmitting two laser beams from one aircraft to instruments
aboard another aircraft at distances from 13 to 198 kilometers and at
altitudes from 39,000 to 46,000 feet.  These measurements provided
the data used to calculate the average turbulence strengths
encountered by the beams over these distances. 

The ABLEACE project also took non-optical measurements of turbulence
using temperature probes mounted on the exterior of one of the
aircraft.  Rather than taking measurements over the path of a laser
beam between two aircraft, as with the optical measurements, the
probes measured temperature variations of the air as the aircraft
flew its route. 

Opinions vary within DOD about whether a correlation between optical
and non-optical turbulence measurements can be established.  Some
atmospheric experts, who are members of the program office's Working
Group on Atmospheric Characterization, criticized the program
office's plan for collecting additional atmospheric data because it
did not include additional optical measurements.  Minutes from a
Working Group meeting indicated that some of these experts believed
that "current scientific understanding is far too immature" to
predict optical effects from non-optical point measurements.  In
contrast, the chief scientist for the ABL program said it would be
surprising if the two measurements were not directly related; he
added that evaluations at specific points in the ABLEACE tests have
already indicated a relationship.  According to the chief scientist,
it would be prudent for the program office to continue to collect
non-optical data while it completes its in-depth analysis of the
ABLEACE data. 

According to a DOD headquarters official, because the ABL is an
optical weapon, gathering non-optical data without first establishing
their correlation to optical data is risky.  The official concluded
that, if the program office cannot establish this correlation,
turbulence data will have to be gathered through optical means. 


--------------------
\4 This review is the point in time at which a new acquisition
program is approved. 


      TECHNICAL REQUIREMENTS FOR
      OVERCOMING TURBULENCE MAY BE
      UNDERSTATED
---------------------------------------------------------- Letter :4.2

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. 

The ABL program office set the ABL's design specifications for
optical turbulence at a level twice that, according to a model, the
ABL would likely encounter at its operational altitude.  This model
was based on research carried out in 1984 for the ground based
laser/free electron laser program, in which non-optical measurements
were taken by 12 balloon flights at the White Sands Missile Range in
New Mexico.  Each of the 12 flights took temperature measurements at
various altitudes.  These measurements were then used to develop a
turbulence model that the program office refers to as "clear 1
night."

The clear 1 night model shows the average turbulence levels found at
various altitudes.  The ABL is being designed to operate at about
40,000 feet, so the turbulence expected at that level became the
starting point for setting the design specifications.  To ensure that
the ABL would operate effectively at the intended ranges, for design
purposes, the program office doubled the turbulence levels indicated
by its clear 1 night model.  The program office estimated that the
ABL could be expected to encounter turbulence at or below that level
85 percent of the time.  This estimate was based on the turbulence
measured by 63 balloon flights made at various locations in the
United States during the 1980s. 

When the ABL design specifications were established, the program
office had very little data on turbulence.  However, more recent
data, accumulated during the ABLEACE program, indicated that
turbulence levels in many areas were much greater than those the ABL
is being designed to handle.  According to DOD officials, if such
higher levels of turbulence are encountered, the effective range of
the ABL system would decrease, and the risk that the ABL system would
be underdesigned for its intended mission would increase.  DOD
officials also indicated that a more realistic design may not be
achievable using current state-of-the-art technology. 

ABLEACE took optical measurements in various parts of the world,
including airspace over the United States, Japan, and Korea. 
According to the program office and Office of the Secretary of
Defense (OSD) analyses of optical measurements taken during seven
ABLEACE missions, overall turbulence levels exceeded the design
specifications 50 percent of the time.  For the two ABLEACE missions
flown over Korea, the measurements indicated turbulence of up to four
times the design specifications.  Additionally, according to
officials in OSD, ABLEACE data were biased toward benign,
low-turbulent, nighttime conditions.  According to these officials,
turbulence levels may be greater in the daytime. 


   DEVELOPING AND INTEGRATING ABL
   COMPONENTS POSE MANY TECHNICAL
   CHALLENGES
------------------------------------------------------------ Letter :5

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.  Although DOD has
integrated a weapon-level laser and beam control system on the ground
at White Sands Missile Range, it has not done so in an aircraft
environment.  Therefore, it has not had to contend with size and
weight restrictions, motion and vibrations, and other factors unique
to an aircraft environment. 

The COIL is in the early development stage.  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.  It is to be constructed in a configuration 
that links modules together to produce a single high-energy beam.  The
laser being developed for the program definition and risk reduction
phase will have six modules.  The laser to be developed for the
engineering and manufacturing development phase of the program will
have 14 modules.  To date, one developmental module has been
constructed and tested.  Although this developmental module exceeded
its energy output requirements, it is too heavy and too large to meet
integration requirements.  The module currently weighs about 5,535
pounds and must be reduced to about 2,777 pounds.  The module's width
must also be reduced by about one-third.  To accomplish these
reductions, many components of the module may have to be built of
advanced materials, such as composites. 

The ABL aircraft, a Boeing 747-400 Freighter, will require many
modifications to allow integration of the laser, beam control system,
and other components.  A significant modification is the installation
of the beam control turret in the nose of the aircraft.  The beam
control turret is to be used for acquisition, tracking, and pointing
actions used in destroying a missile.  Consequently, the location of
the turret is critical to the success of the ABL.  Issues associated
with the turret include the decreased aircraft performance resulting
from the additional drag on the aircraft; the interaction of the
laser beam with the atmosphere next to the turret, which can cause
the laser beam to lose intensity; and vibrations from the operation
of the aircraft that affect the accuracy of pointing the
beam control turret.  The contractor has conducted wind tunnel tests
of these expected effects for three different turret locations and
found that installing the turret in the nose of the aircraft would
cause the fewest negative effects.  However, the operational
effectiveness of the beam control turret will not be known until it
undergoes additional testing in 2002 in an operationally realistic
environment. 

The laser exhaust system is another critical modification.  The
system must prevent the hot corrosive laser exhaust from damaging the
bottom of the aircraft and other structural components made of
conventional aluminum.  The exhaust created by the laser will reach
about 500 degrees Fahrenheit when it is ejected through the laser
exhaust system on the bottom of the aircraft.  This exhaust system
must also undergo additional testing on the aircraft in 2002 to
determine its operational effectiveness. 

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.  In
deciding the on-board location of the beam control system's
components, the Air Force used data gathered by an extensive study of
aircraft vibrations on the 747-400 Freighter.  The beam control
components are expected to be located in those areas of the aircraft
that experience less intense vibrations and, to the extent possible,
be shielded from vibrations and other aircraft motion.  To date, the
Air Force has not demonstrated how well a beam control system of such
complexity can operate on an aircraft.  The contractor has modeled
the ABL's beam control system on a brassboard but has not tested it
on board an aircraft.\5


--------------------
\5 A brassboard is an experimental device (or group of devices) used
to determine feasibility and develop technical and operational data. 
It may resemble the end item but is not intended for use as the end
item. 


   CONCLUSIONS AND RECOMMENDATIONS
------------------------------------------------------------ Letter :6

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.  As such, the concept faces a number of technological
challenges.  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.  The Air Force will not have resolved
that challenge until it has demonstrated whether there is a reliable
correlation between its non-optical and optical turbulence
measurements, or, should such a correlation not exist, gather
additional optical data, which may delay the ABL program.  Whether
relevant and reliable data are confirmed through correlation or by
additional optical measurements, the data are critical in assessing
the appropriateness of the design specifications for turbulence.  If
the specifications need to be set higher, that should be done as soon
as possible. 

Therefore, we recommend that the Secretary of Defense direct the
Secretary of the Air Force to take the following actions: 

  -- 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 turbulence
     data.  If a correlation between optical and non-optical data
     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. 

  -- 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 COMMENTS
------------------------------------------------------------ Letter :7

DOD concurred with both of our recommendations.  DOD's comments are
reprinted in appendix I.  DOD also provided technical comments that
we incorporated in this report where appropriate. 


   SCOPE AND METHODOLOGY
------------------------------------------------------------ Letter :8

We reviewed and analyzed DOD, Air Force, ABL program office, and
contractor documents and studies regarding various aspects of the ABL
program.  We discussed the ABL program with officials of the Office
of the Under Secretary of Defense (Comptroller); the Office of the
Under Secretary of Defense (Acquisition and Technology); the Air
Combat Command; the ABL program office; the Air Force's Phillips
Laboratory; and the ABL Contractor team of Boeing, TRW, and Lockheed
Martin.  We also discussed selected aspects of the ABL program with a
consultant to the ABL program office. 

We conducted our review from September 1996 to August 1997 in
accordance with generally accepted government auditing standards. 


---------------------------------------------------------- Letter :8.1

We are sending copies of this report to the congressional committees
that have jurisdiction over the matters discussed and to the
Secretary of Defense; the Secretary of the Air Force; and the
Director, Office of Management and Budget.  We will make copies
available to others on request. 

Please contact me at (202) 512-4841 if you or your staff have
questions concerning this report.  Major contributors to this report
were
Steven Kuhta, Ted Baird, Suzanne MacFarlane, and Rich Horiuchi. 

Sincerely yours,

Louis J.  Rodrigues
Director, Defense Acquisitions Issues




(See figure in printed edition.)Appendix I
COMMENTS FROM THE DEPARTMENT OF
DEFENSE
============================================================== Letter 



(See figure in printed edition.)

Now on p.  13. 



(See figure in printed edition.)

Now on p.  13. 

*** End of document. ***