Abstract
Smart bombs are the weapons capable of destroying enemy targets without the need for launch aircraft to penetrate the envelopes of the air defense systems. These essentially comprise a terminal guidance unit that guides them in the last phase to achieve pinpoint accuracy. Increase accuracy means that a single, moderate size bomb can give a better result than multiple strikes with larger ,non-guided bombs.
Smart bombs are desirable both from
ethical and tactical standpoints. On ethical grounds, the military desires that
each warhead deployed should strike only its intended targets so those innocent
civilians are not harmed by misfire. From tactical standpoint, it wants weapons
with pinpoint accuracy to inflict maximum damage on valid military targets and
minimize the number of strikes necessary to achieve mission objectives. Gravity
bombs with laser or GPS/INS guidance is smart bombs that have changed the face
of modern warfare.
You can see how lethal and merciless smart
bombs can be a realistic battlefield scenario was amply demonstrated in Gulf
War and recently reiterated during US attack on Iraq. This paper will explain you
the operational mechanisms, salient feature and limitations of this rapidly
grooming smart bomb
Introduction
"In World War II it could take 9,000 bombs to hit a target
the size of an aircraft shelter. In Vietnam, 300.Today we can do it
with one laser-guided munition from an F-117."
USAF, Reaching Globally, Reaching Powerfully: The United States Air Force in the Gulf War (Sept. 1991) The United States Army began experimenting with radio-controlled remotely guided planes in the First World War, but the program had few successes. The first successful experiments
USAF, Reaching Globally, Reaching Powerfully: The United States Air Force in the Gulf War (Sept. 1991) The United States Army began experimenting with radio-controlled remotely guided planes in the First World War, but the program had few successes. The first successful experiments
with guided bombs were conducted
during World War II
when television-guided bombs, flare sighted bombs and other steerable
munitions, such as the 450 kg (1000 lb) AZON bomb, were developed.
The Germans developed several types of steerable munitions, such as the 1400 kg
(3085 lb) Fritz X,
the closest Axis equivalent of the US Army Air Force's
AZON device. There was
even an attempt to produce a glider bomb that was released from a larger plane
over the target, but the program stopped with the nuclear attacks in Japan.
The programs started again in the Korean War,
where the political ramifications of nuclear war would have been unthinkable.
In the 1960s,
the electro-optical bomb (or camera bomb) was introduced. They were equipped
with television
cameras
and steerable flare sights, in which the bomb would be steered until the flare
superimposed the target. The camera bombs transmitted a "bomb's eye
view" of the target back to a controlling aircraft. An operator in this
aircraft then transmitted control signals to steerable fins fitted to the bomb.
Such weapons were used increasingly by the USAF in the last few years
of the Vietnam War
because the political climate was increasingly intolerant of collateral damage.
Laser Guided Bombs: -
The development of laser-guided weapons has dramatically improved
the accuracy of weapon guidance and delivery. With the assistance of build-up
guidance kits, general GP bombs are turned into laser-guided bombs (LGBs). The
kits consist of a computer- control group (CCG), guidance canards attached to
the front of the warhead to provide steering commands, and a wing assembly
attached to the aft end to provide lift. LGBs are maneuverable, free-fall
weapons requiring no electronic interconnect to the aircraft. They have an
internal semi active guidance system that detects laser energy and guides the
weapon to a target illuminated by an external laser source. The designator can
be located in the delivery aircraft, another aircraft, or a ground source.
All LGB weapons have a CCG, a warhead (bomb body with fuze), and
an airfoil group. The computer section transmits directional command signals to
the appropriate pair(s) of canards. The guidance canards are attached to each
quadrant of the control unit to change the flight path of the weapon. The
canard deflections are always full scale (referred to as "bang, bang"
guidance).
The LGB flight path is divided into three phases: ballistic,
transition, and terminal guidance. During the ballistic phase, the weapon
continues on the unguided trajectory established by the flight path of the
delivery aircraft at the moment of release. In the ballistic phase, the
delivery attitude takes on additional importance, since maneuverability of the
UGB is related to the weapon velocity during terminal guidance. Therefore,
airspeed lost during the ballistic phase equates to a proportional loss of maneuverability.
The transition phase begins at acquisition. During the transition phase, the
weapon attempts to align its velocity vector with the line-of-sight vector to
the target. During terminal guidance, the UGB attempts to keep its velocity
vector aligned with the instantaneous line-of- sight. At the instant alignment
occurs, the reflected laser energy centers on the detector and commands the
canards to a trail position, which causes the weapon to fly ballistically with
gravity biasing towards the target.
Target designators are semi-active illuminators used to
"tag" a target. Typical laser guided bomb receivers use an array of
photodiodes to derive target position signals. These signals are translated
into control surface movements to direct the weapon to the target. An airborne
detector can provide steering information to the pilot, via his gun sight, for
example, and lead him on a direct heading to the target, finally giving him an
aim point for a conventional weapon. Alternatively, a laser guided "smart"
bomb or missile may be launched when a pilot is satisfied that the detector
head has achieved lock-on and launch envelope requirements are satisfied. In
either of these cases, the pilot may never see the actual target, only the aim
point as indicated by the laser.
Laser designators and seekers use a pulse coding system to ensure
that a specific seeker and designator combination work in harmony. By setting
the same code in both the designator and the seeker, the seeker will track only
the target designated by the designator. The pulse coding is based on Pulse
Repetition Frequency (PRF). The designator and seeker pulse codes use a
truncated decimal system. This system uses the numerical digits 1 through 8 and
the codes are directly correlated to a specific PRF. Dependent upon the laser
equipment, either a three digit or a four-digit code can be set. Coding allows
simultaneous or nearly simultaneous attacks on multiple targets by a single
aircraft, or flights of aircraft, dropping laser guided weapons (LGWs) set on
different codes. This tactic may be employed when several high priority targets
need to be expeditiously attacked and can be designated simultaneously by the
supported unit(s).
Fire control laser systems are laser rangefinders (LRFs) and laser
designators (LDs). These laser systems can be far more harmful to the eye than
laser training devices such as MILES and Air-to-Ground Engagement System/Air
Defense (AGES/AD) laser simulators. Consequently, fire control lasers require
control measures to prevent permanent blindness to an unprotected individual
viewing the laser system from within the laser beam.
Development:-
Laser-guided
weapons were first developed in the United States in the early 1960s. The USAF issued the first
development contracts in 1964, leading to the development of the Paveway™
series, which was used operationally in Vietnam
starting in 1968. Although there were a variety of
technical and operational problems, the results were generally positive. LGBs
proved to offer a much higher degree of accuracy than unguided weapons, but
without the expense, complexity, and limitations of guided air-to-ground missiles like the AGM-12 Bullpup.
The LGB proved particularly effective against difficult fixed targets like
bridges, which previously had required huge loads of "dumb" ordnance,
and large numbers of sorties, to destroy.
It was determined that 48 percent of Paveways dropped
during 1972–73 around Hanoi
and Haiphong
achieved direct hits, compared with only 5.5 percent of unguided bombs dropped
on the same area a few years earlier.[1] The average Paveway landed within 23
feet of its target, as opposed to 447 feet for gravity bombs.[1] The leap in accuracy brought about
primarily by laser guidance made it possible to take out heavily defended,
point objectives that had eluded earlier air raids. The most dramatic example
was the Thanh Hoa Bridge, 70 miles south of Hanoi, a
critical part crossing point over the Red River.
Starting in 1965, U.S. pilots had flown 871 sorties against it, losing 11
planes without managing to put it out of commission. In 1972 the “Dragon’s Jaw”
bridge was attacked with Paveway bombs, and 14 jets managed to do what the
previous 871 had not: drop the span, and cut a critical North Vietnamese supply
artery.
In the wake of this success, other nations, specifically
the Soviet Union, France, and Great Britain, began developing similar weapons
in the late 1960s and early 1970s,
while US weapons were refined based on combat experience.
The USAF
and other air forces are now seeking to upgrade their LGBs with GPS guidance as a back-up.
These weapons, such as the USAF Enhanced Guided Bomb Unit (part of the Paveway™
family), use laser designation for precision attacks, but contain an inertial navigation system with GPS
receiver for back-up, so that if the target illumination is lost or broken, the
weapon will continue to home in on the GPS coordinates of the original target.
Problems And Limitations:-
While LGBs are highly accurate under ideal conditions,
they present several challenges for successful use, making them somewhat less
than the "silver bullet" sometimes suggested.
The first problem is designation. To ensure accurate
guidance, the target must be illuminated for several seconds before launch,
allowing the weapon's seeker to obtain a positive lock, and the target must
remain illuminated during much of the weapon's transit time. If the
designator's "sparkle" is turned off, blocked, or moved, the weapon's
accuracy will be greatly reduced.
For an accurate attack against a small target,
uninterrupted designation is essential. But, the guidance controls of many LGBs
(such as the American Paveway™ II) cause large deflections (visible as a
noticeable wobble) which reduce the bomb's range. To compensate, crews will
often release their weapons in an unguided, ballistic arc, activating the
designator only to refine the bomb's final impact point. This is more demanding
of crew and aircraft, requiring a high standard of basic, unguided bombing
accuracy and more attention to the bomb's flight.
Laser designation is very sensitive and vulnerable to
weather conditions. Cloud cover, rain, and smoke often make reliable
designation impossible. In war conditions, many attacks have been aborted due
to poor visibility.
In the 1970s
and 1980s
it was common for aircraft to rely on a separate designator, either carried by
ground forces, operated by the forward air controller, or carried by another
aircraft in the strike group. It was often deemed more practical for one
aircraft to designate for its comrades. Modern conflicts and a growing emphasis
on precision-guided weapons have pointed to the need for autonomous
designation, and many fighter-bomber aircraft are now being fitted with designator
pods to self-designate for laser-guided munitions.
Even if the launch aircraft is capable of autonomous
designation, problems remain. Laser illumination can be interrupted by smoke,
fog, or clouds, limiting the usefulness of LGBs in poor weather or very dusty
conditions. In desert warfare, such as the 1991 Gulf War,
laser designation sometimes reflected off the sand, causing weapons to home on
false targets. Furthermore, the need to provide designation may leave the
aircraft dangerously exposed to ground fire or enemy air support.
An additional concern is the limited "launch
envelope" of an unguided weapon. The reflected laser "sparkle"
can be described as a basket into which the weapon must be steered to hit the
target. If the weapon is released too low or to far from the target, or in a
trajectory that puts the weapon outside the seeker's field of view, it is
likely to miss. Optimum altitude for an effective LGB attack is relatively
high, increasing the aircraft's vulnerability to surface-to-air missile (SAM) attacks.
For these reasons, while all modern air forces have put
an increasing emphasis on LGBs and other precision-guided munitions, some
tacticians still see an important role for the accurate delivery of unguided
bombs. During their 1981
raid on the Iraqi nuclear reactor
at Osirak,
the Israeli Air Force chose to use unguided Mark 84 bombs
rather than laser-guided weapons because they felt the need to designate the
target would leave the attackers unacceptably vulnerable.
Figure 1 A
laser-guided GBU-24 (BLU-109 warhead variant) strikes its target
Figure 2 BOLT-117, the World’s first laser guided bomb & Carrier
Specifications
|
|
Mission
|
Offensive counter air, close air support,
interdiction
|
Targets
|
Fixed hard
|
Class
|
4,000 lb. Penetrator, Blast/Fragmentation
|
Service
|
Air Force
|
Contractor
|
Lockheed (BLU-113/B), National Forge (BLU-113A/B),
|
Program status
|
Production
|
First capability
|
1991
|
Weight (lbs.)
|
4,414
|
Length (in.)
|
153
|
Diameter (in.)
|
14.5
|
Explosive
|
6471bs. Tritonal
|
Fuze
|
FMU-143 Series
|
Stabilizer
|
Air Foil Group (Fins)
|
Guidance method
|
Laser (man-in-the-loop)
|
Range
|
Greater than 5 nautical miles
|
Development cost
|
Development cost is not applicable to this
munition.
|
Production cost
|
$18.2 million
|
Total cost
|
$18.2 million
|
Acquisition unit cost
|
$145,600
|
Production unit cost
|
$145,600
|
Quantity
|
125 plus additional production
|
Platforms
|
F-15E, F-111F
|
