Laser-guided Bomb - Problems and Limitations

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 by a laser designator and the pilot must deliver the weapon within the "weapon basket" (the zone in which the weapon seeker can observe the laser target marker and the weapon has sufficient energy to guide to the target). Laser guided bombs can be launched without the laser designator turned on, in which case it will follow a ballistic path, until such time as the seeker picks up the reflected laser signal. This allows the aircraft to deliver an LGB using techniques such as loft or toss bombing. However, if the designator is turned off, the laser spot moved, the laser signal is blocked (for example by cloud or smoke), the weapon's accuracy will be greatly reduced. A particular problem with laser designation can be path length under certain environmental conditions. Laser designators operate in the Infra-Red wavebands and attenuation of the laser signal by the moisture content of the atmosphere can reduce the signal strength below the threshold of the seeker. Laser designators modulate their output on a number of discrete codes and to guide correctly the bomb and designator must be matched.

For an accurate attack against a small target, uninterrupted designation is desirable. But, the simple guidance system of early LGBs (such as the American Paveway II) resulted in a rectilinear flight path, with a tendency to lag below the sightline. To compensate, crews will release their weapons on an unguided, ballistic flightpath, 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.

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, the problems described above 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 "weapon basket", if the weapon is released too low or too far from the target, or in a trajectory that puts the weapon outside the seeker's field of view, it will miss. Optimum altitude for an effective LGB attack is from medium altitude (20,000 - 30,000 ft), 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.