A laser-guided bomb (LGB) is a free-fall bomb, usually dropped from an aircraft, that is guided to its target by a laser designator
The laser is directed at the target, illuminating it. The LGB has a sensor that detects the light from the laser which is reflecting off the target and which guides the bomb towards the target. The bomb has aerodynamic fins, which allow it to steer itself closer to the target.
Examples of LGBs include the American Paveway series. Laser-guided Bombs can be guided either from a laser being projecting from the aircraft dropping the bombs, from another aircraft or from ground assets near the target such as special forces and infantry. The laser beam is typically coded with certain frequency and pulse characteristics in order to avoid spoofing or jamming.
The Paveway is actually a kit consisting of a set of actuated fins, a guidance nose unit and a connecting component which can be attached to a regular "iron" bomb. The nose unit uses the air flowing past the nose of the bomb to sense the direction in which it is falling, and a laser light sensor at the tip senses how far offset the source of the reflected laser light is from the path of the bomb and in which direction. It then passes directions to the fins to direct the path of the bomb closer to the direction from which the laser light is eminating. This causes some of the earlier LGBs to "wobble" their way to the target, constantly over-correcting and re-correcting. However this did nothing to reduce the accuracy; the original Paveway series was easily able to get direct hits on truck-sized targets. Later series provided smoother and smarter trajectories to allow for the bombs to be released within a much larger envelope and to allow maneuvres such as toss-bombing where the bomb is released during a climb and it in a ballistic trajectory towards its target, increase the distance between the release point and the target, making the launch platform's job safer.
The Paveway I and II series consist of kits for converting the 2000 pound (907 kg) Mk. 84 "iron" (unguided) bomb or BLU-109B penetrating bomb into the GBU-10 or GBU-10I respectively, the 500 pound (227 kg) Mk. 82 into the GBU-12 and the 1000 pound (450 kg) Mk. 83 into the GBU-16.
The Paveway III series consists of a kit for converting the 2000 (907 kg) pound Mk. 84 iron bomb, BLU-109B or BLU116 penetrating bombs into the GBU-24 series. Paveway III feature proportional guidance, mostly avoiding the overcorrection mentioned above and greatly enhancing the release envelope. The GBU-27 is similar to a GBU-24 but with smaller fins so that it will fit into an F-117 "Stealth Fighter". This is the F-117's primary weapon.
The GBU-28 is a 5000 pound (2270 kg) bomb manufactured out of a modified eight inch (203 mm) artillery tube. It is referred to as the "bunker buster" as it was designed specifically to penetrate the ground and reinforcement in Saddam Hussein's bunkers and explode inside them. At least two were dropped during the Gulf War but Saddam was evidently not in either bunker at the time. It can penetrate 20 feet (6 m) of concrete or 100 feet (30 m) of earth when dropped from a high enough point to give it sufficient kinetic energy. It was designed and built in a short period of just weeks after Iraq invaded Kuwait in 1991.
Other countries producing laser-guided bombs include the former USSR (Russia) with their KAB-500L (500 kg), KAB-1000L (1000 kg), and KAB-1500L (1500 kg).
- The FAS website has a good overview of [laser-guided bombs (http://www.fas.org/man/dod-101/sys/smart/lgb.htm)].