Smart bombs are weapons capable of destroying enemy targets with out the need for a launch aircraft to penetrate the envelops of the air defense systems. These essentially comprise a terminal guidance unit that guides them in the last phase to achieve pinpoint accuracy. Increased 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 indented target so that 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 are smart bombs that have changed the face of modern warfare
Laser-guided bombs have an internal semi-active guidance system that detects laser energy and guides the weapon to the target illuminated by an external laser designator.Laser designators radiate a narrow beam of pulsed energy in the near infrared wavelength spectrum. These are semi active illuminators used to tag the desired spot. These can be aimed such that laser energy precisely designates the chosen spot on the target. Laser designator can be located in the delivery aircraft, another aircraft or on a ground source.
Typical LGB seekers comprise an array of photo diodes to decode the laser pulsed repetition frequency (PRF) and derive target position signals. 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 will track only the target designated by the chosen designator.
Laser designators provide precision target marking for air support. LGBs with TV or infrared seeker in their nose show the target to the attacking pilot on a screen in the cockpit. The pilot fixes cross hairs on the target and marks it for the weapon to aim at. The target scatters the received laser energy in all the directions. LGB seeker having a limited field of view receives a small part of the scattered energy and decodes it. If the received PRF code matches the preprogrammed code, the pilot fires the bomb. It then horns onto the reflected laser energy to attack the target
Some LGBs require laser target illumination before launch or release and/ or during the terminal portion of flight. The LGB flight path can be 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 this phase, the delivery altitude takes on additional importance, since maneuverability of the unguided bomb is related to the weapon velocity during terminal guidance. Therefore, airspeed lost during the ballistic phase equated to a proportional loss of maneuverability. So the closer to the target the release of the bomb, the more the accuracy of the bomb