Smart Bombs in Modern Aerial Warfare
Seeking targets from the skies
The use of exploding weapons can be traced back to the first two decades of the thirteenth century. Sources report that the East Asians used gun powder to make bombs as well as propulsive charges for missiles. These weapons were made up of simple materials such as paper, wood, and cloth, and were tied to arrows and spears. They were later improved upon by the European countries. The first air-to-ground bombs were dropped from hot air balloons over target locations. After the development of airships and the Wright Brothers’ invention, air-to-ground and air-to-air combat greatly improved.
Artilleries were carried and deployed by bombers. These bombs were dropped from a calculated altitude when the aircraft is flown at a calculated velocity, to ensure that the bombs followed the trajectory required for precisely attacking the desired target. They are known as ‘free-fall bombs’ or ‘gravity bombs’ because they freely fall from an aircraft and follow a projectile trajectory. The weapon casings are designed to offer aerodynamic and stability advantages after they are released from the aircraft. Gravity bombs typically use contact fuze or delayed-action (timing) fuze for detonation, depending upon the requirement. They are simpler to design, can be manufactured in mass numbers, and do not increase the complexity of an aircraft’s system. All bombs used until the second half of World War II were gravity bombs.
However, gravity bombs also have their own set of disadvantages, as follows:
- Can only be used to strike stationary targets.
- Are imprecise.
- Cannot be re-routed in case there is an error in the trajectory.
- Because of their low striking accuracy, more warheads are required to achieve the desired result. This consequently increases the cost and payload of the aircraft.
- The launcher must be closer to the target to ensure a higher probability of success in strikes.
To mitigate the drawbacks posed by purely projectile/ballistic munition, precision-guided munitions (PGM), or ‘smart weapons’, were invented. These are essentially gravity bombs or missiles that have a special guidance kit installed in them to navigate and control their trajectory to precisely hit a target. An operator can actively control their paths, or they can be made self-guided or semi-automatic.
A simple, pre-set bomb guidance system consists of:
- Flight control surfaces
- Control system
- Guidance system/ sensor
- Power source
- The power source powers the entire guidance system.
- The guidance system senses the position of the munition in space and relative to the target. This information is then fed to the control system.
- The control system compares the actual position of the munition with respect to the trajectory it needs to take in order to reach the target. The error signal is amplified and sent to the controller, which then sends appropriate signals to the actuators to reduce this error.
- The actuators move the control surfaces according to the signals received from the controller. The actual position of the munition is again picked up by the sensor and the feedback from the actuators is given to the control system. This cycle is carried out repeatedly and thus it is ensured that the weapon hits the right target. In addition, PGMs can also receive targeting or guidance data from an external source (aircraft, another weapon, ground station etc.)
- The control surfaces of the weapon are analogous to the control surfaces in an aircraft. They are used to control and adjust the attitude of the armament. They are typically in the form of fins located at the tail (rear-most) section of the bomb.
PGMs offer several advantages over unguided bombs. They:
- Can strike stationary and moving targets.
- Can evade enemy countermeasures (to some extent).
- Can also be pre-programmed to take a specific route.
- Possess the ability to select another target mid-flight and re-route accordingly.
- Can be programmed to coordinate attacks with other smart weapons.
There are different types of guidance systems available to guide a bomb. Each type works on a unique underlying principle. They include either one of the following or a combination of some of them:
Inertial guidance:
It guides the weapon by continuously dead reckoning position, velocity, acceleration, and attitude at any point in time. The acceleration and orientation are measured by accelerometers and gyroscopes, respectively. The controller takes appropriate action to ensure that the weapon remains on the desired flight path and intercepts its target. One advantage of the inertial guidance system is that it requires no communication between itself and any external source.
IR/electro-optical guidance:
The bomb is fitted with a television camera, or an IR camera, on its nose. It sends real-time images or motion pictures to the operator, who can then actively control its trajectory. In the case of IR cameras, the bomb seeks the target by sensing the heat generated by the target. An electro-optical or laser-guided bomb can also be semi-automated. The operator can lock the weapon onto the target with the help of data from the onboard camera. The control system of the bomb then directs its trajectory to intercept the target. For instance, the GBU-15 guidance system is equipped with either a television or an infrared seeker, and the bomb can be fully manually operated or semi-automated. The IR guidance system can be used in situations of poor visibility, unlike cameras that operate in the visible light region.
Laser guidance:
In this system, a uniquely pulsed laser beam is directed at the target, by an external source (aircraft or ground station). The laser beam reflected by the target is sensed by the sensor. The control system sends signals to the actuators such that the bomb is directed in the direction of the reflected laser beam. Although this guidance system can be used without active human control, it cannot be used when the reflected laser beam is obscured to the sensor, or when the target is coated with special paint/material that does not reflect laser energy effectively. The Sudarshan, developed by the Aeronautical Development Establishment (ADE, India), is a laser-guided bomb kit.
Radar guidance:
Radar is used to track the movement and/or location of both target and bomb. A computer then calculates the best path that needs to be taken by the munition to reach the target. An operator can track the target and track and control the bomb, or one/all the above function(s) can be automated. The German Fritz X, which was the first-ever precision-guided weapon deployed in warfare, and the American ASM-N-2, were radar-controlled glide bombs.
Satellite guidance:
The aircraft feeds the geodetic coordinates of the target and those of itself to the bomb’s computer, just before dropping the bomb. In the air, the bomb uses its receiver to determine its position relative to the target. This information is passed on to the control system, which then calculates its flight path to strike the target. The GNSS guidance system can function even in poor weather and poor visibility, but can be misguided by using jammers. Hence, another system that operates on an entirely different principle, such as the inertial navigation system (INS) or electro-optical system, is used for redundancy. Examples of this type of guidance system include the American Joint Direct Attack Munition (JDAM) and the Israeli SPICE (Smart, Precise Impact, Cost-Effective) guidance kits.
Today, despite having a variety of armaments available to choose from for the successful completion of a mission, bombs have not lost their importance in aerial warfare. Significant progression in the field of computers and electronics has not only offered a wide array of ammunition, such as guns, cannons, missiles, rockets, and torpedoes but have also improved the precision of a weapon. Today, both bomb guidance systems and bombers have developed to an extent that humans are now the bigger source of error in aerial warfare. Further studies must be undertaken to improve the efficacy of air-to-surface weapons. Some possible improvements include: bio-mimicry, lower payload without any compromise in performance, methods of detonation other than combustion, ability to evade enemy attacks while still pursuing the target, improvement against enemy countermeasures, and finally improvement in countermeasures against enemy attacks.
