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Laser-Guided Bombs - Building LGB Capability

Issue: 07-2012By Air Marshal (Retd) V.K. BhatiaPhoto(s): By SP Guide Pubns, Lockheed Martin

The IAF still has a long way to go before it acquires desired level of ‘PGM’ capability, which incidentally could run into thousands for a two-front scenario

June 30, 1999: The gleaming twin-seat Mirage 2000 had taken off from Adampur (its operational base) for a daylight mission against Pak intruders sitting on the Kargil heights. Equipped with a recently acquired Israeli Litening pod and armed with an indigenous 1,000 lb dumb iron bomb but converted into a smart weapon with the help of a laser-guided bomb (LGB) strap-on kit, it climbed quickly to a height of 30,000 ft heading north. In less than 15 minutes, it was over Dras sector searching for its prey on top of the—by now famous—Tiger Hill. Strapped in the rear seat was the AOC-in-C, Central Air Command, with the job of acquiring and engaging the target through the Litening pod after its location had been generally determined visually. The aircraft had plenty of fuel, so there was lots of time available for a proper search of the target, which even though a Battalion HQ of the enemy, was nothing more than a cluster of stone and rock Sangars, making them extremely difficult to spot from the air because of the way they so perfectly blended with the surrounding terrain. It was in the second pass, the intended target was picked up with clarity. The desperate enemy had by now launched a couple of Stinger missiles but couldn’t harm the aircraft as it was maintaining height out of the missile’s lethal envelope. In the third and the final pass, the target was acquired, designated, illuminated and engaged with the lone LGB. Bomb away, Cursor firmly on the target till impact, it was a direct hit, devastating the enemy position to smithereens.

The Indian Air Force (IAF) used the laser-guided bombs for the first time during the 1999 Kargil War. However, it was decided not to use the highly expensive Matra LGBs only a handful of which had been acquired from France as ‘Special’ precision guided munitions (PGMs) for the Mirage 2000 aircraft. Instead, as stated earlier, the indigenous 1,000 lb iron bombs were transformed into smart weapons with the help of strap-on LGB kits. These were most ingeniously mated to the Mirage airframe. Innovatively modified, the combination of Litening pod and the indigenous LGBs proved to be a lethal mix against the enemy. Tiger Hill, which was causing untold havoc to the Indian Army deployed in and around Dras, was effectively neutralised by the Mirage LGB attacks. So much so, it was a literal cakewalk for the Army when it set out to recapture it.

But for the uninitiated, how does a laser-guided bomb function? Simply put, a LGB is a guided bomb that uses semi-active laser homing to strike a designated target with greater accuracy than an unguided bomb. LGBs are one of the most common and widespread guided bombs, used by a large number of the world’s air forces. Laser-guided munitions use a laser designator to mark (illuminate) a target. The reflected laser light (sparkle) from the target is then detected by the seeker head of the weapon, which sends signals to the weapon’s control surfaces to guide it towards the designated point. Laser-guided bombs are generally unpowered, using small fins to glide towards their targets.

Most laser-guided bombs are produced in the form of strapon kits: seeker heads, and steering fins that can be attached to a standard general-purpose bomb or penetration bomb. Such kits are modular, allowing relatively easy upgrades, and are considerably cheaper than purpose-built weapons.

Laser-guided weapons were first developed in the United States in the early 1960s and 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. The LGB proved particularly effective against difficult fixed targets like bridges, which previously had required huge loads of ‘dumb’ ordnance to destroy.

The most dramatic example of successful LGB attacks in Vietnam War was against the Thanh Hoa Bridge, 110 km south of Hanoi, a critical crossing point over the Red River. Starting in 1965, US 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.

While LGBs are highly accurate under ideal conditions, they present several challenges for successful use. The first problem is target 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 and 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 infrared 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.

To overcome these problems, GPS guidance is being seen as a viable backup to upgrade LGBs to function in all weather conditions. These weapons such as the US Air Force Enhanced Guided Bomb Unit (part of the Paveway family of LGBs), use laser designation for precision attacks, but contain an inertial navigation system (INS) with GPS receiver for back-up, so that if the target illumination is lost or broken, the weapon still continues to home in on the GPS coordinates of the original target.

The IAF learnt its lessons well from the Kargil experience and has made sincere efforts to enhance its precision attack capabilities by widening the use of LGBs on its different combat aircraft fleets. Today, practically all its frontline fighter aircraft have the capability to launch LGBs either in a buddy mode through manned and unmanned aircraft or through self-lasing modes. The IAF also continues to enhance its arsenal of LGBs through indigenous and direct import routes. For example, it has been recently revealed by Lockheed Martin that the IAF plans to induct more than 100 bunker-buster laser-guided bombs (LGBs) for its warplanes and that they have offered the IAF their highly successful Paveway II LGBs. It may be recalled, the IAF had issued a global request for proposal (RFP) for the purpose last year, and Lockheed Martin along with Raytheon and Israeli Rafael had taken part in the tender. However, the IAF sources have indicated a figure of as much as 850 LGBs for this tender.