|By Air Marshal AK Trikha (Retd)|
NEW DELHI. In an era of already prohibitive and still escalating cost of tools of warfare, and competing demands on limited defence budgets, it is necessary to carefully calculate what delivers the most bang for the buck. Costs are particularly awe inspiring in aerial systems. Most modern combat platforms carry price tags upwards of hundreds of millions of dollars. In addition to the very high initial price tag, the real cost of ownership has also to reckon with costs on account of maintenance and infrastructure requirements. Coupled to the exorbitant cost of platforms, increasing density and lethality of air defences also has to be reckoned with. To achieve balance between risk inherent in exposing extremely expensive and therefore limited assets (not excluding the aircrew) to highly lethal environment, and the benefits thereof, it is necessary that each mission be optimised for maximum effect. Applied to strike aircraft, it implies that weapons must be perfectly matched to the target characteristics and applied with utmost precision to hit the bull’s eye each time. Precision permits iniaturisation which in turn enables carriage of many more weapons within a specified load limit – thus making it possible to engage multiple targets in a single mission. In addition to precision, weapon should be employable in all weather conditions by day and night, from outside the lethal envelope of opposing surface-to-air weapons and should also be able to defeat enemy’s attempts to interfere with its trajectory. A weapon encapsulating all these attributes would be ultra smart.
From first use of smart weapons as early as during WWII, (Germans used 1,400-kg Fritz X to successfully attack the Italian battleship Roma in 1943), technology has advanced sufficiently to make all the above desirable attributes achievable. However each increment in capability comes at a substantially increased price. A cursory survey of weaponry currently in use would reveal the wide variety of choices available and the consequent necessity of careful assessment in order to equip for the widest spectrum of capabilities within the constraints of a restricted budget.
LASER GUIDED BOMBS (LGBS)
The best known and most widely adopted route to conversion of dumb bombs into smart ones is through laser guidance – typified by the Paveway series. Laser Guided Bomb or LGB made its operational debut in May 1972 when USAF demonstrated its potential in a spectacular raid on the Thanh Hoa bridge, 15 miles South of Hanoi. US Navy and Air Force had flown 871 sorties over six years, losing 11 aircraft in an unsuccessful effort to put the bridge permanently out of commission. Then in a single raid of fourteen fighter bombers carrying LGBs demolished the bridge by scoring direct hits on the supporting piers.
All laser-guided bombs work essentially the same way, relying on the target being illuminated by a laser
target designator either from the ground or carried onboard an aircraft.
Paveway route to converting dumb free fall gravity bombs into smart ones is in its essence relatively simple because it requires no airframe or electrical modification to the mother aircraft. The conversion kit which is attachable to a variety of existing warheads consists of a guidance module comprising a semi active laser seeker, guidance and control electronics, a thermal battery and pneumatic control augmentations system. Control canards and rear wings provide stability and a limited manoeuvre capability to guide the bomb to the target within the ballistic reach of the weapon.
Based essentially on this operating principle, a family of Paveway laser-guidance units has been developed incorporating performance enhancements along the way. Paveway II system built on an improved seeker and the weapon release range was extended by adding foldable wings atthe rear which give the weapon some glide performance.
Paveway III employs an even more sophisticated seeker with a wider field of view. Instead of constantly adjusting trajectory to align itself with the target as in Paveway II, this version uses proportional navigation technique which extracts lesser energy thus giving the bomb considerably longer glide range. It is also much more accurate. However the improvements come with so much higher cost that its employability has been restricted to specialised high value weapons only.
Laser guidance suffers in conditions of poor visibility due to difficulty of target illumination. To overcome this shortcoming both Paveway II as well as Paveway III were enhanced to accommodate a GPS aided Inertial Navigation in its guidance system which makes them usable in all weather conditions.
Paveway IV in service with the RAFintroduces air burst fuzing option in the Computer Control Group of enhanced Paveway II and Paveway III series. It also features resistance to jamming of the GPS receiver.
SATELLITE GUIDED WEAPONS
Arrival of mil grade GPS has ushered a virtual revolution in technology of precision targeting. JDAM (Joint Direct Attack Ammunition) and Joint Stand-off Weapon (JSOW) are prime examples of this era. JDAM is also a bolt on package in the same mould as the Paveway series. Its guidance package consists of a tightly coupled INS unit/GPS receiver which gives it an accuracy of 10 meters. In the event of GPS signal being lost, INS can still guide the weapon to within 100 ft of the target. By doing away with the necessity of laser designation of a target (like in Paveway kits) JDAM achieves all weather, day and night, fire and forget status. To engage mobile targets, a version of JDAM carries a link 16 receiver through which it can receive continuous updates of target position. JDAM has been enhanced further by addition of a laser target seeker which enables Laser JDAM to achieve pin point accuracy. Using the same GPS/INS mode of guidance, JSOW is a low signature glide bomb intended for release from outside point defences of the target system. Its aerodynamic profile enables it to achieve standoff distances in excess of 100 Km. Some versions are also fitted with terminal imaging Infra -red seekers to improve accuracy of impact.
OTHER GUIDANCE SYSTEMS
Paveway makes conventional bomb smart. Precision guidance has also been applied to weapons other than iron bombs using a variety of guidance technologies. The Raytheon Maverick air to ground missile among its various marks employs electro-optical (AGM-65A), imaging infra-red (AGM-65D), and laser homing (AGM-65E) guidance systems. The first two, by guiding themselves based on the visual orIR scene of the target, are fire-and-forget in that the pilot can release the weapon and manoeuvre to exit the target area while the weapon guides itself to the target without any further input.
RAFALE IN IAF COLOURS
After decades of waiting, IAF (Indian Air Force) is finally set to receive delivery of first of the 36 Rafale jets
in a few years time. In an order worth $8.85 billion, nearly $800m have been set aside for additional weapons package. For air superiority missions, METEOR beyond the visual range (BVR) and MICA Close Combat AAMs would undoubtedly be a part of the agreed weapons package. For the strike role, there would be an option to choose amongst the most sophisticated weapons available anywhere. The aircraft has 13 hard points on which it can carry 9 tonnes of external load of various types. Considering the very limited numbers, there is no doubt that it will be employed for very specialised missions.
French route to conversion of dumb bombs has been through add-on kits called AASM (also called ‘HAMMER’). Basic version incorporates INS/GPS guidance while the more advanced variants add IR imaging or laser guidance to increase accuracy. Rare mounted aerodynamic range extension and conrol surfaces provide stand-off capability ranging from some 15 Km at low level to 55 Km when released from high altitude. The kit is modular and can be adapted to a variety of bomb bodies.
SCALP is a more specialised precision weapon for employment against hardened high value targets in depth. It is a long range, standoff attack, cruise missile with a range of approx 300 Km. It is all weather, fire and forget weapon which navigates to the target at low level guided by GPS and terrain mapping data pre-programmed in its memory. Once in the target’s vicinity, it climbs to height to achieve optimum strike angle and to precisely identify the programmed impact point through its IR sensors using Digital Scene Matching Area Correlator (DSMAC) concept. The warhead is designed to penetrate several inches of concrete before activation of fuze to detonate the main warhead.
The brief survey in this article of the variety of weapons in current use serves to highlight the reality that precision guided munitions are no longer in the realm of the exotic. In fact risks to mission success imposed by lethality and density of air defence weapons suggests that dumb weapons may have already gone past their ‘Use By’ dates. However the wide array of impressive capabilities built into smart weapons also carry a high price tag.
Therefore, it has become all the more necessary to evaluate and shortlist target systems tightly related to defined outcomes as a part of overall strategy. Basic technologies involved in conversion of dumb to smart weapons are neither secret nor are beyond the ken of indigenous talent. Focus and intensification of R&D effort to get to grips with detail can create national manufacturing base to fulfill the need for a sizeable guided munitions inventory to meet the likely demand for a short sharp conflict.