posted by Jirka Wagner
It has long been clear that the free-fall or 'iron' bomb is a cheap weapon that is also highly effective if it hits its target. Early experience in the Vietnam War (US involvement between 1961 and 1973) persuaded the US Air Force that even its most advanced sights were inadequate to provide the free-fall bomb with the terminal accuracy for the destruction of point targets without an enormous and therefore costly expenditure of such weapons in large numbers of sorties that were also likely to result in the loss of highly trained aircrew and their valuable warplanes. During the mid-1960s, therefore, considerable effort was expended in the creation of a program to improve the terminal accuracy of free-fall bombs. One of the key elements in this program had been started in 1965 by the Armament Development and Test Center at Eglin AFB, Florida, with the industrial partnership of Texas Instruments, with the intention of creating a cheap system for giving any of the Mk 80 series and other tactically important free-fall bombs, most notably the 750 lb (340 kg) M117 and 3,000 lb (1,361 kg) weapons, a high degree of terminal accuracy by the addition of a semi-active laser homing system and associated control package.
This program led to the 'Paveway' series of laser-guided bombs, of which the first were introduced in 1967 after the initial release of a laser-guided development weapon in 1965. The designation 'Paveway I' was adopted only in 1978, when a PEP (Production Engineering Program) was started for an overall improvement in laser-guided bomb capabilities, and is used for a series of add-on laser-homing kits, which are marked-target seekers and associated control surfaces developed by Texas Instruments. Each kit, designed to be added on the nose of the basic bomb, weighed about 30 lb (13.6 kg) and increased the bomb's overall length by some 6 in (0.15 m): the complete unit was in fact 3 ft 4 in (1.01 m) long, but this was offset by a reduction in the length of the tail surfaces, which were fixed surfaces of trapezoidal planform. The kit could be fitted to standard low-drag bombs for maximum accuracy when used in conjunction with an air- or ground-based laser designator. The 'Paveway I' soon proved in operations from 1968 that its primary benefit, other than the very high degree of terminal accuracy, was that the launch warplane needed no modification to carry the weapon and after weapon release could depart from the target area unless it was also the laser-designator machine. The system worked at night and in poor visibility, and the minimum cloud base for successful operation was 2,500 ft (760 m). The airborne designators most commonly associated with the series were three podded systems, the AVQ-23A 'Pave Spike' day, AVQ-26 'Pave Tack' day and night, and LANTIRN (Low-Altitude Navigation and Targeting Infra-Red for Night) day and night units carried by many US tactical warplanes such as the General Dynamics F-111 interdictor, the Lockheed Martin F-16 Fighting Falcon multi-role fighter, and the McDonnell Douglas F-4E Phantom II and F-15 Eagle multi-role fighters. Moreover, any warplane capable of lifting the baseline 'iron' bomb could deliver a 'Paveway I' weapon against a target designated by a third party. In all cases the guidance unit was the same, the differences between the various systems lying in their attachments and variously enlarged fins. The guidance system drew current from a thermal battery activated at launch, and was steered by canard control fins powered by a hot gas generator.
Resulting from the Production Improvement Program effort and entering service in 1980, this is an improved series based on the same basic concept but with a simpler (thus cheaper) guidance package and a folding wing group (comprising spring-open extensions to the fixed tail fins for extra maneuverability and additional horizontal range) added at the tail. The weapons within this important basic designation are:
In each case the weapon functions in a manner basically similar to that of the 'Paveway I' series: the 3.25 in (0.0825 m) diameter freely gimbaled laser seeker at the extreme nose is aligned by its 6.25 in (0.159 m) ring tail with the velocity vector of the falling bomb, and detects laser radiation (reflected from the 'illuminated' target) at different strengths on each of its four internal quadrants; this strength differential is used to generate error signals passed to the computer in the 8 in (0.20 m) section just forward of the canard control fins; the computer turns these inputs into commands to the four solenoids operating the cruciform of canard control fins (spanning 2 ft 7.25 in/0.79 m in the GBU-10 and 1 ft 5.65 in/0.49 m in the GBU-12), steadily reducing the angular difference between the seeker's line of sight and the velocity vector of the bomb to zero, at which point an equal strength of laser radiation is being received by each of the seeker's quadrants as the weapon is falling directly towards the target. Operational service revealed that while the system was extremely accurate, the use of a 'bang/bang' control system, in which the control surfaces were moved to their maximum deflection position each time a command was received, increased drag and therefore reduced range.
Entering service in 1987 after the start of its development program in 1980, this is an improved version of the 'Paveway II' intended mainly for use in the degraded weather and high-threat scenario of European operations and accordingly fitted with high-lift folding wings at the rear, microprocessor-based control system offering proportional control surface deflections for increased range and accuracy, a digital autopilot (with BAe Dart precision gyro) and an improved scanning seeker. The 'Paveway III' is also designated the Low-Level Laser-Guided Bomb or Laser-Guided Penetrator Weapon, and was designed for release at low level (in either level flight or a zoom climb) and thus fitted with high-lift folding wings, but can also be released at higher altitudes in dives as steep as 60°. The result is a weapon of far greater operational flexibility than its predecessors. The variants with the 2,000 lb Mk 84 bomb and BLU-109/B Improved 2,000 lb Warhead as their payloads, have the service designations GBU-24/A 'Paveway III' and GBU-24/B 'Paveway III' respectively. The variants of these two weapons for internal carriage by the Lockheed F-117A Nighthawk are the GBU-27/A 'Paveway III' and GBU-27/B 'Paveway III' respectively with the adapter collar between the guidance/control section and the warhead shortened by 3 in (0.076 m) to 6 in (0.152 m), canard surfaces of reduced span, the wing group of the 'Paveway II', and a choice of three guidance units in the forms of the WGU-25/B, WGU-25A/B and WGU-39/B systems. The result of these changes to allow the internal carriage of the GBU-27 by the F-117A is a weapon with shorter gliding range, but this is offset by the fact that the ‘stealthy’ F-117A can operate at higher altitudes than less ‘stealthy’ warplanes, and this restores range to a significant degree.
Another weapon of the same basic family is the 4,700 lb GBU-28/B 'Paveway III Deep Throat' for use by the F-15E Eagle and F-111F. This is based on the BLU-113 penetration weapon with the BSG-92/B wing group and the WGU-36/B control section, and the full-length adapter collar. This weapon was designed, produced, deployed and used within in a mere 17 days during the 1991 UN-led war against Iraq. The GBU-28 was dropped from high altitude by warplanes in supersonic flight, its resulting gravity-aided speed resulting in such kinetic energy at impact that the BLU-113 core could penetrate more than 20 ft (6.1 m) of reinforced concrete or 100 ft (30.5 m) of earth before detonation in command centers and the like. The GBU-28/B has a diameter of 1 ft 2.5 in., length of 19 ft 2 in (5.84 m), span of 2 ft 4.33 in (0.72 m) closed and 5 ft 6 in (1.68 m) open, weight of 4,700 lb (2,131.9 kg) with a 675 lb (306.2 kg) filling of Tritonal explosive, and the FMU-143/B or FMU-143(D-2)/B fuses. In general terms, the 'Paveway III' weapons allow low-level and off-axis stand-off delivery in conditions of low visibility, with the midcourse guidance providing the possibility of delayed laser-designating and trajectory shaping with all their tactical advantages of a considerably expanded launch envelope. Operators of the 'Paveway' series of laser-guided bombs are known to total some 34 countries including Australia, Canada, Greece, Israel, Netherlands, Saudi Arabia, South Korea, Spain, Taiwan, Turkey, UK and USA.
General characteristics (GBU-10 'Paveway II')
|Weight||Bomb unit||2,100 lb||953 kg|
|Warhead - Mk 84||1,970 lb||894 kg|
|Explosives ( Tritonal)||945 lb||429 kg|
|Length||14 ft 2 in||432 cm|
|Diameter||1 fta 6 in||45.7 cm|
|Wingspan||Closed||2 ft 6 in||76.2 cm|
|Open||5 ft 6 in||167.6|
|Range||from a high-altitude||20,000 yards||18,300 m|
|from a low-altitude||1,650 yards||1,500 m|
|Warhead||Mk 84 conventional high-explosive/fragmentation|