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Guided bombs are getting better; coalition efforts in the 1991 Gulf War involved the first large-scale use of laser-guided bombs, and demonstrated their excellent cost-effectiveness in medium altitude releases against high-contrast fixed targets in clear weather daylight conditions.

Guided bombs are getting better; coalition efforts in the 1991 Gulf War involved the first large-scale use of laser-guided bombs, and demonstrated their excellent cost-effectiveness in medium altitude releases against high-contrast fixed targets in clear weather daylight conditions. However, Nato operations in Kosovo in 1999 underlined the limited usefulness of such weapons in the presence of low cloud. The leading nations are now striving to achieve precision air-to-ground delivery under day/night all-weather conditions. Parallel efforts are directed toward longer ranges and more effective warheads. (Airborne Warfare)

Precision delivery of air-to-ground ordnance enhances terminal effectiveness, while reducing costs in both human and materiel terms. Another important advantage is the consequent reduction in collateral damage to civilian property and personnel. It may be noted that international law rules out attacks on military objectives that may be expected to result in collateral damage, which would be excessive in comparison to the direct military advantage in prospect. It is also noteworthy that the 10,484 Nato strike sorties in Operation Allied Force resulted in only 90 fatal incidents of collateral damage, killing around 500 Yugoslav civilians.

One of the lessons learned was that in some circumstances the presence of civilians may be detected at literally the last moment, in which event there is a strong argument in favour of man-in-the-loop guidance. One alternative to laser spot-homing is manual electro-optical guidance, as in the case of the Rafael Spice, which combines the guidance kit from the company's Popeye rocket-powered missile with a low-cost general-purpose bomb.

In the Gulf War, 210,000 pieces of unguided air-dropped ordnance totalling 73,600 tonnes were complemented by 15,500 precision guided munitions weighing 6700 tonnes. This 6.85 per cent of air-to-ground weapons accounted for more than 50 per cent of the targets destroyed. Raytheon Paveway LGBs represented 52 per cent of the precision weapons, the same company's AGM-65 Maverick a further 29 per cent and its AGM-88 Harm approximately 12 per cent.

After the war some pricing figures were released from the US, giving at least some indication of the relative cost of dumb and smart ordnance. For example, General Accounting Office report GAO/NSIAD-97-134 (Operation Desert Storm -- Evaluation of the Air Campaign) gives a purchase price of only $498 for a low-drag Mk 82 bomb, or $1100 for the high-drag Snak-eye version, compared to $9000 for the corresponding GBU-12. Likewise, the Mk 84 general-purpose bomb cost $1871 in low-drag or $2874 in high-drag form, compared to $22,000 for the GBU-10. The most expensive of the Paveway series were the $65,000 GBU-24, the $75,539 GBU-27 developed for the F-117A, and the heavy $100,000 GBU-28 developed for the F-111 and F-15E. However, the LGBs were cheap in comparison with imaging infrared (IIR) guided weapons: the GBU-15 is stated to have cost $227,000.

In air operations over Kosovo in 1999 (Operation Allied Force), precision-guided munitions represented 35 per cent of all ordnance dropped. This was also a different war in other respects. For example, there was at least 50 per cent cloud cover more than 70 per cent of the time. Air strikes were performed unimpeded on only 24 of the 78 days of the operation.

The Royal Air Force was one of the services badly affected by the adverse weather, the effects of which were exacerbated by a 15,000 ft minimum weapon release altitude, a limit dictated by the threat of the Serbs' air defence systems. Britain contributed 1008 strike sorties by Harriers and Tornadoes, releasing only 1011 air-to-ground weapons. Of these, 230 were unguided 450 kg bombs and 531 were RBL 755 cluster weapons. Only 236 were 450 kg Raytheon Paveway II LGBs and 18 were 1360 kg Paveway IIIs, the remaining six guided weapons being MBDA Alarm anti-radiation missiles.

At the time of this writing, statistics are not available for Operation Enduring Freedom over Afghanistan, which began on 7 October 2001. It is known, however, that in the Raytheon Paveway II LGB series the US Air Force's GBU-10 and -12 were used, as was the US Navy's GBU-16. In the Paveway III series, the GBU-24 is used, as well as the 2130 kg GBU-28A/B Super Penetrator Weapon with the BLU-113 warhead. The GBU-28A/B, informally referred to as Deep Throat, was developed as a bunker-buster during Desert Storm, and (since the withdrawal of the F-III) is employed only from the F-15E.

Other guided bombs used during Enduring Freedom included the Boeing AGM-130, a rocket-powered derivative of the GBU-15 TV/IIR-guided glide bomb, based on the Mk 84 munition. This appears to have been used primarily to strike at the entrances to caves. Following its successful use in Kosovo, the 900 kg-class Boeing GBU-31 Jdam was dropped over Afghanistan from a variety of platforms, including the B-52H. In an interesting example of inter-service collaboration, target coordinates generated by the GPS-equipped Lantirn pod of a US Navy F-14D were transmitted via a US Air Force E-3 Awacs aircraft to B-52Hs. The availability of the Link 16 data bridge will allow such information to be transmitted directly from the reconnaissance aircraft to the bomber.

The problem in Afghanistan of dealing with insurgents who took refuge in mountain caves led the Pentagon to the early introduction of some new penetration weapons, notably the Raytheon GBU-24C/B Paveway III with the Lockheed Martin Advanced Unitary Penetrator (AUP) warhead and Hard Target Smart Fuze (HTSF). Also accelerated were various ACTD (advanced concept technology development) programmes, including Hard Target Defeat, which uses high temperature incendiary material to destroy chemical and biological weapon stores.

Maverick

In view of the Royal Air Force's embarrassingly poor air-to-ground performance in Kosovo, Britain is now buying the Raytheon AGM-65G2 Maverick as an interim anti-armour weapon, although it is expected to be retained in service alongside the new Alenia Marconi Systems Brimstone, which has active millimetre-wave radar guidance. The AGM-65G2, which has a unit price in excess of $ 250 000, employs an imaging infrared seeker for day/night capability, and a 136 kg warhead.

Although the original television-guided, contrast-lock, launch-and-leave AGM-65A was used operationally 30 years ago, Maverick remains a viable anti-armour weapon. Some 66,000 have been produced, and the series is in service in 29 countries. Approximately 14 000 have been fired, including 5300 in the Gulf War and 800 in Kosovo. The overall success rate in combat has been 93 per cent. Delivery accuracy is given as one metre.

Some 1200 US Air Force AGM-65Gs are having their IIR guidance sections replaced by charge coupled device (CCD) seekers, providing high quality television imagery, enhanced reliability and the capability to operate in dusk/dawn conditions. Most of the IIR seekers from these AGM-65Gs are to be fitted to AGM-65As taken from storage for international sales. Future Maverick developments will reportedly employ GPS+INS (satellite and inertial) midcourse guidance and a data-link, making possible longer ranges, aim-point refinement and last-minute aborts.

Gam and Jdam

Although atmospheric conditions during Desert Storm were generally better than in Allied Force, there were times when the weather precluded the use of laser-guided bombs. The Pentagon subsequently emphasised the development of GPS guidance as a means to achieve what is classed as near-precision delivery in adverse weather conditions.

The Northrop Grumman Gam (GPS-Aided Munition) series was developed to meet an interim US Air Force requirement for an all-weather near-precision bunker-buster. The Gam tail-kit converts the 900 kg Mk 84 bomb into the GBU-36/B, and the 2040 kg BLU-113 penetration warhead into the GBU-37/B. Both types entered service in 1996, and it is believed that four GBU-37/Bs were dropped by B-2As over Kosovo. An unspecified number were dropped more recently over Afghanistan. A further development of the Gam is the GGM (GPS-Guided Munition), which Northrop Grumman is currently marketing in collaboration with Thales' TDA Armement as a low-cost alternative to Boeing's Jdam.

Research and development for the baseline 900 kg class Boeing GBU-31 Jdam (Joint Direct Attack Munition) with GPS+INS guidance began in 1992, operational testing was carried out in 1998-99, and 652 were dropped by B-2As against targets in Kosovo during Operation Allied Force. Each aircraft carried 16 individually targeted Jdams.

The 925.4 kg GBU-31 (v)1/B Jdam is based on the Mk 84 bomb, while the 961.4 kg GBU-31(v)3/B employs the BLU-109 penetrator. Both have a Honeywell INS and Rockwell Collins GPS receiver, a Lockley tail fairing, a Lockheed Martin mission computer, an HR Textron tail actuator subsystem, an Enser and Eagle-Picher battery, Stremel Manufacturing longitudinal strakes to provide a 3G manoeuvre capability and a glide range of up to 24 km, and a Dayron FMU-152 Joint Programmable Fuze.

In tests the Jdam demonstrated a reliability of 95 per cent. With combined GPS+INS guidance, it gave an accuracy of 9.6 metres, compared to a requirement for 13 metres. If GPS is not available, the Jdam is still required to provide an accuracy of 30 metres, given a GPS-handoff from the launch aircraft. It is actually achieving 14 metres with INS alone.

Following the delivery of the 937 Jdam kits of Lot 1, a twelve-channel GPS receiver was introduced, allowing the munition to make use of signals from all satellites in view, rather than just five. This presumably accounts for the remarkable 8.0 metre accuracy achieved with GPS+INS guidance in recent tests. Other improvements introduced include a selective availability anti-spoofing module (SAASM) to reduce vulnerability to GPS jamming.

The later 460.5 kg GBU-32(v)1B Jdam, which is still in development, is based on the Mk 83 bomb. In September 2000 Boeing was awarded a contract for the development of a Jdam version of the 225 kg class Mk 82 bomb, for completion by the end of 2002.

Following the first four GBU-31 Jdam batches totalling 15,998 low-rate production kits for the US Air Force, in March last year Boeing was awarded a $ 235.5 million contract for the full-rate production of a further 11,054 Jdams (this total consisting of 8272 for US Air Force Mk 84 bombs, 2110 for the service's BLU-109s, 433 for US Navy Mk 84s, and 239 for the Navy's BLU-109s), with a $ 25 million option for 1150 more kits for the Navy. Unit cost is about $ 21,000. These two US services plan to acquire a total of 87,496 units (62,000 for the Air Force and 25,496 for the Navy) by 2008, with production peaking at over 1000 per month. The Pentagon reportedly plans to sell 700 GBU-31 Jdam kits to Israel and 400 to Denmark, both for use on the F-16.

Boeing, as prime contractor for the Jdam programme, has teamed with Alenia Marconi Systems (AMS) to fund flight testing of Jdam with the latter company's Diamond Back variable-geometry joined tandem-wing kit. This gives the weapon substantially extended range, hence the informal designation Jdam-ER. The first flight of a GBU-31 with the Diamond Back kit took place in April 2000, achieving a range of 38.6km from a height of 20,000 ft, compared to the standard range of 12.9 km from that altitude. Later testing was aimed at combining extended range with lateral offset, increasing the footprint area (relative to the basic Jdam) by a factor of more than 20. The same wing kit has also been tested on Boeing's version of the 113 kg Small Diameter Bomb (SDB) fitted with Jdam guidance.

Boeing and AMS have signed a teaming agreement for worldwide sales of the Jdam family and its derivatives, including Boeing's proposal for SDB, which is currently in the competition phase. The two companies are already teamed on the Brimstone anti-armour weapon (a Hellfire derivative) referred to earlier.

Although a 900 kg GBU-31 Jdam, delivered with an accuracy in the region of ten metres, is a very effective weapon against most targets, it is clear that a terminal-phase seeker could reduce average miss distance to the order of three metres, making it even more effective. In the case of the lightweight SDB, a seeker appears to be essential for attacks on hard targets. Modifying the flight profile to give an impact at around 90 degrees to the target surface will further enhance effectiveness.

The SDB is now in the component advanced development phase, and is being competed by Boeing and Lockheed Martin under two-year US Air Force $ 47 million contracts. At the end of this phase one contractor will be selected to proceed with the system development and demonstration (SDD) phase, lasting from FY04 to FY05. Low-rate initial production (Lrip) would then be launched, and a baseline SDB could be in service on the F-15E in 2006.

Production of the selected SDB is planned as a three-phase programme. The initial version is to enter service in 2006 and is expected to deliver a warhead of around 70 kg over a range of 55 km with an accuracy of 13 metres against fixed targets, a figure that implies GPS guidance. Target unit cost is less than $ 50,000. Pending the availability of the Phase 1 SDB, the US Air Force will use a standard Mk 82 bomb equipped with GPS guidance. The Phase 2 SDB is intended to deal with mobile or relocatable targets, using a seeker that will begin development in 2006 to provide initial operational capability in 2009. It is anticipated that the US Air Force will buy at least 12,000 examples of each of these two versions. The Phase 3 SDB is expected to represent an evolution from a guided bomb into a powered attack missile, combining loiter performance with autonomous wide area search and attack capability.

In August 2000, the US Navy successfully tested an IIR seeker known as Damask (Direct Attack Munitions Affordable SeeKer) on what is referred to as a Precision Jdam. A seeker would normally add significantly to the cost of the weapon, but Damask is an uncooled commercial off-the-shelf (cots) Raytheon product from a Cadillac automobile, costing around $ 20,000 and using a low-cost lens. Damask is activated at around 1600 metres from the target, the IIR image of which it compares with a stored template produced from a reconnaissance photograph taken by an aircraft or satellite, or from imagery generated by a synthetic aperture radar. The Damask reportedly gives a one-metre accuracy in a GPS-denied environment. If approved for development, it would eventuate as a pre-planned product improvement (P3I) for Jdam.

Combined GPS+INS guidance is being employed in several new air-tog-round weapon systems, including the Raytheon Jsow (Joint Stand-Off Weapon) or AGM-154, and the Israel Military Industries Delilah and MSOV (Modular Stand-Off Vehicle). It is combined with EO/IIR terminal guidance in such weapons as the Boeing EGBU-15 and the Kentron Raptor II. Future all-weather seekers are exemplified by the Lockheed Martin ladar used in the company's Locaas (Low-Cost Autonomous Attack System).

Enhanced Paveway

Another application for GPS+INS guidance is Raytheon's Enhanced Paveway II/III, which gives laser-homing munitions an all-weather capability. In June 2000, the first tests were performed with a production configuration GBU-27 Enhanced Paveway III. Relative to the Paveway II (of which more than 117,000 examples have been delivered), the Paveway III has enlarged wings for increased range from low-level release, an adaptive mid-course autopilot and a seeker with improved sensitivity and an enlarged field of view.

The Paveway III is compatible with the standard Mk 82 (used in the GBU-22/B), the Mk 84 (GBU-24/B) and the BLU-109 (the GBU-24A/B,-24B/B and -27/B) warheads. The GBU-24C/B and the -24D/B are Paveway IIIs based on Lockheed Martin's BLU-116B Advanced Unitary Penetrator (AUP).

The GBU-28A/B is based on the BLU-113 penetrator, but its weight of 2130 kg and length of 5.84 metres restricts carriage to large aircraft, and its limited manoeuvrability reportedly demands precise release. The GBU-28B/B adds an IMU (Inertial Measurement Unit), allowing the weapon to use inertial or satellite navigation, semi-active laser homing, or a combination of the three. Last year Raytheon Missile Systems was awarded a $ 3.6 million contract to integrate the GBU-28B/B with the F-15E and B-2A.

The American services are primarily concerned with the application of Enhanced Paveway kits to the GBU-24,-27 and -28 penetration weapons (resulting in the EGBU- series), but Raytheon offers similar kits for other members of the Mk 80 bomb series.

It may be noted that the US Air Force has been attempting to achieve deep ground penetration with relatively light LGBs and Jdams, by releasing two weapons in rapid sequence to achieve an effect similar to that of a tandem warhead. This so-called optimal dual-delivery technique clearly relies on the effectiveness of the second bomb to follow the first precisely, which suggests the addition of a flare on the , tail of the first and a simple IR homing device in the nose of the second.

In August 2000, the British Ministry of Defence selected Raytheon's Enhanced Paveway II and III bombs in response to a UOR (Urgent Operational Requirement) for an Interim Precision Guided Bomb (IPGM). The UOR demanded operational capability on the Tornado GR4/4a by October 27, 2001. The production contract was signed in December 2000 and operational trials at Eglin AFB, Florida, gave a median accuracy of better than three metres. The IPGM entered service on schedule, although initial deliveries are reported to retain external interface units and conduits.

A further development of Raytheon's Enhanced Paveway is one of the principal contenders for Britain's Precision Guided Bomb (PGB) or SR(A) 1248 programme. This began as a simple upgrade for existing bombs, but has developed into a requirement for an improved 225 kg class Mk 82 bomb, to be used by the Tornado, Harrier, EF2000 and possibly the F-35 Joint Strike Fighter. Britain has not previously employed America's Mk 82, but this will give commonality with other Nato air forces, and with a guidance kit will provide greater effectiveness than the current unguided 450 kg Mk 13.

Other PGB contenders will include the Boeing/MBDA Jdam with a set of Diamond Back wings, a further development of the Elbit Systems Lizard laser-guided bomb, a weapon with the Leigh Aerosystems LongShot range-extension wings, the Northrop Grumman/TDA Armement GGM referred to earlier, and the Sagem AASM (Armement Air-Sol Modulaire). The ITT (Invitation To Tender) for the PGB programme was scheduled to be released sometime in late 2001, leading to a service entry date of April 2006.

Recent developments in the LGB field include the BPG-2000 weapon, jointly developed by Raytheon and Explosivos Alaveses (Expal) of Spain. It combines a Paveway III laser guidance kit with the newly developed Expal CPE-800 penetrator bomb and the ER501 impact delay hard target penetrating fuze. Flight trials were completed in 2000. Weighing 917 kg, the BPG-2000 is fourteen per cent lighter than the BLU-109 variants of GBU-24, and will be more easily integrated with Spain's EF/A-18A/B, Mirage F1 and EF2000.

AASM

The Sagem AASM is scheduled to replace the LGB and AS.30L laser homing missile in French service. It is to be a fire-and-forget missile with a range of 15 to 60 km, depending on release altitude, and capable of dealing with a variety of target types. The AASM will initially be based on a 250 kg bomb (Mk 82, BLU-111 or CBEMS) and have a maximum weight of 340 kg, including range-extension kit. Later variants are expected to include a 400 or 1000 kg penetrator and a submunition dispenser. The initial guidance module is to provide an accuracy of ten to fifteen metres in all weather conditions, and deliveries of this version are to begin in February 2005. A later imaging-infrared seeker for a day/night version will reduce errors to around three to five metres, deliveries of which will begin in February 2007. Under a contract signed in September 2000, the French Air Force is acquiring 2000 AASMs and the French Navy is to have 1000 units. Production is expected to last until 2012.

Counter-Countermeasures

The day/night all-weather delivery accuracy made possible by America's GPS will be further enhanced by a new generation of military satellites and the use of differential GPS (DGPS), in which local signal corrections are transmitted by a ground station at a precisely known location.

The quantum leap provided by satellite navigation has, however, always had an Achilles Heel as a result of its weak signal strength, making it quite vulnerable to disruption from atmospheric effects and an easy target for hostile jamming. In 1998, the US Air Force tested a Boeing modification to the Jdam, in which the single GPS antenna was replaced by a four-element array, along with software to apply variable gains to the individual antennas, thereby producing a steerable null system that minimised jamming. More recently, the Raytheon GPS Anti-jam Antenna System Gas-1N has been selected for the US Army RAH-66 and the Navy's AV-8B. In parallel with such efforts, Darpa (Defense Advanced Research Projects Agency) has been working under the GPX Pseudolite programme on the use of UAV-borne or ground-based transmitters that would create a high-powered artificial GPS environment over the battle area.

Such focused measures will help maintain the inherent accuracy of GPS-based systems against fixed ground targets. However, the problems arising whilst attacking mobile targets in day/ night adverse weather conditions will persist. In this context it is noteworthy that Northrop Grumman has been selected by Darpa to continue development on network-based airborne radars under the AMSTE (Affordable Moving Surface Target Engagement) programme.
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Comment:Guided bombs are getting better; coalition efforts in the 1991 Gulf War involved the first large-scale use of laser-guided bombs, and demonstrated their excellent cost-effectiveness in medium altitude releases against high-contrast fixed targets in clear weather daylight conditions.
Author:Braybrook, Roy
Publication:Armada International
Geographic Code:1USA
Date:Feb 1, 2002
Words:3588
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