July 21, 2011 defense-aerospace.com
(Source: Sagem; issued July 20, 2011)
As we have seen throughout recorded history, each new conflict seems to bring its own share of innovations. Recently, for example, the air strikes over Libya – Operation Harmattan for France, and Operation Unified Protector for NATO in the framework of the UN resolution 1973 – have spotlighted the unexpectedly powerful performance of a new French-made weapon, the AASM Hammer (Highly Agile Modular Munition Extended Range) air-to-ground modular weapon developed and produced by Sagem.
The AASM made a discreet debut in the spring of 2008, when the French air force deployed a 250-kg version in Afghanistan. Today, it is part of the standard combat suite carried by the Dassault Rafale F3 multirole fighter. In fact, it’s an integral part of the tactical air-to-ground arsenal deployed by both the French air force and naval air arm, and has also been chosen by the Royal Moroccan air force as part of their current program to modernize Mirage F1 fighters.
The AASM Hammer is a medium-range guided weapon that can be used day or night and under all weather conditions – which is not the case of regular laser guided bombs, which have to be launched in the vicinity of air defense systems. Furthermore, these bombs’ guidance may be compromised, or even rendered ineffective, by cloud cover or hard rain.
France has already ordered more than 1,500 AASMs in the 250-kg version. The AASM is a rocket propelled bomb with terminal guidance, capable of very high precision attacks on targets at a range of more than 60 km. In other words, it can be fired by Rafale or Mirage fighters from a comfortable standoff distance, outside the reach of enemy air defenses.
The AASM stands out because it’s a modular weapon system, totally autonomous and jam-proof, flying resolutely towards its target once the coordinates have been manually loaded into the onboard computer by the pilot. The most advanced AASM models, like the Laser version now undergoing final tests, allow the modification of terminal guidance if needed to hit moving targets. In short, the AASM is a real “fire & forget” weapon. It could also be considered the equivalent of an air-to-surface missile, if only because its exceptional performance makes it the only weapon of its kind of the market for now.
Furthermore, the AASM "Hammer" is a family of precision weapons, with guidance and propulsion kits fitted to standard bombs of different sizes: 125 kg, 250 kg, 500 kg and 1,000 kg – the latter dubbed the “bunker buster” because of its ability to penetrate several meters of reinforced concrete. The aft-mounted propulsion kit comprises a solid rocket motor and four winglets for flight control, deployed when the weapon is released.
The most commonly used version today is the SBU-38 (Smart Bomb Unit) AASM 250, with hybrid inertial/GPS guidance. There is also the SBU-54 version, combining an inertial guidance system (INS), GPS correction and terminal guidance via an infrared imager (IIR). The latest addition to the family is the SBU-64, which adds laser terminal guidance to the INS/GPS hybrid package, enabling the AASM to hit moving or even highly agile targets.
The AASM’s sophisticated terminal guidance means that this weapon features capabilities unmatched by a conventional laser-guided bomb. In particular, the AASM offers a virtually vertical terminal trajectory, enabling it to attack, for example, a tank hidden behind a sand embankment or a concrete wall, or even a target in a narrow street or trench.
To date, the French air force has deployed about one hundred bombs in combat, all the SBU-38 INS/GPS version. This uses the basic guidance kit, with three inertial gyros whose directional pulses are managed by a Kalman filter and corrected in real time by satellite data from a military-standard GPS (Global Positioning System) receiver.
The Kalman filter is actually a mathematical method, or set of algorithms used to improve accuracy. It is applied in the form of an infinite impulse response electronics filter that estimates the various states of a dynamic system, based on a series of incomplete or scrambled measurements. Sagem’s engineers paid particular attention to this issue, to ensure that the AASM flight path could be continuously corrected and recalculated according to a predicted path that would enable it to hit its target within several meters – after a flight of 60 kilometers or more, as was demonstrated in the Libyan theater of operations recently.
To further improve precision, Sagem has developed two new versions of the AASM, currently undergoing final tests, that are no longer impacted by erroneous target coordinates: the SBU-54, which adds an infrared imaging mode, capable of recognizing a fixed target, the coordinates of which were first entered in its memory; and the SBU-64, using terminal guidance by acquisition of a laser spot, enabling it to destroy moving ground targets with a high degree of accuracy – to less than a meter in this case! A recent test demonstrated the effectiveness of this version against a target moving at 80 km/h.
Deploying both Mica air-to-air missiles and Hammer air-to-ground weapons, the Rafale fighters deployed in Libya have demonstrated unprecedented operational flexibility. The weapon system fulfills its assigned "swing role" capability, between air-to-air and air-to-ground missions. But in its configuration with four Mica and six Hammer missiles, the Rafale also provides real swing-role capability between different ground attack missions.
For instance, a patrol in this configuration prepared for a Battlefield Air Interdiction (BAI) mission can change to a ground attack mission when already in flight, to perform dynamic targeting of very different types of targets, including air defense sites or armored vehicles arriving at the front lines, without being affected by different weather conditions.
The most eloquent testimony undoubtedly comes from the French air force and navy pilots who deploy the SBU-38 daily, alongside their GBU-12 Paveway laser guided bomb, the standard 250-kg bomb used by NATO air forces.
According to Captain P, who is very satisfied with the performance of this new weapon, "In the Libyan theater of operations, as soon as we have the slightest suspicion of air defenses, which are always widely scattered in Libya, we remove the Paveway bombs and equip our Rafales with the AASM, because it allows us to effectively engage the enemy, away from their air defenses, especially the dangerous ’SAM rings’.
“In TST (Time-Sensitive Targeting) mode, the AASM’s range also allows us to hit a target without being detected from the ground, a possibility in asymmetrical combat. What’s more, a single Rafale can carry up to six AASMs. These are all significant advantages. Plus, since we can fire our weapons from further away than with the Paveway, and don’t need approach maneuvers, we save fuel – and in the combat environment, fuel is a key factor.
"The AASM is guided autonomously after being released, once the target coordinates have been obtained, whether they were uploaded to the system prior to the mission or in-flight.
“In TST mode, the target coordinates are generally provided by the Rafale’s optronics systems, either the front sector optronics (FSO) or the Damoclès pod. For the SBU-38 AASM, the Damoclès is considered an excellent coordinates extraction sensor. From the cockpit, we can also determine the terminal angle-of-attack in relation to the target.
"Over the last twenty years, the nature of warfare has changed completely: the enemy is more diffuse and the risks of collateral damage a major concern. So we need new systems that reduce detection and allow us to engage several targets simultaneously.
“The AASM full meets these requirements for our operations in Libya, since it can be used not only for symmetrical combat, but also for asymmetrical combat as well as guerrilla operations”.