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Denel Dynamics considering C-RAM

Denel Dynamics, a subsidiary of the state arsenal, says it is collaborating on the development of at least three technologies to counter rockets, artillery and mortar ammunition.

Denel Dynamics chief scientist Dr Gerrit Viljoen told the recent South African Joint Air Defence Symposium (SAJADS) rockets, artillery and mortars posed a serious threat to peacekeepers, and especially their base camps.

“Insurgents attack these facilities with 60 mm and 81 mm mortars or with 107 mm rockets fired from improvised grenade and rocket launchers. The accuracy of these weapons is frequently poor, but the threat to peacekeeping forces is considerable,” he said. “Much to their chagrin, modern, well-equipped armed forces frequently find that they lack an adequate means of countering such attacks. Apart from taking cover and letting loose with counter-battery fire, often the only other option is to retaliate from the air.

“However, none of these solutions is really conducive to protecting vulnerable facilities – and can even undermine the viability of peacekeeping missions. Opening fire on suspected enemy positions in built-up areas and in peacetime can be problematic or even out of the question,” he said in a paper presented at the SAJADS late last month.

“Although artillery does not constitute a current threat to peacekeepers, it is a situation that can change quite quickly. There are a very large number of artillery pieces available in the world that can be brought into a conflict at short notice.

“Artillery rockets are launched from multiple tube launcher systems to provide a very high rate of fire. Artillery rockets also provide longer range at a lower mass than conventional tube artillery systems and are thus more mobile. For this reason the 107mm 12-tube launcher is one of the favourite weapons used by insurgents. The 107mm Type 63 launcher can fire 12 rockets in 7-9 seconds.”

The weapon's warhead is a good example of how tough these threats are, Viljoen adds. “Its casing is 20mm thick and consists of a combination of outer steel casing and steel spheres on the inside. The steel spheres provide a lethal area that is very impressive for such a modest weapon. Any countermeasure will have to be able to penetrate at least 20mm of steel before it can explode the filling inside the rocket.”

The 60mm mortar can be hand held and fired and it is a very concealable weapon, Viljoen said. “Insurgents can fire a large number of mortar shells in a very short period (up to 30 bombs/minute per tube, there are 2-3 tubes per mortar section), pick up the mortars, conceal them and blend in with the local population. Mortars are very small targets to shoot down. They also have quite hard shells (5-10mm steel) and they can be fired at very high rates. The amount of ammunition fired is usually limited due to the fact that the attack is of a hit and run type, they have to be packed up and going before the counter-fire reaches them, typically in less than a minute. A sneak mortar attack would then typically be done with only about 10-20 mortar bombs thrown within 20s from one to two tubes.”

Viljoen told conferees systems to counter rockets, artillery and mortar ammunition (C-RAM) have to:
1. Detect and track a very large number of very small threats from a long enough range for the system to react in.
2. Shoot a countermeasure that will be able to destroy the incoming threat at enough standoff range to ensure that the residual damage will be acceptable (100m+). “The best way to do this is to detonate the incoming RAM warhead.”
3. Deliver countermeasures to counter threats at a rate of at least 1-2 threats per second. A minimum of 12 countermeasure firings are required per system before reloading to counter a 107mm launcher salvo.
4. Provide a success rate of intercept that is exceptionally high to give effective protection for a camp (>98%).
5. Provide enough area protection to cover a typical forward operating base or base camp under all weather conditions.

Current solutions to C-RAM include the Raytheon Centurion Phalanx System, the Oerlikon (now Rheinmetall) Mantis and the Israeli Iron Dome.

The Centurion was rapidly developed between 2004 and 2006 to address conditions in Iraq and Afghanistan by adapting the Naval Phalanx CIWS to land use. Viljoen says it has proved to be highly successful and is still providing protection to a number of US facilities in Afghanistan. “It has shot down more than 110 threats including mortar rounds and rockets.”

Mantis is a further development of the Oerlikon Skyguard system utilising the 35mm Millenium gun with AHEAD ammunition.

The Iron Dome is the only operational anti-missile system that is specifically designed for the C-RAM missions today, Viljoen continued. “It detects and tracks incoming threats with radar and first determines if it is going to hit a sensitive area. Only those threats will be engaged by the system. It launches a missile from a 20 missile vertical launcher. The system has a minimum range of 5km and a maximum range of around 30km. The system is deployed operationally in Israel and has been credited with a number of successful rocket intercepts.

Viljoen notes the main shortcomings of current gun systems are:
1. The large amount of ammunition expenditure per kill (Centurion 300 rounds/threat, Mantis 35 rounds/threat) limits the number of threats that can be engaged before reloading to 5/gun for Centurion and 7-9/gun for Mantis.
2. Long dwell time (Centurion around 5s per threat, for Mantis around 3.5s per threat) during which the system is locked on to a single threat.
3. Short range (around 100-1000m)
4. Inability to counter threats at a high rate as a result of the long dwell time and relative short range.
5. Cost per single threat engagement (US$30-60 000) due to large ammunition expenditure. For Iron Dome the cost is reported to be around U$40 000 per missile.

“Existing systems also have a very large capital cost. The system cost for Centurion is reported to be about US$15 million per system. The Mantis system, consisting of one fire control unit, two sensor units and eight guns costs 55 million Euro. An Iron Dome battery consisting of one radar and three launchers costs US$37 million.”

Turning to lasers, Viljoen was dismissive. “Although the cost per kill can be very low (around US$1-2000) … ground-based laser countermeasure systems are simply not all weather, they do not work in fog, rain, cloud and smoke. They also have long dwell times on the target which limits the rate at which they can shoot down threats.”

Viljoen identified the three solutions SA were considering as an
- Advanced active protection system (AAPS)
- Guided shells
- Guided missiles

AAPS System Design

Viljoen noted SAAB Electronic Defense Systems is developing the EDS150 active protection system that uses the Mongoose 1 unguided missile from Denel Dynamics. “Denel Dynamics is doing technology development on the Mongoose 2 guided missile in parallel with an extended range capability. The increased range is achieved by adding sideways thrusters on the missile and an autopilot that can guide the missile to the predicted impact point. Flight tests have been done with intercept ranges at 60m and the system has a theoretical maximum intercept range of 150m. It flies to 150m in less than a second with a miss-distance of less than 0.5m. Up to four Mongoose 2 missiles can be in the air at any one time, giving a kill rate of four threats per second.

“The Mongoose 2 missile targets threat warheads with a specialised radial shape charge warhead that can penetrate 20mm steel and detonate any non-IM explosives behind it. It is designed to destroy threats such as the 107mm [rocket]. The Mongoose 2 missile can attack threats up to an intercept angle of 30 degrees at a maximum range of about 150m. The maximum area that one system can cover against terminal RAM threats is about 100x100m. Larger areas can be covered by using more systems, each covering a sector. The current LEDS150 radar sensor range has to be increased to 500m support Mongoose 2’s capability.

“The system cost of the Mongoose 2 solution is very competitive at about US$500 000 per system. The Mongoose 2 gives a cost per kill in the order of about US$10 000. The Mongoose 2 APS is thus a much more cost-effective solution than the existing systems, the only disadvantage is it short range capability and the limited area of protection. If larger areas need protection, more systems can be deployed.” Viljoen added the future LEDS300 system that is based on the Mongoose 3 missile (also in technology development) will have a much longer intercept range against RAM threats and will be able to provide a much larger coverage area (about 300mx300m). “Its system cost and cost to kill would however be higher than Mongoose 2.”

Guided Shell

Turning to gun systems, Viljoen noted the basic problem for guns is shooting down small RAM targets (60-155mm) because of the inherent dispersion of their shells. Closed loop tracking of the shells can be used to compensate for residual bias effects such as wind, so bias is not really the problem. “Even with closed loop tracking and accurate guns with less than 1mrad dispersion, the probability to hit a 60mm mortar at 1000m is extremely small. If the shell can be guided to compensate for its dispersion error, the miss distances can be reduced dramatically. A proximity fuze on the shell will also increase the hit probability substantially. The required control power is small, to move a shell by 1m in 1000m in one second (typical minimum flight time) requires an average acceleration of only 2m/s2, or 0.2g.

“The simplest guidance law will be command to intercept. RAM targets have highly predictable trajectories due to their ballistic nature. It is proposed to add a tracking-radar boresighted to the gun to track the shell and the incoming threat. As the incoming RAM shells will be attacking the area to be defended, their trajectories will be clustered close together. The tracking radar thus requires multiple tracking channels to track more than one threat in its field of regard, as well as more than one shell. A typical field of view of 5-10 degrees should suffice. The relative tracking accuracy between the incoming threat and the outgoing shell should be high, a resolution of 0.1 to 0.2mrad would be required. The fire control system shall calculate the guidance command on the ground and transmit it to the shell in flight over a datalink. The shell will then execute the required maneuver to ensure a small miss distance of less than 0.5m. A proximity fuze on the guided shell will ensure the correct detonation point of the shell to ensure the destruction of the incoming RAM threat.”

Two guided shell solution are possible: 76mm and 35mm.

Many navies are equipped with the OtoMelara 76mm rapid fire gun or derivations thereof. “The idea is to convert this gun to an effective C-RAM system by adding guidance to its shells. A 3D air-defense radar that can detect and track the RAM threats, a fire control system to designate the gun, together with a tracking radar and datalink on each gun have to be added to the system.

“Denel Dynamics is currently busy developing a guided fuze unit that is compatible with MIL-STD333 2inch fuzes for artillery and mortar systems, including 76mm shells. To adapt this fuze to the C-RAM role the GPS unit will have to be replaced with a command link to receive guidance commands from the fire control unit on the ground. A proximity fuze that is optimized for air to air threats have to replace the current ground proximity function. The challenge would be to package this functionality into the small available space provided by the military standard.

Given such a fuze, any 76mm HE round can then be converted to a guided shell. The 76mm HE round warhead has enough energy to destroy any RAM threat if detonated at a miss distance of less than 0.5m. The 76mm naval guns can fire these shells at a rate of 80-120 rounds per minute. The cost of such a fuze is estimated to be around US$5000 that makes it very affordable. The system cost is estimated at around US$10-15 million depending on the radars to be integrated.

Viljoen summarised that a 76mm system could dDetect and track a very large number of very small threats from a range of more than 2000m which gives enough time for the system to react in; destroy the incoming threat at a maximum range of 1000m by detonating the incoming RAM warhead; deliver countermeasures to counter threats at a rate of at least 1.5-2 threats per second with 80-85 rounds in the magazine per gun; and provide a success rate of intercept of between 90-95%. “With the large ammunition holding, it should be possible to fire 2 rounds per threat to increase the success rate to well over 99%,” Viljoen said. A single system can provide C-RAM cover for a 1000mx1000m … under all weather conditions.

Looking at 35mm, Viljoen noted the most widely used anti-aircraft gun systems in the western world are the 40mm Bofors and the 35mm Oerlikon guns. “The concept is to make specialised guided ammunition versions for these guns. As the 35mm shell is the most challenging in terms of size and the Rheinmetall Mantis system already exists to detect, track and do fire control on RAM threats, it is the logical choice to use this vehicle for the next guided shell.

“A tracking radar and datalink will have to be added to each gun. The warhead will contain heavy tungsten fragments that are optimized to destroy RAM warheads at a distance of 0.5m. Typical intercept speeds between the fragment and the RAM will be about 1500m/s. The warhead will be fuzed by a compact proximity fuze, similar to the one in the guided fuze. The unit cost per shell will be similar to that of the guided fuze unit, about US$5000. The addition of the tracking radar and datalink to each gun is estimated to add about US$10 million to the Mantis system for all eight guns.

Viljoen says the guided 35mm solution can detect and track a very large number of very small threats from a range of more than 2000m which gives enough time for the system to react in; destroy the incoming threat at a maximum range of 1000m by detonating the incoming RAM warhead; deliver countermeasures to counter threats at a rate of at least two threats per second with 250 rounds in the magazine per gun; and provide a success rate of intercept of between 90-95%. “With the large ammunition holding, it should be possible to fire 2 rounds per threat to increase the success rate to well over 99%.” He avers a single system can provide C-RAM cover for a 1000mx1000m forward operating base or base camp under all weather conditions.

Guided C-RAM missile system

Lastly it should be technologically feasible “to develop a C-RAM missile system that is more cost-effective and capable than the Israeli Iron Dome system, which was a crash development based on the integration of existing systems and subsystems. But the cost per missile will still be high compared to the threat being shot down. We know the argument is that it is the cost of the area being protected that should be taken into account and not that of the incoming threat, but as the RAM threat can be delivered in very large numbers, unit missile cost will stay a major consideration. A missile system that will meet all of the requirements … is the local area protection system (LAPS) concept that was developed by Denel Dynamics.

“Missile systems do have the potential to provide larger areas of protection and a very large number can be fired simultaneously, LAPS can control at least 80 missiles in the air at the same time. Where LAPS really come into play is against highly manoeuvrable targets such anti-ship missiles and supersonic cruise missiles such as Brahmos. Even guided projectiles will not be effective against these threats, but they fall outside the scope of current C-RAM systems.”

Viljoen notes the technologies required for the proposed systems are in various stages of readiness. “SAAB and Denel have been working on the LEDS150 APS technology for the last fifteen years. The Mongoose 2 solution described … can be developed within 18 months and will consist mainly of further sensor development (radar range extension and further IIR tracking sensor development) and qualification of the system. The guided artillery fuze is already four years in development. What is available technologically is an actuator, power supply and IMU. A proximity fuze and a datalink have already been developed on the APS technology program, but they still have
to be miniaturised, for which LTCC technology is required. The IMU, battery and warhead technology for the 35mm guided round is in place, what is outstanding is the miniature SAD (which requires MEMS technology), datalink, proximity fuze and miniaturised actuator.

“The guided shells promise to provide the most cost-effective solution for C-RAM but the technology is not yet ready for full scale development. It is recommended to start developing
the technologies required for a guided 76 and 35mm shell as soon as possible, mostly MEMS and LTCC technologies for compact packaging.

“The LAPS system should be developed where there is also a requirement to counter airborne guided missile and bomb threats. The LAPS system will also have a full C-RAM capability.”

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