by Michael Puttré
Aug. 1, 2001

 

A Soviet-era helicopter spews flares promiscuously. It fires rockets into a hillside, turns, and flies away scattering more flares in its wake. This is Afghanistan in 1981. It is also Macedonia in 2001.

From one generation to the next, expendable countermeasures ejected from platforms remain the most widely used self-protection method. The reasons are simple: They are inexpensive, in ready supply, easy to use, and relatively effective. In a 21st century, where unobtrusive, solid-state jammers and slick, turret-mounted directed IR countermeasures (DIRCM) should rule, it is flare and chaff that reigns over the battlefield.

Since the First World War, when warships made smoke to obscure enemy gunnery, efforts have been made to protect valuable platforms with expendable countermeasures. As eyeball gave way to electron for tracking and targeting, countermeasures appeared in the form of chaff. In the night skies over Germany in World War Two, aircrews of British bombers threw bales of "Window" chaff into the slipstream to blind the enemy's radar. When infrared seekers appeared on missiles that were unaffected by chaff, flares followed soon after to lead the missiles astray. Over time, deployment and dispersal methods evolved to where mortars and rockets fired decoys from the decks of ships and squibs and mechanical systems ejected them from aircraft. The one constant over time -- other than the wind -- is the dance macabre of weapon and countermeasure.

The primacy of expendable countermeasures is subject to the occasional costly interregnum. During the Soviet campaign in Afghanistan IR flares were used extensively from Soviet helicopters with high success against Soviet-type man-portable air-defense systems (MANPADS). After delivery of Stinger MANPADS to the Mujahedin by the US, these decoys were no longer effective because the seekers filtered out their spectral signatures. Analysts have said the Soviets lost more than 200 helicopters to Stingers, which became the decisive weapon of the war. Subsequent improvements in flares once again made them effective against "second generation" MANPADS missiles. On the other hand, "third generation" MANPADS are now taking the field (see "Facing the Shoulder-Fired Threat").

Israeli Military Industries Ltd. (IMI) (Ramat Hasharon, Israel) has said it will formulate custom flares to defeat any specific infrared (IR) missile seekers, provided they have an example of the seeker to work with. This is easier said than done. Missile manufacturers jealously guard their seeker technologies and are extremely reluctant to allow their products to fall into the hands of countermeasures developers, even if these hands are "friendly." In this day and age, this results in some awkward situations. Engineers at the Jam Lab at BAE Systems North America (Nashua, NH) said that they would love to get their hands on a Mistral MANPADS but can't, even though its BAE Systems parent is a partner in MBDA Missiles Systems (London, UK), producer of the Mistral.

Overall, expendable countermeasures have short development cycles compared with active countermeasures (RF jammers and DIRCM) and stealth. This enables expendable countermeasures developers to produce decoying materials with characteristics that are effective against specific seekers in a relatively short period of time. However, seeker developers are able to adapt their technologies to disregard advanced decoys. This takes longer than making new expendables, but less time than developing a new active countermeasure or platform incorporating stealth. In some ways, the principal of evolution is at work.

 

A snapshot of the situation as it exists today reveals that flares and chaff can still be highly effective against the vast majority of currently deployed missile threats. Assuming that a nation planning to send its forces into harm's way has some appreciation of the threats its mission platforms are liable to encounter -- or better yet, solid intelligence -- then it can equip them with appropriate expendable countermeasures. The limiting factor then is one of the numbers of countermeasures that a platform can carry.

Dr. David Schmeider, senior research scientist at the Electro-Optics, Environment, and Materials Laboratory at Georgia Institute of Technology, noted that in certain cases, protection can still be difficult to achieve, even when suitable expendable countermeasures are avail-able for expected threat types. That is because dispenser placement on the platform and countermeasures ejection pattern and timing selection are tricky and complex problems to solve. These are especially complex problems on large aircraft and ships because of the possibility that not all of the platform will be in the threat seeker's field of view at once. "So if you are not careful, you will end up dispensing [countermeasures] that are either obscured by the platform or simply out of the threat's field of view," he said. "If you dispense too soon the seeker will reacquire the target; if too late you will fail to get sufficient separation."

This problem is getting considerable attention. For instance, Gregory Rohling and Dr. Darrell Lamm, two of Schmeider's colleagues at Georgia Tech, have developed a unique genetic- algorithm-based optimization technique that shows promise for finding suitable solutions that can be widely applied.

How countermeasures are dispersed becomes the most important consideration. With expendable countermeasures, what counts is having enough of the right stuff in the right place at the right time when the threat comes along. Techniques of dispersing countermeasures will determine how long a platform can remain in the target area and how effective it will be in performing its mission. This is a very black world. Governments guard their techniques and strategies closely -- almost as closely as missile makers.

Something In The Air

In air operations, the missile threat can come from other aircraft or from the ground. The latter threat can be from suspected sites, or in the case of low-altitude operations, from MANPADS that could really be anywhere. Aircraft operating in such environments require countermeasures deployable on hair-triggers.

"Pilots prefer automatic systems rather than relying on tactics and maneuvers to counter the threats," said Ronen Factor, expendable countermeasures program manager at IMI. "When automatic systems are not available to protect the aircraft, the only alternatives left for the pilots are maneuver and other avoidance tactics, and some missiles shot from close range simply cannot be avoided."

Ronen, who is himself a pilot in the Israeli Air Force, said the use of sensors, computers, and automatic self-protection systems drastically reduces the crew workload while performing their mission, and provide instant protection only when it is necessary. "[Automatic dispensing systems] enable a more aggressive approach. Of course, more important is the fact that they enable the crew to execute their mission and come back home safely."

Ronen said that when IMI performed flight trails to qualify its AIRMOR system of missile approach warning sensors, processor, and countermeasures dispensers against missiles, it tested the automatic and manual modes through many scenarios. During these trails, testers were able to evaluate, among other issues, the efficiency of the automatic system versus the manual pilot-activation approach. "The results showed clearly that when the automatic mode was selected, the helicopter was protected in all cases against the IR-guided missile, but, when the system was off, and the pilot had to manually dispense the countermeasures after he was alerted for the approaching missile, this action took too long - much slower than the missile," Ronen said. "There are some human factors in the acknowledgment and the response time of the crew that can be compensated only by computers and real time automatic systems that compute the optimal solution for the specific threat."

In Ronen's view, "smart" and automatic systems that are triggered by events or situations such as missile approach or other type of early emission detection are much more effective than automatic crew-activated dispensers. The countermeasures are dispensed only at the right time and location, providing more protection time while not revealing the aircraft location to threats when it is not necessary. In addition, these automatic systems can tailor their solution to each specific threat and therefore be much more effective to the relevant threat than the other approach of manual crew activation.

However, the smart approach is not without its faults. "The false alarm rate problem is one of the most important issues when a system needs to be evaluated," Ronen said. "Aircrew will have more confidence in the system if the false-alarm rate is low. Low-false- alarm-rate systems will reduce workload drastically and will assist the crew to succeed in their mission safely."

Historically, missile-warning systems have had high false-alarm rates. Several companies, including IMI and Avitronics (Centurion, South Africa) have developed "solar blind" filters for their UV missile-warning systems to eliminate false alarms due to reflections. Other types of false alarms, such as from acetylene torches or other urban UV sources, can be minimized by "teaching" the controller to ignore certain signatures known to trigger a false alarm.

Of course, another solution to the false-alarm problem is to eliminate the missile-approach-warning system altogether and train aircrews to set their dispensers to deploy a constant stream of flares or chaff while over targets or high-risk areas where hostile missiles are expected. Paul Egbert, advanced IR countermeasures program manager at BAE Systems North America said preemptively launching expendable countermeasures makes it possible to deny a missile launch by preventing the launcher from gaining a target lock.

Thus, in many ways preemptive use of flares can achieve superior results to reactive systems, particularly if missile warners with low false- alarm rates are not affordable or available. Nevertheless, there are just so many flares and chaff dispensers you can pack onto an aircraft. "If you intend to make preemptive use of flares or chaff, then you absolutely must perform intensive mission planning first," Egbert said. "Through mission planning, it is possible to limit the exposure of the aircraft and help ensure that it will have enough countermeasures rounds to perform its mission effectively."

Simulation and modeling can be effective tools for incorporating optimal preemptive deployment of countermeasures into mission planning. Problems of tactics and questions of effectiveness versus numbers can be resolved by playing out scenarios that simulate engagements where countermeasures will be employed.

Surface Tension

Guided anti-ship missiles have claimed many victims in numerous wars: from the Six Day War in 1967, the Indo-Pakistan War of December 1971, the October War in 1973, the Falklands War of 1982, US-Libyan skirmishes across the "Line of Death" in 1986, to the "Tanker War" of 1987-88 and the crippling of the USS Stark. Two conclusions can be drawn from these encounters: The first is that ships seem to get hit whenever anybody wants to hit them. The second is that the operations of major powers are inconvenienced - not prevented - by the actions of minor powers equipped with anti-ship missiles. The second conclusion tends to make people more complacent about the first.

The crew complement, value, and symbolic presence of warships makes their loss more significant than the loss of an aircraft. Yet if anything, it is arguably easier to hit a ship with a missile than a tactical aircraft, provided the opportunity presents itself. In the fog of war, such opportunities can be made. According to some observers, protecting a ship from missiles is a much more complicated problem than protecting an aircraft, and so governments will tend to count on other agents of protection, such as covering forces, deterrence, and even politics. None of these can be of much comfort to the crew that spots that characteristic smoke plume on the horizon.

"From my point of view the biggest problem of shipboard countermeasures is its 'black magic' aspect," said Heinz Bannasch, product manager at Buck Neue Technologien GmbH (Neuenburg, Germany). "With all these different IR and RF grenades and rockets for short-, medium- and long-range deployment for confusion, distraction, or seduction in combination with jamming devices, hard kill, ship maneuvers, etc., the use and the understanding of countermeasures is too complex. Low acceptance among navies for shipboard countermeasures is not so much due to a perception of overall low effectiveness of the technology, but from insufficient predictability in action."

How do you -- predictably -- get the right decoy in the right place at the right time? According to Bannasch, the answer is simple on paper: The right stuff is a substance that provides a ship-like signature in all spectral, temporal, and spatial features. The right place is for the decoy to be deployed at the ship, with moderate separation afterwards. This guarentees that the decoy pattern and ship's signature will overlap in the seeker's narrow field of view. Moderate separation is required to remove the target ship from the area of impact, but not so as to give the seeker an oportunity to reaquire. The right time is as soon as possible, due to late lock-on profiles or supersonic speed of current generation anti-ship missiles such as the Gabriel IV and the SS-N-22 Sunburn, respectively.

A proper decoy is not an answer to a specific threat, but an intensified copy of the intended target. The target is the "master." Both missile seeker and expendable decoys are "slaves" in that their features are derived from the target. Variable features, such as the size and aspect (shape) of the ship, cannot be discriminated by the seekers of current anti-ship missiles. Therefore, decoys need only match the signature of the ship to seduce the missile seeker off target.

As always, things are changing. According to Jean-Marc Puech, marketing manager at Lacroix Defense (Muret, France), newer RF missile seekers are better able to identify and filter out chaff. As a result, Lacroix is replacing conventional chaff with structural elements whose signature is very close to that of the vessel. In future low temperature infrared decoys will be used and the development of these devices is directed to the design of effective imaging decoys once the capabilities of these types of seeker system become operational.

Some manufacturers of ship decoy launchers, such as Buck, Wallop, and Rafael place great emphasis on the trainability of the launcher itself in order to achieve optimal deployment patterns. "Accurate and rapid deployment of countermeasures within in the reduced field of view and reduced range gates of modern anti-ship missiles is required," Bannasch said. In his opinion, standard decoy deployment procedures; where the decoy is deployed, the ship "catches" the decoy, and then the ships runs for separation; cannot be achieved in the face of a supersonic missile threat, or one that has late lock-on capability.

Even so, it is not clear how an unsupported ship would survive a coordinated attack of staggered waves of missile launches, particularly if the attacks came from more than one quarter. Consider also a series of attacks from the same quarter a minute or so apart that would not provide sufficient time to reload the decoy launcher. The US Navy responds to these possibilities with an elaborate task force system that protects key assets, such as nuclear aircraft carriers, with escorts and aircraft. On the other hand, this offers scant protection to the pickets, and the Japanese kamikazes exploited this shortcoming to good effect during World War Two. And what are anti-ship missiles but the kamikazis of today?

 

 

SIDEBAR:
Flare Natural Selection: Genetic algorithms can help select optimal flare patterns

Greg Rohling and Dr.Darrell Lamm

When a single flare will not decoy a threat, design of an integrated flare pattern is required to protect a platform. Unfortunately, this can become a daunting task. For example, a flare pattern for a large aircraft may contain up to 16 flares, with each flare needing a definition of three attributes: the choice of one of the four aircraft dispensers, the choice of one of the eight possible flares in inventory, and the time of ejection between 0 and 2.56 seconds to 10 millisecond accuracy.

This typical example defines a 48 dimensional search space with 1062 possibilities. Since an exhaustive search is impossible, researchers at Georgia Tech Research Institute (GTRI) have successfully applied Genetic Algorithms (GAs) for searching the search space to find flare patterns that provide countermeasures for several types of threats under numerous conditions. GAs have proven superior to traditional gradient decent algorithms for problems such as these where the search space is of high dimension and the output of the fitness function contains high frequencies, and many local maxima and minima. GAs mimic the three major features of natural evolution: natural selection, exchange of genetic material during mating, and random mutations.

Specifically for the flare pattern applications, those flare patterns that are determined to be best of the current generation have the highest probability of propagating their characteristic into future generations. The mating process then takes attributes from the parent patterns and combines them to create the next generation of flare patterns. The mutation process randomly perturbs the attributes of the flare patterns, providing a natural resistance to getting trapped on a local maxima.Evaluations for flare patterns are done using either hardware or software simulations of the threats, which involves simulations for many threat scenarios. For example, a flare pattern must be effective regardless of variations in threat type, attack angle and attack range. It must handle variations in atmospherics and warning time. Also, the pattern must be effective at many aircraft speeds, altitudes and maneuver conditions.

These numerous variations in threat scenarios define an Objective Space. Multiple Objective Genetic Algorithms (MOGAs) find a set of solutions where each individual is not out performed in all objectives by any other individual. The designer is then able to choose the pattern that best fits his needs. Unfortunately, algorithms to date require the solution of all objectives before assigning a fitness value.

Fortunately, dispenser such at the ALE-47 are able to dispense different patterns based on the current state of the aircraft. Likewise, warning systems are beginning to estimate the angle of arrival and threat types. Because this additional information can be used to eject a flare pattern specific to the detected threat scenario, there are many fewer objectives for a single pattern to meet.

Greg Rohling and Dr. Darrell Lamm are researchers at Georgia Tech Research Institute. 

 
 

Copyright 2001 eDefenseonline.com & Horizon House Publications