Military Aerospace Technology Online Archives
This article was Originally Published on Apr 18, 2003 in Volume: 2 Issue: 2
Protecting the Big Birds
Sluggish air speeds coupled with limited evasive maneuverability and large radar and infrared signature equates to a large bull’s-eye for the enemy. There is no doubt that the large military aircraft, which are relatively slow and lumbering, make for attractive targets.
In addition to air-to-air missiles (AAMs) and surface-to-air missiles (SAMs), one of the most dangerous threats to Air Mobility Command’s 1,178 C-5s, C-17s, C-141s, C-130s, KC-10s and KC-135s is the shoulder fired, infrared (IR), man-portable, air defense missile system, commonly referred to as MANPADS. During the past 25 years MANPADS in general have been responsible for 90 percent of aircraft combat losses, and according to GlobalSecurity.org, 80 percent of the fixed-wing aircraft loses during Operation Desert Storm were at the hands of MANPAD operators.
Typically fired from a tube-like disposable launcher, MANPADS seek the heat of jet engine exhaust via IR, or heat-seeking, sensors located in the warhead. The characteristics of each MANPADS vary depending on make, model and origin. The five-foot long U.S. Stinger missile travels at about twice the speed of sound (Mach 2) and is effective within a range of 5 miles and altitude of 11,500 feet. The system is relatively light—about 35 pounds—and can easily be moved or hidden.
In May 2002, a Russian-made SA-7 MANPAD launcher was found a few miles from Prince Sultan Air Base in Saudi Arabia where U.S. planes takeoff and land—well within the range of the shoulder-fired missile.
Similar launchers were also found in November outside the airport in the resort town of Mombassa, Kenya after the failed attack on an Arkia Israeli Airline’s Boeing 757-300 charter jet carrying more than 200 people. This event, along with recent reports, has spiked the growing concern of MANPAD threats to the commercial airline industry (For more information on civilian aircraft countermeasures, visit the MAT Web site for another article by Jordan N. Fuhr).
A Light LAIRCM
With Operation Iraqi Freedom underway and the continued presence in Afghanistan, there has been a push to accelerate the latest program to field large aircraft countermeasures in order to further protect the transports that play an imperative role in the continuing military operations.
The Air Force Aeronautical Systems Center (ASC) at Wright-Patterson Air Force Base, OH, issued Northrop Grumman Systems Corp. of Rolling Meadows, IL, an award to ensure delivery of a C-17 infrared countermeasure capability as soon as possible. This award came only weeks after it had previously awarded the company a contract to procure two Large Aircraft Infrared Countermeasures (LAIRCM) low rate initial production systems for the C-17.
Northrop Grumman received the $7.2 million cost-plus award-fee contract as a result of a combat mission need statement issued by Air Mobility Command for infrared countermeasures capability.
The LAIRCM system is a laser-based, IR countermeasure system designed to enhance individual aircraft survival by providing an effective defensive capability for tanker and transport aircraft, specifically protecting against vehicle launched and shoulder-fired, IR missiles. The LAIRCM system autonomously detects and declares IR missile threats, then tracks and emits infrared laser energy to disrupt and jam the missiles’ guidance, causing even the most advanced heat-seeking missiles to miss its target.
Phase I calls for installation of the system on 12 C-17s and eight C-130s, and Phase II specifies modification of 59 aircraft and completion of another 79 (43 C-17s, 24 C-130s and 12 KC-135s).
However, this timeline has been impacted due to the most recent contract modification. Air Force LAIRCM Program Director Colonel Mike Cappelano told MAT, the first phase should be completed in June 2005, 15 months earlier than originally planned.
The accelerated project plans will design, develop and test a single transmitter configuration of the LAIRCM system, consisting of one BOSS processor, minus two interface technique generators and two video processors, one control indicator unit, one small laser transmitter assembly, six ultraviolet missile warning subsystems sensors and two repeaters.
Due to difficulties Northrop Grumman had in producing the amount of hardware necessary to equip the full system on a few aircraft in a limited time, the Air Force opted for equipping a small number of the C-17s with one jamming turret rather than the full two-turret version. This will accelerate delivery to the Air Force.
The BOSS configuration, or “LAIRCM light” as some refer to the one-jamming turret version, is intended to be an interim system and eventually those aircraft will be equipped with the standard LAIRCM two- or three-turret configuration. The effort, which will take place at Boeing-Long Beach, will also include: re-direct and procure hardware to outfit up to 12 C-17 aircraft with the BOSS configuration; modify and configure software to operate BOSS system with the currently installed AN/ALE-47 dispenser system; upgrade 508 U.K. Ministry of Defence (MoD) processors to the LAIRCM; prepare abbreviated test plan and generate interim safety of flight certification paperwork; provide BOSS training for aircrews and maintainers; drawing and configuration updates to reflect BOSS requirements; and provide deployable field service representatives for field training and support.
The standard LAIRCM system consists of five basic elements: a control indicator unit (CIU); a missile warning subsystem (MWS) which may consist of either or both ultraviolet and infrared sensors; a pointer/tracker transmitter (P/T) subsystem; a countermeasures processor (CP); and a laser jam source subsystem. The CP is the master system controller and the interface among subsystems.
Up to three laser jammers will be installed on each aircraft type. All the subsystems, with the exception of the laser jammer, are non-developmental items that have been tested and fielded as part of the special operations C-130 Directed IR Countermeasures (DIRCM) program, which is managed by U.S. Special Operation’s Command (USSOCOM) in Tampa, FL. USSOCOM awarded Northrop Grumman a contract in 1999 to produce and install the AN/AAQ-24 DIRCM NEMESIS systems on 59 special operations AC-130 gunships and MC-130 Combat Talon aircraft.
The DIRCM system was developed to protect the large transport aircraft in the same way the LAIRCM operates, first detecting a missile launch, determining if it is a threat and activating the countermeasures to track and defeat the threat. The main difference between the two systems is that the jamming energy in the LAIRCM system comes from Northrop Grumman’s multi-band Viper laser.
Cappelano said, “We leveraged our system off Air Force Special Operations Command’s Directional Infrared Countermeasures system and added the Viper laser to protect larger aircraft and provide growth for more capable emerging missile threats.”
The future of IR countermeasures is looking toward a closed-loop infrared countermeasures (CLIRCM) capability. The proposed closed-loop IRCM would detect and classify incoming missiles, then emit a custom jamming energy to defeat the specific threat. The process would cause the missile to break its lock-on with the aircraft, allowing the system to detect and defeat another potential target after only a few seconds. The current open-loop IRCM systems do not defeat targets with specific jams, therefore, the possibility exits that a missile could reacquire its target if the jammer moves to defeat another missile.
CLIRCM technology has been under development at Wright-Patterson Air Force Base, under the direction of the Air Force Research Laboratory’s Sensor Directorate’s Laser Infrared Flyout Experiment (LIFE) program.
The Air Force has conducted successful tests of the system that proved CLIRCM technology holds the potential to offer performance improvements and cost reductions over that of the current open-loop LAIRCM system.
While LAIRCM is the latest development in the group of aircraft countermeasures to be equipped, other systems have been helping to protect the large aircraft for decades. As advances in technology pave the way for more sophisticated weapons systems, countermeasures must adapt to the evolving threats.
Because no one single antenna or receiver can cover the entire spectrum of operating weapons, the variety of protection onboard an aircraft must be as large—if not larger—as the array of enemy threats. For that reason, multiple systems are installed and work in conjunction to guarantee that potential threats will be detected and the necessary measures taken to avoid a hit.
It could be argued that receivers are ultimately the most important piece of any defensive system. Receivers monitor and detect potential threats allowing the crew to take appropriate actions or automatically deploying countermeasures.
One system that is common on the C-5s, C-17s and C-130s is the Lockheed Martin/Alliant Defense AN/AAR-47 missile approach warning system (MAWS). According to officials at Warner Robbins Air Logistics Center, the C-141 was specifically excluded from this program due to its scheduled retirement in 2006. However, the SOL II version of the C-141 has an AAR-44 passive infrared receiver and infrared jammer manufactured by Cincinnati Electronics.
The AAR-47 is a passive electro-optic system that uses sensors to detect missile exhaust and advanced signal processing algorithms and spectral selection to analyze and categorize threats. Like most systems, it consists of two or more sensor domes—usually mounted near the nose and in the tail cone—a central processing unit and a control indicator. Frequency selection and signal processing techniques are used to minimize false alarms. When a threat is detected the control indicator provides a missile warning and alerts from the direction the missile was fired. The receiver will then send a signal to a countermeasure dispenser. The system allows the crew to set the dispenser to manual, semi-automatic and fully automatic. In fully automatic mode once the threat is positively identified, the system will immediately deploy its countermeasures.
Chaffs and Flares
The dispenser that is used in concert with the AAR-47 is BAE Systems Integrated Defense Solutions (formerly Tracor) AN/ALE-47 countermeasure dispenser. The ALE-47 is a reprogrammable, computer-controlled system that can deploy chaff and infrared flares in addition to the POET and GEN-X active expendable decoys.
Chaff and flares are used to confuse radar and heat seeking missiles. Decoy flares are typically made of magnesium and when dispensed, burn white-hot to confuse and defeat a missile’s infrared tracking mechanisms. Flare dispensers are located strategically around the aircraft to provide optimal protection. For example, the C-5 Galaxy is equipped with 12 flare dispensers armed with six flares each (four under each wing and four under the nose).
In 2000 the MJU-50/B infrared countermeasure flare was introduced to the Air Force. The 1-inch by 1-inch by 8-inch expendable is unlike magnesium flares and instead is composed of proprietary pyrophoric special material. When dispensed, specially treated metal foils rapidly oxidize in the air. The oxidation reaction produces heat and in large quantities produces what ASC refers to as a “cloud of heat,” generating enough infrared energy to decoy surface-to-air and air-to-air missiles.
Alloy Surfaces Company Inc. of Pennsylvania developed the MJU-50/B for the C-130—which was the primary developmental and operational testing platform.
This particular flare is almost nonexistent in the visible spectrum, offering the ability to achieve uncompromising covertness even when dispensing flares. Other flares characteristically illuminate the sky and can alert other potential threats to an aircraft’s location. While these special material flares serve in this low-profile role, the other flares still serve a purpose in aircraft inventories.
In addition to the IR threat, large aircraft are also easy targets for radar seeking missiles. Chaff is used as a decoy for radar seeking missiles and consists of glass silicate fibers with an aluminum coating. They are approximately 60 percent glass fiber and 40 percent aluminum by weight. The fibers, or dipoles, look like small strips of aluminum foil cut to length to match the various wavelengths of the radar. Half-wave dipoles make very good radar reflectors. Typical dimensions for use against a 10-GHz radar would be 0.6 inch long, 0.01 inch wide, and 0.001 inch thick. Only 0.1 pound is needed to cause an echo equal in size to that of a large bomber.
After the chaff is ejected from the dispenser and into the aircraft slipstream, the chaff packages burst open to form a radar-reflective cloud called a chaff corridor. Each chaff package is designed to simulate an aircraft and several aircraft can create a chaff curtain, consisting of thousands of false targets, which confuse the radar guidance package on a missile so they are unable to locate the real targets within the chaff cloud.
Because chaff particles have considerable aerodynamic drag, their forward velocity quickly drops to near zero. When this happens, radars such as pulse Doppler and moving target indicator (MTI) can identify chaff as airborne “clutter.” This allows continued tracking of a target within a chaff cloud as long as the target has a radial component of velocity.
Increasing Electronic Countermeasures Systems
The Special Operations Forces (SOF) AC/MC-130s recently received the go ahead for a fiber optic towed decoy. Boeing, Fort Walton Beach Division, selected BAE Systems ALE-55 Fiber Optic Towed Decoy (FOTD) over Raytheon’s ALE-50 towed decoy.
Although the BAE FOTD system was passed over for the B1-B bomber, according to Donald R. Michaels, director of the Special Operations Forces System Program Office, the government concurred with the selection for the AC-130 Spectre gunships and MC-130 Combat Talon I/IIs based on the thorough source selection process Boeing used.
When installed, potentially four reel-out/reel-in towed decoys could be housed in two underwing pods. The decoys will be connected to New Jersey-based ITT’s ALQ-172 high-band jammers. The decoys on the MC-130 Talon IIs will be equipped with the ALQ-172(V)3 low-band jammer as well.
The ALQ-172 system has been on Special Operation aircraft since the early 1990s when it replaced the AN/ALQ-131 ECM pod as the primary radio frequency jammer for AC-130H aircraft. The digital frequency discriminator (DFD) based systems originally had only high-band countermeasure capability, but since that time upgrades have made to offer low-band capabilities of the ALQ-172(V)3 as well.
However, with the direction to outfit the ALE-55 on those SOF aircraft, newer warning systems and receivers will most likely follow. BAE is competing to furnish remaining MC-130s with its low-band system—the ALQ-196—and ITT is working to replace the ALQ-172s with a more comprehensive radio frequency countermeasures system.
Despite being passed over for the towed decoy program, Raytheon—along with Alloy Surfaces and Meggitt Defense Systems—is on the brink of a possible contract for its Comet infrared countermeasure pod. According to Roy Azevedo, manager of Advanced Decoy Programs at Raytheon Electronic Warfare Systems, Comet preemptively dispenses a material that creates a false target and spoofs infrared seekers. Each pod consists of six canisters of material and dispenses countermeasures for up to 30 minutes. The material, which is invisible in the visible spectrum, can be released automatically or by crew control at varied rates to fit the situational environment and the plume tailored to mimic any aircraft’s engine signature.
Using technology derived from advanced flares, Comet also has shown prospective for C-130 outfitting during testing.