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Missile Approach Warning Systems

The Infra Red Heat Seeking Missile Threat

Guided Surface to Air Missile (SAM) systems were developed during World War II but only really started to make their presence felt in the 1950s. In response, electronic counter measures (ECM)and flying tactics were developed to overcome them. This proved to be quite successful provided that reliable and timely treat warning is given to apply the counter measures and appropriate flying tactics effectively.

Analysis of aircraft losses due to enemy action since the 1960s shows that at least 70% of all losses were attributed to passive heat seekingi.e. Infra Red (IR)guided missiles. This might appear surprising considering that radar guided SAMsystems have longer engagement ranges, are faster, have higher manoeuvring potential, carries larger warheads and are equipped with proximity fuses.

The main reason why IRguided missiles were so effective was that it took much longer to develop effective warning systems against them. Most aircraft that were shot down never knew that the missile(s) were coming! Radar warning receiverson the other hand already proved their effectiveness by the early 1970s which improved the survival rate of aircraft against radar threats considerably.

The first air to air IR missiles appeared in the 1950s. The technology allowed more compact missile designs and made it possible to develop IR Man Portable Air Defence Systems (MANPADS)i.e. shoulder launched missiles, which became operational by the 1960s.

IR MANPADS are relatively cheap, quite robust, easy to operate and difficult to detect. They also do not require the infrastructure often associated with radar guided SAM deployments which is often a give away of their presence.

Vast quantities MANPADS have been manufactured (more than 700,000 produced since 1970 according to CSIS “Transnational Treats Update“ Volume 1. No 10. 2003). Large numbers proliferated during the Cold War and immediate post Cold War era. Substantial quantities are available and affordable on the black market and have found their way into the hands of “non state” organizations or the so called “asymmetric” threat. (An estimate by Jane’s Intelligence Review of Feb 2003puts this number as high as 150 000). According to an article “Proliferation of MANPADS and the Threat to Civil Aviation” of August 13, 2003 by Jane’s Terrorism and Insurgency Centre, estimates that the black market price of MANPADS could be as low as $150,000.

Intelligence regarding the whereabouts of MANPADS, especially in the hands of “non state” organizations, is usually vague and unreliable. This in turn makes it difficult to anticipate where and when to expect MANPADS attacks.

Advanced new seeker head technology, improved rocket motors and aerodynamic refinements have further increased the performance and effectiveness of MANPADS significantly as 2nd and 3rd generation MANPADS appeared by the 1980s. Their performance were improved in terms of lethal range, minimum launch angle, manoeuvring potential and all aspect engagement angles (1st generation MANPADS were restricted to only rear sector attacks). They also became more ECMresistant.

MANPADS therefore became even more lethal and specifically against more vulnerable platforms such as helicopters, light aircraft, as well as commercial and military type transport aircraft (during approaches and departures). The slower speed of these platforms forces them to spend more time within the kill zones of MANPADS compared to high performance fighter and strike aircraft.

At least 35 MANPADS attacks on civilian aircraft are on record. Twenty four were shot down killing about 500 people in the process.

Missile Approach Warning (MAW) System Requirements

Protecting aircraft against IR guided missiles depends firstly on reliable detection and warning of missiles and secondly on applying effective ECM. This discussion will mainly focus on the missile warning aspect.

Note: The above statement is not applicable to Omni Directional IR jammers which do not make use of missile warning at all as they simply radiate modulated IR energy for as long as they are switched on. Omni Directional IR jammers have been around since the 1970s and when the correct jamming modulation techniques were applied, were reasonably effective against 1st generation amplitude modulated MANPADS which operated in the near-IR band (1 to 2 micron).

The arrival of 2nd and 3rd generation MANPADS however changed all that. They operate in the mid-IR band (3 to 5 micron) and make use of more advanced modulation techniques (for example frequency modulation). Therefore instead of jamming these missiles, the Omni Directional IR jammer now actually became a source for the missiles to home in!

Functional requirements

Providing timely warning against IR MANPADS is a big challenge. They give no warning of their presence prior to launch, they do not rely as radar and laser guided missiles do, on transmitted RF energy for guidance purposes and are also quite small in size. They are therefore not easy to detect.

MANPADS are relative short range weapons, typically up to about five kilometers with the heart of the kill envelope one to three kilometers. They therefore allow very little margin for error to effectively counter them as the time to impact (TTI) on a target at one kilometer, is only about three seconds. The TTI for targets at three and five kilometers is also relatively short – only seven and a little over eleven seconds respectively.

The MAW must therefore provide reliable and timely warning to allow appropriate counter measure responses. Near 100% probability of warning (POW) and very fast reaction times to counter nearby missile launches (in the order of one second) are therefore essential.

Air crew will only rely on the system if they have high confidence in it. The MAW must therefore also have low false alarm rates (FAR), even when engaged by multiple threats from different directions.

Quick response times and low FAR are however inherently conflicting requirements. An acceptable solution therefore requires a balanced approach to provide the most successful end result without compromising the POW.

Accurate azimuth and elevation angle of arrival (AOA) information is another very important requirement. Directional IR Counter Measures (DIRCM) systems depend on MAW systems for accurate enough initial pointing (about two degrees) to ensure that the DIRCM acquires and engages incoming missiles timely and successfully.

Accurate AOA is also important in deciding the dispensing direction of the counter measure decoys (flares). It is vital to avoid the situation where the platform and the dispensed decoys both remain within the instantaneous field of view (IFoV) of incoming missiles. Missiles could very well in situations like that, once they pass the decoys, still hit the platform! This is of particular importance where separation between the decoys and the platform takes too long as is the case with slow flying aircraft.

Accurate AOA is further important where the platform should preferably maneuver when dispensing decoys to increase the miss distance. This is however more applicable to fast jets where their high speed tends to negate the separation caused by the decoy’s ejection velocity. A turn towards approaching missiles to establish/increase the angle between the decoy and the platform is especially important in cases where a missile approaches from the rear between the five or seven ‘o clock sectors. If the AOA is not accurate enough, the pilot could very well turn in the wrong direction and set himself up for the situation as described in the previous paragraph.

The system must also be fully automated as the human reaction time in critical cases (short range launches), is too long.

Physical Requirements

Light aircraft, helicopters and fighters usually have limited space for additional equipment and are often quite sensitive to mass increases. Unavoidable mass increases should therefore be limited to prevent reductions of the platform’s payload. The system should also not cause adverse aerodynamic drag which demands that the physical size and number of boxes must be minimized. The power consumption must further be kept within the capacity of the platform’s electrical system.

To reduce the installation and integration costs, provision should also be made for the necessary interfaces to ensure proper communication and co-existence with other onboard avionics.

Human Machine Interface (HMI) Requirements

Integrated display and control functions are highly desirable to avoid unnecessary duplication on instrument panels where space is often severely limited. If a platform is for example equipped with both radar and missile warning systems, the HMI should be integrated to display the respective threats clearly and unambiguously.

The integrated HMI must also indicate the system’s operating status, serviceability status, mode of operation, remaining decoy quantities etc. Separate control panels are only justified for safety of flight purposes such as ECM on/off and decoy jettison functions.

Cost considerations

Procuring EW self protection systems has direct and indirect cost implications.

Direct costs involve the initial price of the system, spare parts as well as test equipment to ensure that the performance and availability of the systems is maintained throughout their entire life cycle.

Installing and integrating EW systems on aircraft is another direct cost

Indirect cost on the other hand involves degradation of the aircraft’s performance as a result of having the system onboard which in turn impacts negatively on the operating cost of the aircraft.

The lowest initial price of a system does therefore not necessary offer the best solution as all the factors needs to be considered. The overall cost effectiveness of systems i.e. price versus performance is more important in deciding which system to select.

Types of Missile Approach Warning (MAW) Systems

Three different technologies have been used for MAW systems i.e.

Pulse Doppler Radar

Infra Red

Ultra Violet

based systems. Each technology has their advantages and shortcomings which can be summarized as follows:

Pulse Doppler Based MAW

Advantages

Can measure distance and speed of approaching missiles. It can therefore determine the time to impact (TTI) and optimize the timing of decoy counter measures (flares) dispensing.

Does not depend on the motor of missiles to be burning.

Less sensitive to weather conditions.

Disadvantages

In sophisticated environments active systems could compromises own presence and therefore increase vulnerability.

Detection range of small missiles with low radar cross section like MANPADS is limited which in turn could result in marginal warning time and therefore late decoy dispensing.

Provides only sector warning as it cannot measure direction accurately. It can therefore not point DIRCM systems. It could also lead to bad decision making regarding the dispensing direction of decoys and maneuvering in certain cases.

Susceptible to false alarms due to other RF sources.

Can cause interference with ground air traffic control radars if operating frequency is not selected carefully.

Probability of warning deteriorates in high ground clutter environments i.e. reflections caused by vertical rock surfaces in mountain and possibly also built up environments.

More difficult to integrate than passive systems.

Infra Red Based MAW

Advantages

In general the atmospheric transmission of IR radiation is better than that of solar-blind UV radiation.

Can potentially achieve longer detection ranges at altitude where there are no ground clutter.

Can potentially detect the kinetic heat of missiles after motor burnout at altitude but probably not at low level due to high IR background clutter.

Provide good AOA information for pointing a DIRCM and good decision making regarding decoy dispensing direction and maneuvering.

Disadvantages

Must compete with massive amounts of natural (sun) and man made IR clutter.

False alarm rate is therefore a huge problem against surface to air missiles due to high IR background clutter originating from the earth.

Needs vast computing power to overcome false alarm problem which in turn drives the cost up.

Two colour detectors are used in some systems to assist in the suppression of background clutter and lower FAR. Even though it solves some problems, it creates others as it complicates the system further due to the optical, sensitivity and extremely high pixel rate requirements which impacts negatively on cost and reliability.

Cannot provide actual range information.

Traditionally IR detectors have very narrow instantaneous fields of view to achieve good enough signal to target ratio. Large detector arrays are therefore required to provide 360° azimuth coverage which is another cost driver.

Requires cooled detectors which complicates life cycle logistic support and result in high cost of ownership.

Detection range could be limited against future new technology low IR/UV emission rocket motors.

Ultra Violet Based MWS

Advantages

Operates in solar blind UV spectral wave length region and therefore has no natural (sun) false alarms. UV based MAW systems therefore have a much reduced false alarm problem to solve compared to IR based systems.

Very good probability of warning in high clutter background environments.

Wide instantaneous field of view.

Provide very good AOA information for good decoy dispensing decision making, maneuvering and for pointing DIRCMs.

Has fast response time against nearby missile launches.

More simple system compared to Pulse Doppler & IR technologies.

Does not require cooling and needs only moderate computing power.

Low life cycle cost.

Disadvantages

To detect approaching missiles, the rocket motor of the missile must be burning - it requires the high effective burning temperatures associate with solid fuel rocket motors.

IR based systems probably better at altitude but UV better against surface to air missiles.

Cannot provide actual range information but can derive TTI from the rapid increase in amplitude of the approaching missile’s signal.

Detection range could be limited against future new technology low IR/UV emission rocket motors.

MAW Systems

Current available MAW systems as well as those under development, represent all three types of technologies. Each technology has strong and weak points and none provide a perfect solution.

Pulse Doppler Radar Based

France

MWS - 20 (Damien) originally from Dassault Electronique (now Thales)

Israel

EL/M-2160 (ALQ – 199) from ELTA

Japan

J/APQ – 1 * from Mitsubishi Electronic Corporation

Russia

LIP MAW (Obsolete system)
Arbalet-D from Phazatron NIIR Corporation

UK

PVS 2000 originally from GEC Marconi and Plessey Avionics (now SELEX and Thales) (Obsolete system)

UK and Italy

AMIDS from BAE Systems (now SELEX) and Elettronica (Uncertain of production/development status)

USA

AN/ALQ – 127 originally from Westinghouse (now Northrop Grumman) (Obsolete system)
AN/ALQ – 153 originally from Westinghouse (now Northrop Grumman) (Obsolete system)
AN/ALQ – 154 from AIL (Obsolete system)
AN/ALQ – 156 from BAE Systems North America