Countermeasure
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A countermeasure is a system (usually for a military application) designed to prevent sensor-based weapons from acquiring and/or destroying a target.
Countermeasures that alter the electromagnetic signature of a target thereby altering the tracking and sensing behavior of an incoming threat (e.g. guided missile) are designated softkill measures.
Measures that physically counterattack an incoming threat thereby destroying/altering its payload/warhead in such a way that the intended effect on the target is majorly impeded are designated hardkill measures.
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[edit] Softkill measures
Softkill measures are applied when it is expected that a sensor-based weapon system can be successfully interfered with. The threat sensor can be either an artificial one, e.g. a solid-state infrared detector, or the human sensory system (eye and/or ear).
Softkill measures generally interfere with the signature of the target to be protected. In the following the term signature refers to the electromagnetic signature of an object in either the ultraviolet (wavelength: 0.3-0.4 µm), visual (0.4-0.8 µm), or infrared (0.8 - 14 µm) spectral range as well as cm-radar range (frequency: 2-18 GHz), mmw-radar (35, 94, 144 GHz) and finally sonar range (either 50Hz - 3 kHz and/or 3- 15 kHz).
One or more of the following actions may be taken to provide softkill:
- Reduction of signature
- Augmentation of signature
- Imitation of signature
Softkill countermeasures can be divided into on-board and expendable countermeasures. Whereas on-board measures are fixed on the platform to be protected, expendable measures are ejected from the platform.
Preemptive action of countermeasures is directed to generally prevent lock-on of a threat sensor to a certain target. It is based on altering the signature of the target by either concealing the platform signature or enhancing the signature of the background, thus minimizing the contrast between the two.
Reactive action of countermeasures is directed toward break-lock of a threat already homing in on a certain target. It is based on the tactics of signature imitation, augmentation, or reduction.
[edit] Aerial countermeasures
Generally one has to distinguish between infrared and radar countermeasures. As infrared (IR), the wavelength range between 0.8 and 5 µm is considered. As radar, the frequency range between 2 and 18 GHz is considered.
In the wake of missile attacks against civilian passenger and cargo airliners in the early 2000s, various agencies investigated the feasibility of equipping countermeasures chaff and flares. Many commercial carriers found the estimated price of countermeasures to be too costly. However, the Israeli airline El-Al, having been the target of a failed missile attack in Mombassa, Kenya in 2002, began equipping its fleet with radar-based, automated flare release countermeasures from June 2004[1]. This caused concerns in some European countries, which proceeded to ban such aircraft from landing at their airports[2].
[edit] IR-decoy flares
IR-decoy flares serve to counter infrared-guided surface-to-air missiles (SAM) or air-to-air missiles (AAM) and can be expelled from a craft according to an anticipated threat in defined sequences.
As stored, chemical-energy-source IR-decoy flares contain pyrotechnic compositions, liquid or solid pyrophoric substances, and/or liquid or solid highly flammable substances[3].
Upon ignition of the decoy flare, a strongly exothermal reaction is started, releasing infrared energy and visible smoke and flame, emission being dependent on the chemical nature of the payload used.
There is a wide variety of calibres and shapes available for aerial decoy flares. Due to volume storage restrictions onboard platforms, many aircraft of American origin use square decoy flare cartridges. Nevertheless, cylindrical cartridges are also available onboard American aircraft, such as MJU 23/B on the B-1 Lancer or MJU-8A/B on the F/A-18 Hornet; however, these are used mainly on board French aircraft and those of Russian origin, e.g. PPI-26 IW on the MiG 29.
Square calibres and typical decoy flares:
- 1x1x8 Inch . e.g. M-206, MJU-61, (MTV based) M-211, M-212 (spectral flares)
- 2x1x8 Inch . e.g. MJU-7A/B (MTV based), MJU-59/B (spectral flare)
- 2x2,5x8 Inch e.g. MJU-10/B (MTV based)
Cylindrical calibres and typical decoy flares:
- 2,5 Inch e.g. MJU-23/B (MTV based)
- 1,5 Inch e.e. MJU 8 A/B (MTV based)
- 1 Inch e.g. PPI 26 IW
[edit] Pyrotechnic Payloads
[edit] Blackbody Payloads
Certain pyrotechnic compositions, for example Magnesium/Teflon/Viton (MTV), give a great flame emission upon combustion and yield a temperature-dependent signature and can be understood as Gray bodies of high emissivity (e~0.95). Such payloads are called blackbody payloads. Other payloads, like iron/potassium perchlorate pellets, only yield a low flame emission but also show temperature-dependent signature [4]. Nevertheless, the lower combustion temperature as compared to MTV results in a lower amount of energy released in the short-wavelength IR range. Other blackbody payloads include ammonium perchlorate/anthracene/magnesium and hydroxy-terminated polybutadiene binder (HTPB) [5]
[edit] Spectrally balanced payloads
Now other payloads provide large amounts of hot carbon dioxide upon combustion and thus provide a temperature-independent selective emission in the wavelength range between 3 and 5 µm. Typical pyrotechnic payloads of this type resemble whistling compositions and are often made up from potassium perchlorate and hydrogen lean organic fuels [6]. Other spectrally balanced payloads are made up similarly as double base propellants and contain nitrocellulose (NC), and other esters of nitric acid [7] or nitro compounds als oxidizers such as e.g. hexanitroethane and nitro compounds and nitramines as high energy fuels [8]. The main advantage of the latter payloads is their low visibility due to the absence of metals such as sodium and potassium that may be either easily thermally excited and give prominent emissions or give condensed reaction products (such as carbonates and chlorides), which would cause a distinct smoke trail.
[edit] Pyrophoric Payloads
As with the pyrotechnic payloads these will also give either graybody radiation or selective emissions. In contrast to pyrotechnic payloads, pyrophoric substances use the oxygen from the environment for oxidation. Hence specific energy density of pyrophorics is always higher as compared to any pyrotechnic; however, pyrophorics suffer from low oxygen partial pressure at greater heights. A typical liquid pyrophoric fuel is triethylaluminum(TEA). Upon combustion of TEA, a selective IR spectrum is obtained, which is mainly determined from carbon dioxide and water vapour. Any transient or permanent combustion product of aluminum are not IR-active in this region of the electromagnetic spectrum [9].
Solid pyrophoric payloads are based on iron platelets coated with a porous aluminium layer. Based on the very high specific surface area of aluminum those platelets instantaneously oxidize upon contact with air. In contrast to TEA combustion, those platelets yield a temperature-dependent signature.
[edit] Highly flammable payloads
These payloads contain red phosphorus (RP) as an energetic filler. The RP is mixed with organic binders to give brushable pastes that can be coated on thin polyimide platelets. The combustion of those platelets yields a temperature-dependent signature. Endergonic additives such as highly dispersed silica or alkali halides may further lower the combustion temperature[10].
[edit] Radar decoys
To counter radar-guided missiles, chaff is used. These are aluminum-coated glass fibers or silver-coated nylon fibers having lengths equal to half of the anticipated radar wavelength.
[edit] Naval decoys
Land and sea-based forces can also use such countermeasures, as well as smoke-screens that can disrupt laser ranging, infrared detection, laser weapons, and visual observation.
[edit] Intercontinental Ballistic Missiles (ICBMs)
Countermeasures are a complicating factor in the development of anti-ballistic missile defense systems targeting ICBMs. Like aircraft, ICBMs theoretically could evade such systems by deploying decoys and chaff in the midcourse phase of flight. Novel proposed chaff mechanisms describe the creation of a "threat cloud" by deploying large aluminized PET film balloons which could conceal a warhead among a large number of inert objects having similar radar profiles.
[edit] Hardkill measures
Except for countering ICBMs, hardkill measures generally refer to measures taken in the so-called "end-game" shortly before a warhead/missile hits its target. The hardkill measure in general physically affects the incoming warhead/missile by means of either blast and/or fragment action. The action may lead to:
- disturbance of the stability of a kinetic energy penetrator which in turn will greatly lose its penetration ability as the deflection angle increases.
- premature initiation of a shaped charge (e.g. too great stand-off), but most likely improper initiation, thereby impeding optimum jet development.
An example of a Hardkill countermeasure is the reactive armour found on many modern armoured vehicles.
[edit] See also
- Electronic countermeasures
- Infrared countermeasures
- Anti-aircraft
- Anti-ballistic missile
- National Missile Defense
- Strategic Defense Initiative
[edit] References
- ^ Missile defense for El Al fleet, CNN, May 24, 2004. Accessed July 18, 2006.
- ^ Europe objects to El Al's anti-missile shield, Ynetnews, Feb 26, 2006. Accessed July 18, 2006.
- ^ [1]E.-C. Koch, Pyrotechnic Countermeasures: II. Advanced Aerial Infrared Countermeasures, Prop.,Expl.,Pyrotech.31 2006, 3
- ^ J. Callaway, Expendable Infrared Radiating means, GB Patent 2 387 430, 2003, GB.
- ^ D. B. Nielson, D. M. Lester, Blackbody Decoy Flare Compositions for Thrusted Applications and Methods of Use, US Patent 5 834 680, 1998, USA.
- ^ J. Callaway, T. D. Sutlief, Infrared Emitting Decoy Flare, US Patent Application 2004/0011235 A1, 2004, GB.
- ^ R. Gaisbauer, V. Kadavanich, M. Fegg, C. Wagner, H. Bannasch, Explosive Body, WO2006/034746, 2006, DE
- ^ E.-C. Koch, Infrarotleuchtmasse, DE 1020040043991, 2006, DE
- ^ [2]D. B. Ebeoglu, C. W. Martin, The Infrared Signature of Pyrophorics, AD921319, National Technical Information Service, May 1974.
- ^ H. Bannasch, M. Wegscheider, M. Fegg, H. Büsel, Spektrale Scheinzielanpassung und dazu verwendbare Flarewirkmasse, WO 95/05572, 1995, D.
