Decoy flare

The terms decoy flare or countermeasure munition are used to denote a system, which imitates the IR signal of a plane and therefore ground-air, water-air or air-air rockets, so-called heat-seeking missiles, get lured away from their targets. One of the first and best-known IR seekers Sidewinder - was developed in China Lake (Fig. 2.20). 

In order to be protected against such heat-seeking guided missiles, pyrotechnic decoy flares, which are based on blackbody radiation (or better greybody radiation), have been and are still being developed since the late 1950 s. The specific radiant emittance of a radiating body (IFin W cm pm ) can be described using Planck s rule  

In accordance with the rule of Wien, the maximum wavelength of the blackbody radiation Amax (pm) shifts towards shorter wavelengths (higher energy) with increasing temperature  

Since in reality there is no actual blackbody radiator (for which the Planck law applies, W), but a more realistic so-called greybody radiator (W ), the value f has been defined as the quotient W7W, where can be given values between 0 and 1 (1 = genuine blackbody). For example, soot ( 0.95) behaves almost like a blackbody radiator, whereas MgO behaves more like a greybody radiator. 

The highly exothermic reaction for the formation of MgF2 heats up the carbon soot formed to approx. 2200 K, which then emits the IR radiation. Moreover, in Mg rich formulations (m 2), the evaporating Mg is oxidized in the gas phase (3100 K). In addition, the carbon which is formed from the reductive elimination of fluorine from Teflon can be oxidized further to CO or CO2 by atmospheric oxygen  

The use of IRCM flares is either pre-emptive or reactive. In the pre-emptive use, flares are deployed in a hostile environment in anticipation of a threat. Thus the release serves to reduce the contrast of the scene to impede lock-on and to make tracking of the actual target more diflicult. In the reactive mode, the actual target is already tracked by a seeker system and the flare aims to break the lock and to lure the missile away. In view of these necessities, the basic key requirements of decoy flares are the peak intensity, Jx(W sr ) and the rise time, dix/dt. A typical time/intensity specification for decoy flare defines rise time profile (d//dt), peak 

Metal-Fluorocarbon Based Energetic Materials, First Edition. Emst-Christian Koch. 

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Polymerization Binder for M48 Decoy Flares , NAD-RDTR No 232 (1973) 60) R.C. Harris,... 

The shape is generally similar to the shape of a storage canister or dispenser from which the decoy flare is ejected by the aircraft upon command of the pilot. The decoy body generally has a circular or rectangular cross-section because of the cost considerations and ease of manufacture. The shaped flare is covered with a priming coat that facilitates ignition when the decoy is released from the aircraft. 

The salient features of some IR flares and decoy flares burning time, IR output along with end use, are given in Table 5.6. 

The IR intensity of formulations based on Mg/KN03/hydrocarbons are equally high and are used in new decoy flares. These formulations are good for decoy... 

Table 5.6 Salient features of some infrared flares/decoy flares.

Modern missiles employ counter-counter measures. Their advanced seeker heads use two or more spectral bands in an attempt to distinguish between the flare and the target. Trajectory discrimination may also be used by some seeker heads. The physical size of the heat source is more important as imaging seekers that can discriminate a spot target of IR flares, have been developed. Depending on their application, IR decoy flares can be further classified into ... 

MTV Magnesium, Teflon, Viton (based decoy flares)... 

Fig. 2.21 Comparison of the relative radiation intensity of a plane and a MTV decoy flare.

The schematic construction of a IR decoy flare is shown in Figure 2.22. The main reaction between Mg and Teflon can be formulated as follows, where m > 2 ... 

Therefore, during the radiation of a MTV decoy flare, the greybody radiation of the carbon soot (intensive) is superimposed with the less intensive selective radiation of the CO or C02, respectively. In addition to the typical wavelength dependent intensity of the radiation of a plane, Figure 2.21 also shows that of a MTV decoy flare. 

Fig. 2.22a Typical reaction zones of a conventional decoy flare (left) and a high-nitrogen flare based on perfluoroalkylated tetrazoles (right).

Decoy flare, using fluorine compounds (PTFE) ... 

Decoy materials of this composition undergo the above reaction to reach temperatures of 820°C in less than one second and above 750°C for twelve secrmds after their exposure to air. Presently this type of material is used in a commercial decoy flare that is composed of pyrophoric iron coated onto steel foil articles [35]. Due to increasingly demanding materials performance, environmental standards, aging, and duty-cycle, there exists a need for continued development of new materials and approaches to achieve pyrophoric materials with tailorable output. 

In 1965, the Russian chemist Alexander Alexandrovich Shidlovskii (1911-1985) in his book on pyrotechnics refers to the possibility to use FIFE as an oxidizer in pyrotechnic mixtures [53]. Finally, Herbert Ellern (1902-1987) in his epochal monograph on pyrotechnics in 1968 for the first time in the open and accessible literature refers to the use of magnesium/PTFE mixtures in infrared decoy flares and gives details on caloric data and ignition sensitivity [54]. From then on, magnesium/ PTF E has made its way into numerous appHcations as will be discussed in the following chapters. 

Douda, B.E. (2009) Genesis of Infrared Decoy Flares, Naval Surface Warfare Center,... 

Hahma developed high-density pyrolants for autophagous nose cones for advanced infrared decoy flares with improved kinematic separation behaviour [46]. Typical payloads are depicted ... 

Apart from their widespread use in tactical air-warfare pyrotechnic, infrared decoy flares allegedly serve to increase the survivabihty of intercontinental ballistic missile warheads (re-entry vehicles) against any ballistic missile defense measures. Practice targets for ballistic missile defense purposes have been developed based on 155 mm parachute illuminant shells. A prototype shell received 2500 g Ailing of magnesium/Teflon/Hycar . This material yields burning times between 160 and 190 s and radiant intensities in the 600 W sr range in a particular band at 18 000 m altitude [11]. 

Other uses of compositions similar to those used in decoy flares are... 

The radiant intensity profile for equal amounts of standard MTV decoy flare mix with the above composition is depicted in Figure 10.23. The spectral efficiency for the latter is about twice ( 2.03) in the 2-2.6 pm band. This is due to the much higher Mg content in MTTP formulation (66 vs 54wt% Mg). However, despite the high Mg content, the latter formulation shows a very slow rise in intensity, indicating a slower burn rate. Thus this material would require a different grain geometry to meet with operational rise time specifications. 

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