L-166 Review of Expendable Infrared Countermeasures
FOR GOVERNMENT AGENCIES ONLY
This document is solely based on non-classified information.
The purpose of this report is to provide a general review of expendable infrared countermeasure technologies. More specifically developments of both MTV and spectral flares and their implications on munitions safety and occupational health are discussed.
Aeroplanes are high intensity infrared targets with spatially resolved patterns and an overall mean spectral temperature of ~ 700 K. If the integrated intensities in selected bands are evaluated band A: (1.8-2.5 μm) and band B: (3.5-4.8 μm) than aircraft display a ratio B/A of >> 5, i.e. 7 - 10.
To fight aerial targets infared guided missiles have been developed that are using seeker heads working in the 1,8 – 2,5 μm band which is commonly known as the PbS (lead sulphide) band. To counter these guided missiles pyrotechnic decoy flares are in use. Upon use of a pyrotechnic decoy flare the highly exothermic reaction of the pyrotechnic payload yields an electromagnetic signature, that depending on the composition of the combustion products is either selective in nature or satisfies Planck’s law.
Blackbody payloads are based on MTV (Magnesium/Teflon®/Viton®), and give hot carbon particles as the primary combustion product that strongly influences the signature. MTV flares thus show Planck’ type intensity distribution and mean spectral temperatures in the order of T ~ 2000 K. Thus they deliver much higher intensities in band A as real targets.
Due to this seeker heads have been developed that are able to discriminate the band ratio B/A. By virtue of this MTV flares may be rejected by a seeker as having B/A ratio of ~ 0.3 opposed to anticipated values of >>5 which characterize real targets. This has caused efforts to develop spectrally matched decoy flare payloads. Suitable selective emitters to further intensity in B-band, with decreasing band strength, are CO2 >FBO > HBO2 >HBO > CO > HCl. Rather unsuitable emitters with selective emission in band A with decreasing band strength are HF > CH4 > H2O. Spectral decoy payloads thus must generate large amounts of CO2 or FBO, but only few HF and H2O and must not generate particulate carbon. To fulfill this requirement all kinds of carbonaceous payloads are in use, some of which even use high explosive materials such as nitrocellulose, nitroglycerine, trinitrotoluene and the like. From an occupational health point of view the combustion products of flares may pose a problem when inhaled. However, use in tactical heights may not lead to significant levels at sealevel. The most prominent combustion products are carbon particulates and both magnesium oxide and fluoride with blackbody payloads and carbon dioxide and volatile boron trifluoride with spectral payloads.
MTV is friction insensitive but ignites upon strong impact or/and shock as encountered with e.g. bullet impact. Loose MTV may shock up to detonation if present in amounts larger than 3 kg. Spectral flare compositions are oxygen balanced and even oxygen rich thus they are very sensitive. Some compositions are even capable of sustaining a detonation.
