Infrared and Visual Smoke Countermeasures for Army

Transcription

1 Infrared and Visual Smoke Countermeasures for Army K. Smit, A. Lee and M. Burridge DSTO(Edinburgh) PO Box Edinburgh SA Abstract Red phosphorus based smoke munitions produce a high performance countermeasure to threat systems that utilise electro-optic sensors. In particular, red phosphorus based vehicle discharged smoke grenades produce rapid image bleaching of threat infrared imagers, and good obscuration in both the visual and infrared for the protection of Australian Army vehicles. Results are presented for 66 mm Buck (RWM) MASKE discharged from the M1A1 Abrams and M88A2 Hercules Recovery Vehicle, as well as the 76 mm variant discharged from ASLAV-25 and Leopard Tank. Results are also presented for a number of practice smoke grenades in 66 mm and 76 mm. Introduction Anti-armour weapons are widely available and include visual line-of-sight, heat seeking, TV guided, laser designated, and wire guided line-of-sight missiles. To counter these threats, and to create opportunity time for military vehicles or personnel to seek cover in an engagement, military vehicles often have the capability to generate or discharge smoke screens. In the late 1990s the capability of the Australian Army to employ vehicle discharged smoke grenades was temporarily halted when the use of in-service hexachloroethane (HCE) smoke grenades was discontinued as a result of occupational health and safety (OH&S) concerns. This led to a series of trials initially by the Defence Material Organisation (DMO), and subsequently by DSTO, to choose a replacement smoke grenade for Australian Army vehicles The initial requirement was to have 76 mm smoke grenades available for Australian Army vehicles overseas, including the Long Range Patrol Vehicle and the Surveillance Reconnaissance Vehicle, as well as to provide a capability for the Leopard Tank. During the past year 66 mm smoke grenades have also been trialled for the newly acquired M1A1 Abrams, and the M88A2 Hercules Recovery Vehicle. The new high performance obscurant grenades chosen for the Australian Army are based on red phosphorus (RP) pyrotechnic composition. Unlike white phosphorus, RP composition will not spontaneously ignite upon exposure to air, and as a solid it is much less toxic than white phosphorus. RP fuel combined with inorganic nitrates and binders burns to produce phosphorus pentoxide, which rapidly hydrates in air with a very high yield factor 3-7,13, to produce phosphorus acids, such as phosphoric acid. The combustion of the pyrotechnic composition produces infrared (IR) emission (i.e. heat) and light, and the subsequent hydration of the phosphorus pentoxide produces additional less intense IR emission. The clouds of phosphorus acid droplets scatter light effectively, and are therefore white, and they also have high mass extinction coefficients in the infrared resulting in good absorption of infrared energy 3-6,13. Therefore unlike HCE smoke, RP smoke can obscure in both the mid-ir (3 5 µm) and far-ir (8 14 µm) wavelength bands.

2 RP combustion products are not known to be significantly toxic when employed in the open air, however there is the potential for carbonaceous combustion products to be present from the combustion of plastic components in the smoke munitions 3. Therefore RP smoke exposure by personnel is prudently avoided, or suitable personal protection equipment worn 3. Alternatives to red phosphorus smoke grenades are available for high performance obscurant protection 7,13,14. In particular, brass flake is employed in a number of vehicle discharged smoke munitions, particularly in France, as well as being available to the US Army 7,13. Brass flake is a very effective far-ir obscurant, however while it can be very rapidly discharged, its duration of obscuration is often severely shortened by wind. In addition there are significant personnel OH&S concerns, and substantial training range environmental limitations on the use of brass flake in Australia. Other high performance obscurants include millimetre waveband chaff which address a region of the electromagnetic waveband in which pyrotechnic smokes are generally ineffective. Research has been undertaken in the UK to combine mm chaff with both a brass flake and an RP payload 7. In addition to high performance smoke munitions, trials were also undertaken on practice smokes whose use is generally confined to visual obscuration and training 4,5, These munitions were based on cinnamic acid condensation smoke, a hygroscopic potassium chloride obscurant, or dolomite dispersed obscurant powder. RP smoke munitions have propensity to start grass fires, and where there is significant fire danger training smokes enable year round training to be undertaken. Experimental Digital optical cameras and various thermal imagers were employed in the field trials at Puckapunyal Military Area, Vic, including an Inframetrics Model 610 and an AGEMA 900, each operating in the mid and far-ir. The AGEMA used detectors cooled with Stirling cycle coolers, a twin indium antimonide serial scanning detector for the mid-ir, and a mercury cadmium telluride (MCT) detector in the far-ir operating independently and providing time-synchronous imagery of resolution 272 x 136 pixels. Other thermal imagers included: AN/PAS-19 Thermal Weapons Sight (TWS) from Hughes Aircraft Company, Mahwah, NJ, USA operated in the mid-ir with thermo-electrically cooled MCT sensor of 320 x 160 pixels; ThermaCAM S65 from FLIR Systems with a far-ir focal plane array with uncooled microbolometer 320 x 240 pixels; TISIGHT from Texas Instruments operating in the far-ir using an uncooled ferroelectric detector with a 328 x 245 staring array. An image intensifier was employed for imagery in the near-infrared (NIR, µm)). The munitions for which results are presented in this report include: MASKE 76 ST from Buck Neue Technologien GmbH (now Rheinmetall Waffe Munition (RWM) GmbH) from Neuenburg, Germany, with Type 10 electric igniter squibs, RF shielded, fired from twin four tube Wegmann Multibarrel Smoke Grenade Dischargers (MBSGD) of an ASLAV-25 or Leopard Tank. In addition, the M1A1 Abrams employed 250M smoke launching systems incorporating two banks of six barrel 66 mm No. 19 Mk2 smoke dischargers firing MASKE L114A1 (EL RP/RP) vehicle multispectral screening grenade, and 66 mm MASKE L114A1 (EL Ueb 0609) dolomite practice grenade. The M88A2 Hercules Recovery Vehicle was equipped with the M239 smoke launching system with the same twin banks of six barrel dischargers as the M1A1. The 66 mm munitions used T14A1 igniters, and the 76 mm MASKE (ST Ueb 0610) dolomite practice grenade fired from ASLAV-25 employed a

3 T10A1 igniter. Training smoke variants in 76 mm included Pains Wessex Defence Ltd (PWD, now Chemring Defence) Low Toxicity Screening Smoke (Derby, UK), and the Nico KM Training Smoke 76/80 from Nico-Pyrotechnic Hanns-Jurgin Diedrichs GmbH & Co KG (Trittau, Germany), both with Type 10 igniters. Results and Discussion 76 mm Smoke Munitions The 76 mm RP smoke munitions burst at about 2 s after firing, resulting in mid-air combustion of fast burning RP composition, and the dispersal of slow burning RP composition on the ground. The obscuration produced by the discharge of full salvos of eight 76 mm RP smoke rounds is shown in Figures 1-4. The rounds burst about 10 m above the ground, and burning RP composition and debris was scattered about 44 m from the vehicles over an arc of approximately 70 m in length. Visual smoke obscuration was generally for about one minute or more depending upon wind conditions, and IR obscuration about half that. When only a half salvo consisting of four RP rounds was discharged from one of the two smoke dischargers, the width of the smoke screen was approximately halved. Figure 1: Full salvo 76 mm MASKE RP smoke rounds at 4 and 10 s after discharge, in visual. Figure 2: Full salvo 76 mm MASKE RP smoke rounds2.5 and 7 s after discharge in mid-ir. The initial obscuration of the vehicles from thermal imagers is caused by radiant heat of pyrotechnic combustion, resulting in image bleaching, however some additional infrared emission results from the hydration of phosphorus pentoxide in the smoke. At night the RP produces considerable radiance across the EO spectrum, as displayed by an image intensifier in Figure 4.

4 Figure 3: Full salvo 76 mm MASKE RP smoke rounds at 12 s after discharge in far-ir. Figure 4: Full salvo 76 mm MASKE RP smoke rounds at 5 s in image intensifier vision. Images from 76 mm training smokes are shown in Figures 5 7. The PWD (now Chemring Defence) cinnamic acid based training smoke, and the Nico KM training smoke each take a number of seconds to develop dense visual smoke from ground burning smoke pots, and the visual smoke then persists for about a minute. The 76 mm dolomite practice smoke however comprises only air bursts, simulating the MASKE RP round air bursts, and this does not generally obscure the vehicle. Figure 5: Full salvo 76 mm PWD Low Tox. training smoke at 20 s after discharge.

5 Figure 6: Full salvo Nico KM training smoke at 20 s after discharge. Figure 7: ASLAV-25 discharging 76 mm dolomite practice rounds at: 3.0 s (left), and 7.0 s (right). 66 mm Smoke Munitions The 66 mm RP smoke munitions burst about 1 s after discharge and some of the sequence of images are shown for the visual in Figures 8-10 below. Similar obscuration times were achieved compared to the 76 mm RP, however the length of the smoke cloud for the full salvos of 12 rounds was wider. Figure 8: RP smoke discharged from M1A1 at 1.5, 2.0, 2.5 and 3.0 s after discharge.

6 Figure 9: RP smoke discharged from M1A1 at 10, 20, 50 and 60 s after discharge. Figure 10: A side-on camera view showing M1A1discharging smoke at right angle to the line of fire. A visual image and some corresponding infrared images of 66 mm smoke discharge are presented in Figure 11. In addition, an image of 66 mm dolomite obscurant discharge in the far-ir (Figure 12) shows that the dolomite powder is cooler than the surroundings and briefly obscures in the infrared. Generally for training purposes it is recommended that the high performance RP smoke is employed, both in Australia and overseas, however where high grass/bush fire danger occurs training can be undertaken using non-rp based dolomite practice smoke to simulate air bursts, or longer duration visually obscuring condensation smoke, or KM smoke, to simulate deployed smoke screens. For RP stores held in magazines for significant periods of time it is also recommended that phosphine gas concentrations are monitored as this gas is a product of RP ageing associated with its interaction with moisture and oxygen 15. Some manufacturers of RP use various techniques, such as micro encapsulation, to minimise degradation of the RP in munitions 15.

7 Figure 11: Discharge of RP smoke at 4 s after discharge. Top left, visual; top right FLIR far-ir, bottom left TWS far-ir, bottom right mid- IR. Figure 12: Far-IR image of vehicle firing 66 mm dolomite obscurant. Conclusion The RWM 66 mm and 76 mm MASKE smoke munitions can provide high performance protection for Australian Army vehicles in the visual to far-ir regions. RP smoke is also recommended for Army training purposes in-country. In regions of high fire danger there are also various training smokes available, and there should therefore be no impediment to employing vehicle discharged smoke obscurants all the year round for training.

8 Acknowledgements A number of people and organisations have contributed to the field trials described in this report, in particular staff from the Explosives and Pyrotechnics Group, WSD DSTO(E); Land Warfare Development Centre, Puckapunyal, Vic.; School of Armour, Puckapunyal, Vic.; DMO GWEO Orchard Hills, NSW; DMO Land 907 Project Office, Victoria Barracks, Melbourne; and Directorate of Ordnance Safety, Canberra, ACT. References (1) R. Culvenor, Trial Report 76 mm Smoke Grenade Discharger, Function & Performance, DMO LMSB Tracked Manoevre Systems Program Office, Melbourne, Trial Report TMSPO/Out/2002/127 [RESTRICTED], (2) D. Eason, Task Report Task No , Trial 76 mm SMK Gren Discharger Function and Performance SRV/LRPV, DMO JALO P&EE Graytown, Vic., (3) K.J. Smit Safety Related Aspects of Red Phosphorus Based Smoke Munitions, Proc. PARARI 2003, 6 th Australian Explosives Ordnance Symposium, Canberra, ACT, (4) K.J. Smit, A. Lee, M. Stinger, T. Collaton, N. Potticary, M. Burridge and M. Wilson, Smoke Obscurants for Leopard MBT and ASLAV Protection, Proc. Land Warfare Conference, pp , Melbourne, Vic., (5) K.J. Smit, A. Lee and M. Burridge, Smoke Countermeasures for Australian Defence Force Vehicle Protection (U), DSTO Technical Report, DSTO-TR-1652 [RESTRICTED COMMERCIAL-IN- CONFIDENCE], (6) K.J. Smit, A. Lee, W.F. Woods and A. Catford, Effectiveness of Red Phosphorus Smoke Countermeasures Against an Anti-Armour Imaging Missile (U), DSTO Technical Report DSTO-TR-1725 [SECRET], (7) K.J. Smit and A. Lee, Smoke Obscurant Expendable Countermeasure Options for M1A1 Abrams, Proc. PARARI 2005, 7 th Australian Explosives Ordnance Symposium, Melbourne, Vic., (8) F. Dedehayir, Test Instruction for L114 Smoke Grenades Compatibility with M1A1 and M88A2 Vehicles, Land Engineering Agency, Test Instruction No. 2007/01 (9) F. Dedehayir Trial Report Smoke Grenade MASKE 66 mm Series, DMO Minute 30 April (10) K.J. Smit, A. Lee and M. Burridge, Smoke Countermeasure Testing for the M1A1 Abrams, Proc. Land Warfare Conference, Adelaide, SA, (11) K.J. Smit, A. Lee and M. Burridge, Multispectral Smoke Obscurants for M1A1 Abrams Tank and M88A2 Hercules Recovery Vehicle, Proc. PARARI 2007, 8 th Australian Explosives Ordnance Symposium, Melbourne, Vic., (12) K. Smit, A. Lee and M. Burridge, Performance Evaluation of Smoke Discharge by M1A1 Abrams and M88A2 Hercules Recovery Vehicle (U), DSTO Technical Report, DSTO-TR-2088 [RESTRICTED], 2008.

9 (13) E.-C. Koch, Recent Developments in Pyrotechnic Obscurant Technology, Proc. 36 th International Conference of ICT & 32 nd International Pyrotechnics Seminar, p. 1/1, (14) K.J. Smit, Countermeasures Against IR Imaging Missiles: Survey of Pyrotechnic Options (U), DSTO Technical Report, DSTO-TR-0645 [CONFIDENTIAL], (15) P.J.D. Collins, K.J. Smit and B.R. Hubble, The Use of Red Phosphorus in Pyrotechnics Results of an International Investigation, Proc. 31 st International Pyrotechnics Seminar, Fort Collins, CO, USA, pp , 2004.