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The protection concept for helicopters defence against guided missile weapons with IR seekers

The aircraft ADS 'Talisman' and the helicopter ADS 'Amulet' are intended for self-defence of the respective air platforms against all types of radar guided missile weapons and guided missile weapons (GMW) with infra-red seekers (IRS). The first task is accomplished by the radio electronic protection equipment, included in ADS. The second one is performed by the radar for acquisition and tracking of all types of air-to air (AAM) and surface-to-air missiles (SAM) with IRS, aimed at controlling flare dispensers and based on the pyrotechnic generators of IR emission, 'concealing' the IR signature of the ADS-carrier.

The concept for radio electronic protection, implemented in the ADS 'Talisman' and 'Amulet', is revealed in the article 'Design concept for individual protection of air platforms against guided missile weapons'.

The concept for defence of aircraft and helicopters against GMW is based on the assumption, stating that the effective protection against the given type of GMW shall be considered possible only on condition of obtaining the timely information about the approach of the attacking IRS-fitted missile. The given postulate is implemented in the missile approach warning radar (MAWR), included in the ADS 'Talisman' and ADS 'Amulet'.

At present the radar acquisition of attacking aircraft missiles with IRS and SAMs of MANPADS has become common practice when it comes to protection against such types of missiles and has already been utilized in lots of foreign military and even civil aircraft and helicopters.

However, the acquisition of attacking IRS missiles itself shall be regarded only as a mere requirement for effective protection. It stands to reason, that the primary and sufficient conditions for the protection of the ADS-carrier against missiles with IRS shall be the following:

the arrangement of special flare dispensing;

timely anti-missile maneuvering (AMM).

The given issues have been set forth in the concept for protection of aircraft and helicopters against GMW with IRS.

The concept key principles

1. Countermeasures against GMW with IRS

The main tool for generating countermeasures against GMW with IRS shall be considered the flares, dispensed together with IR radiation generators. The above-mentioned method of protection is regarded as the only universal tool applicable for all types of aircraft and helicopters.

As for the protection options, based on the modulated radiation of high-power xenon lamps and on the laser impact on the IRS photosensitive elements, those are not even considered for the following reasons:

First, because of rather limited application (its impact only on modulated IRS), high power consumption and challenges stemming from the placement of emitters on the carrier, with their shading and blocking all the angular area of any possible attacks.

Second, due to extremely high cost, absence of any proof in flight tests, stating the possibility of homing the laser beam towards the missile's IRS right from the maneuvering aircraft, as well as the unacceptable high rate of false alarms, coming from the UV sensor system, defining the coordinates of an attacking missile.

Additionally, no consideration is offered to the protection method based on dispensing and initiation of the cloud of powdered fuel from turbojet engines, since it is entirely inapplicable to gas-turbine engines of helicopters, in addition to its unproven effectiveness in aircraft protection.

2. Universal Protection

The effective protection shall be universal and go for the whole class of GMW with IRS. Namely, the protection shall be securely provided against all three existing generations of GMW with IRS and shall preserve the fixed, though maybe decreased, effective impact on the 4th generation IRS GMW.

The first generation of GMW with IRS shall be understood to mean single-spectrum, one-element (with one point receiver) and modulated (not instantaneous) technique of directing finding. The vanishing type of GMW.

The second generation comprises two-point ones (the main and auxiliary channels) with a joint optical system, dual spectrum receivers and modulated technique of directing finding. The most popular type of GMW.

he third generation is recognized by matrix (multi-point) single-spectrum receivers with the application of instantaneous direction finding. The type of GMW, replacing the 2nd GMW in the armed forces of advanced countries of the world.

The fourth (expected) generation comprises matrix dual-spectrum GMW with IRS.

3. The use of fundamental (unremovable) properties of the targeted objects

The key principle of effective protection lies in the employment of only fundamental (unremovable) properties of targeted objects (IRS, control and ammunition systems) and protection means as well as prohibition to design a defence system, based on the private drawbacks and peculiarities of GMW with IRS.

IRS of the missiles utilize the heat direction finding of low-temperature emission sources of aircraft and helicopter engines with a wavelength of λ=4-5 m, =500-900 . The pyrotechnic generators (sources) of IR radiation (IRR), also known as thermites, have a temperature of ~ 2000 K and wavelength of 1.5-2 m. For the first generation of GMW with IRS, unable to discern the emission sources in terms of spectrum, the dispensing generators for IRR, due to their superior power, performed the effective interception of the target tracking and diverted the missile away from the carrier. Starting from the very outset of employing countermeasures against GMW with IRS of the 1st generation, such dispensing generators of IRR with good reason were termed as 'IR decoys', and later on were labelled as 'flares' by more advanced analysts. With the defence pattern itself known as 'the missile's distraction', i.e. diverting the missile with IRS away from the target.

When it comes to the second generation GMW, the spectral difference between the engines' IR emissions and those of generators for IRR are reliably discriminated by the IRS photodetectors, based on InSb (indium antimonide or antimonious indium), λ~4-6 m) and PbS (lead sulphide, λ~2-3 m). Thus, it became basically unachievable to carry out 'the distraction' of such seekers in terms of sources, different in spectrum.

Therefore, much effort was focused on the development of 'low temperature' generators for IRR, spectrally similar to the emission of at least relative to high-temperature engines. This approach holds two insuperable obstacles.

First, it is the Planck's law, to be more specific, its two consequences: Stefan-Boltzmann's law and Wien's law. Which state that the source of IR emission with high energy may only be high temperature and short-wave.

The second impediment is of chemical nature and stems from the fact, that high specific (per unit mass) emission power may be obtained only on the basis of high-temperature pyrotechnic reactions. It is the thermites and thermites alone, which are able provide the emission of tremendous power, with the higher rate of build-up, and small mass required for the formation of small-sized expendable elements. But thermites deliver short-wave IR emission, intense emission in the visible range and even a bit of ultraviolet. Therefore any spectral similarity is out of the question.

Thus, the present concept for defence is based on the ground that the emission from thermites, even though the peak of such emission stays in the vicinity of 1.5 m, provides their power superiority over gas-dynamic sources of IRR and stretches beyond 6-8 m.

In doing so, the point at issue is not the development of spectrally similar false targets, but the masking (concealment) of emission from the aircraft under protection, both in the forward and rear hemispheres. Helicopters require a 360-protection. The main sources for IR radiation of air platforms, tracked by the missile's IRS, are the sources of IR radiation from exhaust gas pipes, nozzles, exhaust pipes and plumes of engines.

Therefore, if the concept for radio electronic defence, implemented in the ADS 'Talisman' and 'Amulet', is based on the generation of false targets, spectrally identical to the echo signals (flatly rejecting broadband noise masking countermeasures), then the concept for defence against IRS, irrespective of the IRS type, 'pinpoint' or 'matrix', is based on the masking high-energy broadband emission of IRR generators.

4. Maneuvering of ADS-carrier

A crucially important principle embed in the concept for defence against 'pinpoint' and 'matrix' IRS, is the maneuvering of the ADS-carrier, launched simultaneously with the onset of flare dispensing and with the maximum possible acceleration rate.

The maneuver, started right after the attack has been detected, but before the flare dispensing makes no sense, since AAM with its 40 g of available acceleration and the missile's control loop with a band of 4-5 hz easily 'fends off' the miss, generated by those 'pathetic' 5-7 g of the ADS-carrier with acceleration rate of 1-2 secs.

The effective protection against GMW with IRS (regardless of their type): ('pinpoint' or 'matrix') may be accomplished only by means of coordinated flare dispensing and anti-missile maneuvering. The flare dispensing allows to conceal the carrier's IR radiation, thus resulting in 'breaking' the guidance loop of the attacking missile with the 'activation' of the mechanism for targets discrimination (counter countermeasures). The anti-missile maneuvering, performed under the cover provided by flares ('concealment' of IR-emission) , makes it possible for the carrier to go beyond the field-of-regard of the attacking missile with IRS, which in the long run results in the missile miss, or survival of the ADS-carrier.

5. Measure of merit

The effectiveness of the developed means of protection against GMW with IRS shall be characterized by one parameter only, which is the probability of survival of the ADS - carrier when attacked by the given (standard) number of AAMs and SAMs.

The concept for defence against GMW with IRS, formulated above, clearly determines the configuration of the defence solution, implemented in the ADS 'Talisman' and 'Amulet', thus comprising:

a missile approach warning radar (MAWR);

a system for flare dispensing;

recording equipment for registering MAWR parameters.

Missile approach warning radar

The missile approach warning radar is a multi-position radar system with 3 stages of operation available:

the detection of missiles (all types), attacking the aircraft, with the measurement of approach velocity and direction of attack;

the measurement of range to each detected missile, which in conjunction with the approach velocity allows to determine the impact point time, being the key characteristic, required for the application and launch of flares and anti-missile maneuvering. The tracking of detected missiles in range and velocity;

high-precision range measurement in the terminal phase of the missile's approach (100-150m) for the flares application, aimed at masking the IR-emission coming from the carrier's airframe and , possibly, for setting special countermeasures against magnetic-induction non-proximity fuses of some MANPADS' SAMs.

Apart from the tasks, defined by the particular stage of works, the onboard radar in its cooperation with EPE provides the type of the attacking missile.

The missile types discriminated:

AAMs with radar seekers (RS);

SAMs with RS;

SAMs of mobile short-range SAM-systems;

SAMs of MANPADS (with IRS);

AAMs with IRS.

The use of data on the type of the attacking missile makes it possible to avoid flare dispensing and anti-missile maneuvering when detecting the attack by the missile with RS. Thus, the limited expendable resources are saved and the operating crew are spared from the performance of any unnecessary maneuver while carrying out their operational task.

The system for flare dispensing

The system for flare dispensing in the ADS 'Talisman' and 'Amulet' includes:

a system, consisting of sector flare dispensers , providing the optimal angles and rates of flare dispensing and quantity of spent cartridges.

cartridges with accelerated build-up and burning of the pyrotechnic mixture, decreased dispensing rate and burning time.

The recording equipment for registering OR parameters

All modules of the onboard radar, in addition to the communications links with the weapon control system of the carrier, convey the performance data to the recording equipment for registering the OR data, which links them up to the satellite time of the navigation systems NAVSTAR or GLONASS. After the flight they are read out and displayed in the form, convenient for further analysis.

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