"Red eyes" T-90, what are you protecting against?
At the end of the 80s of the last century, the Soviet Army adopted the Shtora optical-electronic suppression system, which ensured the disruption of anti-tank missile guidance. missiles and guided artillery ammunition. It was serially installed on various modifications tanks The T-80U, as well as the T-90, have become a kind of calling card for the latter thanks to two recognizable infrared searchlights on either side of the gun, glowing red in digital photographs.
Today, these "red eyes" can already be called an atavism within the framework of our tank building, since they are not installed on new modifications of the "ninetieth" and other tanks. However, myths about their purpose still pop up every now and then in various publications.
Flies separately, cutlets too
Generally speaking, the Shtora (Shtora-1) optical-electronic suppression system consists of more than just the notorious infrared spotlights on the turret. In addition to them, it also includes indicators in the form of "coarse" and "precise" laser radiation detection heads, accompanying computing equipment, and an aerosol curtain system. Therefore, when considering even the simplest descriptions of this EOCS, one can often only see a lengthy text about how it counteracts laser rangefinders, missiles with semi-automatic guidance by wire, radio channel, or "inside the laser beam", as well as munitions with a laser homing head (GHS).
All this gives rise to speculation that all components of the "Shtora" work in tandem, where one component is useless without the other. Accordingly, the notorious searchlights are almost the main part of the system, acting as a blinding means for missiles. Moreover, assigning this status to "red eyes" is often combined with absurd conclusions that they are the ones that confuse laser-guided munitions attacking the tank. Here, people knowledgeable in the subject, of course, can only laugh, but opinions of this nature are still broadcast in various Internet communities, and sometimes even in the media.
However, as they say, one bird at a time, and another at a time. And this division should begin with the fact that searchlight installations (called OTShU-1-7), operating in the infrared spectrum, are in principle incapable of influencing laser guidance systems in any way. They do not create radiation of similar parameters that could confuse laser homing heads of missiles (such as old variations of the Hellfire or Maverick) or guided artillery shells that work by illuminating the target with laser target designators.
They will not help in the case of the enemy using anti-tank missiles of the type of the domestic tank "Reflex", controlled "in a laser beam", since they correct their flight, automatically orienting themselves not by the beam reflected from the target, but by the beam emanating from the guidance system, trying to be in its center. So, even if the "Shtora" searchlights were laser, they would be of no use in this matter.
In fact, laser radiation detectors with the corresponding computing and executive equipment, as well as aerosol grenade launchers, are intended to counteract this entire "laser economy". They (the detectors) recognize that the vehicle is being irradiated by a laser from rangefinders, missile control channels, or illumination for ammunition with a laser homing head, which makes it possible, firstly, to quickly determine the direction of the radiation source and turn the turret in that direction so that the gunner can quickly destroy the dangerous target. Secondly, to fire aerosol grenades, camouflaging the tank both from the enemy's eyes and from the homing heads of missiles and shells.
As for the Shtora searchlights themselves, they create interference in the infrared spectrum, but not for missiles with thermal homing heads, since they do not significantly deform the silhouette of the tank and can generally do a disservice to their carrier in terms of detection by the enemy and ammunition with a seeker, but with a semi-automatic command guidance system with direction finding by IR radiation like the Soviet Fagots and Konkurs, as well as old modifications of foreign TOW, HOT, Milan, and so on. That is, mostly controlled by wires.
Eclipsing the tracer
Anticipating the quite natural questions about how the Shtora can recognize the launch of a missile guided by wires and without any laser tracking, we will answer in advance - no way. Everything depends on the enemy's location. The OTShU-1-7 searchlights, although they are an active means of counteraction in terms of jamming, work on the principle: in whichever direction they shine - there they protect. Two searchlights installed on one tank create a zone of suppression of guided missiles 640 to 840 meters wide along the front from a distance of 2-2,5 kilometers from the supposed ATGM installations and, accordingly, in which direction the tank's turret turns - there this zone shifts.
Optical suppression setting ranges
Now about how the spotlights work. And here, in general, we need to first recall that the process of controlling the flight of a missile with a semi-automatic guidance system from the operator's side is quite simple and consists of keeping the aiming mark on the target - the missile itself will correct its flight trajectory. But this is from the operator's side, and the guidance system itself still needs to "understand" where the missile is and what commands to give it so that it moves exactly along the aiming mark.
In the ATGMs in question, an onboard optical emitter serves for this purpose - a tracer in the form of an IR lamp or a pyrotechnic charge installed in the tail section of the missile. During flight, the lamp emits a light signal of a certain frequency and wavelength (the pyrotechnic tracer has no frequency modulation, it simply records IR radiation), which is read by a photocell of the coordinator installed on the launcher and aligned with the operator's sight line. It is he who issues the appropriate commands to correct the missile's flight.
BOI - on-board optical emitter
For example, the Soviet "Fagot" has an optical-mechanical coordinator and consists of a photodetector with a rotating disk with transparent and opaque sectors installed in front of it, like in a stroboscope. When the missile deviates from the aiming line (from the center of the disk), when the gunner moves the aiming mark, the photodetector receives light radiation from the tracer (IR lamp), passing through the transparent and opaque sectors of the disk.
The coordinator determines the direction in which the missile has deviated relative to the line of sight by the position of the light signal, and the degree of missile deviation by its frequency (the frequency of the light beam "flickering" when passing through transparent and opaque sectors closer to the center or to the edge of the disk will be different). Then the photoreceiver converts the light signal into an electrical signal, after which the coordinator's equipment unit produces two voltages corresponding to the correction of the missile's flight in course and pitch.
In fact, this is just an example, since coordinators in design and operating principles can be completely different. However, they have one thing in common - relatively low noise immunity. It was this vulnerability that was taken as a basis for the development of infrared searchlights for the Shtora KOEP. And, it is worth noting, this idea is not new - back in the early 1980s, proposals appeared in specialized Soviet literature to combat ATGMs using IR searchlights of the Luna type, which were installed on tank turrets to illuminate targets at night.
It consists in literally "confusing" the anti-tank missile system coordinator with a false light source. This is exactly what the OTShU-1-7 searchlights do. They emit modulated and, most importantly, offset from the center of the turret (and the tank's figure in the frontal projection as a whole) infrared radiation, which coincides in wavelength and frequency with the radiation from missiles.
At the same time, the radiation of the searchlights is very powerful, therefore, when the missile approaches the tank and, accordingly, moves away from the launcher, the signal level from the tracer on the coordinator decreases, and from the Shtora searchlight remains constant. Therefore, at the moment when the signal level from the searchlights exceeds that of the tracer, the ATGM guidance system coordinator captures the searchlight signal, identifying it as a missile. Moreover, this interception is carried out both by coordinators with separate recording of radiation sources perceived in the field of view (for example, in the TOW ATGM), and with recording of the energy center of radiation, installed on the Milans and HOT.
As a result, the coordinator, in an attempt to align the newly-made tracer with the aiming line, begins to issue false commands to correct the missile's flight path, or the tracking circuit completely breaks down. In any case, this leads to a miss - sometimes a very effective one in the form of a sharp takeoff of the guided missile upward. And, naturally, the missile complex operator can no longer influence the situation - the missile completely loses control.
However, it is important to note that the OTShU-1-7 cannot be called omnipotent. They can be counteracted, firstly, by changing the modulation frequency of the IR lamp signals on the missile, perceived by the coordinator - in essence, complicating the encryption of the optical communication channel between the missile and the guidance equipment. Secondly, by changing the wavelength of infrared radiation, so that the coordinator simply filters out "garbage" signals from the searchlights.
At one time, domestic engineers expected such a development of events and proposed new versions of the KOEP with optical sensors that could automatically turn on the searchlights only when a missile approaches (so as not to reveal the tank) and read the frequency of the missile's IR signals to adjust the radiation modulation. There were also attempts to create searchlights with diode sector panels emitting in several ranges at once, but this did not end in anything. Although, it is worth admitting that these innovations could be very useful today, because the old ATGMs have not disappeared from the battlefield.
Well, in general, this is the sacred secret of searchlights: no false targets, no counteraction to laser guidance systems - only interference for ATGMs with command semi-automatic guidance via wires and some systems with radio command guidance, where direction finding by IR radiation is also used. However, their functionality also includes target illumination at night, for which one of the searchlights must be locked in such a position that its light axis is parallel to the gun axis, and the diffuser must be removed, but this is useful only in cases where the tank is equipped with a sight and observation devices on electro-optical converters.
Sources:
"Tank Defense". V.A. Grigoryan, E.G. Yudin, I.I. Terekhin and others.
"Using a Tank IR Searchlight for Protection against ATGMs" G.A. Gumenyuk, V.Ya. Evdokimov
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