9K32 Strela-2
The 9K32 Strela-2 is a light-weight, shoulder-launched, surface-to-air missile or MANPADS system. It is designed to target aircraft at low altitudes with passive infrared-homing guidance and destroy them with a high-explosive warhead.
Broadly comparable in performance with the US Army FIM-43 Redeye, the Strela-2 was the first Soviet man-portable SAM – full-scale production began in 1970. While the Redeye and 9K32 Strela-2 were similar, the missiles were not identical.
The Strela-2 was a staple of the Cold War and was produced in huge numbers for the Soviet Union and their allies, as well as revolutionary movements. Though since surpassed by more modern systems, the Strela and its variants remain in service in many countries, and have seen use in nearly every regional conflict since 1972.
Development
The end of World War II led to a major shift in Soviet defence policy. The advent of long range, high altitude, nuclear-armed American bombers, capable of penetrating Soviet airspace at heights and speeds unreachable and unmatchable by anti-aircraft guns and most interceptors, appeared to render every conventional weapon obsolete at a stroke. Numerous long-range, high-altitude SAM systems, such as the S-25 Berkut and S-75 Dvina, were rapidly developed and fielded to counter this large vulnerability. Due to the apparent obsolescence of conventional arms, however, relatively little development took place to field mobile battlefield air defences.This direction was soon changed with the beginning of the Korean War. An entirely conventional conflict, it proved that nuclear weapons were not the be-all and end-all of warfare. In the face of a powerful and modern American air force, carrying non-nuclear payloads, the Soviet Union invested heavily in a multi-tier air defence system, consisting of several new mobile SAMs, to cover all altitude ranges and protect ground forces. The new doctrine listed five requirements:
- Front-level medium-to-high-altitude area defense system 9K8 Krug
- Army-level low-to-medium-range area defense system 3K9 Kub
- Division-level low-altitude short-range system 9K33 Osa
- Regiment-level all-weather radar-guided gun system ZSU-23-4 "Shilka" and very-short-range missile systems 9K31 Strela-1
- Battalion-level man-portable 9K32 Strela-2
As development began in the Turopov OKB, detailed information on the design of the US FIM-43 Redeye became available. While it was not a reverse-engineered copy, in many ways the Strela design borrowed heavily from the Redeye, which had started development a few years earlier. Due to the comparatively primitive Soviet technical base, development was protracted, and many problems arose, especially in designing a sufficiently small seeker head and rocket. Eventually, the designers settled for a simpler seeker head than that of the Redeye, allowing the initial version, the 9K32 "Strela-2" to finally enter service in 1968, five years behind schedule. At the time, it was described by one expert as being "the premier Russian export line".
Improvements
The initial variant suffered from numerous shortcomings: it could only engage targets flying at relatively slow airspeeds and low altitudes and then only from rear hemisphere, it suffered from poor guidance reliability, and even when a hit was achieved, it often failed to destroy the target. Poor lethality was an issue especially when used against jet aircraft: the hottest part of the target was the nozzle behind the actual engine, which the missile therefore usually hit; but there its small warhead often failed to cause significant damage to the engine itself.In order to address the shortcomings, two improved versions were ordered in 1968; as an intermediate stop-gap the slightly improved 9K32M "Strela-2M" to replace the original, as well as the more ambitious Strela-3.
As the modifications introduced with the Strela-2M were relatively minor, the process was fast and it was accepted in service in 1970. The Strela-2M replaced the Strela-2 in production lines immediately. Improvements were made particularly to increase the engagement envelope of the new system:
- Higher thrust propellant increased slant range from and ceiling from
- Improved guidance and control logic allowed the engagement of helicopters and propeller-driven aircraft approaching at a maximum speed of
- Maximum speed of receding targets was increased from
- More automated gripstock provided a simplified firing method against fast targets: a single trigger pull followed by lead and superelevation replacing the separate stages of releasing the seeker to track, and launching the missile
The seeker head improvements were only minor changes to allow better discrimination of the target signal against background emissions. Some sources claim that the seeker sensitivity was also improved. The only defence against infra-red countermeasures remained the seeker head's narrow field of view, which could be hoped to help the rapidly slowing flare fall off the missile field of view as it was tracking a fast-moving target. In practice, flares proved to be a highly effective countermeasure against both versions of the Strela-2.
The seeker is commonly referred to as a hot metal tracker. The seeker can only see infrared energy in the near infrared spectrum, emitted by very hot surfaces only seen on the inside of the jet nozzle. This allows only rear-aspect engagement of jet targets, earning the weapon its other moniker as a revenge weapon, since the missile has to "chase" an aircraft after it has already passed by.
The Strela-2M was also procured for use on-board Warsaw Pact warships; installed on four-round pedestal mounts aboard Soviet amphibious warfare vessels and various smaller combatants, the weapon remained unchanged, but was assigned the NATO reporting name SA-N-5 "Grail".
Description
The missile launcher system consists of the green missile launch tube containing the missile, a grip stock and a cylindrical thermal battery. The launch tube is reloadable at depot, but missile rounds are delivered to fire units in their launch tubes. The device can be reloaded up to five times.When engaging slow or straight-receding targets, the operator tracks the target with the iron sights in the launch tube and applies half-trigger. This action "uncages" the seeker and allows its attempt to track. If a target IR signature can be tracked against the background present, this is indicated by a light and a buzzer sound. The shooter then pulls the trigger fully, and immediately applies lead and superelevation. This method is called a manual engagement. An automatic mode, which is used against fast targets, allows the shooter to fully depress the trigger in one pull followed by immediate lead and superelevation of the launch tube. The seeker will uncage and will automatically launch the missile if a strong enough signal is detected.
The manufacturer lists reaction time measured from the carrying position to missile launch to be 13 seconds, a figure that is achievable but requires considerable training and skill in missile handling. With the launcher on the shoulder, covers removed and sights extended, reaction time from fire command to launch reduces to 6–10 seconds, depending greatly on the target difficulty and the shooter's skill.
After activating the power supply to the missile electronics, the gunner waits for electricity supply and gyros to stabilize, puts the sights on target and tracks it smoothly with the launch tube's iron sights, and pulls the trigger on the grip stock. This activates the seeker electronics and the missile attempts to lock onto the target. If the target is producing a strong enough signal and the angular tracking rate is within acceptable launch parameters, the missile alerts the gunner that the target is locked on by illuminating a light in the sight mechanism, and producing a constant buzzing noise. The operator then has 0.8 seconds to provide lead to the target while the missile's on-board power supply is activated and the throw-out motor ignited.
Should the target be outside acceptable parameters, then the light cue in the sight and the buzzer signal tell the gunner to re-aim the missile.
On launch, the booster burns out before the missile leaves the launch tube at and rotating at around 20 revolutions per second. As the missile leaves the tube, the two forward steering fins unfold, as do the four rear stabilizing tail fins. The self-destruct mechanism is then armed, which is set to destroy the missile after between 14 and 17 seconds to prevent it hitting the ground if it should miss the target.
Once the missile is five and a half meters away from the gunner, about 0.3 seconds after leaving the launch tube, it activates the rocket sustainer motor. The sustainer motor takes it to a velocity of, and sustains it at this speed. Once it reaches peak speed, at a distance of around from the gunner, the final safety mechanism is disabled and the missile is fully armed. All told, the booster burns for 0.5 seconds and the driving engine for another 2.0 seconds.
The missile's uncooled lead sulfide passive infra-red seeker head detects infrared radiation at below 2.8 μm in wavelength. It has a 1.9 degree field of view and can track at 9 degrees per second. The seeker head tracks the target with an amplitude-modulated spinning reticle, which attempts to keep the seeker constantly pointed towards the target. The spinning reticle measures the amount of incoming infrared energy. It does this by using a circular pattern that has solid portions and slats that allow the IR energy to pass through to the seeker. As the reticle spins IR energy passes through the open portions of the reticle. Based on where the IR energy falls on the reticle the amount or amplitude of IR energy allowed through to the seeker increases the closer to the center of the reticle. Therefore, the seeker is able to identify where the center of the IR energy is. If the seeker detects a decrease in the amplitude of the IR energy it steers the missile back towards where the IR energy was the strongest. The seeker's design creates a dead-space in the middle of the reticle. The center mounted reticle has no detection capability. This means that as the seeker tracks a target as soon as the seeker is dead center, there is a decrease in the amplitude of IR energy. The seeker interprets this decrease as being off target so it changes direction. This causes the missile to move off target until another decrease in IR energy is detected and the process repeats itself. This gives the missile a very noticeable wobble in flight as the seeker bounces in and out from the dead-space. This wobble becomes more pronounced as the missile closes on the target as the IR energy fills a greater portion of the reticle. These continuous course corrections effectively bleed energy from the missile reducing its range and velocity.
The guidance of the SA-7 follows proportional convergence logic, also known as angle rate tracking system or pro-logic. In this method, as the seeker tracks the target, the missile is turned towards where the seeker is turning towards – not where it is pointing at – relative to the missile's longitudinal axis. Against a target flying in a straight-line course at constant speed, the angle rate of seeker-to-body reduces to zero when the missile is in a straight-line flight path to intercept point.