9K31 Strela-1

The 9M31 missile

According to a number of Russian sources, the original 9M31 (US DoD designation SA-9A "Gaskin-Mod0") had a zone of reliable target destruction from 900 to 4200 metres. Several western and also some Russian sources give much higher range estimates of 800 to 6500 m (0.5 to 4 miles); these may refer to maximum firing range against an approaching target and minimum against receding, which are obviously larger envelopes as the target only has to reach the intercept zone by the time the missile would reach it.

The missile is effective against targets receding at a maximum speed of 220 m/s, or approaching at 310 m/s.

The warhead was primarily intended to impact the target directly, and had contact and magnetic fuzes, but also contained a back-up optical proximity fuze to detonate the warhead in case of a near miss. The missile also had an unusual safety mechanism in case of a miss; rather than a self-destruct fuze, if the optical fuze didn't detect a target within 13–16 seconds, the warhead safety mechanism would be engaged to prevent its detonation upon impact.

Propulsion is by a single-stage solid-fuel rocket motor, which is ignited a few meters from the launch tube. As the throw-out charge ejects the missile from its canister, it trails a wire from its rear The main rocket ignites when the missile reaches the wire's end at a few metres distance, and is cut off from it. To achieve roll stabilization, the rollerons on the tailfins are used. In contrast with the rollerons used on some IR guided air-to-air missiles which are spun by the airflow, 9M31 missile uses four wires which are wound on the rollerons' discs, with other end connected to the launch tube. On launch their wires crank the discs to speed.[6]

The seeker head is an unusual construction, using uncooled lead sulphide (PbS) detector elements, but with an unusual tracking mechanism. Uncooled PbS elements are commonly used to detect radiation at only short wavelengths of less than 2 micrometers. Only very hot objects emit strongly at such short wavelengths, limiting heat-seeking systems using uncooled PbS detector elements to rear-hemisphere engagements against jet targets, although propeller-driven aircraft and helicopters can of course be engaged from any direction from which the exhaust or other very hot parts of the engine are visible.

The seeker head of 9M31, however, utilizes the PbS elements differently from usual. Taking advantage of the fact that the clear sky gives strong and constant background emission at below 2 micrometer range, peaking at visual light (0.4 to 0.7 micrometer) wavelengths at which PbS in 295 kelvins temperature still provides a response, the seeker head is used to track the absence of radiation when the target blocks the background. The method is called optical photocontrast homing (Rus.: фотоконтрастное наведение). The advantage of photocontrast homing method over traditional heat-seeking homing heads using PbS elements is that it negates the most serious drawback of early-generation IR-homing missiles: complete lack of front-aspect engagement capability against approaching jets. Even early cooled seeker heads had usually only limited forward hemisphere engagement abilities, often reducing to zero in case of jets approaching exactly towards the shooter.

The new photo-contrast seeker also had serious limits, which came in the form of rather strict meteorological conditions that had to be met to enable the seeker to detect and track the target. It could only engage targets against background conditions of either clear sky or solid overcast, at least 20 degrees away from the sun, and at least 2 degrees above horizon. Nevertheless, following a study of battlefield conditions and aircraft tactics in past conflicts where short-range air defences had been used, it was concluded that conditions allowing the use of such homing system were common enough to make it a cost-effective design choice and a better trade-off than the only practical alternative available at the time, which was infrared homing restricted to rear-hemisphere engagements.

The fact that Strela-1 would be supplemented by IR-homing Strela-2 and radar-controlled ZSU-23-4 self-propelled AA gun system may have influenced the decision in favour of such an unusual homing system. The main advantage of the choice was that it made Strela-1 the only ADA system in the Soviet tank or motor rifle regiment that could engage approaching targets out to a range of several kilometers – the ZSU being hampered by very short range, and Strela-2 by its limitation to tail-chase engagements of ground attack jets, after the jet had already delivered its attack.

While the 9M31 was accepted to service after state trials in 1968, the trials committee also suggested improvements that should be incorporated into the weapon as soon as possible. As a result of these improvements, the 9M31M "Strela-1M" (US DoD designation SA-9B "Gaskin-Mod1") entered service in 1970.

The new version introduced many incremental improvements in the performance characteristics of the missile: it had a slightly heavier warhead (increased from 2.6 kg to 3 kg), a more accurate guidance system to increase the probability of a hit, and extended range. Range is again reported to be as high as 8000 m (0.35 to 5 miles) in a number of western and also a few Russian sources, whereas for example Petukhov & Shestov, Lappi, and a number Russian web sources give much more modest performance figures; considering the performance of similar systems, at least an intercept range of 8,000 m seems unlikely for such a small, high-drag missile design.

•  Algeria – 46[7]
•  Angola - 20[8]
•  Armenia
•  Benin – 4[3]
•  Cuba – 60[3]
•  Bosnia and Herzegovina 34 + (5)
•  Egypt – 20
•  Ethiopia
•  Hungary – 28
•  India – 400[3]/200[9]
•  Mauritania – 4[3]
•  Mongolia – unknown number[10]
•  Mozambique
•  Nicaragua
•  Russia – Russian ground forces – 200 9K31, as of 2012,[9] Russian marines – 50 9K31 and 9K35, as of 2012 [11]
•  Romania – 48 produced under license as CA-95 (based on a heavier, wheeled vehicle originating from a domestically produced version of the BTR-70). Romania also received rights to license build the guided missile, where it is known as the A-95.
•  Sahrawi Arab Democratic Republic[12]
•  Serbia 56[13]
•  South Africa – Captured several vehicles in Angola and even attempted minor upgrades to them.[14]
•  Syria 20[15][16]
•  Uganda
•  Uzbekistan
•  Vietnam

•  Bulgaria – 50[3] Phased out.
•  Croatia – 9[3] Phased out.
•  Czechoslovakia – 80+ systems in 1992.[17]
•  East Germany[18] – Passed on to the unified German state and retired shortly after.
•  Iraq[17] – All destroyed or scrapped after the 2003 invasion of Iraq.
•  Libya – 60 in 1992,[17] unknown number operational prior to the 2011 Libyan civil war.[19]
•  Palestine Liberation Organization[17]
•  Poland – 16 launchers; first unveiled to the public in 1974 and mostly retired by 1994. Assembly of the missile was undertaken at the Mesko arms factory in the city of Skarżysko-Kamienna, with fully domestic production of missile bodies, warheads and rocket motors, while the electronics group and control mechanisms were all delivered from the USSR. Polish missiles were sent to domestic units but mostly exported to partner nations.[14]
•  Slovenia
•  South Yemen[20]
•  Ukraine
•  Soviet Union – 430 in 1991.[21] Passed on to successor states.
•  Yemen - around 24.[22]
•  Yugoslavia – 100+ launchers in 1992.[17] Passed on to successor states.