The missile does not roar out of the tube. It pops. A small motor kicks it clear of the launcher, and only when the missile is several metres away does its main motor light with a crack and a streak of smoke.

That gentle start is one of the tricks inside a MANPADS, a man-portable air-defence system. One or two soldiers can carry it, and it can bring down a helicopter, a transport aircraft or a fast jet that strays low enough. Here is how a shoulder-fired missile finds its target, and how aircraft fight back.

A tube, a grip and a battery

A MANPADS has three main parts. The missile lives in a sealed launch tube that doubles as its shipping container. Clipped to the tube is the gripstock, the reusable pistol grip with the trigger and, on many systems, a link to an identification friend-or-foe (IFF) interrogator. The third part is the power and coolant supply.

Typical MANPADS are about 1.5 to 1.8 metres long and weigh roughly 17 to 18 kilograms, depending on the model. The American FIM-92 Stinger is lighter: the missile alone weighs about 10.1 kg, and the whole ready-to-fire package with tube, sight and gripstock about 15.2 kg.

On the Stinger, the power and coolant come from a battery coolant unit, or BCU, that slots into the gripstock. It holds high-pressure argon gas, which is squirted into the seeker to chill its infrared detector, and a thermal battery to power the electronics. One BCU lasts roughly 45 seconds.

Waking the eye

Why chill the seeker? A warm detector glows in the same infrared band it is trying to see, which drowns out faint targets. Cooling it lets the missile see the cooler exhaust plume and warm skin of an aircraft, not just the tailpipe, which made head-on shots possible. Afterburner has a full explainer on why a heat-seeker freezes its own eye.

Once the seeker is cold, the gunner points the tube at the target and lets the seeker search. The first-generation Soviet 9K32 Strela-2 is a well-documented example: when its seeker found a strong enough heat source, a light in the sight and a buzzer told the gunner the missile had locked on. Successors such as the Igla-1 added automatic lead and superelevation, so the gunner no longer had to aim ahead of a fast target by eye.

Military Aviation History takes a detailed look at MANPADS, from the first Redeye and Strela to today’s systems.

The soft launch

Firing a rocket from a tube on a human shoulder needs a two-step launch. A small launch or ejection motor fires first and burns out before the missile has even left the tube, so the gunner is not caught in the blast. Only once the missile has coasted a safe distance does the main flight motor ignite.

On the Strela-2, the booster pushes the missile out of the tube at about 32 metres per second, and the sustainer lights roughly five and a half metres from the gunner. The warhead is only fully armed at about 120 metres. The Stinger works the same way, with an ejection motor followed by a two-stage solid-fuel flight motor that drives it to more than twice the speed of sound. Sources differ on the exact top speed: Wikipedia gives Mach 2.54, the Federation of American Scientists Mach 2.2.

Steering for a collision

A heat-seeker does not fly straight at its target. Instead most modern MANPADS use proportional navigation: the missile watches how fast the line of sight to the target is rotating and turns at a rate proportional to it. If the angle to the target stops changing, the two are on a collision course.

Both the Stinger and MBDA’s French Mistral use proportional navigation. Many MANPADS, including the Soviet 9K38 Igla family, are rolling-airframe missiles, spinning in flight so that a single pair of nose canards can steer in every direction. Late in the flight, both the Stinger and the Igla shift their aim point from the hot exhaust towards the airframe itself, so the warhead hits the fuselage rather than the jet nozzle.

The envelope

Every MANPADS has an engagement envelope: a minimum range, below which the warhead cannot arm and the missile cannot manoeuvre in time, a maximum range set by how long the motor burns, and a ceiling. The Stinger’s is typically quoted as roughly 200 metres to 4.8 km in range and up to about 3,800 metres in altitude. The Federation of American Scientists gives the Igla a maximum range of about 5.2 km and targets between 10 and 3,500 metres up.

Newer systems reach further. MBDA figures quoted by defence press give the Mistral 3 a range of up to 8 km at up to Mach 2.7, and an interception altitude of around 6,000 metres. Saab gives more than 9 km and 0 to 5,000 metres for its RBS 70 NG. As a rule of thumb, Wikipedia’s summary of CRS data puts typical MANPADS engagement ranges at about 6 km, with aircraft at 6,100 metres (20,000 feet) or higher relatively safe.

MBDA’s own film of the Mistral MANPADS, a fire-and-forget missile with a two-colour infrared seeker.

Two colours beat one flare

A flare is a ball of burning magnesium that is hotter and brighter than an engine, so the earliest heat-seekers happily switched to it. The fix was to look in more than one band. The Stinger POST and RMP variants pair an infrared detector with an ultraviolet one: modern flares can mimic an engine’s infrared signature, but their ultraviolet signature still looks different.

Other makers took different routes. The Igla family’s seeker adds a second detector whose job is to spot decoys, the Mistral uses a two-colour infrared seeker working in the 2 to 4 and 3 to 5 micron bands, and Russia’s fourth-generation 9K333 Verba, in service since the mid-2010s, cross-checks three sensors: ultraviolet, near-infrared and mid-infrared. Seekers can also judge a hot spot by its trajectory, because a flare falls away and slows while the aircraft keeps flying. Our explainer on how heat-seeking missiles work covers the cat-and-mouse in depth.

Riding the beam

Not every MANPADS hunts heat. Sweden’s RBS 70, in service since 1977, is a laser beam-rider. The gunner keeps the sight on the target, the launcher projects a laser beam along that line, and a sensor in the missile’s tail keeps it centred in the beam. Nothing on the aircraft tells the missile where to go, so flares do nothing, and with no radio link there is nothing to jam. Saab markets the guidance as “unjammable”.

Britain’s Starstreak, built by Thales in Belfast, goes further. Its first stage burns out inside the tube, the second fires about four metres from the operator and accelerates it past Mach 3, and then it releases three tungsten darts. Each dart, about 900 grams, rides a two-dimensional laser grid painted by the aiming unit and is fused to explode after penetrating the target. Thales says it flies at “in excess of Mach 3”, while some references quote Mach 4. The trade-off for all beam-riders is skill: the operator must track the target until impact.

The Wall Street Journal explains Starstreak, the laser beam-riding missile with three darts.

How aircraft fight back

The first line of defence is knowing a missile is coming. A heat-seeker emits nothing, so radar warning receivers stay silent. Spotting it is the job of a missile approach warning system, which watches for the ultraviolet or infrared flash of a rocket motor; Afterburner’s MAWS explainer covers how they work.

Flares are the classic answer, fired in sequences to give the seeker something more attractive to chase. A Royal Air Force CH-47 Chinook was photographed doing exactly that over Afghanistan. Against two-colour seekers, though, flares alone are less reliable.

The newer answer is directional infrared countermeasures, or DIRCM. A turret slews a laser at the incoming missile and floods its seeker with modulated infrared energy, so the missile loses the real target. Because the energy is aimed rather than scattered, a small device can overpower the seeker. Northrop Grumman’s AN/AAQ-24 Nemesis, for example, is fitted to large aircraft such as the C-17 Globemaster III and the CV-22 Osprey.

Northrop Grumman footage of its CIRCM laser countermeasure defeating a shoulder-fired missile in testing.

Why low and slow is most exposed

The envelope explains who is most exposed. Helicopters spend most of their time low, often hovering or flying slowly near the ground. Transports and airliners are safe at cruise altitude but have to come down to land and climb out after take-off, slowly, on predictable paths. The Federation of American Scientists estimates that arriving and departing airliners fly within range of many MANPADS for about 25 miles.

That is why MANPADS are tightly export-controlled under the Wassenaar Arrangement, why steep spiral descents and climb-outs are flown into threat areas, and why so few airliners carry any protection. In 2003 a DHL A300 freighter was hit over Baghdad and landed on engine thrust alone, a story Afterburner told in Impactado por un misil, aterrizó solo sobre los motores..

A MANPADS is a cheap answer to an expensive aircraft: a chilled eye, a soft launch and a guidance law that works out the collision course on its own. Every flare, laser turret and steep approach in the sky today exists because of a missile one soldier can carry.

Sources: Wikipedia (Man-portable air-defense system; FIM-92 Stinger; 9K38 Igla; 9K333 Verba; 9K32 Strela-2; Mistral; Starstreak; RBS 70; Directional Infrared Counter Measures; Flare), Federation of American Scientists, Arms Control Association, GlobalSecurity.org, RTX, MBDA, Saab, Thales, Defence Industry Europe, The Defense Post