HOT (missile) - Design and Function

Design and Function

Project studies by both firms started in 1964, at about the same time the US Army started a project which resulted in the TOW missile, but unlike the TOW which entered service in 1973, the development and testing phase for the HOT took considerably longer. The design goal was to produce an antitank missile which could be fired from both vehicles and helicopters; that employed the SACLOS guidance system instead of the less reliable MCLOS system used by the SS.11; had a longer range combined with a better minimum engagement range; had a higher missile speed than the SS.11 resulting in a shorter flight time; and packed in a sealed container that also served as the launcher.

The HOT missile is tube-launched and optically tracked using the SACLOS guidance system with command link through trailing wires which steers the missile using thrust vector controls on the sustainer motor during the missile's flight. When the gunner fires the HOT missile, the missile activates a thermal battery, flares and a small gas generator spins up the gyro. The same gases for the gyro pop the covers off of both ends of the cylindrical container the HOT missile comes packed in. Moments later, both the sustainer motor and the booster are fired, ejecting the missile from the container.

Unlike most antitank missiles, in which the booster burns completely before leaving the container and then the missile coasts a safe distance before the sustainer motor ignites, the HOT's booster burns both inside the container and outside the container for approximately one second giving the missile a high speed. The sustainer motor burns for 17 seconds, a flight time whose path exceeds the length of the trailing wires which dictate the maximum range of the missile. Because of the more powerful booster and sustainer motor that burns during its complete flight, the HOT missile had a much shorter flight time than any other wire guided antitank missiles when it was introduced. The booster's four nozzles are located at the roots of the four spring out fins. The sustainer motor's single exhaust is located in the rear of the missile body, where a vane controls the missile through thrust vector control as it rotates in flight.

After the missile is fired, all the gunner has to do is keep the target in the sight's cross hairs, and the system will automatically track the missile's rear-facing flares, gather the missile into the gunner's sight, and send commands to steer the missile into the gunner's line of sight. Approximately 50 meters after ejecting from the container, the safety system arms the HEAT warhead's fuze and will detonate when the outer skin of the two-layer nose cone is crushed to contact with the inside skin, completing an electrical circuit. With this type of fuzing system, the missile does not have to hit the tip of the missile's nose to detonate the HEAT warhead. The HOT 1 and HOT 2 use the warhead fuzing system previously described.

The latest version of the HOT family, the HOT 3, uses a unique feature found on no other missile to defeat tanks fitted with explosive reactive armor. A laser-proximity fuze located in the front half of the nose measures the distance between the target and the missile. At the correct range, the small nipple on the front nose containing a small HEAT warhead is ejected forward from the missile body to pre-detonate the reactive armor followed by the detonation of main HEAT warhead.