How do heat-seeking missiles work? do they work exactly like in the movies?
In: Technology
When in doubt, assume the movies are portraying everything incorrectly.
In this case, the big difference between the movies and real life is that missiles are wildly faster than planes. The classic visual of a pilot frantically dodging while a missile follows just on their tail is nonsense.
I still haven’t seen an explanation of the “heat-seeking” logic of the problem that I really like so here’s my attempt.
Starting with the old IR (infrared) missiles it’s fairly simple. If you take an IR camera and point it at the back of an engine it there will be a very obvious hot spot. (https://youtu.be/2C6ZcqeIvjw). Because the difference in temperature between the engine/its exhaust and the environment is so large its easy to identify that as a targeting point. That is why the earliest missiles could only be fired from directly behind the target where they could see directly into the engine where the largest temperature difference would be. Then versions were made where they could detect the difference using just the exhaust instead of the engine core which greatly expanded the angles they were usable from, but still weren’t effective if the exhaust was out of line of sight.
Flares exploit the simplistic nature of this temperature difference logic by creating a larger temperature difference so the missile tracks them instead. To combat this engineers changed what the IR camera is looking at essentially. With better sensor technology the missiles no longer look at just what is the brightest thing in the field of view, instead they look for airframe heating. As a plane flys it encounters air resistance which is essentially friction between the plane and the air. That friction heats up the plane (this is part of why the fastes aircraft require special materials). The temperature difference between the friction heated aircraft and the rest of the sky is measurable but still fairly small. There can certainly be other things in the missiles field of view that have a larger temperature difference, so the missile has to know what it’s looking for. To solve this these missiles have a form of image recognition built into their computers so that they can recognize aircraft shaped temperature differences and target those specifically. That makes it much harder for flares to fool these missiles while also allowing the guidance computers do a better job figuring out where the target is going so the missile can get there first.
Others have covered this in other ways but “Do they work exactly like in the movies?” No. If a missile goes past a target will it turn around to try again? No, at that point it has been defeated. Will a missile chase for over a minute while right behind a plane very slowly getting closer? No, most missiles travel far faster than the aircraft they’re targeting and aren’t going to slow down to give you time to think. Can you out maneuver a missile? Yes… But it’s very very rare and will usually leave you in a very vulnerable position to the next missile. There are methods to reliably defeat missiles, but that isn’t one usually.
As Scott O’Grady pointed out, they are much, much faster than depicted in movies. Like no time to react at all fast and one nailed him brought the plane down.
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One thing usually gotten wrong in movies is that most missiles, including many if not all heatseekers, have a rocket engine that burns only for the first few seconds of flight.
Hence, kinetic energy of the missile starts getting lower once the engine shuts off, and the missile is less maneuverable and therefore has a lower chance of hitting a maneuvering target at longer range.
Therefore, maximum range and maximum effective range can be quite different.
Some missiles do have sustainer rocket engines to maintain propulsion over a longer period of flight but I can’t think of any heatseeker missiles with sustainerers.
Early ones were really simplistic and just pointed the missile to the hottest thing it sensor could detect, be that a planes exhaust, the sun or flares (decoys). They had limited steering ability and only worked when shot at a plane from behind it (called “rear-aspect”), and even then weren’t that reliable.
Modern ones are much much more sophisticated. They have high-resolution infrared cameras, can detect and track planes from all angles, ignore flares, plot efficient intercept courses, are much more manouvrable and fully integrated into the planes targeting systems.
A modern AIM-9X for example can be given targeting data from the planes radar or helmet mounted sight prior to launch and can track a target up to 90° to the sides (of boresight), allowing pilots to shoot at targets without having to point their own planes nose even close to it.
The missile knows where it is at all times. It knows this because it knows where it isn’t. By subtracting where it is from where it isn’t, or where it isn’t from where it is (whichever is greater), it can obtain a difference or deviation. The guidance subsystem uses deviations to generate corrective commands to drive the missile from a position where it is in to a position where it wasn’t. And, arriving at a position where it wasn’t, it now is.
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