: how does a air-air missile track an aircraft that is constantly changing it’s direction while also traveling supersonic?
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There are some good answers here, but most are not comprehensive alone. The most fundamental aspect of your question is answered [here](https://www.reddit.com/r/explainlikeimfive/comments/yensor/eli5_how_does_a_airair_missile_track_an_aircraft/itzcqqd). From the perspective of the missile, the maneuvering craft isn’t actually moving that much. Not to mention, unless the pilot actively evading a missile, planes tend to fly more “straight and level” than anything else.
There are also two major types of AA missile guidance systems: radar and infrared. The general methods for adjusting the missile’s trajectory are similar. The difference is in how they “see” the target.
Infrared, or “heat-seeking” missiles work by following a bright spot on an infrared camera image. They work best when fired from behind the target, because they can easily “see” the hot exhaust from the jet engine. Modern IR missiles can be fired “head-on”, though the chances of missing go up significantly. As others have said, they basically try to manuever such that the target “stops moving” (in the missile’s camera image”). Whenever it is “holding still”, the missile goes straight. Whenever the target manuevers, the image starts shifting towards one side of the frame again, and the missile starts turning towards it to balance it out.
Radar-guided missiles work similarly, but instead of “seeing” with a camera, they have a radio transmitter and series of antennae to listen for the signal to “bounce back” off the target. Depending on the direction, as well as changes in the signal itself (i.e. Doppler shift), the missile can calculate the position of the target (relative to itself). It’s similar to echolocation, but with radio. Just like the IR missile tries to hold the target in the same part of the image, the radar-guided missile tries to hold a similar trajectory based on what it “sees” with radar. Another point of interest here is that the missile doesn’t necessarily have to go off it’s own radar alone. If the “firer” still has a radar lock on the target, it can continue to transmit the location to the missile, even if the missile itself “loses track” of its target.
It doesn’t always work. Countermeasures are designed to “look like” the plane they’re deployed from, at least to a missile. A flare is very bright on IR, for instance, and may confuse the missile into thinking the plane hasn’t turned, when in fact it has. (Flares don’t really work on modern missiles if the hot exhaust is still in the frame. You have to turn simultaneously so that the exhaust is pointed away from the missile, and thus you look “dimmer” than the flare on IR.)
Chaff is used to confuse radar guidance, and mostly works when the missile is relatively close, by tricking it into thinking it “got to you” already, and thus detonating harmlessly, far away from the plane itself.
Regardless, the best chance of dodging a missile is to wait until it gets really close, and then turning sharply outside it’s field of view before it has a chance to react. (Diminishing the advantage discussed in the linked comment at the top.) Even then, fuel permitting, some missiles will “remember” where they last saw you, and try to “reacquire” by turning towards where they think you should be. If you’re lucky, they’ll guess wrong.
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