Proportional navigation

Common card · No. 290303

Proportional navigation (also known as PN or Pro-Nav) is a guidance law (analogous to proportional control) used in some form or another by most homing air target missiles. It is based on the fact that two objects are on a collision course when their line of sight (LOS) does not change direction as the range closes. Proportional navigation dictates that the missile should accelerate (such as by steering with its control surfaces) at a rate proportional to the line of sight's rotation rate, and in the same direction. This gradually nullifies the LOS rotation and keeps the missile on a collision course. A rather simple hardware implementation of this guidance law can be found in early AIM-9 Sidewinder missiles. These missiles use a rapidly rotating parabolic mirror as a seeker. Simple electronics detect the directional error the seeker has with its target (an IR source) and apply a moment to this gimballed mirror to keep it pointed at the target. Since the mirror is in fact a gyroscope it...

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