 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.Yanushevsky, page 3. It is based on the fact that two vehicles are on a collision course when their direct Line-of-Sight does not change direction as the range closes. PN dictates that the missile velocity vector should rotate at a rate proportional to the rotation rate of the line of sight (Line-Of-Sight rate or LOS-rate), and in the same direction. Where is the acceleration perpendicular to the missile's instantaneous velocity vector, is the proportionality constant generally having an integer value 3-5 (dimensionless), is the line of sight rate, and V is the closing velocity. For example, if the line of sight rotates slowly from north to east, the missile should turn to the right by a certain factor faster than the LOS-rate. This factor is called the Navigation Constant. image:Navigation Constant illustration.png
For example, if the line of sight rotates slowly from north to east, the missile should turn to the right by a certain factor faster than the LOS-rate. This factor is called the Navigation Constant. 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.Yanushevsky, page 3. It is based on the fact that two vehicles are on a collision course when their direct Line-of-Sight does not change direction as the range closes. PN dictates that the missile velocity vector should rotate at a rate proportional to the rotation rate of the line of sight (Line-Of-Sight rate or LOS-rate), and in the same direction. Where is the acceleration perpendicular to the missile's instantaneous velocity vector, is the proportionality constant generally having an integer value 3-5 (dimensionless), is the line of sight rate, and V is the closing velocity. 
A
For example, if the line of sight rotates slowly from north to east, the missile should turn to the right by a certain factor faster than the LOS-rate. This factor is called the Navigation Constant.
D
For example, if the line of sight rotates slowly from north to east, the missile should turn to the right by a certain factor faster than the LOS-rate. This factor is called the Navigation Constant. image:Navigation Constant illustration.png