In missile guidance, Line of sight is the straight line between the missile and the target. At the end of the engagement the distance will be zero. See Command guidance#Command to Line-Of-Sight (CLOS).
By Pursuit guidance the missile is steered so that the velocity vector of the missile always points at the target, i.e. has the direction of the Line of sight.
Literature[]
- Tactical and Strategic Missile Guidance, Paul Zarchan, American Institute of Aeronautics and Astronautics Inc.
The original article can be found at Line of sight (missile) and the edit history here.