"One of the things that has always stuck in my mind from my childhood addiction to science fiction was Robert Heinlein’s explanation of rocket guidance, where a special “cam” was machined to control the trajectory of a rocket every time it took off. The cam would be rotated with a constant speed and its radius at any given point would determine the average direction of the thrust. It turns out that exactly the same method is used in SCUDs."

-- Geoffrey Forden