What is "q-guidance"

Q-guidance is a method of missile guidance used in some U.S. ballistic missiles and some civilian space flights. It was developed in the 1950s by J. Halcombe Laning and Richard Battin at the MIT Instrumentation Lab.

Q-guidance is used for missiles whose trajectory consists of a relatively short boost phase (or powered phase) during which the missile's propulsion system operates, followed by a ballistic phase during which the missile coasts to its target under the influence of gravity. ( Cruise missiles use different guidance methods). The objective of Q-guidance is to hit a specified target at a specified time (if there is some flexibility as to the time the target should be hit then other types of guidance can be used).