Recently, aerospace (flight) engineers, having more solid mathematical backgrounds, have become familiar with the newest results in control theory and are able not only to formulate control problems but also solve them without attracting the attention of control experts. Moreover, they try to apply new results in control theory to specific aerospace and missile guidance problems. As a result, control theory is losing its biggest supplier and, to a certain degree, this slows down its progress.

In order to guide itself to a successful target intercept, the missile must obtain information about the target. The prelaunch and post launch information too, must be gathered. Before a missile is launched, that is, during the prelaunch phase, the missile needs to know where to go. It knows that it is supposed to go to the target, but it must be told where the target is. The missile is told where the target is by electrical signals entering through the umbilical from the launcher. These signals are head aimed (to point the missile head at the target), English bias (to point the missile at the intercept point), and an estimate of true target Doppler on the simulated Doppler line.