seminar on missile:part 6

5.2 Command Guidance

Command guidance is similar to beam riding in that the target is tracked by an external radar. However, a second radar also tracks the missile itself. The tracking data from both radars are fed into a ground based computer that calculates the paths of the two vehicles.

This computer also determines what commands need to be sent to the missile control surfaces to steer the missile on an intercept course with the target. These commands are transmitted to a receiver on the missile allowing the missile to adjust its course. An example of command guidance is the Russian SA-2 surface-to-air missile used against US aircraft in North Vietnam.

Also note that command guidance is not limited just to radar. Another method that falls under command guidance is the use of wire guided systems. In this technique, commands are sent to the missile through a conventional wire or fiber optic cable that reels out from the missile back to its launcher

Command guidance

. Wire guidance is often used on anti-tank missiles like TOW, which can be launched from both ground vehicles and helicopters. Many naval torpedoes fired from submarines also use wire guidance.

5.3 Homing Guidance

Homing guidance is the most common form of guidance used in anti-air missiles today. Three primary forms of guidance fall under the homing guidance umbrella--semi active, active, and passive. We will discuss each of these in turn, as well as a more unusual form called retransmission or track-via-missile homing.

Homing guidance

5.3.1 Semi-Active Homing Guidance

A semi-active system is similar to command guidance since the missile relies on an external source to illuminate the target. The energy reflected by this target is intercepted by a receiver on the missile. The difference between command guidance and semi-active homing is that the missile has an onboard computer in this case. The computer uses the energy collected by its radar receiver to determine the target's relative trajectory and send correcting commands to control surfaces so that the missile will intercept the target.

The example shown above illustrates the guidance method used on an air-to-air missile like Sparrow. This missile relies on radar energy transmitted by the launch aircraft to track and home in on the target. This system is also sometimes referred to as bistatic meaning that the radar waves that intercept the target and those reflected back to the missile are at different angles to one another.

Semi-active homing guidance

However, it should be noted that semi-active guidance is used by other types of seekers besides radar. Laser-guided weapons like the Paveway series can also be considered semi-active weapons because the laser energy these bombs track as they steer towards a target is supplied by an external source. The source could be a laser designation pod on the launch aircraft, on a second aircraft, or aimed by a soldier on the ground.