seminar on missile:part 7

5.3.2 Active Homing Guidance

Active homing works just like semi-active except that the tracking energy is now both transmitted by and received by the missile itself. No external source is needed. It is for this reason that active homing missiles are often called "fire-and-forget" because the launch aircraft does not need to continue illuminating the target after the missile is launched.

Active homing missiles typically use radar seekers to track their target. These seekers are also sometimes called monostatic because, unlike semi-active guidance, the transmitted and reflected waves are at the same angle with respect to the line of sight between the missile and target. Examples of active homing missiles include the AMRAAM air-to-air and Exocet anti-ship missiles.

5.3.3 Passive Homing Guidance

A passive homing system is like active in that the missile is independent of any external guidance system and like semi-active in that it only receives signals and cannot transmit. Passive missiles instead rely on some form of energy that is transmitted by the target and can be tracked by the missile seeker.

Passive homing guidance

This energy could take many forms. For example, infrared seekers like those used on Sidewinder home in on the heat signature generated by a target. Anti-radiation missiles like HARM track the radio frequency energy transmitted by ground-based radar stations. Passive torpedoes use sonar, or sound waves, created by the engines of ships to attack their targets. Electro-optic sensors like those used on Maverick rely on visual images to guide towards a target.

5.3.4 Retransmission Homing Guidance

A more unusual example of homing guidance is the retransmission method. This technique is largely similar to command guidance but with a unique twist. The target is tracked via an external radar, but the reflected signal is intercepted by a receiver onboard the missile, as in semi-active homing. However, the missile has no onboard computer to process these signals. The signals are instead transmitted back to the launch platform for processing. The subsequent commands are then retransmitted back to the missile so that it can deflect control surfaces to adjust its trajectory.

Retransmission homing guidance

               Active homing guidance
This method is also sometimes called "track via missile" (TVM) since the missile acts as a conduit of tracking information from the target back to the ground control station. The advantage of TVM homing is that most of the expensive tracking and processing hardware is located on the ground where it can be reused for future missile launches rather than be destroyed. Unfortunately, the method also requires excellent high-speed communication links between the missile and control station, limiting the system to rather short ranges. Retransmission homing guidance is used on the Patriot surface-to-air missile.