Which are the three main types of homing systems?

The three main types of homing systems are categorized as passive, active, and semi-active, which corresponds to the correct answer.

Passive homing systems detect the energy emitted by a target, such as radar or infrared radiation. These systems do not emit any signal themselves but instead rely on the target's emissions to guide themselves. This makes them harder to detect and counter, as they do not reveal their position through active communication.

Active homing systems, on the other hand, emit their own signals and track the return echoes to guide themselves to a target. This method allows for real-time adjustments to the course toward the target, typically resulting in higher accuracy.

Semi-active homing systems combine elements of both passive and active systems. In this approach, the homing device relies on a signal transmitted from a separate source that illuminates the target. The homing device then detects the reflected signal from the target to navigate towards it.

Each of these types has distinct operational characteristics that are crucial in military applications and weapon systems. The other options presented do not accurately describe the fundamental classifications of homing systems within this context.