seminar on missile:part 5

5.0 Missile Guidance

  missiles are able to seek out and accurately navigate their way to the correct target without assistance from a human operator. However, there is no need for alarm because a weapon very rarely makes a mistake unless it is mis programmed by the human who launches it in the first place. In fact, many of the methods used for missile guidance are the same as those used to navigate manned planes like the commercial airliners you and I fly aboard.

Phases of missile guidance

Missile guidance concerns the method by which the missile receives its commands to move along a certain path to reach a target. On some missiles, these commands are generated internally by the missile computer autopilot. On others, the commands are transmitted to the missile by some external source. The missile sensor or seeker, on the other hand, is a component within a missile that generates data fed into the missile computer. This data is processed by the computer and used to generate guidance commands. Sensor types commonly used today include infrared, radar, and the global positioning system. Based on the relative position between the missile and the target at any given point in flight, the computer autopilot sends commands to thecontrol surfaces to adjust the missile's course.

In many missiles, the guidance system is divided into three phases, as pictured above. The first is a launch or boost phase in which the guidance system is usually disabled to allow the missile to safely travel away from the launch platform. The majority of the flight is flown using midcourse guidance, during which the missile makes slight adjustments to its trajectory allowing it to reach the vicinity of the target. The final phase is terminal guidance when the missile uses a highly accurate tracking system to make rapid maneuvers for intercepting the target. Many missiles use a different type of guidance in the midcourse phase than in the terminal phase, as will be discussed later.

The primary forms of missile guidance are described below with examples of missiles and seekers used to accomplish that type of guidance.

5.1 Beam Rider Guidance

The beam rider concept relies on an external ground- or ship-based radar station that transmits a beam of radar energy towards the target. The surface radar tracks the target and also transmits a guidance beam that adjusts its angle as the target moves across the sky.

Beam rider guidance

The missile is launched into this guidance beam and uses it for direction. Scanning systems onboard the missile detect the presence of the beam and determine how close the missile is to the edges of it. This information is used to send command signals to control surfaces to keep the missile within the beam. In this way, the missile "rides" the external radar beam to the target.

Beam riding was often used on early surface-to-air missiles but was found to become inaccurate at long ranges. Limited improvement was possible using two different surface-based radar beams, but the beam rider method has been largely abandoned. The technique was used on the US Navy's Terrier ship-launched surface-to-air missile of the 1950s.