Missile guidance

Some tools can find a spot.

They use tools to see. They can follow a moving thing. They can also find a fixed place.

One way is to use sensors. These sensors can use light or heat. The tool tracks the target on its own. This is called homing.

Another way uses a remote link. A person or a machine sends signals. This tells the tool where to go. It can use a radio or a wire.

Some tools use a set path. They have a map inside. They do not need outside help. They follow the plan to reach the spot.

Some tools even look at stars. The stars stay in the same place. This helps the tool know its location. It is very smart work.

Missiles and guided bombs are tools used to hit a target.

Engineers design guidance systems to make them more accurate. There are two main ways these tools work. Some systems follow a moving target. Others find a fixed place in space.

Homing is one way to guide a missile. The missile uses its own sensors to track a target. These sensors can use light, heat, or radar. Some missiles use active homing. This means they send out their own radar signals. Other missiles use passive homing. They only track the signals the target gives off.

Some missiles use command guidance. This means a person or machine sends directions from the outside. They might use a radio link or a wire. Another way is beam riding. The missile stays inside a beam of light or radar.

Some missiles do not need outside help. They use inertial guidance. This uses parts called gyroscopes to find their place. They can even use stars to stay on track. This is called astro-inertial guidance. The stars act as fixed points to help the missile find its way.

Missile guidance is a special field of engineering. It focuses on how to control missiles and guided bombs. These systems help weapons reach their targets with high accuracy.

Engineers divide these systems into two main groups. The first group is called Go-onto-target, or GOT. These systems are used to hit moving targets. The second group is called Go-onto-location-in-space, or GOLIS. These systems target a fixed spot on the ground. While missiles have their own engines, guided bombs use gravity and speed to move.

Homing guidance is a way for a missile to track a target using its own sensors. These sensors might use light, heat, or radar to find the way.

There are three types of homing. Active homing means the missile sends out its own radar signals. Semi-active homing uses a separate source of radiation from outside. Passive homing only tracks the signals that the target itself gives off. Many modern missiles use a method called proportional navigation to steer during the final part of their flight.

Other systems use remote control to stay on path. Command guidance happens when directions come from outside the missile. This requires an information link and a command link. A person or a machine sends the steering instructions via radio or a wire.

Another way is beam riding. In this method, the missile stays inside an electromagnetic beam like a laser. Sensors on the back of the missile help it stay inside that beam. This can be helpful because one beam can guide many missiles at once.

Some missiles do not need any outside signals to find their way. They use inertial guidance, which is a type of navigational guidance. This system uses tools called gyroscopes and accelerometers. These tools help the missile estimate its position and speed after it is launched.

This is called dead reckoning. Modern systems use ring laser gyros to be very accurate. Some missiles even use astro-inertial guidance. This method uses the positions of stars to help fix any small errors in the flight path.

The history of these tools is quite long. In the late 1880s, the writer Jules Verne wrote about a rocket with a target seeker. During World War I, many nations began to experiment with guided tools. In Germany, the V-weapons program developed missiles during World War II. Later, the United States had many programs for flying bombs. In 1946, President Harry S. Truman cut funding for research. This event was known as the "black Christmas of 1946." However, development grew fast again when the Korean War began. The PGM-11 Redstone was the first U.S. ballistic missile to use a highly accurate inertial system.

Missile guidance is a specialized field of engineering. It belongs to the study of guidance, navigation, and control. These systems are designed to maximize the reliability and accuracy of missiles and guided bombs. By improving the likelihood that a weapon reaches its target, these systems ensure precision.

Engineers generally divide these systems into two broad categories. The first is Go-onto-target (GOT) systems, which are used against moving targets. The second is Go-onto-location-in-space (GOLIS) systems, which attack fixed geographical positions. While missiles use onboard engines for propulsion, guided bombs rely on gravity and the speed of the launch aircraft.

Homing guidance is a primary method used in GOT systems. In this process, the missile tracks a target using its own onboard sensors. These sensors can detect radar, infrared light, or other forms of light. Homing missiles are often called "fire-and-forget" weapons because they do not need constant communication with a ground station. There are three distinct types of homing. Active homing occurs when the missile illuminates the target with its own radiation, such as radar. Semi-active homing relies on an external source of radiation to find the target. Passive homing is different because it only tracks the emissions or the contrast produced by the target itself. Many modern missiles use proportional navigation to steer during the final terminal phase of flight.

Another category is remote control guidance, which requires a link between the missile and a control point. This connection can be a radio signal, a beam, or a physical wire. Command guidance is a specific type where instructions originate from outside the missile. This system requires two separate links: an information link to find the missile's position and a command link to send steering instructions. One disadvantage is that the target must be illuminated by an external energy source, which might allow the target to perform evasive maneuvers. Beam riding is a related method where a missile follows an electromagnetic beam, such as a laser or radar. Sensors on the rear of the missile calculate steering commands to keep the projectile within the beam.

While beam riding allows multiple missiles to use one beam, it can become less accurate as the beam spreads out over long distances.

GOLIS systems operate without a target tracker. Instead, they use navigational guidance to reach a preset location. The guidance computer and the missile tracker are both located on the missile itself. This is often called a self-contained guidance system. The simplest form is preset guidance, where the flight path is programmed into the system before the missile is even fired. The missile then uses internal components like accelerometers or gyroscopes to follow that path. The V-2 rocket is a historical example of a missile that used this type of preset guidance.

Inertial guidance is a sophisticated form of navigational guidance. It uses gyroscopes and accelerometers to estimate a missile's position and velocity through a process called dead reckoning. Early mechanical versions were not very precise and often needed external adjustments to hit targets. Modern technology has improved this significantly. Today, solid state ring laser gyros can be accurate to within meters even over distances of 10,000 km.

Some advanced systems, like the AIRS on the MX missile, allow for accuracy of less than 100 meters at intercontinental ranges. Because inertial guidance does not rely on external signals, it is very difficult to jam.

For even greater precision, some systems use astro-inertial guidance. This is a form of sensor fusion that combines inertial guidance with celestial navigation. This method is particularly useful for submarine-launched ballistic missiles (SLBMs). Because submarines are moving, calculating a starting point is much harder than it is for a fixed silo. Astro-inertial guidance uses star positioning to fine-tune the accuracy of the inertial system after launch. By observing the fixed positions of stars, the missile can correct small errors in its calculated position. For example, the Trident missile system uses a camera to spot a single star to ensure the missile remains on its intended path.

The history of these technologies spans over a century. In the late 1880s, the writer Jules Verne imagined a rocket-powered missile with a target seeker in his fiction. During World War I, various nations began experimenting with guided systems. Archibald Low is known as the father of radio guidance for his work on early drones. During World War II, Germany developed guided missiles as part of its V-weapons program to bypass treaty limits. After the war, the United States faced significant budget cuts in 1946, known as the "black Christmas." This led to the cancellation of 10 guided missile projects. However, the start of the Korean War caused development to accelerate rapidly once again. The PGM-11 Redstone became the first U.S. ballistic missile to use a highly accurate inertial guidance system.