Precision Guidance: A Method for Targeting Missiles

  With the development of weapons and equipment and the form of warfare, compared with the shock caused by the pouring of ammunition on the fierce battlefield, the high hit rate of missiles on the target is easier to achieve the combat purpose.
  In the 1982 Anglo-Amazon War, the Argentine Air Force used an “Exocet” missile to sink the British destroyer “Sheffield” worth 200 million US dollars. In October 2015, the Caspian Sea Fleet of the Russian Navy launched 26 “Caliber-NK” cruise missiles from a Cheetah-class light frigate and three “Mob-M”-class light missile frigates, with an accuracy of no more than 3 meters. It hit 11 intended targets in Syria 1,500 kilometers away. In January 2020, the United States used the MQ-9 drone to launch the “Hellfire” laser-guided missile, beheading Iran’s “flower of the famous general” Soleimani.
  In a sense, modern warfare can be said to be a contest of technological level among countries in the world. For air targets with strong maneuverability or non-maneuverable targets thousands of kilometers away, ordinary weapons are powerless. Even if they can barely attack, their killing effect is extremely poor. The missile has been developed and widely used due to its ultra-long range and precise attack characteristics. In fact, missile weapons have been used to varying degrees in almost every war since the 1960s. From land to sea, from air to space, from offense to defense, missiles are everywhere. The use of missiles in combat has quietly brought about profound changes in the combat style, not only replacing protracted local wars with quick battles, but also increasing the suddenness of long-range fire attacks unprecedentedly.
  So, how does the missile hit the target accurately?
  In fact, the reason why the missile can hit the target accurately is that we can control the missile according to certain guidance laws. First, we need to clarify the concept of guidance. Guidance is the technology and method to guide and control the aircraft to fly to the target or predetermined orbit according to certain rules. The fundamental difference between a missile and an ordinary weapon is that it has a guidance system.
  The guidance system takes the missile as the control object. The basic function is to ensure that the missile can overcome various uncertainties and interference factors during the flight, so that the missile can correct its own trajectory at any time according to the predetermined trajectory, or according to the movement of the target, and finally accurately hit the target. If the entire missile weapon system is compared to a person, then the guidance system is the “nerve center”, which shows the important position it occupies. Of course, for different targets, missiles will choose different guidance methods.
Thousands of miles away, how to strike precisely

  During the Gulf War in 1991, the U.S. Air Force launched two stand-off ground attack missiles (SLAM) at a hydropower station in Iraq 100 kilometers away. The first missile accurately hit a wall, and then the second The missile penetrated the hole, entered the power plant, and completely destroyed the target. Not only did the attack not affect the dam, but nearby buildings and residential areas were not damaged. We can’t help but marvel at its high accuracy.

AGM-84 SLAM anti-ship missile

  After being amazed, I can’t help but ask: How does the missile used by the US Air Force accurately strike the target thousands of miles away? SLAM is a stand-off ground attack missile modified from an American anti-ship missile, which can be launched outside the enemy’s air defense fire area. Before the launch, SLAM received the clock data of the US GPS satellite, and after capturing the GPS signal over the target, it flew under its guidance and hit the target. Compared with traditional air-to-ground attacks, this does not require the target to be within the visible range, and can effectively guarantee the safety of the carrier aircraft.
  Using satellite guidance to hit the target is an effective way for the missile to hit the target after a long-distance launch. Its principle is to use the receiver installed on the missile to receive the navigation satellite signal to correct the flight trajectory of the missile. Satellite guidance systems are widely used in the guidance of various precision strike weapons, such as the American AGM-84 SLAM anti-ship missile, AGM-158 joint ground standoff attack missile, GBU-37 ground penetrating bomb, etc. Its advantages are low cost and high guidance accuracy, but it also has a fatal shortcoming, that is, it is easy to be interfered.
Electromagnetic influence, how to counteract interference

  The electromagnetic environment of the current battlefield is complex. If the signal is interfered, it is very likely that the missile guided by the electromagnetic signal will be difficult to hit the target and cannot complete the combat mission. So, how should the missile counteract the interference and ensure the hit? This requires the use of inertial guidance.
  Inertial guidance does not require relay control, but controls the flight path through the missile’s determination of its own flight state. Therefore, a missile that only uses one method of inertial guidance will automatically fly to the target without the operator’s control after launch, that is, “launch and forget”.

The core element of inertial guidance system – gyroscope

  The inertial guidance system usually consists of an inertial measurement device, a calculator, a controller, etc., and was first applied to the German V-2 missile at the end of World War II. Both the U.S. and the Soviet Union used full inertial guidance systems in early missile programs to improve hit accuracy and reliability. For example, Russia’s SS-18 missile is designed to strike hardened targets such as silos, and is called “Satan” by NATO. Because its payload is close to 9 tons, it can carry multiple nuclear warheads, and its single warhead has reached the equivalent of 20 million to 25 million tons of TNT. You must know that the power of the atomic bomb dropped by the United States on Hiroshima, Japan, was only 15,000 tons of TNT equivalent, which is equivalent to more than 1,600 Hiroshima atomic bombs. With such a huge power, if the radio guidance is used to be jammed and hit other targets, the consequences will be disastrous. The use of the inertial guidance system ensures that it can fly according to the predetermined trajectory and accurately hit the target.
  The advantages of missiles using inertial guidance systems are strong anti-interference, good concealment, and will not be limited by weather conditions. The disadvantage is that it can only attack preset fixed targets, and it is powerless to moving targets.

Where to hide, how to track a lock

  In war, in order to effectively maintain combat effectiveness, various means are used to conceal and camouflage high-value targets, or take advantage of high mobility and adverse weather such as dark nights to carry out operations. For example, hidden air defense radars and high-speed fighter jets are difficult to capture under normal conditions. So, for these targets, how to track the lock? At this point, a homing guidance system needs to be used.
  The homing guidance system refers to the use of energy radiated or reflected by the target to guide the missile to attack the target. For example, for air defense radar, when it is turned on and working, anti-radiation missiles can lock its position according to the signal it emits, and then attack it. A typical representative is the American AGM-88 “Ham” anti-radiation missile, which has a better actual combat effect. In 1986, during the “Golden Canyon” operation carried out by the US military against Libya, several “Ham” anti-radiation missiles were launched, which accurately destroyed many Libyan air defense radars that were turned on. During the Gulf War, more than 600 “Ham” missiles together with other anti-radiation missiles destroyed and suppressed 90% of Iraq’s early warning radar and surface-to-air missile guidance radar system, effectively reducing the battle damage rate of its own aircraft.
  For moving targets such as fighter jets moving at high speed, their infrared characteristics have become the key to the attack of infrared guided missiles. Infrared guidance is a technology that uses infrared detectors to capture and track the energy radiated by the target itself to achieve homing guidance. It can operate at night and in low visibility, and is a very effective means of precision guidance and strike. For example, the AIM-9 “Sidewinder” missile is the world’s first infrared-guided air-to-air missile. After it is launched, the infrared sensor in front of the missile control cabin detects the infrared radiation emitted by the high-temperature target, so that the missile automatically tracks the target and flies until If it hits the target, it can be fired and ignored. It has been widely used in actual combats such as the Vietnam War, the Falklands War and the Gulf War.
Complex terrain, how to kill with one hit

  Ground targets are different from sea targets, because the terrain on land is complex, the ups and downs are changeable, there may be mountain barriers, and there may be interference from multiple other targets. So, for targets in complex terrain, how does the missile search for it? At this point, you need to use image matching guidance and TV homing guidance.
  Image-matching guidance is a technology in which the missile itself guides the missile to attack the target according to the matching relationship between the actual terrain and the internally stored map. Compared with the maps we see every day, the map information features stored in it are different. Some use terrain contour lines (contour lines) as matching features, and some use regional topography as matching features. In fact, they are divided into terrain matching. And map matching guidance, in which the reference source data of terrain matching guidance is stable and not affected by meteorological changes, but it is not suitable for use in plains and other terrains with small fluctuations. For example, the air-to-ground cruise missile carried by the U.S. B-52 bomber uses terrain matching guidance technology. Map matching guidance can be used in plain areas, but the reference source data will be affected by climate and seasonal changes, which is not stable enough. For example, the US “Pershing 2” ballistic missile uses this kind of guidance method.
  The missile using the TV homing guidance method relies on the TV automatic homing head on the missile to automatically track the target, and controls the missile to fly to the target through the missile autopilot. Its core component is a TV automatic homing head, which is composed of a TV camera, an image information processing device, and a tracking servo mechanism. This kind of missile has the ability to distinguish between targets and complex backgrounds, and has high guidance accuracy for attacking ground targets. However, the range of action is limited by the visibility of the atmosphere and is not suitable for all-weather work. There are many missiles that use TV guidance or have TV guidance in the guidance mode, such as Russia’s KH-59ME TV-guided air-to-ground missile, and Israel’s “Pyramid” TV-guided bomb.

US “Standard 2” anti-aircraft missile

  According to different targets and combat missions, missiles will use different guidance systems. According to whether the work of the guidance system requires any information other than the missile, the guidance system of the missile can be divided into two categories: non-autonomous guidance and autonomous guidance. Autonomous guidance includes program guidance and inertial guidance. Non-autonomous guidance includes homing guidance, remote control guidance, astronomical guidance, satellite guidance and map matching guidance.
  Of course, a single missile does not have to use only one guidance method, but multiple guidance methods can be used in combination, so as to avoid the defects of a single guidance method and achieve complementary advantages. For example, the SM-2 “Standard” air defense missile of the U.S. Navy adopts inertial guidance in the initial and middle stages of flight, and uses semi-active radar guidance in the final stage to track the target. This makes the missile not only have a strong anti-electronic jamming capability, but also have multi-target tracking and attack capabilities.
  In addition, when a missile attacks targets at different distances, the guidance methods used are also different. For example, the US AIM-120 series of air-to-air missiles use different guidance methods when attacking targets at different distances. When attacking at close range, it adopts the attack method of active radar homing throughout the whole process; when attacking at medium and long distances, it adopts the attack method of inertial guidance and active radar homing.
  With the demand for weapons in war and the continuous development of various anti-missile technologies, under the increasingly complex battlefield environment, the missile guidance system will further integrate with information and intelligent technologies, and develop in the direction of system integration and technology integration. , so as to effectively cope with the emerging countermeasure technologies, and achieve the best damage effect while improving the accuracy, and realize the transformation from precision to high efficiency.