NMD (National Missile Defense), its working mode is: early warning radar first finds the target, that is, attacks the "enemy" of intercontinental missiles; The early warning radar sends an early warning signal to the military satellite; Military satellites transmit alarm signals to headquarters; The headquarters issued an order to launch anti-missile missiles; Anti-missile missiles use infrared tracking principle to search for enemy attack missiles, identify true and false warheads, and then intercept enemy attack missiles outside the earth's atmosphere and destroy them with laser weapons. During the Cold War, in order to gain military superiority over the Soviet Union, the United States put forward the "strategic defense" plan (also known as the "Star Wars" plan) in 1983. 1993, Clinton announced that the era of "Star Wars" was over and was replaced by "NMD" (National Missile Defense) and "TMD" (Theater Missile Defense). NMD consists of 2 launching positions, 3 command centers, 5 communication relay stations, 15 radars, 30 satellites, 250 underground silos and 250 interceptor missile systems. Specifically, NMD consists of five parts: early warning satellite, improved early warning radar, ground-based radar, ground-based interceptor and operational management command and control communication system. Early warning satellites are used to detect the launch of enemy missiles and provide early warning and information on the launch and landing of enemy ballistic missiles. These satellites belong to space-based infrared system, that is to say, missiles are detected by the infrared radiation signals of fireworks released by the enemy when launching missiles. The improved early warning radar is the "eye" of the national missile defense system, which can warn targets 4000-4800 kilometers away. In addition to improving the existing ground-to-ground missile early warning radars deployed in Alaska and paving claw radars deployed in California and Massachusetts, the United States will also build new early warning radars in Asia. Ground-based radar is an X-band, broadband and large-aperture phased array radar, which guides ground-based interceptors to attack airspace. Ground-based interceptor is the core of NMD, which consists of booster rocket and interceptor (warhead). The former can send the interceptor near the target, and the latter can automatically adjust the direction and height, collide with the target after finding and locking it, and shoot it down in space. The operational management command and control communication system uses computers and communication networks to link the above systems. After the deployment of these systems, 24 low-orbit early warning satellites and 6 high-orbit satellites orbiting the earth all day will track their infrared radiation signals once they detect the enemy launching missiles. Through the operation and management of the command and control communication system, the satellite not only "informs" the flight trajectory of the missile to the command center, but also indicates the target for the early warning radar and ground-based radar. After the early warning radar finds the target, it transmits the tracking and evaluation data of the missile to the ground-based radar. The interceptor will fly as soon as it receives the launch command from the US Space Command. After staring at the incoming missile with the infrared detector carried by the interceptor, it collided with it with all its strength (by kinetic energy) and ended up with the other side. The development trend of the national missile defense system in the United States evolved from the "strategic defense plan" in the 1980s and the "global limited strike protection system" in the early 1990s. The development of NMD and TMD in the United States will upset the global strategic balance and stability, hinder the nuclear disarmament process, undermine international non-proliferation efforts, and may trigger a new round of arms race, so it is opposed by most countries in the world. The development of TMD is from low to high. Patriot missiles used to intercept missiles flying below 40 kilometers have made great progress. In the Gulf War of 199 1, the hit rate of Patriot PAC-2 missile was 60%. Since then, the United States has spared no effort to improve the performance of this missile. On March 15 this year, the United States announced that the interception test of the improved Patriot PAC-3 missile was successful. It is reported that the United States will conduct 16 interceptions of different targets to further improve this missile. At present, Patriot missile is the only effective interception weapon in TMD, that is to say, TMD is still in the low-altitude defense stage. NMD is a defense system used to protect the United States from ballistic missile attacks. From this perspective, it is a replica or successor of Reagan's "Star Wars" plan. The difference is that the "Star Wars" plan relies on air defense systems, while NMD is based on land-air integration and land defense systems. According to the materials provided by the US Department of Defense, NMD includes six parts: ground-based interceptor missiles, ground-based radars, space-based sensors, improved early warning radars, and operational management, command and control systems and communication systems. It is envisaged that the United States can use this system to detect, track, locate and lock enemy missiles as soon as they are launched, and destroy them before they enter US airspace. The plan is still in the demonstration stage, and no one can say clearly what it looks like. It is said that if foreign missiles are compared to raindrops, this system is like an umbrella, covering the United States tightly without any damage. However, some people have questioned this. During the congressional debate, a member of parliament once erected a leaky umbrella with only an umbrella stand on the spot to describe NMD's defense capability. TMD (Theater Missile Defense System) TMD plan was put forward by US President Bill Clinton in 1993. The premise is that "theater ballistic missiles" spread rapidly in third world countries after the Cold War and became the main threat to American frontier forces and overseas allies. The United States believes that all ballistic missiles that do not threaten the United States are "theater ballistic missiles", and only ballistic missiles that can hit the United States are "strategic ballistic missiles." Therefore, TMD is relative to the "National Missile Defense System" (NMD) which defends "strategic ballistic missiles". TMD and NMD*** are isomorphic to form two major contents of the American concept of "ballistic missile defense" (BMD), and its development work is specifically undertaken by the Ballistic Missile Defense Agency of the US Department of Defense. "War zone" refers to "areas outside the United States under the jurisdiction of the Joint Command and the Special Command". Therefore, theater missile defense system is "a weapon system used to protect theaters outside the United States from short-range, medium-range or long-range ballistic missiles." There are three main strategies for the US military to defend theater missiles: one is to detect and destroy incoming missiles before they are launched; The second is to destroy incoming missiles when they are launched; The third is to intercept and destroy incoming missiles in flight or re-entering the atmosphere. TMD consists of low-level defense and high-level defense. The low-level defense includes Patriot -3 (PAC-3), Extended Medium-range Air Defense System (MEADS) and Naval Area Defense (NAD), and the high-level defense includes Army Theater High Altitude Area Defense (THAAD), Naval Theater Defense System (NTW) and Air Force Boost Phase Defense (BPI). Among them, "Patriot -3", "Naval Area Defense" system, "Army" theater high-altitude area defense system and "Naval theater defense system" constitute the core and key development projects of TMD. PAC-3 missile PAC-3 is the latest model of Patriot system, which is a mobile air defense system of group army and military level, and can launch multiple missiles at the same time to push down targets at different distances. Patriot system is famous for its outstanding performance in the Gulf War. PAC-3 system will be fully upgraded to low-level ballistic missile defense (BMD) system in 20001year, and its task is to provide protection for troops and fixed facilities against attacks from short-range and medium-range ballistic missiles, cruise missiles and fixed-wing or rotary-wing aircraft. In design, PAC-3 is required to be easy to deploy in the world and can be transported by C- 17 or C-5 aircraft. PAC-3 consists of three configurations, all of which are upgraded products. In order to provide the troops with missile defense means as soon as possible, two original configurations were deployed during 1995- 1996. The third configuration is deployed at 200 1. Its final configuration will all adopt the modified system components. The upgraded ground radar has improved the multi-function, low-altitude and threat detection and identification capabilities. After the target enters the earth's atmosphere, the new PAC-3 missile destroys it by violent impact, which is called dense atmosphere impact kill interception. The command, control and communication system of PAC-3 has been improved better than the earlier products, and its combat capability has been greatly improved. The launching device of PAC-3 is mainly composed of ground radar equipment, interception control station and eight missile launching equipment. Naval Regional Theater Ballistic Missile Defense (TBMD) The naval regional theater ballistic missile defense plan includes Aegis cruisers and destroyers equipped with standard missiles. The Aegis weapon system will be improved so that it can detect and track theater ballistic missiles with AN/SPY- 1 radar and intercept them with SM-2 Block ⅳ A missiles. Sm-2block Ⅳ A missile is improved from SM-2block Ⅳ missile. An infrared seeker has been added, and the warhead, autopilot and fuse have been improved to intercept theater ballistic missiles. The plan includes verifying Aegis's ability to detect theater ballistic missiles. At present, it is also planned to develop the User Combat Evaluation System (UOES) to enable the early participating units to conduct experiments and provide limited capabilities to defend tactical ballistic missiles in the atmosphere in case of national emergency. The development of THAAD system THAAD began in 1992, and the Army plans to deploy it in 2007. THAAD is a key part of TMD. THAAD is mainly used to intercept long-range theater-class ballistic missiles. THAAD's goal is to shoot down missiles in the distance and at high altitude, so as to increase the ability to guard against the threat of ballistic missiles in the theater, especially some weapons with greater lethality, which can be shot down in the distance and at high altitude to prevent future troubles. THAAD system has the volley capability needed to intercept theater ballistic missiles. In order to destroy the threat of carrying weapons of mass destruction at a higher altitude and further distance and ensure the required level of defense, volley capability is necessary. Another important part of THAAD project is the User Combat Evaluation System (UOES). The system can evaluate the operational performance of the system at an early stage and provide limited atmospheric defense capability in national emergencies. The missile part of THAAD consists of interceptor missile, pallet loading and launching system and operational management/command, control and communication system. Interceptor missile is a hit-and-kill aircraft, which adopts the latest guidance, control and kill aircraft technology. The pallet loading and launching system makes the missile launching box, control and launching execution platform easy to transport, and the battle management/command, control and communication system consists of the communication and data system required by THAAD mission. THAAD's operational management/command, control and communication system also provides a general interface with theater air defense command and control system and an interface with THAAD radar. THAAD radar can meet the urgent demand for wide-area defense radar with stronger performance. As a part of THAAD system, THAAD radar provides surveillance and fire control support, and provides tips for low-level defense systems such as Patriot missiles. THAAD radar uses the existing radar technology to realize the expected functions: threat attack early warning, threat type identification, interceptor missile fire control, external sensor prompt, launch and impact point judgment. In particular, THAAD radar will be able to distinguish the types of tactical ballistic missiles and evaluate the damage after interception. THAAD radar will carry out a series of comprehensive performance tests to prepare for THAAD project entering milestone 2. The research results of THAAD radar will be the basis of national missile defense-ground-based radar (NMD-GBR) radar technology verification machine.