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Historically, Missile Defense has been part of the Air Defense systems. Most frequently the term implies a missile-based defense -- an Anti-ballistic Missile . However non-missile defenses such as Lasers will be operational within about two years. Historically U.S. missile defense responsibility has been assigned to the Army , but in more recent years the Navy and Air Force have developed their own antimissile systems. MISSILE DEFENSE CATEGORIES Missile Defense can be divided into categories based on various characteristics: type/range of missile intercepted, the trajectory phase where the intercept occurs, and whether intercepted inside or outside earth's atmosphere: Classified by type/range of missile intercepted The types/ranges are strategic, theater and tactical. Each entails unique requirements for intercept, and a defensive system capable of intercepting one missile type frequently cannot intercept others. However there is sometimes overlap in capability.
Classified by trajectory phase Ballistic missiles can be intercepted in Three Regions Of Their Trajectory : boost phase, midcourse phase or terminal phase.
Classified by intercept location relative to the atmosphere Missile defense can take place either inside (endoatmospheric) or outside (exoatmospheric) the earth's atmosphere. The trajectory of most ballistic missiles takes them inside and outside the earth's atmosphere, and they can be intercepted either place. There are advantages and disadvantages to either intercept technique.
Some missiles such as THAAD can intercept both inside and outside the earth's atmosphere, giving two intercept opportunities. HISTORY In the 1950s and 1960s , the term meant defense against strategic (usually nuclear-armed) missiles. The technology mostly centered around detecting offensive launch events and tracking in-bound ballistic missiles, but with limited ability to actually defend against the missile. In the late 1960s, technology had matured to the point to allow limited rudimentary missile defense by using Anti-ballistic Missile s. At first, these anti-ballistic missiles were armed with their own Nuclear Weapons , since precision technology (to "hit-a-bullet-with-a-bullet") did not exist. Laser s were considered for shooting down the warheads, but various problems including atmospheric interference and warhead hardness impeded this effort. Throughout the 1950s and 1960s, the United States Project Nike air defense program focused initially on bombers, then ballistic missiles. In the 1950s, the first United States antiballistic missile system was the Nike Hercules , which had a limited ability to intercept incoming ballistic missiles, although not ICBMs. This was followed by Nike Zeus , which using a nuclear warhead could intercept ICBMs. However Nike Zeus had other limitations which prevented it being deployed. However in the early 1960s, the Nike Zeus was the first antiballistic missile to achieve hit-to-kill (physically colliding with the incoming warhead). The Zeus missile was enhanced, and the shorter range Sprint Missile was added to the Nike defense system, then called Nike-X. The system included large powerful radars and a computer complex. Eventually, the Nike-X program was realigned and renamed Sentinel . This program goal was to protect major U.S. cities from a limited ICBM attack, especially focusing on China . This in turn reduced tensions with the Soviet Union, which retained the offensive capability to overwhelm any U.S. defense. The Soviet Union deployed an antiballistic missile system around Moscow in 1966, which also defended nearby ICBM sites. That system has been upgraded several times and is still operational. The United States announced an ABM program to protect twelve ICBM sites in 1967. In 1967, then-Secretary of Defense Robert McNamara stated: ''"Let me emphasize -- and I cannot do so too strongly -- that our decision to go ahead with a limited ABM deployment in no way indicates that we feel an agreement with the Soviet Union on the limitation of strategic nuclear offensive and defensive forces is in any way less urgent or desirable."'' The SALT I talks began in 1969, and led to the Anti-Ballistic Missile Treaty in 1972, which ultimately limited the U.S. and U.S.S.R. to one defensive missile site each, with no more than 100 missiles per site. As a result of treaty and technical limitations, plus public opposition to nearby nuclear-armed defensive missiles, the U.S. Sentinel program was redesignated the Safeguard Program , with the changed goal of defending U.S. ICBM sites, not cities. The U.S. Safeguard system was deployed to defend the Minuteman ICBMs near Grand Forks, North Dakota. It was deactivated in 1976 after being operational for less than four months. The reason was a changing political climate plus concern over limited effectiveness, low strategic value, and high operational cost. The end of the cold war In the early 1980s , technology had matured to consider space based missile defense options. Precision hit-to-kill systems more reliable than the early Nike Zeus were thought possible. With these improvements, the Reagan Administration promoted the Strategic Defense Initiative , an ambitious plan to provide a comprehensive defense against an all-out ICBM attack. See National Missile Defense for additional details. In the early 1990s , missile defense expanded to include tactical missile defense, as dramatically seen in the first Gulf War . The effectiveness of a the Patriot system in disabling or destroying incoming SCUD was the subject of Congressional hearings and reports in 1992 {Link without Title} . In the late 1990s, and early 2000s , the issue of defense against Cruise Missile s became more prominent as the new Bush Administration . In 2002, President George W. Bush withdrew the US from the Anti-Ballistic Missile Treaty , allowing further designing and testing of ABMs under the Missile Defense Agency beyond the single site allowed under the treaty. There are still technological hurdles to deploying an effective defense against any ballistic missile attack. The proposed national ballistic missle defense system came has also come under scrutiny about its technological feasibility. Intercepting midcourse (rather than launch or reentry stages) ballistic missiles traveling at several times the speed of sound with a "kinetic kill vehicle" has been characterized as trying to hit a bullet with a bullet, despite this high difficulty there have been several successful intercepts. Moreover, the warheads or payloads of ballistic missiles can be concealed by a number of different types of decoys. Sensors that track and target warheads aboard the kinetic kill vehicle may have trouble distinguishing the "real" warhead from the decoys, but several tests that have included decoys were successful. Nira Schwartz 's and Theodore Postol 's criticisms about the technical feasiblity of these sensors have lead to an on-going investigation of research misconduct and fraud at the Massachusetts Institute Of Technology {Link without Title} . As of 2006 the U.S. has an limited operational antimissile system consisting of ground-based interceptors in Alaska. The system was initially called National Missile Defense (NMD), but in 2003 the ground-based component was renamed Ground-Based Midcourse Defense (GMD). Defending against Cruise Missile s is similar to defending against hostile low-flying manned aircraft. As with aircraft defense, countermeasures such as Chaff , flares, and low altitude can complicate targeting and interception. High-flying radar aircraft such as AWACS can often identify low flying threats by using Doppler Radar . Another possible method is using specialized satellites to track these targets. By coupling a target's kinetic inputs with Infrared and radar signatures it may be possible to overcome the countermeasures. WELL-KNOWN DEFENSE SYSTEMS AND INITIATIVES SEE ALSO
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