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Anti-ballistic missile

From Academic Kids

An anti-ballistic missile (ABM) is a missile designed to counter intercontinental ballistic missiles: the strategic ballistic missiles used to deliver nuclear weapons or their elements in flight trajectory. ABMs may also be used against chemical or biological payloads.

For current US developments, see Missile Defense Agency.

For defense against short-range missiles, see Arrow missile, MIM-104 Patriot, Aster 15 or Crotale missile.

Contents

Defense of Moscow

There is a limited ABM system around Moscow, an upgraded Galosh known in the west as the ABM-4 Gorgon. The interceptor missiles are armed with a nuclear warhead. See also below.

History of ABMs

Early developments

The idea of shooting down rockets before they can hit their target dates from the first use of modern missiles in warfare, the German V-1 and V-2 program of World War II. British and American fighters attempted to destroy V-1 "buzz bombs" in flight prior to impact, with some success. The V-2, the first true ballistic missile, proved impossible to intercept using Spitfires and similar craft. Instead, the Allies launched Operation Crossbow to find and destroy V-2s before launch. The operation failed, as would a similar operation during the first Persian Gulf War nearly fifty years later against the V-2's direct descendant, the Iraqi Scud missile.

The American armed forces began experimenting with anti-missile missiles shortly after World War II, as the extent of German research into rocketry became clear. But defenses against Soviet long-range bombers took priority until the later 1950s, when the Soviets began to test their missiles (most notably via the Sputnik launch in October 1957). The first experimental ABM system was Nike Zeus, a modification of existing air defense systems. Nike Zeus proved unworkable, and so work proceeded with Nike X.

Another avenue of research by the U.S. was the test explosions of several hydrogen bombs at very high altitudes over the southern Atlantic ocean, launched from ships. When such an explosion takes place a burst of X-rays are released that strike the Earth's atmosphere, causing massive secondary showers of charged particles over an area hundreds of miles across. The movement of these charged particles in the Earth's magnetic field causes a powerful EMP which induces very large currents in any conductive material. It was felt that this would effectively destroy any electronics on the warheads, thereby ruining terminal guidance. The project was found to be unworkable, although the exact reasons are not given.

A number of other countries were also involved in early ABM research. Perhaps surprisingly one of the more advanced projects was at CARDE in Canada. Here several teams researched the main problems of ABM systems, developing several advanced infrared detectors for terminal guidance, a number of missile airframe designs, a new and much more powerful solid rocket fuel, and numerous systems for testing it all. After a series of drastic budget cuts in the late 1950s the research was wound down. One offshoot of the project was Gerald Bull's system for inexpensive high-speed testing, consisting of missile airframes fired from a sabot round, which would later form the basis of Project HARP. Equally surprising was the lack of similar development on the part of the British or French militaries, neither of whom appear to have had serious programs in place.

Prototypes and deployment plans

Nike X was a US "system" of two missiles, radars and their associated control systems. The original Nike Zeus was upgraded for longer range and a much larger 5 megatonne warhead, known as the Nike EX, intended to destroy warheads with a burst of x-rays outside the atmosphere. A second shorter-range missile with very high acceleration was added to deal with warheads that managed to get past the slower but longer-ranged Nike. Sprint was a very fast missile (some sources claimed it accelerated to Mach 10 within 5 seconds of flight--an acceleration of 65 g!) and had a smaller warhead in the low kiloton range for in-atmosphere interceptions. Further upgrades to the Nike would eventually lead to it being renamed Spartan.

The new Spartan changed the deployment plans as well. Whereas in the past the plans for the Nike systems had been to be clustered near cities as a last-ditch defence, the Spartan allowed for interceptions at hundreds of miles range, so the basing changed to provide almost complete coverage of the United States in a system known as Safeguard.

The only remaining ABM system to reach production was the Soviet A-35 system based on the A-350 missile (known in the west as the ABM-1 Galosh and ABM-1b Gammon) deployed at four sites around Moscow in the early 1970s. Originally intended to be a larger deployment, the system was in fact downscaled to the two sites allowed under the 1972 ABM treaty in the late 1970s in preparations for replacement by newer systems. These did not in fact arrive until the 1980s, when they were supplanted with the ABM-3 Gazelle short-range system, and then replaced with an upgraded Galosh known in the west as the ABM-4 Gorgon. In general the system is thought to have capabilities similar to that of the US's Safeguard sites, and with one of the main battle management radars aimed at the People's Republic of China, it appears they also felt that the ability to fend off an attack by an advance MIRV-equipped force was not worth trying.

The MIRV problem

When ABM systems were being developed they were attempting to counter single warheads from large ICBMs. The economics seemed simple enough; since rocket costs are exponentional with power, the cost of the interceptors should be considerably less than those of the ICBMs which had much longer range and heavier loads. In an arms race the defense would always win.

Things changed dramatically with the introduction of MIRV warheads. Suddenly each launcher was throwing not one warhead, but several. Nevertheless the defense would still require a rocket for every warhead, as they would be re-entering over a wide space and could not be attacked by several interceptors on a single rocket. Suddenly the defense no longer "worked", it was much less expensive to add more warheads, or even decoys, than it was to build the interceptor needed to shoot it down.

The experimental success of Nike X persuaded the Lyndon B. Johnson administration to propose a thin ABM defense in a September 1967 speech by Defense Secretary Robert McNamara, known as Sentinel. McNamara, a private opponent of ABM because of cost and feasibility (see cost-exchange ratio), claimed that the ABM system would be directed not against the Soviet Union's missiles (since the USSR had more than enough missiles to overwhelm any American defense), but rather against the potential nuclear threat of the People's Republic of China.

Cynics thought that the system was really an "anti-Republican" shield designed to give the Democratic Johnson political protection against Republican election charges in the 1968 presidential election. Due to its immense cost and strategic importance, ABM systems have often been the subject of low-key but intensely bitter partisan struggles.

All the while a huge public debate over the merit of ABMs broke out in public, notably the science magazines such as Scientific American. Even before the MIRV problem made the ABM system non-workable in the late 1960s, a number of serious technical difficulties were highlighted as potentially making any such system essentially useless. Primary among these complaints were the use of Fractional Orbital Bombardment System (FOBS) that would give little warning to the defence, as well as the high-altitude bursts that the U.S. had researched, used in reverse to blanket the defending radars with an opaque shield they would have to shoot through.

Technical difficulties aside, the debate soon turned to an odd position—that no defense was better than any defense. Key to this opinion was that a false sense of security might prompt the owner into a position of escalating minor threats, feeling safe that the opposition was helpless to do anything about it as their offensive force could be countered. The argument was even made that simply starting to deploy such a system would prompt a full-scale attack, before it could become operational and thereby render such an attack useless. This curious set arguments thus put the system in a terrible position: it couldn't possibly work, but if it did that would be even worse.

The ABM Treaty of 1972

The great cost and dubious feasibility of building successful missile detection and interception systems with 1970s technology, led to the ABM treaty of 1972, which restricted the deployment of missiles designed to shoot down each other's ICBMs. Under the ABM treaty and a 1974 revision agreed to by the Soviets and Americans, each country was allowed to deploy a single ABM system with only 100 interceptors to protect a single target. The Soviets deployed a system named Galosh, designed to protect Moscow. The U.S. deployed a system called Safeguard to defend ballistic missile sites at Grand Forks Air Force Base, North Dakota, in 1975. Few people seriously think either system would have been very effective. (In December 2001, the U.S. announced its intention to withdraw from the treaty.)

Why did the Soviets and Americans accept this limitation? Nuclear strategists in the United States believed that allowing either country to develop a first-strike capability would be destabilizing and increase the likelihood of the use of nuclear weapons in a crisis. Soviet leaders suspected that the United States, with its mammoth resources and technological superiority, might well be able to create a leakproof defense. By limiting ABM systems to a marginal role, strategic stability would be assured (this is the logic better known as mutually assured destruction). In what appears to nonexperts to be ironic, this limitation of defensive arms led to treaties limiting the construction of offensive arms known as the SALT I treaties.

Conservatives in the United States, suspicious of the foreign policy machinations of Henry Kissinger and dubious of the Soviet-American d้tente engineered by President Richard Nixon, never accepted the logic of the ABM Treaty, which was designed and ratified under Nixon and Kissinger. Over the next decade, activists pressured Republican leaders to overturn the ABM Treaty and begin the construction of a massive anti-Soviet defense.

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Reagan and "Star Wars"

The Reagan-era Strategic Defense Initiative (better known as "Star Wars"), along with research into various energy-beam weaponry, brought new interest in the area of ABM technologies. Extensive research and some experiments proved that several concepts for space-based systems (X-Ray Lasers, "brilliant pebbles", etc) were not feasible with then-current technology.

Nothing was deployed operationally until Patriot antiaircraft missiles were used in the 1991 Gulf War to attempt to intercept Iraqi Scud missiles. Post-war analyses show that the Patriot was largely ineffective because of the limited range of its radar and the control system's inability to discriminate payloads from other objects when the Scud missiles broke up (or were broken up -- it's not clear which) during reentry. On the other hand, the Scud itself was highly inaccurate and not very reliable. It was more a psychological than real threat to military targets. Theodore Postol of MIT wrote a study which concluded that the Patriot (originally designed, like the early Nike systems, as an anti-aircraft system) may not have hit a single Scud.

Testing of ABMs and ABM technology continued through the 1990s with mixed success. Use of non-nuclear interceptors requires that the interceptor physically contact the incoming payload -- a much more difficult problem. There are also many unresolved issues with warhead discrimination and decoy deployment. There is little doubt that occasional intercepts are possible. The issue is whether an ABM system is a cost effective deterrent or whether a potential enemy will simply deploy a few more missiles with more warheads.

The George W. Bush administration and ABM

The election of President George W. Bush in 2000 has led to the renewed interest and several ABM tests, as the U.S. military seeks to demonstrate the feasibility of shooting down ballistic missiles. In contrast to the Reagan era Strategic Defense Initiative which was intended to shield the United States from a massive attack by the Soviet Union, the stated purpose of this era's ABM's (National Missile Defense, see also there) is the much more limited goal of shielding the United States from a limited attack by a rogue state. It remains to be seen whether a system reliable enough to be useful operationally can be developed.

President Bush and his advisors appear to be determined to deploy a system, and have proposed to develop a dual purpose test and interception facility in Alaska. The Alaska site, it should be mentioned, might be effective against missiles launched from East Asia (such as North Korea), but is not likely to provide much protection from missiles launched from Southwest Asia (Iran or Iraq, for example). President Bush has used the September 11, 2001 Terrorist Attacks to justify the need for such a shield.

Often overlooked in the ABM debate in the United States is the resistance of many Pentagon leaders to the construction of a National Missile Defense. Admirals and generals of all services oppose spending huge sums (currently $8bn/yr in 2003) to research, develop, and procure NMD systems. They would prefer to have that money spent on new conventional weapons, training, equipment, or pay. By conventional procurement methodologies (cost-benefit analysis and cost-utility analysis) missile defense would be regarded as a 'bad buy' owing to its very high costs, high level of project risk (it is essentially a research project, not acquisition of proven technologies) and the benefits are disputed. In order to prevent its cancellation by the Pentagon, successive administrations have placed missile defense outside of direct Pentagon control in a separate organisation.

International ABM efforts

In 1998 the Israeli military conducted a successful test of their Arrow ABM, developed in Israel with American assistance. Designed to intercept incoming missiles traveling at up to 2 mile/s (3 km/s), the Arrow is expected to perform much better than the Patriot did in the Gulf War. Taiwan is also engaged in the development of an anti-ballistic missile system, based on its indigenously developed Tien Kung-II (Sky Bow) SAM system. Although reports suggest a promising system, the ROC government continues to show strong interest towards the American THAAD program.


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