ICBM

An Intercontinental ballistic missile, or ICBM, is a long-range missile using a ballistic trajectory involving a significant ascent and descent, including suborbital and partial orbital trajectories. An ICBM differs little technically from other ballistic missiles such as the IRBM, SRBM or newly named United States, Russia, and the People's Republic of China, although North Korea is believed to be developing an ICBM system.

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History

Early ICBMs formed the basis of many space launch systems. Examples include: Atlas, Delta, Redstone_rocket, Titan, R-7, and Proton. Modern ICBMs tend to be smaller than their ancestors (due to increased accuracy and smaller and lighter warheads) and use solid fuels, making them less useful as orbital launch vehicles.

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Modern ICBMs

Modern ICBMs typically carry multiple independently targetable reentry vehicles (MIRVs), each of which carries a separate nuclear warhead, allowing a single missile to hit multiple targets. MIRV was an outgrowth of the rapidly shrinking size and weight of modern warheads and the Strategic Arms Limitation Treaties which imposed limitations on the number of launch vehicles(SALT I and SALT II). It has also proved to be an "easy answer" to proposed deployments of ABM systems – it is far less expensive to add more warheads to an existing missile system than to build an ABM system capable of shooting down the additional warheads; hence, most ABM system proposals have been judged to be impractical, and have never been deployed.

Modern ICBMs tend to use solid fuel, which can be stored easily for long periods of time. Liquid-fueled ICBMs were generally not kept fueled all the time, and therefore fueling the rocket was necessary before a launch. ICBMs are based either in missile silos, which offer some protection from military attack (including, the designers hope, some protection from a nuclear first strike), or on submarines or rail cars, which are mobile and therefore hard to find.

The low flying, guided cruise missile is an alternative to ballistic missiles.

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