Intercontinental ballistic missile

An intercontinental ballistic missile (ICBM) is a land-based surface-to-surface missile, carrying one or more warheads, with a range in excess of 5500 kilometers.. "Ballistic" describes its trajectory, with a powered boost phase into space, midcourse coasting along a suborbital phase, and unpowered reentry at one or more points determined by a precision navigational system. ICBMs were one of the main weapon systems of the Cold War, with between 2000 and 3000 deployed by the U.S. and Soviet Union, and in the tens by China.

While the basic reentry is unpowered, certain missiles may release multiple reentry vehicles. The bus that carries the individual reentry vehicles may aim them at different points, and some reentry vehicles may have mechanisms that can maneuver them from a pure ballistic path. Maneuvering reentry vehicles would have that capability to make the final guidance (e.g., as affected by wind) extremely precise. During reentry, the bus may release penetration aids, such as radar reflectors and jammers.

Of the strategic delivery systems of what been called the "Triad" of nuclear delivery systems, each presenting an adversary with a different defense problem:

• ICBMs
• Manned bombers, dropping gravity bombs and air-launched cruise missiles
• Submarines with submarine-launched ballistic missiles and cruise missiles

ICBMs are considered the most vulnerable, and their numbers have been considerably reduced both by bilateral arms control agreements between the U.S. and Russia. States of the former Soviet Union that had ICBM bases have shut them down. France and the United Kingdom have never deployed ICBMs, although they had shorter-ranged land-based ballistic missiles, nuclear weapons delivery aircraft, and submarines that launched nuclear missiles.

No other nation had demonstrated an operational ICBM capability, although nations with significant satellite launch capability clearly have missile technology that could be converted to ICBM applications. North Korea has threatened development of one, but their tests have not indicated that they are close to operational status. In addition, practical ICBMs need compact thermonuclear warheads, which some countries with advanced rocket programs, such as Japan, do not have in their inventory.

Categories

ICBMs, variants of which are used as space launch vehicles, are categorized as "heavy" or "light". Heavy ICBMs have a total launch weight greater than 106,000 kilograms or a payload throw-weight greater than 4,350 kilograms. Heavier ICBMs can lift larger single reentry vehicles, as were needed for early high-yield thermonuclear bombs, or multiple reentry vehicles.

"First generation" ICBMs, such as the US Atlas (missile), required liquid fueling before they could be launched, a process taking hours and leaving the missile quite vulnerable. The second generation used either solid propellants or storable liquid propellants, and could be launched from a hardened silo. Third generation ICBMs were far more accurate, were capable of using multiple reentry vehicles, were even more accurate, and could be in even more hardened launch facilities.

Guidance and accuracy

Guidance most often uses inertial navigation, sensing accelerations and decelerations on the path away from a precisely surveyed launch point. Some also use celestial navigation, primarily before reentry, in which they determine their location based on the bearings to a set of stars. Certain early first-generation ICBMs also received guidance commands from their launch point, during the boost phase.

Payloads

ICBMs most commonly had nuclear warheads, although there are reports that some Soviet missiles may have had biological warheads. Several U.S. Minuteman ICBMs carried radio transmitters of the Emergency Rocket Communications System, which could send launch orders to other nuclear forces.

With the reduction of nuclear payloads through arms control, there is experimentation with the use of "kinetic kill" warheads for ballistic missiles. The kinetic energy of the reentry vehicle is so high that a conventional explosive warhead would not add as much energy as a dense inert mass.

History

Soviet

Central to the Soviet strategic ballistic missile program from World War II until 1960 was the development of the MBR R-7. It proved a poor weapon but a superb space launcher that served in advanced forms as the workhorse of the Soviet space program for nearly 30 years.

Dupont (1991) examines the Soviet behind the deployment of the SS-9, SS-11, and SS-13 ICBMs. American observers debated three alternate views of Soviet behavior: that they #acted to fulfill their military doctrine,

1. deployed the ICBMs for domestic political reasons,
2. acted in response to American deployments.

The early Soviet ICBM programs resulted in the SS-13, which began deployment in 1969. The startup dates that U.S. intelligence had assumed are contradicted by the new historical evidence. Moscow began the SS-9 and SS-11 programs several years later than has previously been thought, suggesting that the Soviets acted largely in response to American deployments. Evidence from Soviet procurement bureaucracy and the missile design practices suggests that Kremlin politics was not a major motivation. The overall Soviet strategy was a pre-emptive military strategy up to at least 1967, chiefly because they lacked a launch on warning (LOW) capability. Circumstantial evidence suggests that the Soviets targeted their SS-9s against the launch control centers of U.S. ICBMs--which tends to support the doctrinal explanation for the SS-9. Deployment of the SS-11 was motivated by two considerations falling clearly under the arms racing explanation. Taken together, then, the deployments were motivated by a mixture of doctrinal and international, political considerations.

U.S.

The years 1958-1964 were characterized by rapid, extensive change in the technology of nuclear weapons delivery systems, centering on ICBMs replacing ong-range bombers, especially the B-52, as the chief vehicles. Simultaneously, national military strategy changed with the transfer of power from the Eisenhower to the Kennedy Administrations, shifting from reliance on overwhelming nuclear retaliation to emphasis on balanced conventional and nuclear forces. Kennedy had campaigned in 1960 warning about a supposed "missile gap," that is, a Soviet lead.

To close the gap during the early 1960s, the U.S. began a crash program to install 132 Atlas, 108 Titan, and 1,000 Minuteman ICBM's in dispersed underground facilities in the continental U.S., along with the Polaris submarine-launched ballistic missile (SLBM)s. It required a giant task force of contractors, workers, and the military and entailed complex bureaucratic tangles and jurisdictional disputes, countless construction problems, and the necessity of maintaining a very high standard of cleanliness on the sites. Nevertheless, the project was completed on schedule, in large part because the project managers instilled the whole task force with their "wartime" sense of national priority.

Minuteman

In the 1950s long-range rockets were liquid fueled because solid-fuel motors did not produce sufficient thrust and were difficult to control. In the late 1950s advances in solid-fuel propellants enabled the Air Force to develop its first solid-fuel ICBM, the Minuteman I (LGM-30A/B). In 1957 Col. Edward Hall at the Air Force Ballistic Missile Division's (AFBMD) designed the Minuteman. Unlike the first generation Atlas and Titan I liquid-fuel missiles, Hall proposed a relatively small, three-stage solid-fuel missile that would be inexpensive to build and maintain. He envisioned basing thousands of the missiles in unmanned, heavily hardened and widely dispersed silos linked electronically to a series of central launch control facilities. Senior Air Force officials, initially hostile, reversed course when the Navy proposed modifying its Polaris submarine-launched ballistic missile (SLBM) for use as an ICBM.

The first ten Minuteman ICBMs became operational in October 1962. Deployment proceeded on a crash basis; by 1967 1,000 Minutemen were operational. Minuteman is a three-stage, solid-propellant, rocket-powered ICBM with a range of approximately 5,500 nautical miles. It has an all-inertial guidance system and the capability of being fired from hardened and widely-dispersed underground-silo launchers. Five contractors produced four improved versions: Minuteman I (models "A" and "B"), Minuteman II (model "F"), and Minuteman III (model "G"), the latter capable of carrying multiple independently-targetable reentry vehicles (MIRVs).

The current Minuteman force consists of 500 Minuteman III's based in silos at F.E. Warren Air Force Base, stretching across Wyoming, Montana and North Dakota. The chief contractor is Boeing. The missile uses three solid-propellant rocket motors, built by Thiokol, Aerojet-General and United Technologies Chemical Systems Division. The rocket is 59.9 feet long and 5.5 feet in diameter; it weights 79,400. The inertial guidance system from Boeing North American guides it over a range of 6,000-plus miles at a speed of 15,000 mph (Mach 23) at burnout. The re-entry vehicle, built by Lockheed Martin Missiles and Space, contains a MK 12 or MK 12A warhead.

These missiles are under the control of the 90th Space Wing of the Twentieth Air Force. Twentieth Air Force reports to Air Force Space Command for readiness, and to United States Strategic Command for operational use.

Arms Control

There has been significant reduction, through arms control agreements, of ICBM rockets, and of their capabilities such as multiple independently targetable reentry vehicles (MIRV). Verification of compliance with the treaties involves national technical means of verification and bilateral on-site inspections and overflights by monitoring aircraft.