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Classifications of Ballistic Missiles by Range

The three main factors influencing the effectiveness of a ballistic missile are range, accuracy and the size and type of the warhead.

RANGE

The range of a missile is essentially determined by the velocity it reaches when all its propellant has been used up (its ‘burnout velocity’). These velocities are many times in excess of those of aircraft or cruise missiles. A 500 km-range Short Range Ballistic Missile (SRBM) reaches a burnout velocity of some 2.2 kilometres per second (km/sec). A 5,000 km-range Intermediate Range Ballistic Missile (IRBM) reaches a velocity of some 5.7 km/sec.

The missile’s burnout velocity is affected by a number of other factors. These include the energy produced by the propellant, the weight of the warhead or warheads, casing and guidance systems the missile carries (its ‘payload’) and the missile’s ability to discard the dead weight represented by the parts of its fuselage in which the propellant has been burnt up.

A ballistic missile may be single-stage or multi-stage. Single-stage ballistic missiles, such as the German V-2 of World War II or the Russian and North Korean Scuds, have one stage containing both the warhead and propellant that will fall to earth in one piece. Multi-stage missiles can discard the stage, or stages, that contain fuel once that fuel has been spent, meaning that only the part containing the warhead will actually hit the target.

Multi-stage missiles have multiple powered stages that fire in sequence during the boost phase and detach themselves when the propellant is burnt up. Thus the dead weight of the used stage (or ‘booster’) does not have to be accelerated throughout the entire period of the boost phase, increasing the burn-out velocity and thus the ultimate range. While multi-staging is far more technically demanding than single staging, it is necessary if a missile is to achieve ranges much in excess of 1,500 km.

In practice, SRBMs and IRBMs with ranges of less than 1,500 km tend to be single-stage; MRBMs and IRBMs with ranges of less than 5,500 km tend to have two stages, while Intercontinental-Range Ballistic Missiles (ICBMs) with ranges of 5,500 km or more tend to have three stages.

The simplest way to increase the range of a missile is to reduce the weight of the payload (i.e. the warhead). For an SRBM, halving the payload increases its range by 150%. However, the lighter warhead reduces the military effectiveness of the missile, especially if the warhead contains conventional high-explosives. This method has been used by Egypt, Iraq, and North Korea to increase the range of their Scud-derived SRBMs. For ballistic missiles with ranges of greater than 1,000 km, however, halving the payload increases the range only by some 20%. A more effective way to increase range without resorting to multi-staging is to ‘cluster’ multiple rocket engines together and fire them simultaneously, as is the case with the North Korean Nodong-1 missile, which uses four Scud engines to achieve a range of 1,000 km.

A ballistic missile’s range may also be increased by boosting the efficiency (or ‘specific energy’) of the fuel used in the boosters. However, exotic fuels such as halogen or hydrogen/oxygen based liquids are technically demanding to develop and highly dangerous to handle. While solid fuels are far more stable, easier to store, and safer to handle, making them particularly attractive for mobile ballistic missiles, the technology required to extract long ranges from solid fuel is highly advanced.

ACCURACY

There is some divergence of evidence and opinion as to the accuracy of ballistic missiles. There is common ground that ballistic missiles with advanced computer-controlled guidance systems, mainly US and Russian nuclear-armed ICBMs and Submarine Launched Ballistic Missiles (SLBMs), are relatively accurate. Most other ballistic missiles, which lack advanced guidance systems, are relatively inaccurate and thus most effectively directed at large target areas such as cities, whether they are armed with weapons of mass destruction (Nuclear, Biological, Chemical or Radiological) or conventional high-explosive warheads. As a general rule, accuracy is likely to diminish as range is increased, particularly if designed range is boosted by modification, as was the case with Iraq’s modified Scuds.

The development of more capable Intermediate Range Ballistic Missiles (IRBMs) by downsizing ICBMs rather than by extending SRBM technology increases the potential threat posed by missile proliferation. The Soviet SS-20 mobile IRBMs of the 1980s, for example, had a degree of accuracy which was of considerable concern to NATO leaders at that time. The missiles themselves have been retired under the 1987 Intermediate-Range Nuclear Forces (INF) Treaty, but their advanced guidance technology has survived and may be amongst those widely offered from Russian sources on the international black and grey markets.

Missile accuracy is usually expressed in terms of Circular Error Probable (CEP), defined as “the radius of a circle around a target within which there is a 50% probability that a weapon aimed at that target will fall.” Elaborating on this technical definition, the US. Office of Technology Assessment notes:

CEP does not take into account either launch failures or the systematic errors associated with mis-aiming the missile in the first place, called the ‘bias.’ The CEP is also a median, rather than a mean; it does not predict how far outside the circle the other half of the missiles will land. (For instance, some of the Iraqi Scuds fired toward Israel during the Persian Gulf War landed quite far from intended targets or in the Mediterranean Sea.) Furthermore, in practice the expected miss-distance is usually elongated in the down range direction, leading to an elliptical rather than a circular error pattern. Therefore, even ignoring the bias, a CEP gives only a rough indication of the likelihood that a missile will hit an intended target.

In practical terms, this means that the Iraqi Al Hussein SRBM, with a CEP of some 3,000 meters, the Soviet-made SS-1 Scud B SRBM with a 900-meter CEP, or the Chinese M-9 SRBM, with a 600-meter CEP, are so inaccurate that, with a high explosive warhead, they can only be used effectively against large targets, such as cities, or ‘soft’ military targets. However this targeting inaccuracy may be compensated for by fitting the missile with a WMD warhead. Inaccuracy might also be compensated for by firing a number of missiles in a salvo attack aimed at a particular target or set of targets.

WARHEADS

Ballistic missile warheads can be single or multiple, and deliver nuclear, chemical or biological payloads as well as conventional high explosives.

Most US and Russian ICBMs and SLBMs have Multiple Independently-Targeted Re-Entry Vehicles (MIRVs), an arrangement of multiple nuclear warheads mounted on a platform which can maneuver outside the atmosphere and release warheads against a number of different targets. Some older Russian ICBMs and SLBMs have Multiple Re-Entry Vehicles (MRV), multiple nuclear warheads that are not independently targetable. The British Trident SLBM deploys with up to five MIRVs, as do French SLBMs. Current Chinese ICBMs and IRBMs and French IRBMs carry single nuclear warheads. Certain US, Russian and Chinese SRBMs also carry single nuclear warheads. The US has also designed a Manoeuvrable Re-Entry Vehicle (MaRV) whose warheads are able to evade active defenses on the way to their targets.

Ballistic missiles belonging to other governments include Short-, Medium- and Intermediate-Range Missiles, most of which carry single, high explosive warheads suitable for use only against large strategic targets such as cities. But while a warhead may contain ‘only’ conventional explosives, as was the case with the V-2s and, contrary to worst fears, appears to have been the case with Iraqi-modified Scuds in the Gulf War, several hundreds of pounds/kilos of conventional explosives can still inflict substantial damage on unprotected targets.

Although all missiles fired in combat, from Hitler’s V-2s onward, have had conventional high explosive warheads, many such missiles could also carry either single or multiple chemical or biological warheads. In addition, such missiles could carry a single nuclear warhead, if it could be made small and light enough for the missile to deliver it.

To be able to plan to do significant damage with ballistic missiles armed only with conventional warheads predicates building and successfully firing a large number of missiles so armed—probably some hundreds. Leaving aside the question of contamination and considering only physical damage, one ballistic missile armed with a nuclear, chemical or biological warhead could wreak destruction over a considerable area, inflicting immeasurably greater damage than that caused by conventionally-armed missiles. Thus the ability to acquire or develop a nuclear, chemical or biological weapon, and the ability to acquire or develop a ballistic missile system to deliver it, are correctly read as the left hand and right hand of a particular form of international political threat by terror. Indeed, the repeated appearance of the names on the list of countries developing ballistic missiles and the lists of those known to possess or suspected of developing Nuclear, Biological or Chemical Weapons confirms that it is the growing problem of the proliferation of these Weapons of Mass Destruction that makes the threat of ballistic missiles such a serious one.