The Missile Programs of North Korea, Iraq, and Iran
Ronald Siegel, Institute for Defense & Disarmament Studies, September 2001.

Introduction

Recent proposals for a National Missile Defense have stressed the emergence of an ICBM threat to the United States from North Korea, Iraq, and Iran. In addition to these countries, China, India, and Pakistan have long-range ballistic missile development programs that bear on the issue. A National Missile Defense (NMD) against North Korea will almost necessarily, perhaps even intentionally, provide a defense against current Chinese strategic forces. North Korea supplies missiles to Iran and Pakistan and has been assisting in their development of longer-range missiles. India has an active ballistic missile development program, and it is engaged in arms competitions with Pakistan and, to a lesser extent, China. While North Korea, Iraq and Iran do not yet have nuclear weapons, they have programs under way to develop nuclear weapons. China, India, and Pakistan already have nuclear weapons.

US government officials have argued that a defense against long-range missiles fielded by countries like North Korea and Iraq is more urgently needed than was, say, a defense against the former Soviet Union. First, these countries have been characterized as having erratic, adventurous, risk-prone leaders who might not be as reliably deterred by the threat of retaliation as other national leaders. Second, these leaders may be capable of using weapons of mass destruction to prevent the collapse of their regimes, and, given their adventurousness, the United States might seek to bring about such a collapse. Finally, defense against them is easier than defense against the former Soviet Union would have been, since the latter possessed thousands more nuclear weapons.

The 1998 Report of the Commission to Assess the Ballistic Missile Threat to the United States (the Rumsfeld Report) and the concurrent National Intelligence Estimate suggest that Iran and North Korea could deploy ICBMs as early as 2005. These estimates have been used as justifications for, among other things, a crash program to develop a National Missile Defense (with reduced testing before a production decision) and early withdrawal from the ABM Treaty. The timetable rests on two assumptions: first, that an ICBM may be considered operational immediately after its first successful test, even though typical development programs involve 20 or more tests over a period of three to five years; and second, that an ICBM capable of delivering a nuclear warhead to the US mainland can be derived from missiles currently under development. Each of these assumptions is questionable.

The missile program of Iraq is currently stalled. That of Iran relies mainly on North Korean technology: Iran tests missiles imported from North Korea. As of 1999–when it suspended missile tests–North Korea had tested at a range of 1600 km a missile which is estimated to have a maximum range of up to 6000 km, that is, long enough to reach Alaska but not Hawaii. The entire threat assessment justifying the crash NMD program seems to be based on the possibility that within a couple of years after ending the moratorium, North Korea will not only successfully test this missile at a range of 6000 km, but develop a version that can reach the continental United States (a distance of 8000-12,000 km). A modest extension to reach Hawaii (7000 km) might be possible within a few years. (The planned Alaska-based NMD would not provide a defense against missiles on a trajectory from North Korea to Hawaii.) Extending the range of the missile to reach the continental United States would reduce the payload well below the minimum needed to carry a first-generation nuclear warhead. Therefore, any threat of a North Korean ICBM attack on the continental United States will require an entire development cycle–for missiles, or for warheads, or for both.

An unimpeded North Korean development program could result in the development of a North Korean ICBM no sooner than 2010. Given their current limited programs, Iran and Iraq are unlikely to be able to develop ICBMs before 2015. The potential dates for all three countries could be further delayed by various contingencies discussed below.

Geography

Table 1 shows flight distances (in kilometers) from various launch sites to various target cities. The launch sites do not represent actual (present or future) bases, but simply the part of a country’s territory that is geographically nearest to the target city. Actual launch sites might well be several hundred kilometers farther away.

North Korea would need an ICBM with a range of at least 8400 km to reach San Francisco. In fact, all targets in the continental United States are at least ICBM range from potential adversaries, while nearly all non-US targets are within IRBM (Intermediate-Range Ballistic Missile) range of all of the countries considered here. India, for example, could reach all of the non-US targets shown in Table 1 with IRBMs; but it would need a missile with a range of at least 11,000 km for continental US targets. Testing an ICBM can mean only one of two things: an intent to launch satellites or an intent to target the United States. Testing an ICBM with a re-entry system can mean only one thing.

Table 1. Flight Distances (km)

Rocket Science

A ballistic missile works by burning propellant and ejecting the hot gases through a nozzle, typically at a velocity of around 2500 meters per second (m/sec). The thrust from the exhaust causes the missile to accelerate. A given thrust will cause progressively higher accelerations as the missile lightens due to the consumption of its propellant. All of the propellant is consumed in the first few minutes of flight, following which the missile coasts above the atmosphere at a speed of several kilometers per second to its target. In an idealized case, the burnout velocity would be equal to the exhaust velocity times the natural logarithm of the ratio of gross missile weight to the payload. In real life, the missile will need additional impulse to reach a given velocity. Account must be taken of: the structural weight of the missile (typically discarded in several stages during boost phase); air resistance during boost; and gravity during boost. Still, the idealized relationship is useful: it provides an optimistic upper bound on what can be achieved when parameters are varied. At short ranges, the range of the missile will go as the square of its burnout velocity. Due to the curvature of the earth, at longer ranges the range will increase more rapidly. Table 2 shows the burnout velocity needed to reach various ranges, together with the payload fractions associated with missiles that attain any given velocity.

For example, a 6000-km range missile would need a 6200 m/sec burnout velocity and could achieve this while devoting 2-5% of its gross weight to payload; a 10,000-km range missile would need 7200 m/sec and could devote 1.3-3.5% of its weight to payload, about two-thirds as much. Thus, the table can be used to scale payload fractions as the missile range is varied. The scaling indicated in Table 2 is probably a bit optimistic from the missile designer’s perspective. The original missile design is optimized to produce the best possible distribution of propellant and structural weight among the stages. Adding a new upper stage (adapted from a different missile) or offloading payload will not necessarily yield an optimal mix. Thus, the payload penalty for increasing the range could be greater than the table indicates.

The concept of payload merits discussion because definitions can vary widely. Consider the weight remaining when the missile reaches burnout velocity. It includes the empty weight of the burned-out final stage. If this is deducted, what remains is the throw-weight or payload (shown in Table 2 as a fraction of gross weight). This includes the MIRV bus (if any), the decoys (if any), the guidance system, and one or more re-entry vehicles (RVs). Typically, a single RV will account for two-thirds or more of the payload; but because of the need for a bus, multiple RVs will add up to only about half the payload. The RV consists of a nuclear warhead, a fuze, and a heat shield. The heat shield may account for about one-third of this weight. Thus, less than half the payload will commonly be available for the weight of a nuclear warhead.

Table 2. Burnout Velocity and Payload Fraction vs. Missile Range

The first US nuclear warheads weighed 4100-4500 kg. The likely weight of a first warhead produced by a proliferating country has been variously estimated at 450-1000 kg. The lower estimate was for the first effort of an advanced, industrialized country and the higher estimate for a third world country. The United States and the Soviet Union each needed six to eight years to reduce their warhead weights to 1000 kg. Existing North Korean ballistic missiles could carry a 500 kg nuclear warhead. ICBM-range derivatives of these missiles could carry only 200-300 kg. Thus, even assuming that North Korea’s first generation nuclear warhead is at the low end of the estimated range (450 kg), an ICBM derivative of the existing missiles could not lift the warhead.

A guidance system is needed to hit a predictable target. This functions only during the boost phase, correcting the flight path to adjust for various deviations. After burnout, the missile is unguided and any further deviations from course, such as those caused by winds during the re-entry phase, are not corrected by the guidance system. The ballistic missiles now in use by North Korea, Iraq, and Iran achieve CEPs (Circular Error, Probable, the radius of a circle within which one-half of the warheads can be expected to fall) of several kilometers. This corresponds to velocity errors on the order of 0.1%, which in turn could lead to CEPs as great as 40 kilometers at ICBM range. With such accuracy, a missile aimed at Los Angeles would run a significant risk of missing the entire metropolitan area. This would seem to preclude any very near-term threat. However, on the extended timetables suggested above (2010 for North Korea, 2015 for Iran and Iraq), guidance should not be a problem. There will be time to develop a new system. If adapted to an ICBM, strapdown systems coming into use in civil aviation could yield CEPs of a few kilometers at full range. Global Positioning System updates (even on the clear channel) could reduce guidance system errors to a level that is small compared to the re-entry error discussed below. Thus, while North Korea, Iraq, and Iran are not remotely prepared for ICBM guidance now, they should not be expected to have difficulty hitting large cities at ICBM range after 2010.

A final problem is re-entry. As the RV re-enters the atmosphere at a velocity of more than 7000 m/sec, it encounters tremendous drag and slows down, eventually striking the ground at somewhere between 200-3000 m/sec. While slowing down, the RV generates tremendous heat that must be removed or else the RV will burn up. The ICBMs that could be developed by North Korea, Iraq, or Iran would use a blunt, high-drag heat sink–essentially a dome of copper armor. As the RV decelerates, the heat sink warms up and transfers most of the heat to the air rushing past. Most

Table 3. Missile Development Programs