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Intercontinental Ballistic Missiles

Intercontinental Ballistic Missiles (ICBMs) have ranges of greater than 5,500 km. ICBMs create a problem because they enable a country to break out of a regional context and move toward potential global impact. Regardless of the origin of a conflict, a country may involve the entire world simply by threatening to spread the war with an ICBM.

Strategic missiles consist of propellant-filled stages, a guidance system, and a payload. Once launched, the missile passes through three phases of flight: boost, ballistic, and reentry. If a missile has more than one stage (as all of ours do) there may be more than one boost phase interspersed with several ballistic (coasting) phases where the missile follows its trajectory. The missile can only be guided during boost phase with inertial or stellar or both. Inertial guidance uses onboard computer driven gyroscopes to determine the missile's position and compares this to the targeting information fed into the computer before launch. Stellar guidance uses an optical tracking system to triangulate star positions and update targeting information when it is out of the earth's atmosphere. Targeting cannot be changed after launch, nor can strategic missiles be recalled or destroyed in flight. These guidance systems produce accuracies measured in hundreds of feet at ranges of 7,000 miles. Payloads of strategic missiles consist of nuclear warheads which cannot arm themselves until the onboard computer confirms that all three phases of flight have been completed.

Current American ICBMs use solid propellants. The solid propellant used in the first three stages of both the Minuteman II and III, as well as the Peacekeeper, uses acrylic acid/aluminum powder for fuel, ammonium perchlorate as the oxidizer, and polybutadiene as the binder. Once ignited, solid propellant cannot be extinguished; it burns until exhaustion. The resulting burn is a metal fire which produces exhaust fumes consisting primarily of aluminum oxide dust and hydrogen chloride gas. In the event of an accident, small levels of hydrochloric acid could be inhaled by nearby personnel, but it is unlikely that much more than eye and upper airway irritation will be experienced.

Minuteman III and Peacekeeper both have a liquid fuel, restartable fourth stage, called the payload bus. The fuel is monomethyl hydrazine and the oxidizer is nitrogen tetroxide. They are stored in a sealed system that is never opened in the field. Both chemicals are highly toxic at low levels and any exposure requires immediate decontamination with copious amounts of water followed by hospitalization for a minimum observation period. Symptoms of eye and airway irritation must be treated promptly.

In the last 20 years, several countries have built, or sought to build, missiles with an intercontinental reach, usually under the auspices of a space launch capability. France led the way with the introduction of the S-2 launch vehicle in the late 1960’s. Derivatives and motor technology from their S-2 missile assisted France in developing its Ariane space launch vehicle, which competes directly with the American Delta class space vehicles. Israel demonstrated the technical capacity to put a satellite in orbit in 1991, indicating to the world that it could deliver WMD to any spot on the globe. Space launch programs came out of South Africa and India in the late 1980’s. The South Africans constructed an especially credible prototype for a three-stage launch vehicle that had immediate use as an ICBM. Finally, Iraq showed that a long-range missile did not necessarily have to be built from the ground up. With the help of foreign consultants, Iraq test fired the al Abid Space Launch Vehicle in December 1990. The al Abid consisted of five SCUD missiles strapped together to form a lower stage, which was designed to boost two upper stages, together with a payload, into orbit. The al Abid did not work as predicted, and, if it had, it would have put only a few kilograms of useful payload into orbit. As an ICBM, though, it established the possibility of building a long-range rocket from dated technology. The various technologies will be addressed as complete systems and as subsystems. Systems

Iraq built its al Abid capability with the direct assistance of foreign scientists and engineers and by attempting to purchase technology, such as carbon-carbon materials, for rocket nozzle throats and nosetips directly from foreign companies. The multiple uses for aerospace materials and the development of aerospace consortiums have multiplied the number of sources of research talent and manufacturing industries that a potential proliferant nation can tap for assistance in building an ICBM.

These foreign outlets have also exposed the proliferant world to the high expense associated with building an ICBM. In the late 1980’s, Iraq could afford to trade some of its oil wealth for the cost of buying the entire corporate talent of one research and development (R&D) firm. Most economies that can sustain such a high level of funding are either already building space launch vehicles (France and China), are in a multilateral arrangement to build one (Germany, Great Britain, Italy), or have recently abandoned building one because of market forces (South Africa). ICBM attacks must also be effective because a launching nation will get few opportunities to continue the attack. The simple cost of an ICBM limits the total size of a missile inventory. This decreases the potential for sustained firing of ICBMs, a tactic used to disrupt a society by the threat of repeated chemical weapons attacks by long-range missiles.

If a country seeks to launch an ICBM, it must either launch the missile from a vulnerable fixed launch site, harden the launch site for better survivability against attack, or invest the additional expense in building a mobile transporter-erector launcher (TEL). Use of vulnerable, fixed launch site ICBMs provides opportunity for opposing forces to eliminate most of these sites quickly. Hardened launch sites are difficult to reload quickly and thus damper a sustained firing tactic. Without the use of fixed launch sites, a nation must rely on mobile launchers. Making enough mobile launchers to support a long missile campaign is an expensive endeavor. It also lessens the possibility of a sustained firing. A small ICBM that delivers 500 kg of payload to a distance of 9,000 km will weigh between 15,000 and 22,000 kg, depending on the efficiency of the design and the sophistication of the technology involved. The FSU and the United States have built TELs to handle missiles of this mass.

Chemical or biological agents are not spread efficiently by the flight path that an ICBM follows. The high velocity along the flight azimuth makes it almost impossible to distribute airborne agents in an even and effective cloud. Submunitions make the problem somewhat more tractable, but the submunitions still require a very capable propulsion system if they are to cancel the azimuthal velocity and impart a cross range velocity to circularize the distribution of an agent cloud. Other problems abound: U.S. experience with fuzes for ballistic missiles showed that much less than 10 percent of chemical and biological agents survived the launch and delivery sequence. Iraq used fuzing for its chemical warheads on its TBMs that would have allowed less than 1 percent of the agent to survive.

The most sensible warhead for an ICBM to carry is a nuclear weapon, and the weaponization section concerns itself primarily with the weaponization of ICBMs to carry nuclear warheads.

Subsystems

Some of the same technologies for extending a TBM’s range provide extra capability to build an ICBM. An ICBM may include strap-ons, a clustered combination of single-stage missiles, “parallel” staging, and serial staging. Iraq increased the range of its missile fleet by reducing the weight of the warhead in one case (the al Hussein missile) and extending the propellant and oxidizer tanks and increasing the burn time in another (the “al Abbas” missile). The particular path that Iraq followed in making the “al Abbas” out of SCUD parts is not technically practical for building an ICBM. An airframe must have a thrust-to-weight ratio of greater than one to lift off, and a SCUD airframe cannot be extended sufficiently to reach intercontinental ranges and still lift off with the current turbopump, given its low stage fraction (the ratio of burn-out weight to takeoff weight—a strong measure of missile performance). Building a new turbopump that provides the needed take-off thrust and also fits within the air-frame is a more difficult task than simply building a new and much more capable missile from scratch.

Both strap-ons and parallel staging provide ways for a proliferant to reach an ICBM capability. Many countries have built small, solid rocket motors that can be tailored to fit within the MTCR guidelines. A number of these motors strapped on to a reasonably capable main stage, such as the S-2, would resemble the Ariane launch vehicle. The country that pursues this path requires a firing sequencer that can ignite all the motors simultaneously. Strap-ons generally operate for a short fraction (roughly one-third) of the total missile burn time of an ICBM. If they are dropped off, the guidance and control requirement can be met by using the main engine thrust vector control to steer the whole assemblage. Aerodynamically, the strap-ons behave much as fins in the lower atmosphere, increasing the amount of total cycle time available for the guidance computer to operate.

Parallel staging offers many of the same advantages for liquid rockets that strap-ons do for solid rockets. The United States built the Atlas missile as a parallel staged rocket because, in the 1950’s, it was the quickest path to developing an ICBM to meet the Soviet challenge. A liquid-fueled, parallel-staged rocket draws propellant and oxidizer from existing tanks but feeds it to several engines at once to sustain the proper thrust level. When these engines are no longer needed, they are dropped. The tanks, however, remain with the missile so a parallel-staged missile is not as efficient as a serially staged missile.

As many designers already know, and most textbooks prove mathematically, a serially staged missile is the best design to deliver a payload to long distances. Examples of an optimal, serially staged ICBM include the U.S. Peacekeeper missile and the Soviet Union’s SS-24. Each of these missiles can reach 11,000-km range and carry up to 10 nuclear warheads. In an optimum serially staged configuration, each stage contributes about twice as much velocity as the stage that preceded it, though many effective ICBMs can be built without following any particular design guideline. To be capable of an 11,000-km range, the ideal ICBM would be composed of four stages. The United States and the Soviet Union both ignored this consideration, though, because of concerns about the overall reliability of the missile. The ignition of each stage in sequence at the staging interval is difficult to time properly, and, inevitably, some period occurs during this staging event when the control authority over the missile is at its worst. To reduce these events and improve the overall reliably of the missiles, the superpowers chose to trade performance for fewer stages.

A proliferant that does not buy a fully equipped ICBM must solve this same staging sequence problem. The technologies to build event sequencers and the short duration, reproducibly timed squibs, exploding bridge-wires, or other stage separation shaped charges to support these sequencers are among the most sensitive material to be con-trolled in trying to prevent the proliferation of ICBMs.

If a proliferant clusters existing single-stage missiles together, it must consider the guidance and control implications of the design. Several ordinary single-stage missiles grouped together make a very stout planform with a high lateral moment of inertia. To control this missile, the thrust vector control system has to produce much greater torque on the airframe than it would for an equivalent mass that is long and thin, as are most missiles. The high moment of inertia, in turn, requires either higher actuation strokes in a thrust vector control system, which reduces the thrust available for range, or a much larger liquid injection system, which reduces the weight available for propellant and again reduces the range. On the other hand, simple thrust vector control strategies, such as vernier nozzles and fluid injection, can satisfactorily control the missile. A proliferant only needs to build the fluidics to support these schemes: fast acting valves and the actuators to control these valves. The same types of valve and piping concerns that are covered in the tables for TBMs apply to the fluid system of an ICBM.

A serially staged missile forces a designer to carefully consider the control of a more dynamically complex vehicle. The stages and interstage breaks make the structure of a serially staged missile behave under some loading conditions as a series of smaller integral segments attached at points with flexible joints. This construction has natural frequencies that are different than a single, integral body, such as a one-stage missile. If flight conditions excite any of these many and complex resonant modes in the missile stack, the guidance and control system must supply the correct damping motion, in frequency or duration, to prevent the missile from losing control. Some of the corrections affect the guidance of the missile, and the flight computer must determine the proper steering to return the missile to its predicted trajectory. A proliferator may use many existing finite element routines and modal analysis hardware to find or predict these frequencies.

In addition to the hardware, a requirement exists to test and validate the computer routines in wind tunnels and structural laboratories. Since these computer routines reduce the number of engineers needed to modify missiles, they are particularly key to reducing the cost of individual missiles. For this reason, automated engineering computer routines are ranked at the same level of threat in the technology tables as hardware items.

The guidance and navigation systems of an ICBM closely mirror those that are used in a TBM, and anyone who has passed through the phase of building a TBM can possibly scale up a version of the guidance system suitable from the earlier missiles. The mathematical logic for determining range is different for ICBMs than for TBMs if a digital guidance computer is used rather than a pendulous integrating gyro accelerometer, which is the standard for most TBMs. However, many text books derive the equations of motion for digital guidance computers. Errors created by the guidance system feedback instrumentation during the boost-phase can be corrected later in the flight with post-boost vehicles (to be discussed in the weaponization section). Navigation technologies, beyond the issues already discussed for TBMs, can be applied in this same post-boost vehicle.

The propulsion system of ICBMs can be either liquid or solid fueled (or in some cases a hybrid of the two). A proliferator that understands the principles of solid fuel burning and how to shape the configuration of the internal grain to achieve the desired thrust/time trace can build any of its stages for an ICBM indigenously. Larger motors, of course, are more difficult to manufacture. The outer case of a solid missile can be made from any conventional material, such as steel, but better propellants with higher burning temperatures often require the substitution of materials with higher strength-to- weight ratios, such as Kevlar and carbon or glass epoxy. Steel cases can be used with cross-linked, double-based solid fuels, but the need for additional liners and insulation to protect the case against the higher burning temperatures of these newer propellants compromises some of the range that can be achieved by using the better propellant in the first place. Most steel cases must be produced from a material having a thickness that closely or exactly matches the final thickness of the motor case to pre-vent excessive milling of the material.

Filament winding technology may lay the filaments in solid motor cases in longitudinal and circumferential plies, in bias plies, and in the most structurally efficient way of all—in helically wound orientations. Any European, former Soviet, or U.S. multi-axis filament-winding machine of sufficient size can be used to wind a solid rocket motor case. The ply’s winding orientation determines the structural, or stage, efficiency of the solid rocket motor.

In a liquid-fueled missile, the supply pressure to feed fuel and oxidizer to the thrust chamber may come either from creating an ullage pressure or pumping the liquids to the thrust chamber with turbopumps. Large volume flow rate pumps, particularly those designed for caustic fuels, have unique applications to ICBM construction. A proliferant may avoid the need for pumps by building tanks within the ICBM to contain an ullage pressure, which forces the liquids into the thrust chambers when the tanks are exposed to this high pressure. In most cases, ullage pressure is structurally less efficient than modern turbopumps because the missile frame must cover the ullage tanks, which are maintained at very high pressure and thus are quite heavy. However, this decrement in range performance is small. Since the technology is simpler to obtain, it may serve the needs of a proliferant. In either case, a liquid missile generally requires valves and gauges that are lightweight, operate with sub-millisecond time cycles, and have a reliable and reproducible operation time. These valves must also accept electrical signals from standard computer interfaces and require little, if any, ancillary electrical equipment.

The choice of liquid propellant may also influence other technology choices. Some liquid propellants are storable, and others must be cryogenically cooled to temperatures approaching absolute zero. The cryogenic coolers make the missile less mobile and more difficult to prepare to fire. The superpowers long ago abandoned nonstorable liquid-propellant missiles for these reasons, but a country that can support the technology to manufacture and store liquid oxygen and hydrogen may find this to be one possible path to making an ICBM.

The ICBM trajectory creates the most stressing problem for weapons integration, mainly because of the enormous heat load that velocity imparts to the reentry vehicle (RV). A TBM reenters the atmosphere at about 2 km/sec, and an ICBM reenters at about 6 km/sec. This increase in velocity creates more than an order of magnitude increase in associated heating.

Traditionally, ICBMs have overcome the heat load with two reentry strategies: one using a very high ballistic coefficient and one using a very low ballistic coefficient. The choice has important and mutually exclusive implications for other aspects of the design. If a low ballistic coefficient is selected for RVs, it may only require that the heat shield be built from very simple and easy to obtain material, such as cork and phenolic. These materials provide sufficient thermal protection because the velocity of the RV is dissipated high in the atmosphere and the surplus thermal energy is transferred to the shock wave that the RV creates and the turbulence of the flow in its wake. Since the RV has slowed almost to terminal velocity, the unpredictable conditions of the winds aloft reduce accuracy. A low ballistic coefficient RV may have a circular error probability (CEP) as great as 20 km from the reentry phase of its flight alone. It has, however, slowed to the point where the dissemination of chemical and biological agents is more feasible.

On the other hand, if a high ballistic coefficient is selected, the nosetip of the RV must endure temperatures in excess of 2,000 °C. Temperatures in this range call for the best thermal insulating materials possible, such as 3-d or 4-d carbon/carbon. In addition to protecting the RV from extreme heating, the nosetip must also experience very little erosion of its contour as it travels through the atmosphere. Materials that provide both of these properties are rare and generally limited to manufacture in technologically advanced countries.

Either of these reentry strategies benefits from the aid of a post-boost vehicle (PBV). The use of a PBV makes a high ballistic coefficient RV especially accurate. The PBV operates in space after the missile has burned completely. It steers out the guidance errors that have accumulated during the boost phase of the firing and puts the RV on a more accurate ballistic path. It can also be used just before the RV reenters the atmosphere to correct any errors in the flight path that have occurred because of as-sumptions about the Earth’s gravitational field between the launch point and the target. In a sophisticated PBV, the vehicle may realign the RV so it reenters the atmosphere with little aerodynamic oscillation. It may also spin the RV to even out contour changes in the nosetip and, thereby, reduce unpredictable flow fields around the body. The spinning gives the RV a gyroscopic inertia that damps out small perturbations in the attitude of the RV.

With a PBV, a proliferator can achieve a targeting accuracy of 500 m over an intercontinental range. In general, the PBV costs about half of the total throw weight of a missile. For these reasons, its use is traded off with chemical and biological agents payload.

Systems

Seven nations—the United States, Russia, China, France, Japan, India, and Israel—have launched space vehicles, demonstrating generalized capability to build an ICBM. Israel has demonstrated the clearest link between a space launch program and a missile delivery system with the Shavit, the first Israeli satellite, and a substan-tial copy and scaled-up version of the Jericho II missile. Although Ukraine has not “launched” any space vehicles, it has produced large space launch systems as well as the world’s only heavy ICBM, the SS-18. Brazil is developing a sounding rocket that has applications to an ICBM program, and Pakistan has made first-generation rockets that indicate an underlying objective of developing an ICBM. No country has yet sold ICBMs abroad.

Under United States pressure, Taiwan all but abandoned its space launch program in 1993. However, a residual infrastructure of knowledge and manufacturing capabil-ity remains in Taiwan. South Korea and Indonesia, once ICBM aspirants, have also dropped their development programs in recent years because of U.S. pressure and economic forces.

No one purchaser names a possible price for the purchase of an ICBM, since none have been sold as unregulated commodities in the way that SCUDs have. However, other sales provide some indication of the rough costs. The Brazilians reportedly ex-pected to receive in excess of $10 million each for their Condor II, whose range of 1,000 km is much less than intercontinental, and the Chinese apparently received about $20 million for each of the 2,500-km range CSS-2s they sold to Saudi Arabia. Many studies within the United States indicate that the Peacekeeper, a highly capable and advanced missile, costs the military about $65 million per copy.

At $50 million per missile, a country would need to invest about $2 billion to purchase or build 40 missiles. When this is compared to the roughly $200 million the Iraqis paid to build their Saad 16 missile manufacturing facility, it becomes clear that the economies of many countries cannot support a nuclear weapons production capa-bility and an ICBM launch capability.

A determined proliferant can make an ICBM by substituting many technologies for the ones that have been listed so far as being militarily sufficient. The proliferants that have not been named as already capable of building an ICBM—Iran, Iraq, Syria, and Libya—need to seek out certain technologies on overseas markets. The nature of an acquisition program need not reveal its intention, if substitutions for certain materials are done properly.

Hardware

Iran, Iraq, Syria, and Libya can manufacture or import steel of an equivalent grade to the material found in the early Minuteman II ICBM. If these countries seek to build a composite motor case instead, they must purchase the filament-winding machine from the United States, the FSU, France, Germany, the UK, or South Africa. The Chinese may be able to supply a reverse engineered filament winding machine based on Soviet technology.

Other than the traditional solid-propellant manufacturing centers in France, Swe-en, Norway, Germany, and the United States, many other European countries with arms manufacturing centers, such as the Czech Republic, have some solid-propellant capability. In addition, Pakistan can manufacture small, solid-propellant motors that can be used as strap-on boosters. South Africa also has an indigenous solid-propellant production capability, which, if it so desired, can export small solid-propellant motors. Proliferators that may wish to follow the liquid-fueled path to ICBMs without using strap-ons are likely to purchase turbopumps primarily from Germany, Sweden, the United States, France, or Russia.

The guidance and control package that a country needs to support an ICBM depends upon the desired accuracy it expects to achieve with its missile. Without a PBV, this accuracy is going to be poor, and more rudimentary technology can be used. Any industrial/advanced nation manufactures equipment and parts that, when properly constructed, can be used to build an inertial measuring unit. In addition to the United States, a proliferant can turn to Belgium, Germany, France, Holland, Sweden, Norway, Finland, Austria, the Czech Republic, Hungary, Russia, Italy, China, North Korea, South Korea, Taiwan, Australia, New Zealand, Egypt, or India. In general, though, a guidance and control unit, using a digital guidance computer and consistent with a staged missile, cannot be built from cannibalized parts of older, analog guidance systems. A PBV requires a small liquid rocket motor, cold gas thrusters, or many small total impulse solid rocket motors. These motors must be supported by a small guidance, control, and navigation unit that flies with the RVs until they are dropped. GPS units have wide application for this particular phase of the ICBM trajectory. Because of existing export controls, a proliferant would have to modify an over-the-counter GPS receiver to operate at high altitude and at ICBM velocities. The knowledge of how to build a GPS receiver is now widespread, however, and many individual hobbyists have built receivers that evade these restrictions. A modified GPS receiver or a GLONASS receiver is completely consistent with the needs of a PBV.

Technical Assistance

Besides supplying whole systems, many corporations and nations have offered technical assistance in the last 10 years to some emerging missile powers. German firms reportedly assisted the missile programs of Argentina, Brazil, Egypt, India, Iraq, and Libya. The Italians have offered assistance to Argentina, Egypt, and India. The French have participated in missile programs in Iraq and Pakistan. Israel has been accused by international arms regulators of participating in technology programs that lend a country the capability to build or modify a ballistic missile. The South Africans reportedly have received significant aid from the Israelis.

Most European countries can lend technical assistance to emerging missiles powers. The French have a long history of developing missiles, not only to support the Ariane space launch capability but to launch the force de frappe nuclear arsenal. The Italians have participated in the European Union space program that helped design the Hermes missile. While the British relied on American missile programs in the 1960’s to supply their TBM needs, a technical exchange program between Britain and the United States trained and educated a sizable pool of missile talent from the British Isles.



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