Kinetic Energy Weapons
The traditional interceptor was taken to new dimensions in the 1970s and 1980s. The first anti-ballistic missile interceptors were tipped with nuclear warheads. The nuclear warhead was needed because early technology could not guarantee that the kill vehicle would get close enough to the target to achieve an intercept with a conventional explosive warhead. When detonated these missiles would contaminate the atmosphere and generate an electromagnetic pulse which would disrupt electronic systems. A new awareness and appreciation of these hazards spurred concerns among the general public and prompted research by the scientific community.
One solution to nuclear warheads was kinetic energy technology. The idea was not new. Muzzle loading artillery projectiles up through the early 19th century relied solely on kinetic energy to destroy targets. Non-explosive iron cannon balls traveling at relatively slow speed (500 - 1,200 feet per second) were amazingly destructive when they bashed into enemy forts, ships or cannon. Even after the advent of exploding shells, solid iron kinetic energy projectiles remained the favored ammunition until late in the 19th century for Army strategic defenders in the seacoast artillery.
Kinetic Energy (KE) Weapons Systems are an integral part of candidate strategic defense systems. System candidates in the 1980s included ground-based exoatmospheric re-entry vehicle interceptors (ERIS) and spacebased Interceptors (SBI), high endoatmospheric defense interceptors (HEDI) and hypervelocity guns (HVG) [electromagnetic (EM), electrothermal (ET), and hybrid systems].
KEW systems include EML systems (e.g., railguns and coilguns), ETC guns, and ET guns. Compact pulsed power sources are a common requirement for the weaponization of EML, ETC, and ET guns. Additional improvements to EML systems are the development of wear-resistant materials and supporting structures, enhancements to ETC guns and nonsensitive propellants, and more efficient plasma ignition propellants. Enhancements to ET guns will require more efficient plasma generators.
There are three major kinetic energy technologies employed by interceptors, hit-to-kill, directed blast fragmentation, and kinetic energy rod warheads. Instead of an explosive warhead, hit-to-kill relies on a very high closing speed to collide with and destroy its target using only kinetic energy - the force of the collision to pulverize the target warhead. It has been described as hitting a bullet with a bullet - a capability that has been successfully demonstrated in test after test. The interceptor uses kinetic energy, that is, the force of the collision, to destroy the threat warhead.
Countermeasures, however, can be used to avoid the "hit-to-kill" vehicle. Moreover, biological warfare bomblets and chemical warfare submunition payloads are carried by some threats and one or more of these bomblets or chemical submunition payloads can survive and cause heavy casualties even if the "hit-to-kill" vehicle accurately strikes the target. Missile defense systems being developed and tested by MDA are primarily based on hit-to-kill technology. Most of the BMDS elements, e.g., GMD, Aegis BMD, THAAD, and PAC-3, use this interceptor technology.
Systems, such as the Patriot missile system used in the Gulf War, use blast-fragmentation. Directed blast fragmentation technology involves the interceptor approaching the threat ballistic missile and exploding close to it, thereby disrupting the path of the threat missile and possibly destroying it. The interceptor does not actually collide with the threat ballistic missile. A directed blast fragmentation kill vehicle explodes near the threat missile and distributes its fragments over a large area to create a kill zone around the path of the threat missile. As the quickly moving threat missile enters the kill zone it collides with the fragments, which alter its path and potentially destroy the threat missile altogether. The explosion also causes a destructive shock wave that mechanically and electrically destroys the airborne threat, and/or renders its electronic systems useless. These blast fragmentation systems are popular for lower-tier defensive applications. Arrow and PATRIOT systems currently include this technology.
Both blast fragmentation and hit-to-kill systems for use in upper and lower tier defensive applications use an (interceptor) missile to destroy an incoming (threat) missile. This requires a highly sophisticated and accurate control and guidance system. Such a control system must be capable of tracking the three-dimensional speed and direction of both the incoming threat and outbound interceptor simultaneously. This allows computers to coordinate the proper flight path and speed, in real time, to ensure that the interceptor intersects the threat with full contact to destroy the threat. Any minute deviation in the course of the interceptor can cause the interceptor to fly right past its intended target. To track threats with such precision, lower-tier systems employ multiple ground radars combined with other tracking resources such as planes, ships, mobile land units and fixed land units. These low tier shorter-range missile defense systems, like the Patriot, have experienced success in both testing and real applications such as the Gulf War.
With both hit-to-kill or blast fragmentation systems, the electronic information that allows for the intersection of the threat and interceptor must be nearly flawless. No deviation or error is acceptable, as it would cause the outbound interceptor to miss the inbound threat. The article by Postol describes numerous flaws of the National Missile Defense effort. Specifically, Postol discusses the Raytheon-built exoatmospheric kill vehicle, the current state-of-the-art hit-to-kill system, designed to locate, track and collide with a nuclear weapon deployed from an ICBM in the upper tiers of the atmosphere.
Hitting a target with a projectile is an effective, established technique of destroying the target through the transfer of KE to the internal modes or structure of the target. Usually, one considers a fast projectile hitting a slower target. For ballistic missile defense (BMD), the opposite is generally the case. Missiles and RVs travel at velocities that enable them to be killed effectively by placing something heavy in their path. The methods described in this section use KE to effect a kill and depend on the collision's KE to be higher than the cohesive energy of the solid target. The problem lies in arranging the collision at a sufficient energy to break the bonds holding the structure together.
For an effective kill, the target has to be tracked, and KEW intercept has to be arranged. For attacking a booster, the rocket plume's brightness serves as the target for IR homing devices. For post-boost vehicles, the plume is not normally available, so other sensors need to be used to detect the target. In the terminal phase, ground-based phased-array radars could track RVs and decoys and provide target information for KEWs.
The ability to destroy a target requires a theoretical understanding of the way various projectiles interact with the structure and the experimental confirmation of the theories. The development of theoretical models and related computer programs that analyze the penetration of generic projectiles (e.g., long rods, spheres, and so forth) is basic science. Experimental results of hypervelocity that impact on generic structures are also considered basic science.
Velocity alone is not a unique measure of the effectiveness of a KEW, and neither is the mass of the projectile, the momentum, or the KE. This is especially true when complex structures are involved (e.g., RVs with a large number of canisters and KE weapons with complex structures, guidance systems, and warheads). For these complex systems, an ongoing argument persists about the actual functional dependence of the "lethality scaling law"(if it exists).
KE propulsion systems include the categories of power supplies, power conditioning and storage, and launcher and barrel. Advanced energy and power conditioning technologies are essential to operating KEWs that have a capability exceeding conventional munitions. Improvements in batteries, capacitors, inductors, pulse compression networks, homopolar generators (HPGs), and compulsators can support this goal.
The anti-missile version of the kinetic energy concept was based on the energy created from the momentum of a relatively small object striking an incoming ICBM at extremely high speed (20,000+ feet per second). The trick of kinetic energy technology, or "hit-to-kill" technology, was not the impact itself, but how to guide the high speed object to the target and make the interception.
Interceptors use kinetic energy either in a direct impact or hit-to-kill mode, or to deflect or possibly destroy a threat missile by directed blast fragmentation. Interceptors are composed of two primary parts, a booster and a kill vehicle. An interceptor may have one or more boosters (also called stages). The number of boosters or stages refers to the number of rocket motors that sequentially activate. Multiple stages allow the interceptor to fly at higher velocities and altitudes, and for longer distances. The kill vehicle is the portion of the interceptor that performs the intercept and destroys the threat missile. It is anticipated that solid and liquid propellants would be used in the boosters and in the kill vehicles.
Interceptors may also use lethality enhancers, seekers, and attitude control systems. Lethality enhancers are non-nuclear explosive devices that increase the probability of destroying the threat missile and its payload (e.g., explosives, chemical or biological agents). Seekers help to detect the threat missile and home in on it. Attitude controls are small motors used to modify the flight path of the kill vehicle and position it into the flight path of the threat missile.
Approaches are sought which extend, facilitates, or reduce the cost of the concepts. Elements of the systems include the space-based carrier vehicles (CV) or ground-based launchers, divert motors/nozzles, smart projectile components, and endo/exoatmospheric guidance and control mechanisms. Technology challenges for KE systems include: SBI acquisition of booster hardbody within the plume, high performance axial and divert propulsion subsystems (especially very low mass divert systems), miniature inertial navigation units, array image processing, C.G. Control algorithms, fast frame and U.V. seekers, acquisition and track; ERIS target discrimination, seeker operational environments, lethality/miss distance; HEDI aero-optical effects, guidance and fuzing accuracy, shroud separation, window thermo-structural integrity, non nuclear kill warhead performance and survivability of electronics in nuclear environment; HVG lifetime, fire rate, projectile guidance and control, and projectile launch survivability; and, common among all systems, reliability, producibility, maintainability, and low cost/low mass.
KE systems depend on the KE of their projectiles to destroy or degrade the target. Consequently, the projectiles are as critical to the system as the propulsion components are. Conceptually, KE projectiles cover the spectrum from small grains of ablative material propelled by lasers at a velocity of 100 km/sec, to large rocket-launched devices such as the Homing Overlay projectile, which closes with a ballistic missile warhead at the relatively low velocity of approximately 6 to 14 km/sec or higher. The commonality of such widely varying projectiles (i.e., destroying or degrading the target by KE) shows the range of projectile characteristics.
The technologies associated with KE projectiles are as diverse as the projectiles. If propelled in the Earth's atmosphere, projectiles with velocities over approximately 4 km/sec must be cooled by active systems. At velocities less than 4 km/sec, passive cooling, such as ablative coatings, can be used. Unless projected at targets in very close range (e.g., in a point defense application), projectiles require in-course guidance. This is a major difference between KE and DE systems. The latter projects beams at nearly the speed of light. These beams of light hit where they are aimed. Extremely small, high-velocity KE projectiles can be guided to the target by laser beams. Larger projectiles must incorporate sensors [infrared (IR), optical, radar] to guide them to the target; thrusters or other devices to alter their course; fuel for the thrusters; and possibly a computer to translate sensor inputs to thruster direction and power.
Projectiles incorporating complex cooling and guidance components will be heavy. The resulting weight will limit the velocity at which a given energy level can propel the projectiles. Consequently, technologies to miniaturize sensor and guidance systems and technologies to increase the energy levels of projectors must be pursued together.
Military interests have driven the physics of impact in large part-from a defensive and an offensive role. The contest between faster projectiles and stronger armor has been the principal motif in military history. In an attempt to build more effective weapons, understanding the interaction between projectiles and targets has been the goal of designers, builders, and testers. Today, this understanding is usually achieved through a combination of experimental work and computer simulations. However, we have reached a point where experimental techniques are inadequate to examine the areas of interest to weapon designers and policy planners.
The recent interest in hypervelocity projectiles with velocities of 5 to 10 km/sec has forced researchers and decision-makers to rely more heavily on computer simulations because the cost and inherent difficulties of conducting the experiments to get the desired data are prohibitive. Also, for some cases, equipment is not even available to generate the appropriate conditions of high KE.
Successful flight tests in the exoatmosphere would result in kinetic energy (i.e., hit-to-kill) intercepts that would produce both target and interceptor debris clouds. Analysis of BMDS flight tests employing ground-launched interceptors shows that the majority (90 to 95 percent) of post-intercept debris reenters the Earth's atmosphere within six hours. A small amount of post-intercept debris may become orbital debris; however, modeling indicates that risk to spacecraft from intercept debris is far lower than the risk posed by existing background debris.
The effects of orbital debris on other spacecraft would depend on the altitude, orbit, velocity, angle of impact, and mass of the debris. Debris less than 0.01 centimeter (0.004 inch) in diameter can cause surface pitting and erosion. Debris between 0.01 to 1 centimeter (0.004 and 0.4 inch) in diameter would produce significant impact damage that can be serious, depending on system vulnerability and defensive design provisions. Objects larger than one centimeter (0.4 inch) in diameter can produce catastrophic damage. Astronauts or cosmonauts engaging in extra-vehicular activities could be vulnerable to the impact of small debris. On average, debris one millimeter (0. 04 inch) is capable of perforating current U.S. space suits.
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