Wednesday, October 31, 2012

Guided Missiles

Air-Launched Missile
Air-Launched Missile
Air-launched missiles are aimed at other airborne targets or at ground objects. This F-15 fighter jet launches a combat missile while in flight.

Guided Missiles, self-propelled projectile weapons or instruments, guided in flight toward a target either by remote control or by internal mechanisms. Guided missiles vary widely in size and type, ranging from large strategic ballistic missiles with nuclear warheads to small, portable rockets carried by foot soldiers. Although most are military weapons with explosive warheads, others may carry scientific instruments for gathering information within or above the earth's atmosphere.
Guided missiles consist of three separate systems: power source, guidance and control mechanism, and warhead or payload. Power sources normally are either self-contained rocket motors or air-breathing jet engines (engines that need the surrounding air to burn their fuel), but may also be airfoils or outside booster charges from ramp or tube launchers. The type of guidance and control system employed depends on the type of missile and the nature of the target. Inertial guidance systems sense the position of the flight path in relation to a fixed target; other guidance systems use a variety of more active sensors to help direct the missile toward a moving objective. Payloads are generally warheads designed for specific missions, from piercing armor plate to destroying entire urban areas.
Before World War II (1939-1945), guided missiles were limited to experimental, pilotless aircraft controlled by radio. During the war, however, rapid technological advances in such fields as aerodynamics, electronics, jet and rocket propulsion, radar, servomechanisms, inertial guidance and control systems, and aircraft structures, coupled with the intensive search for better weapons, led to the construction, testing, and finally mass production of the modern guided missile.
Guided missiles today are grouped into four launch-to-target categories: surface-to-surface, surface-to air, air-to-surface, and air-to-air. “Surface” in each case signifies on as well as below the surface of the land or sea. Missiles may also be grouped by their area of operation: Tactical missiles are used by military forces in direct combat on and above the battlefield; support missiles are employed behind the main battle area; and strategic missiles are designed for intercontinental warfare. Missiles may also be separated by their flight characteristics. Aerodynamic missiles are supported in flight by air pressure around their wing and body surfaces similar to conventional piloted aircraft; ballistic missiles depend solely on their internal power source, usually a rocket engine, to remain airborne. Aerodynamic missiles normally travel on a straight-line or flat trajectory toward their target, and ballistic missiles are usually surface-to-surface weapons that follow curved or arched trajectories similar to that of an artillery projectile.
The first successful guided missiles were the German V-1 and V-2 Vengeance weapons launched against Antwerp and London during World War II. The V-1, or buzz bomb, was an aerodynamic missile powered by a pulse jet engine with a preset guidance system that could sense the correct deviations in altitude and direction. Its average range was about 240 km (about 150 mi), after which the missile automatically sent itself into a steep dive and detonated its 1-metric-ton high-explosive warhead upon impact. The V-2, on the other hand, was a true ballistic missile fueled by a mixture of alcohol and liquid oxygen that produced a 25,000-kg (55,000-lb) thrust for about one minute after takeoff. With a maximum range of about 320 km (about 200 mi), the V-2 carried its 730-kg (1600-lb) warhead through an arching trajectory, reaching a maximum altitude of 95 to 110 km (about 60 to 70 mi) and a speed of more than 1.6 km (more than 1 mi) per second. Both missiles were relatively inaccurate and were used only against large cities. The V-1 could be destroyed easily in flight by conventional fighters, but no defense existed against the V-2. Allied attempts to destroy their mobile launching sites proved ineffective. Germany managed to launch about 4000 V-2s before the end of the war. Wire-guided antiaircraft and antitank missiles and air-to-air guided missiles were tested by German scientists but were never produced.
Appreciating the great potential of the German efforts in guided and ballistic missiles, Allied intelligence teams scoured Germany in 1945 for technical data, design drawings, and missiles, and they interrogated key German scientists and engineers. During the war the Allied powers had made little progress in these fields; they were quick, however, to integrate German research and technicians into their own development programs, and most postwar research was based on the work done in wartime Germany. The German V-2, in fact, served as the prototype for all large space and missile rockets built in the United States and the former Soviet Union.
Strategic Missiles
After World War II, the U.S. defensive policy of strategic deterrence depended on a large fleet of long-range bombers that could deliver accurate nuclear strategic attacks. Defense planners also experimented with air-breathing subsonic missiles similar to the V-1. Three developments in the mid-1950s, however, led to the intercontinental ballistic missile (ICBM): (1) development of the thermonuclear bomb with a much greater destructive power than the original atomic bomb; (2) the rapid refinement of inertial guidance systems for ballistic missiles; and (3) the development of powerful booster engines for multistage rockets, greatly increasing their size and range. As a result, ballistic missiles became sufficiently accurate and powerful to destroy targets 8000 km (5000 mi) away. Atlas, the U.S.'s first successful ICBM, was tested in 1959 and was followed one year later by the Titan. Both were multistage liquid-fueled rockets using extremely low temperature propellants that had to be added just before launching. The U.S. Minuteman II ICBM that went into service in 1962 used solid fuels stored within the missile, could be launched on short notice, and was sheltered in underground concrete silos. It could carry three individual warheads. The U.S. Peacekeeper ICBM (formerly MX), the most modern ICBM used by the United States during the 1990s, can carry ten warheads.
Strategic delivery systems went through the same evolution in the U.S. Navy as slow air-breathing missiles, liquid-fueled rockets, and carrier-based piloted bombers were abandoned for the two-stage, solid-propellant Polaris SLBM, or submarine launched ballistic missile, in the early 1960s. Carried in two parallel rows aboard nuclear-powered ballistic missile submarines, these missiles are launched from underwater. The U.S. Navy replaced Polaris with the longer range Poseidon SLBM in the 1970s. In the 1990s the U.S. Navy updated its submarine missile fleet with the Trident II (D5) missile, which is comparable to the land-based Peacekeeper. The Trident II can also carry multiple warheads, each of which can be aimed at a different target.
Tactical Missiles
Tactical surface-to-surface guided missiles range from hand-portable antitank rockets to large ballistic missiles able to attack airfields, supply lines, and communications stations hundreds of kilometers behind the battlefield. Small missiles often employ line-of-sight guidance systems that relay corrections in the flight path of the missile. Some missiles unravel trailing wires as they fly towards a target, and an operator can “fly” the missile by controlling the wires. Other missiles have guidance systems that follow either infrared heat signals or laser beams aimed at the target by soldiers on the ground or in an airplane. On a larger scale are battlefield support missiles such as the U.S. Army TACMS (Tactical Missile System), which use the Global Positioning System to aid in guidance. Since 1970 midrange cruise missiles such as the U.S. Harpoon have replaced artillery as the major armament aboard warships.
Long-range air-breathing cruise missiles, originally designed for strategic nuclear use, have been adapted in the 1990s for smaller-scale missions with nonnuclear warheads. The Navy’s Tomahawk and the Air Force’s AGM-86 can be launched from ships, airplanes, or submarines to nearby targets such as ships or to tactical targets several thousand kilometers away deep within an enemy country. The antiship version of the Tomahawk travels a few meters above sea level toward the general area of a target. It then climbs, locates the target through its own sensing devices, and dodges before making a final, high-speed diving attack. The land version of this missile also travels at a low altitude to avoid radar detection, guided by an internal terrain contour navigation system.
Air-to-air and air-to-surface guided missiles are generally short-range, light, rocket-powered projectiles with sophisticated internal guidance systems. Both types were tested in wartime Germany, and German radio-controlled glide bombs were responsible for sinking numerous Allied ships. Although these early missile weapons relied on optical tracking and control from parent aircraft, most current air-to-ground guided missiles depend on their own target-sensing mechanism once launched. The U.S. Maverick uses a miniature television homing system, while the HARM missile follows radar emissions from hostile positions. The unpowered “smart bombs” employed in Southeast Asia and the Persian Gulf War of 1991, as well as later powered versions, use laser or infrared target designators to help guide the missile to its objective. The former Soviet Union developed several versions of large, air-breathing missiles similar to U.S. cruise missiles, designed to be used against shipping or as a nuclear delivery system for strategic bombers.
Air-to-air guided missiles are used to destroy hostile aircraft and are generally smaller, lighter, and faster than air-to-ground projectiles. The U.S. Sidewinder uses infrared heat-seeking guidance to locate its target, while the Sparrow and Phoenix missiles rely on radar homing devices. While most fighter aircraft still carry machine guns, air-to-air missiles have replaced automatic gunfire as the main weapon of choice. Like other tactical missiles, however, the success of these missiles depends on the skill of the operator, in this case the aircraft pilot, to identify hostile targets and to maneuver close enough to place the missile in the vicinity of the moving target.
This type of missile was developed to protect ground areas from hostile air attack, especially from high-altitude bombers flying above the range of conventional antiaircraft artillery. During the 1950s and 1960s, batteries of Nike-Ajax and the Nike-Hercules provided strategic air defense for the U.S. against long-range Soviet bombers. Bombers were gradually replaced by the ICBM as the primary nuclear delivery system. The United States and the former Soviet Union signed an antiballistic missile treaty in the early 1970s, resulting in the development of smaller antiaircraft and antimissile systems. Most air defense missiles employ separate radars to locate, track, and guide the missile toward hostile aircraft; final interception is accomplished by the internal guidance system of the missile itself. Some of these missiles are air-to-air weapons adapted for ground units; others, such as the U.S. Navy Standard, can also be used against ground targets. The Patriot antimissile system was used by the United States in the Persian Gulf War to intercept attacking missiles. A new addition has been the hand-portable antiaircraft missile. The U.S. Stinger is sighted optically and uses an internal infrared homing device. More important has been the development of integrated fire-control systems for ground units, enabling them to separate friendly from hostile aircraft and to engage them with the most appropriate air defense systems available.
Military guided missiles carry either high-explosive or nuclear warheads. Short-range tactical missiles employ high-explosive charges that produce damage through their force of impact and blast or through fragmentation. Antitank missiles, for example, normally depend on a concentrated blast effect to penetrate or splinter armor; warheads used against less protected targets such as aircraft rely more on fragmentation to produce the greatest damage. Nuclear warheads are weapons of mass destruction carried primarily by ICBMs and SLBMs. These missiles generally carry multiple warheads. The multiple independently targeted reentry vehicle (MIRV) dispatches several nuclear warheads from a single missile while in flight. During the Cold War, the Soviet Union developed the fractional orbit bombardment system (FOBS), which allows missiles or warheads to remain in earth orbit before beginning their descent. FOBS gave the USSR the ability to launch a mass attack against the United States from any direction rather than just depending on a ballistic pathway arching over the North Pole.
Missiles are guided toward targets by remote control or by internal guidance mechanisms. Remote control missiles are linked to a human or mechanical target locator through trailing wires, wireless radio, or some other type of signal system; internal guidance mechanisms have optical, radar, infrared, or some other type of sensor that can detect heat, light, or electronic emissions from the target. Most missiles have some type of movable fins or airfoil that can be used to direct the course of the missile toward the target while in flight. The inertial guidance systems of ballistic missiles are more complex. Missile velocity, pitch, yaw, and roll are sensed by internal gyroscopes and accelerometers, and course corrections are made mechanically by slightly altering the thrust of the rocket exhaust by means of movable vanes or deflectors. In larger rockets, small external jets are also used to alter direction.

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