Tuesday, November 13, 2012

Cruise Missile

Cruise Missile, small pilotless aircraft that carries an explosive warhead. Cruise missiles can be launched from airplanes, trucks, ships, or submarines.
Modern cruise missiles are designed to be reliable and accurate. A typical example is the Lockheed Martin AGM-158 Joint Air-to-Surface Standoff Missile (JASSM). The JASSM weighs 1,000 kg (2,300 lb), has a range of more than 300 km (200 mi), and can be carried on fighter or bomber airplanes.
Cruise missiles resemble airplanes. They have wings and an engine, but they are built somewhat differently to save money. To reduce the cost of the latest cruise missiles, Lockheed Martin engineers borrowed technology from companies that make consumer goods. To make the body, strong fiberglass braids are laid up in a mold. The air is pumped out and hot liquid plastic is pumped in, similar to the construction of a pleasure boat. The wings and tails of the missile are made of fiberglass skins wrapped around plastic foam cores, similar to a surfboard.
Cruise missiles are small and fast but can still be shot down, so designers make them stealthy (hard to detect on radar). To locate a cruise missile, an enemy uses a radar system to transmit radio waves that reflect off the missile or an airplane carrying the missile. The radar receives the reflected signals and thereby determines the speed and position of the cruise missile or the airplane carrying the missile. The stealthy cruise missile or airplane, however, is designed to thwart the radar system. For example, JASSM’s flat sides, pointed nose, and sweptback wings make it hard to detect on radar because any radar signals aimed at the missile bounce away from the radar that sent them out so the radar does not receive back any reflected signals.
A small jet engine powers a cruise missile, typically at speeds of more than 800 km/h (500 mph). The engine is controlled by a computer. In the JASSM, this computer was originally made to control automobile antilock brakes.
A cruise missile is designed to be extremely accurate. It is steered by an inertial navigation system (INS). Used on many airplanes and missiles, an INS measures every movement of the missile and every change of speed, constantly calculating the missile’s position. Any INS “drifts” or loses accuracy over time, like a clock, so current cruise missiles, such as the JASSM, also have a global positioning system (GPS) receiver that corrects the INS with the help of radio signals transmitted by GPS satellites.
Most modern cruise missiles, including the JASSM, have a precision guidance system that allows them to hit small targets. Before a cruise missile is launched, a photograph of the target is loaded into the missile’s computer. As the missile approaches the target, an infrared camera in the nose takes a picture and the computer matches it to the stored image. A cruise missile is so accurate that it can be aimed not just at a building, but at a specific place in the building, such as a door or window.
A cruise missile has a sharp nose and steel casing so that it can penetrate concrete bunkers. Warheads used in the JASSM cruise missile are filled with a type of explosive material that will not blow up if the warhead is dropped accidentally, or even if the airplane carrying the missile catches fire on the ground.
Other cruise missiles include the United States Navy’s Tactical Tomahawk, which is launched from ships and submarines using a rocket booster. A unique feature of this cruise missile is that it can be programmed with up to 15 targets. The missile flies to the first target on its list, and its camera sends a picture back to the ship via radio. If another Tomahawk has already hit the target, the controller can send the missile to its next target.
Some cruise missiles, including the Anglo-French Storm Shadow, use “terrain matching” guidance to help them navigate. Radar measures the height of the ground below the missile and compares these measurements with a three-dimensional map stored in the missile’s computer. Because ground contours are unique, these measurements enable the missile to determine its position.
Primitive “aerial torpedoes” were designed during World War I (1914-1918), but the first practical cruise missile was the German V-1, used in 1944-1945 during World War II. Launched from a catapult, the V-1 was cheap and simple and could carry an 800-kg (1,800-lb) warhead. More than 8,000 V-1s were launched against Britain.
Both the United States and the Union of Soviet Socialist Republics (USSR) built jet-powered, nuclear-armed cruise missiles during the Cold War. The U.S. Air Force’s Northrop Snark, which became the biggest cruise missile ever placed in service when it was activated in 1958, could fly more than 10,000 km (6,000 mi). It was the first aircraft to use INS, and it also had a system that could lock on to stars to correct INS errors. It measured the exact position of Canopus, a visible star, to fix the missile’s position—just as human navigators take star sightings. An even larger missile, the North American Navaho, could cruise at 3,000 km/h (2,000 mph); it was tested but never entered service because the U.S. Air Force bought ballistic rockets instead. The smaller Martin Mace with a range of 2,300 km (1,400 mi) was the first missile with terrain-matching guidance when it went into service in 1959.
The United States retired these weapons in the 1960s, while the Soviet Union continued to build supersonic cruise missiles, designed to attack U.S. aircraft carriers and other large targets.
By the 1970s the development of smaller nuclear warheads, miniaturized electronics, and small, efficient jet engines made it possible to build cruise missiles that were one-sixth the size of Mace. The United States produced thousands of these new missiles, including the Tomahawk, made by General Dynamics (now Raytheon), which could be launched from ships, submarines, or trucks, and the Air-Launched Cruise Missile (ALCM), made by The Boeing Company, which was launched by B-52 bombers.
With the end of the Cold War, the nuclear warheads on many cruise missiles were replaced with explosive warheads. In the Persian Gulf War attacks on Iraq in January 1991, the first weapons launched were ALCMs fired from B-52s—the first cruise missiles fired in battle since 1945. United States Navy surface ships and submarines fired more than 290 Tomahawks at Iraqi targets.
Tomahawks and ALCMs were used in Operation Allied Force, the campaign to remove the Serbian Army from the province of Kosovo in April 1999. For the first time, a non-U.S. force—the British Royal Navy—used Tomahawks as well.
Tomahawks were also used extensively during the 2003 U.S.-British invasion of Iraq to depose the regime of Saddam Hussein. From late March to mid-April more than 800 Tomahawk cruise missiles were fired at Iraqi targets. Fewer than 10 failed to hit their targets, according to the U.S. Navy commander of maritime forces.
To date, cruise missiles have not been a decisive weapon. Military commanders attack most targets by other means. Until the 2003 war in Iraq, cruise missiles were used sparingly because they are expensive. The Tomahawk, for example, costs well over $1 million per missile. Also, in recent wars, enemy forces have not possessed many of the small, important, fixed targets such as permanent missile sites or airplane hangars, that cruise missiles were designed to attack. Another problem is that it is difficult to know whether a cruise missile has destroyed or even hit its intended target because they lack any means of transmitting a target picture back to the launch airplane or ship. New cruise missiles, however, are much cheaper. For example, a JASSM costs under $400,000 and is likely to be more widely used, especially in situations considered too dangerous for piloted aircraft.
The United States and other countries that have developed cruise missiles—including Britain, France, and Russia—have worked to limit the spread of modern cruise missile technology. Exports of long-range missiles are strictly limited, and the United States discourages the sale of weapons in the JASSM class to other countries. For example, the United States has refused to allow F-16 fighters sold to other nations to have such weapons. Experts are concerned, however, that in the long run other nations could use off-the-shelf technology, similar to that used in modern light airplanes, to develop cruise missiles that could pose a serious threat to the big bases and aircraft carriers used by United States and allied forces.


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