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Technology:Cruise missiles explained
At launch a rocket motor brings about the initial acceleration and after that the turbofan engine takes over, propelling the cruise missile at high subsonic speeds. The missile evades the radars by flying at very low altitudes.
PAKISTAN TEST-FIRED its first indigenously built cruise missile last week, proving once again that it is not going to relax in matters of national defence and that it has the capacity to develop the most technically advanced products, when needed.
With the highly successful test, Pakistan joined the group of nations that possess the technology to build cruise missiles — the US, the UK, China, Russia, Italy, Germany, Japan, Taiwan, France, Israel, Norway, Sweden and India. The missile named after the Mughal king Babur can carry nuclear as well as conventional weapons. The missile’s range of 500km is greater than that of India’s Brahmos missile.
President Gen Pervez Musharraf praised the scientists and engineers involved in the cruise missile project and reiterated the country’s “resolve to continue meeting emerging challenges and geo-strategic developments in its neighbourhood”, said an official statement. The missile was an “Independent Day gift” from scientists and engineers, it added.
In the main, a cruise missile is a small, pilotless plane. Its purpose is to deliver a bomb to a precise location. The term cruise missile covers several vehicles and their capabilities — from the Chinese Silkworm, which has a range of less than 105km, to the American Advanced Cruise Missile, which can fly to ranges of up to 3,000km. These vehicles vary greatly in their speed and ability to penetrate defences.
All, however, meet the general definition of a cruise missile. A cruise missile can be defined as: “An unmanned self-propelled guided vehicle that sustains flight through aerodynamic lift for most of its flight path and whose primary mission is to place an ordnance or special payload on a target.” This definition can include unmanned air vehicles (UAVs) and unmanned control-guided helicopters or aircraft.
The cruise missile is incredibly accurate. It is also good at evading detection by the enemy because it can fly at very low altitudes and is out of the range of most radar systems. It often flies so low that it can be described as a “ground-hugging missile”.
Cruise missiles are relatively inexpensive and can, therefore, overwhelm an air defence system by their sheer numbers. They can be designed as small vehicles, with low thrust, and can penetrate radar and infrared-protected networks. Since they are unmanned they do not require flight crew training and expensive maintenance programmes, besides large hangers for storage.
The basic components of a cruise missile include an airframe, a propulsion system, a guidance, navigation and control system and a weapon integration system. The missile also incorporates a turbofan engine.
At launch, a rocket motor brings about the initial acceleration and after that the turbofan engine takes over, propelling the missile at high subsonic speeds. Once in flight, the cruise missile evades the radars by flying very low or just above the surface.
It takes advantage of the Earth’s curvature for its invisibility, as the radiations emitted by radars travel in straight lines. Four types of systems may guide a cruise missile during its flight:
— Inertial Guidance System (IGS)
— Terrain Contour Matching (Tercom)
— Global Positioning System (GPS), and
— Digital Scene Matching Area Correlation (DSMAC).
The IGS roughly keeps track of where the missile is located, through the accelerations it detects in its flight. Tercom uses a database of the terrain the vehicle is supposed to fly over. It “sees” the terrain it is flying over and matches this to the 3-D map stored in its memory.
The Tercom system allows the missile to fly so low that it seems to “hug” the ground. The GPS system makes use of the network of GPS satellites and an onboard GPS receiver to detect its position with precision.
In the absence of a GPS, the reliability of a cruise missile system becomes problematic. In such situations, a country may attempt to fly its cruise missile with radio or other commands.
Even with GPS, the autonomous cruise missile carrying an onboard map must be supplied with the latest terrain and physical feature changes that might have occurred. Updated autonomous map guidance systems require large computer storage memories aboard the vehicle with units that can withstand flight vibrations and possible thermal extremes during a long-duration flight.
These units must be supplied with latest maps which the delivering nation can obtain. Few nations have space flight vehicles or high-altitude aircraft to build radar maps from overflights alone. Consequently, these maps are often purchased.
Meanwhile, once it is close to the target, the missile uses a “terminal guidance system” to choose the point of impact. The point of impact may be pre-programmed when the GPS or Tercom system is in use.
The DSMAC system uses a camera to find the target. This is particularly useful if the target is moving. A cruise missile may also be equipped with thermal imaging or illumination sensors.
A cruise missile does not face severe stress levels during its flight. It does not perform high “g” manoeuvres and it does not experience propulsion accelerations. Virtually any frame that is structurally sound enough to be used as an ordinary plane is adequate for a cruise missile.
The cruise missile is a lethal weapon, with a variety of platforms to be fired from. Increasing its payload capacity, range, speed or its ability to penetrate defences can increase its capability.
The writer, based in Canada, is a freelance contributor
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