With the tension building up in several parts of the world and talks about nuclear warfare often coming up, the term missiles are often discussed. This post aims to throw some light on these missiles.
A missile can be defined in modern war terms as a carrier vessel which contains a huge load of explosives that is launched from a safe place which upon reaching the target detonates causing huge destruction. Without going into the details, it can be said that missiles are largely classified into two types: ballistic missiles and cruise missiles.
Consider that you have a basketball in hand. Lets say you wish to score a 3 point shoot. You stand at a distance from the ring and throw the ball. If your throw is good enough, it goes through the ring and you score 3 points. Lets look at this deeper. With the ball in hand, you calculate mentally the distance to the ring, the wind speed, other factors and finally calculate the angle at which you must send the ball into the air at a particular speed. If your calculation is correct, it will go through the ring. This is precisely how a ballistic missile works. It is launched from the base after making lots of calculations and if everything is correct, it will hit the target and explodes.
Now consider an intelligent basketball that will automatically navigate in air, find the ring correctly and go through it. That is a cruise missile. As you would have guessed, cruise missiles are costlier than the ballistic ones but are highly accurate. So they are mostly used to carry nuclear weapons of high destruction and are then called nuclear-warheads. Cruise missile is one of the much researched areas in defence in several countries.
Some famous cruise missiles that exist are Brahmos, Tomahawk, C-101, C-301 etc. What is more appealing to these cruise missiles other than their accuracy is their stealth mode. The normal radars used in defence cannot detect objects flying within a certain height. These cruise missiles, since they have their own navigation systems, can fly at very low altitudes, evade the radar detection and hit the target with the element of surprise. What is more interesting is that, some of these missiles can reach speeds upto 3 times the speed of sound and by the time they are spotted, it is already too late to try and stop them. News items say that research work is going on to create cruise missiles that can travel 5 times the speed of sound making them the ultimate deadly weapons in war.
Cruise missiles can be classifed based on speed, range and target. Based on speed, they can be classified as subsonic (upto 0.8 times the speed of sound), supersonic (upto 3 times the speed of sound) and hypersonic (upto 5 times the speed of sound). Based on range they are classified as short range (upto 300 km), medium range (upto 1000 km) and long range (over 1000 km). Based on the target they can be classified by mentioning their source as surface, water or air and target as surface, water or air. So next time when someone tells you medium range subsonic surface to air cruise missile, you will know what it means.
The most interesting thing about a cruise missile is its technology. The technology that helps the missile to stay on track. The path that a missile travels is divided into three segments namely boost phase, mid course phase and terminal phase in that order and specific technologies are used for each.
The boost phase is very similar to a ballistic missile launch. Calculations are made based on the environment and the missile is launched. But in a cruise missile, at the end of the boost phase the missile does not explode or even reach the target. It would have reached its cruising orbit just outside the location of the launch. Not much fancy technologies are used here.
During the mid course phase, the missile travels the entire length of its intended path. It ends once the target is spotted. The most commonly used methods in this phase are GPS, INS and TERCOM. A GPS device that is installed in the missile stays in contact with a sattelite and the missile is guided accordingly. Functionally this is very simple but if the signal to the sattelite is lost or jammed, the system fails. The second method is INS or Inertial Navigation System. There is one cool feature in iPhones, that is if you rotate the phone by 90 degrees, the content displayed also rotates. This is achieved by using accelerometers installed in the phone. The similar technology is used in INS in cruise missiles. The pitch, yaw and roll of the missile is measured by using accelerometers and gyroscopes and the missile is guided accordingly. Though this system cannot be jammed by external factors, even a slight error in a very long range missile can miss the target by miles. The third method is TERCOM or Terrain Contour Matching. It is done by first storing the elevations of land above which the missile is to travel and guiding the missile based on it. There are two problems with this method. One is that getting the correct elevation of the land for long distances is tough and the other is that this method will fail if the missile flies above sea or forest. Since none of the methods is fool proof, a combination of these is used in missiles to guarantee greater accuracy.
Now to the final course, the terminal guidance part. Here, the missile has reached a position from where the target is in the vicinity. Algorithms are needed in this segment which give maximum accuracy with minimal processing because the target is fast approaching. So the algorithms used in the previous courses cannot be used here. One of the methods commonly used is by infra red heat seeking. If the target is another high heat body like a fighter jet, the temperature of its engine or emission is used as a reference and the missile is directed towards it. Yes, this method can be fooled by how you see in Swat Kats by using decoys. This method however cannot be used clearly for normal buildings and other targets which are at comparitively the same heat level as their surroundings. Another common method is to bounce laser off the target, read the properties of the reflected light, find the target and direct the missile towards it. This pretty much works like SONAR in ships. This method though is very simple to implement, it cannot work in adverse climatic conditions. The final and the most popular method is called DSMAC (Digital Scene Matching Area Correlator). Pictures of the target are taken from satellite at various altitudes and stored in the missile. The missile takes pictures using a high speed camera in its head, matches it with the satellite image using the statistical correlation formula, finds the target and directs the missile towards it. This is one of the most effecient algorithms on which a lot of research happens. Various techniques of imagery are used to counter the effects of adverse climatic conditions. This algorithm however fails in deserts and similar places where the terrain changes often. Lot of research is happening on countering this problem as well.
Just in case you were wondering Brahmos is a super sonic short and medium range wherever to wherever cruise missile.