The Physics of War (42 page)

A current, as we saw earlier, is a group of electrons moving through the lattice created by the atoms of a metal or a semiconductor. In effect, the electrons jump from atom to atom. To move through the lattice, however, they have to have enough energy to overcome the “gap energy.” In other words, they somehow have to acquire enough energy to jump from the valence band up to
the conduction band. Semiconductors have relatively small gaps, so it doesn't take a lot of energy for electrons in the valence band to jump up to the conduction band. Conductors such as copper, on the other hand, have little or no gap, and electrons flow very easily when a small voltage is applied.

Conduction and valence bands. Note the gap between them. E
_F
is called the Fermi levels.

Two of the most important semiconductors, as far as electronic systems are concerned, are germanium and silicon. What makes these semiconductors particularly valuable is that they can be “doped” with impurity atoms such as boron and phosphorus. Impurity atoms have either a deficit or excess of valence electrons (valence electrons are responsible for the electrical conductivity of different elements). Doping is the process of inserting these impurities, which make new energy levels available within the gap, either just below the conduction band or just above the valence band. The levels just below the conduction band are created by donor impurity atoms; the levels just above the valence band are created by acceptor impurity atoms. Semiconductors doped with donor
impurities are called n-type. Those doped with acceptor impurities are called p-type. When an electron jumps to an acceptor level it leaves a “hole” in the valence band, and this hole acts like a positive electron.
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Energy-level diagram of a semiconductor with electrons in the acceptor levels and holes in the valence band.

Armed with this information, Bardeen and Brattain began looking into how semiconductors could be used in electronics. One of the simplest electronic devices at the time was the rectifier—a device that would allow current to flow only in one direction. Having decided to look into the possibility of creating a rectifier using semiconductors, they found something that was of even more interest: a simple form of amplification. Amplification is an increase in the signal; it can be an increase in current, voltage, or power. In their experiments Bardeen and Brattain achieved current and power amplification but not voltage amplification. Their first device used point contacts on the surface of the semiconductor.

Bardeen and Brattain continued to improve their device, but there were several problems with the contact probes. One of the major ones was that there was a surface layer on the semiconductor that appeared to be causing problems. William Shockley, who was the leader of the group, now became more involved. He suggested that a three-layered semiconductor structure would work just as well and would be simpler. This would, in essence, be two p-n junctions placed back to back to form either a p-n-p or an n-p-n device, which we now call a transistor.

Several connections can be made to a transistor; usually an input signal through two connections is amplified and the resultant, or output signal, is obtained through two other connections. Over the years the size of transistors has decreased significantly; as a result they are now incorporated into very small circuits of various types. They soon became the central device for computers, and with increasing technology they became even smaller and smaller. As a result, computers also became very small.

Eventually most transistors were integrated into tiny circuits called microchips. Tiny wafers began to hold hundreds, then thousands and even hundreds of thousands of tiny transistors and other electronic components. And surprisingly, as microchips became smaller they also became more reliable. Today literally billions of transistors can be placed on a tiny microchip. As a result, computers of all types now surround us in an incredible variety of devices, and they have revolutionized the weapons of war. They are found in tanks, airplanes, guided missiles, rockets, many types of guns, and almost all types of bombs.

SATELLITES AND DRONES

We don't normally think of satellites as weapons of war, and so far they haven't been involved in direct fighting, although in theory they could be equipped with many different types of weapons, including lasers of various types, particle-beam weapons, and even missiles. As we saw earlier, Sputnik was launched by the Soviets in 1957. Explorer 1, the first American satellite, was launched the following year, but for several years the United States trailed the Soviet Union in space technology. Although satellites are used for many commercial purposes, including transcontinental TV broadcasting, long-distance telephone transmission, weather prediction, and GPS navigation, one of their major uses is for spying, and we will direct our attention primarily to spy satellites.

Within a few years after Sputnik, both the United States and the Soviet Union were launching satellites for spying. Early spy satellites recorded data then ejected it in canisters that had to be retrieved. It wasn't long, however, before radio came
into use as a means of retrieving the information. The first series of spy satellites launched by United States in 1959 was called Corona. Since then a large number of spy missions have been initiated, as spying techniques have become more and more sophisticated. Many other nations, including Israel, the United Kingdom, France, Germany, and India, are now launching their own spy satellites.

This sky is now full of spy satellites, most orbiting overhead at altitudes of one hundred to two hundred miles. They travel at approximately 17,500 miles per hour, taking snapshots of millions of different items of interest to the military and the Central Intelligence Agency. They are, in effect, giant digital cameras pointed at the earth. Everyone has heard of the amazing discoveries made by the Hubble Space Telescope, with its giant mirror. As it turns out, the United States has telescopes in satellites that are now just as large and powerful as Hubble, but they're pointed toward the earth. They are referred to as Keyhole-class (KH) spy satellites, and they provide very high-resolution images; they can, in fact, resolve objects down to five or six inches.
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But high resolution isn't their only feature. The newer satellites can now take pictures in stereo (side-by-side images at a slightly different angle) that, with the help of computers, can give three-dimensional images. In addition to this, radio images and infrared images can be obtained. Infrared imagery is particularly helpful because it allows the cameras to see through clouds and also at night. Furthermore, intelligence collecting has now become so refined and fast that a single radio or cell phone can be located and pinpointed almost immediately, and orders for targeting its owner can be issued within minutes.

Most satellites, in fact, now contain extensive, fast computers that can crunch huge amounts of data within a fraction of a second. This data can be quickly transmitted down to an operation center on earth.

In addition to satellites, unmanned aircraft are now also being used extensively. They are usually referred to as drones. Drones have been used extensively in the wars in Iraq and Afghanistan. The two major types now being used by United States are the MQ-1 Predator and the MQ-9 Reaper (but others are also in use). They are referred to as UAVs (unmanned aerial vehicles) or RPVs (remotely piloted vehicles). And there's no doubt that they are changing the nature of modern aerial combat and combat in general. Their main advantage, of course, is that a pilot is no longer in danger. Nevertheless, the craft can still inflict considerable damage to an enemy. Another important advantage is that they are much cheaper to build than conventional fighter planes. The predator is only about twenty-seven feet long.
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The “pilot” of these drones is usually thousands of miles away. For the ones being used in Iraq, Afghanistan, and Pakistan, the pilot is usually located at a
military installation in the United States, where he or she is positioned in front of a screen that shows what a pilot in a plane would normally see, and manipulates the drone as if sitting in the drone's “cockpit.” Furthermore, the pilot is able to communicate with troops on the ground below the drone. In particular, he or she can give them information about the position and capability of the enemy.

A predator drone.

Most drones are considerably smaller than fighter planes, and they are not as well equipped. Predator drones usually have no armaments, since they are used mainly for spying; Reapers, however, are equipped with missiles. The British are designing a model they call Taranis, however, which will be about the size of a fighter plane. It will be equipped with weapons of several types, and it will be capable of defending itself from attacks by other aircraft. The Israeli air force also has drones called Hermes 450s, which are equipped with missiles. Many of the countries with drones use the Sperwer, which is produced in France. It is capable of twelve hours of sustained flight, and it is equipped with various electrical-optical devices including infrared and radar sensors; it also carries missiles and antitank weapons.

FUTURISTIC WEAPONS OF WAR

You merely have to look at science fiction to see all kinds of futuristic weapons. But how many of them are practical or even possible? Some of them will no doubt eventually be used in war, but most will not. Let's look at some of the futuristic weapons that may one day make it off the drawing board.

One of the most interesting is called the e-bomb, and although it could be devastating to a civilization, it does not kill. The idea for such a bomb first came in 1960 when the first hydrogen bombs were set off. One of the phenomena measured was the intensity of the electromagnetic pulse generated by the blast. Scientists soon determined that this pulse was felt at a considerable distance—as far as nine hundred miles from the blast. Furthermore, the blast compromised the functioning of instrumentation in airplanes miles away.
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Scientists didn't give much thought at first to the danger associated with the electromagnetic pulse that was generated. But they wondered
how
it was generated. And they soon found out. In a nuclear blast, large numbers of gamma rays are generated, and they, in turn, produce high-speed electrons, some of which become trapped in the earth's magnetic field. These electrons produce powerful electric and magnetic fields, which in turn produce extremely high currents and voltages in any type of electronic or electrical equipment. In effect, all electronic equipment is destroyed by these pulses, including all computers, communication equipment, and telephones, as well as electrical systems in cars, airplanes, and so on. Such a blast could bring society to a standstill and cause billions of dollars in damage.
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The military has been looking into how to generate brief but powerful electromagnetic pulses. It would be inconvenient to have to set off a nuclear bomb to create them, and indeed they can be produced relatively easily without a bomb. An explosive packed into the interior of a large copper coil is all that is needed. The instant before the explosion, the coil has to be energized by a bank of capacitors to create a magnetic field. The explosion creates a moving short circuit, which in turn compresses the magnetic field. The result is an intense electric pulse that immediately propagates outward from the device.