The Mechanism of The Bomb

Altimeter

An ordinary aircraft altimeter uses a type of Aneroid Barometer which measures the changes in air pressure at different heights. However, changes in air pressure due to the weather can adversely affect the altimeter's readings. It is far more favorable to use a radar (or radio) altimeter for enhanced accuracy when the bomb reaches Ground Zero.

While Frequency Modulated-Continuous Wave (FM CW) is more complicated, the accuracy of it far surpasses any other type of altimeter. Like simple pulse systems, signals are emitted from a radar aerial (the bomb), bounced off the ground and received back at the bomb's altimeter. This pulse system applies to the more advanced altimeter system, only the signal is continuous and centered around a high frequency such as 4200 MHz. This signal is arranged to steadily increase at 200 MHz per interval before dropping back to its original frequency.

As the descent of the bomb begins, the altimeter transmitter will send out a pulse starting at 4200 MHz. By the time that pulse has returned, the altimeter transmitter will be emitting a higher frequency. The difference depends on how long the pulse has taken to do the return journey. When these two frequencies are mixed electronically, a new frequency (the difference between the two) emerges. The value of this new frequency is measured by the built-in microchips. This value is directly proportional to the distance travelled by the original pulse, so it can be used to give the actual height.

In practice, a typical FM CW radar today would sweep 120 times per second. Its range would be up to 10,000 feet (3000 m) over land and 20,000 feet (6000 m) over sea, since sound reflections from water surfaces are clearer.

The accuracy of these altimeters is within 5 feet (1.5 m) for the higher ranges. Being that the ideal airburst for the atomic bomb is usually set for 1,980 feet, this error factor is not of enormous concern.

The high cost of these radar-type altimeters has prevented their use in commercial applications, but the decreasing cost of electronic components should make them competitive with barometric types before too long.

Air Pressure Detonator

The air pressure detonator can be a very complex mechanism, but for all practical purposes, a simpler model can be used. At high altitudes, the air is of lesser pressure. As the altitude drops, the air pressure increases. A simple piece of very thin magnetized metal can be used as an air pressure detonator. All that is needed is for the strip of metal to have a bubble of extremely thin metal forged in the center and have it placed directly underneath the electrical contact which will trigger the conventional explosive detonation. Before setting the strip in place, push the bubble in so that it will be inverted.

Once the air pressure has achieved the desired level, the magnetic bubble will snap back into its original position and strike the contact, thus completing the circuit and setting off the explosive(s).

Detonating Head

The detonating head (or heads, depending on whether a Uranium or Plutonium bomb is being used as a model) that is seated in the conventional explosive charge(s) is similar to the standard-issue blasting cap. It merely serves as a catalyst to bring about a greater explosion. Calibration of this device is essential. Too small of a detonating head will only cause a colossal dud that will be doubly dangerous since someone's got to disarm and re-fit the bomb with another detonating head. (an added measure of discomfort comes from the knowledge that the conventional explosive may have detonated with insufficient force to weld the radioactive metals. This will cause a supercritical mass that could go off at any time.) The detonating head will receive an electric charge from the either the air pressure detonator or the radar altimeter's coordinating detonator, depending on what type of system is used. The Du Pont company makes rather excellent blasting caps that can be easily modified to suit the required specifications.

Conventional Explosive Charge(s)

This explosive is used to introduce (and weld) the lesser amount of Uranium to the greater amount within the bomb's housing. [The amount of pressure needed to bring this about is unknown and possibly classified by the United States Government for reasons of National Security]

Plastic explosives work best in this situation since they can be manipulated to enable both a Uranium bomb and a Plutonium bomb to detonate. One very good explosive is Urea Nitrate.

Neutron Deflector

The neutron deflector is comprised solely of Uranium-238. Not only is U-238 non-fissionable, it also has the unique ability to reflect neutrons back to their source.

The U-238 neutron deflector can serve 2 purposes. In a Uranium bomb, the neutron deflector serves as a safeguard to keep an accidental supercritical mass from occurring by bouncing the stray neutrons from the `bullet' counterpart of the Uranium mass away from the greater mass below it (and vice-versa). The neutron deflector in a Plutonium bomb actually helps the wedges of Plutonium retain their neutrons by `reflecting' the stray particles back into the center of the assembly.

To illustrate the vast difference between a Uranium gun-type detonator and a Plutonium implosion detonator, here is a quick rundown.

[1] Uranium Detonator

Comprised of 2 parts. Larger mass is spherical and concave. Smaller mass is precisely the size and shape of the `missing' section of the larger mass. Upon detonation of conventional explosive, the smaller mass is violently injected and welded to the larger mass. Supercritical mass is reached, chain reaction follows in one millionth of a second.

[2] Plutonium Detonator

Comprised of 32 individual 45-degree pie-shaped sections of Plutonium surrounding a Beryllium/Polonium mixture. These 32 sections together form a sphere. All of these sections must have the precisely equal mass (and shape) of the others. The shape of the detonator resembles a soccerball. Upon detonation of conventional explosives, all 32 sections must merge with the B/P mixture within 1 ten-millionths of a second.

Lead Shield

The lead shield's only purpose is to prevent the inherent radioactivity of the bomb's payload from interfering with the other mechanisms of the bomb. The neutron flux of the bomb's payload is strong enough to short circuit the internal circuitry and cause an accidental or premature detonation.

Fuses

The fuses are implemented as another safeguard to prevent an accidental detonation of both the conventional explosives and the nuclear payload. These fuses are set near the surface of the `nose' of the bomb so that they can be installed easily when the bomb is ready to be launched. The fuses should be installed only shortly before the bomb is launched. To affix them before it is time could result in an accident of catastrophic proportions.