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Ballistic missiles are powerful missiles that follow sub-orbital trajectories and come in different ranges. They use either solid or liquid fuel, with liquid-propelled missiles requiring constant refrigeration. Most modern missiles use solid fuels and are designed to reach their target in 15-30 minutes.
A ballistic missile is a type of large, powerful missile designed to deliver a warhead great distances to a predetermined target. Ballistic missiles follow sub-orbital trajectories, reaching spatial altitudes (100 km+) and exiting the Earth’s atmosphere, in some cases traveling up to 1,200 km on the surface for ICBMs. Such missiles are called “ballistic” because after an initial thrust phase, the rest of the path is usually determined by ballistics. A smooth parabolic line.
Ballistic missiles come in many shapes and sizes. In the United States, ballistic missiles are divided into four range classes:
intercontinental ballistic missile (ICBM) – over 5500 km
medium-range ballistic missile (IRBM) – from 3000 to 5500 kilometers
medium-range ballistic missile (MRBM) from 1000 to 3000 kilometers
short-range ballistic missile (SRBM) up to 1000 kilometers
For ranges of less than 350 km, the ballistic missile never leaves the earth’s atmosphere. Note that the only three ballistic missiles ever actually used in battle were only in the short-range category and contained conventional explosives. Most ballistic missiles in existence today are designed to carry nuclear warheads, although none of these have yet been used in warfare.
Ballistic missiles use solid or liquid fuel. Older missiles, such as the V2 rocket used by Nazi Germany during World War II and the first US-built ballistic missiles, all used liquid fuel. In many cases, the fuel in a liquid-propellant ballistic missile is liquid hydrogen while the oxidizer is liquid oxygen. The two must be maintained at cryogenic temperatures or they revert to the gaseous phase. During launch, the two gases are rapidly pumped out of the storage chambers in the presence of a spark, which ignites the mixture and propels the rocket forward. The byproduct of burning fuel is water vapor.
The liquid phases of these hydrogen and oxygen are desirable for rocketry because of their improved energy density over the gaseous phase. Another good thing is that liquid-propelled ballistic missiles can have their engines throttled, shut down, or restarted as desired. One downside is that storing such missiles is a hassle, as the fuel requires constant refrigeration to be ready for launch.
Another variety of liquid propellant are hypergolic propellants. Hypergolic propellants ignite on contact, requiring no ignition source. This is useful for frequent starts and restarts for space maneuvering applications. The most popular version uses monomethylhydrazine (MMH) for the fuel and nitrogen tetroxide (N2O4) for the oxidizer.
Most modern ballistic missiles use solid fuels, as they are easier to store and maintain. The Space Shuttle, for example, uses two reusable solid boosters, each filled with 1.1 million pounds (453,600 kg) of propellant. The fuel used in aluminum powder (16%), with iron powder (0.07%) as catalyst and ammonium perchlorate (70%) as oxidizer.
Most ballistic missiles are designed to reach their target in about 15 to 30 minutes, even if the target is halfway around the world. Because they’re so essential to national security, they’re among the most carefully constructed machines on the planet.
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