Ballistic Missiles 101

Yesterday, we saw how ballistic missiles were born. Today, we're looking at what they've become--a family of fearsome weapons that fall from the sky under gravity's guidance. Some carry nuclear warheads, many fly thousands of miles, and all pack a terrifying punch.

Missiles of Mass Destruction

Word mavens will tell you that the word "missile" can mean practically anything you hurl at someone, from a rock to a rocket. But the missiles that make news are nearly always "strategic missiles"--the sort that can carry a nuclear warhead, or at least a very large conventional one.

There are basically two types of strategic missiles: cruise missiles and ballistic missiles. Both use high-tech guidance systems to deliver dangerous payloads to faraway targets at high speeds. But they travel in different ways.

Cruise missiles generally fly along low, level flight paths, powered by jet engines. The earliest ones were essentially unmanned airplanes. Ballistic missiles travel along high, arcing, "suborbital" paths. They're essentially armed rockets.

Firing Range

Ballistic missiles are often classified by range. Short-range ballistic missiles, including the Scud missiles Iraq lobbed at Israel and Saudi Arabia during the 1991 Gulf War, have ranges of less than 600 miles (1,000 km). Considered "tactical" rather than "strategic" weapons, these are the only ballistic missiles that have ever been used in actual attack.

Intermediate-range ballistic missiles have ranges up to around 3,500 miles (5,500 km). North Korea's Taepodong missiles appear to fall into this category, though no one outside North Korea knows much about them. Most submarine-launched ballistic missiles also have intermediate ranges.

Finally, there are intercontinental ballistic missiles (ICBMs), the world's most terrifying weapons. These have ranges greater than 3,500 miles (5,500 km) and carry one or more nuclear warheads. The LGM-30 Minuteman III--America's only operational land-based ICBM--has a range of more than 6,000 miles (10,000 km) and can carry three 350-kiloton thermonuclear warheads.

Three Flight Phases

Ballistic missiles follow a three-phase flight plan. First is the powered-flight or "boost" phase, during which a rocket engine (or series of rocket engines) puts the missile on a particular trajectory. Finding the right trajectory is crucial. The engine will soon shut down, and gravity will take over. Once the missile "goes ballistic"--moving only with momentum and the force of gravity--there isn't much anyone can do to steer it.

Next comes the free-flight or "midcourse" phase, when the missile coasts along, generally above the Earth's atmosphere. During this phase, the warhead (or other missile payload) often separates from the rest of the missile. Today's highest-tech missiles can even release multiple warheads, placing each on its own ballistic trajectory.

Last comes the re-entry or "terminal" phase, when the missile--or at least the warhead--falls back through the atmosphere and down to its target on Earth. Gravity does the work here, and does it well. Impact speeds for an ICBM warhead can reach 9,000 miles per hour (14,500 km/h).

As the terminology suggests, much of the technology behind a successful ballistic missile mission is the same as the technology behind a successful space mission. Put another way, missile missions really are rocket science.