The airframe is the body of the rocket or missile, which determines its flight characteristics. It typically is made of aluminum alloys, magnesium, or other strong but lightweight materials that compensate for the weight of the other components and can withstand extreme heat and pressure.
The power plant is similar in function to the engines of an aircraft except that the latter are reusable, while a rocket’s or missile’s propulsion unit is expended in its one-time flight. Propelling these weapons at very high speeds minimizes the chances of their being shot down before reaching the intended target. Some also operate at very high altitudes where there is little or no atmosphere. They therefore require both fuel and an oxidizer to sustain combustion. Other less expensive power plants are air-breathing and do not need an oxidizer, but they cannot operate above about 70,000 feet. Some rockets and missiles are equipped with additional boosters to extend their range.
The warhead is the part that does the damage. Its explosive may be conventional or nuclear, or it may carry a chemical package to create smoke, fire, etc.
The guidance system in missiles corrects the flight path on the way to the target. Arguably the forerunner of the guided missile was the Japanese kamikaze plane, which relied on a human guidance system. Today there are several different types of (more user-friendly) guidance systems, and some missiles use them in combination—one guiding the missile through midcourse and the other used during the terminal stage.
Inertial guidance uses a predetermined path programmed into an on-board missile computer before launch that makes direction and speed corrections during flight.
Terrain-following guidance systems are preprogrammed with known terrain characteristics along the intended flight path that the missile can “recognize” and use to adjust its course and altitude.
Homing missiles pick up and track their target by radar, optical devices, or heat-seeking methods. In an active homing system, the missile itself emits a signal that is reflected off the target and detected by a receiver in the missile. In a semiactive homing system, the signal comes from the launching platform rather than from the missile itself, and the reflected signal is received by the missile, which uses the information to correct its flight. A passive homing system does not require either the missile or the firing ship or aircraft to emit a signal but instead homes on emissions (heat or radar, for example) from the target itself.
Command guidance systems employ two separate radar systems to track the target and control the missile. A computer (on the launch platform—not the missile itself) evaluates how the missile is doing in relation to the target and transmits orders to the missile to change its track as necessary to ensure it hits the target.
Beam-riding guidance systems rely on a radar beam (transmitted by the launch platform) to the target. A computer in the missile keeps it centered within the radar beam.
Naval missiles can be launched from aircraft, ships, and submarines and, depending on their intended target, may be categorized as air-to-air, air-to-surface, surface-to-air, and so on. Some missiles can be used against air and surface targets alike.
Cruise missiles are a special category that use aerodynamic lift (wings) to extend their range, making them essentially unmanned aircraft that are relatively inexpensive (compared to manned aircraft) to maintain and operate.
Ballistic missiles do not rely on aerodynamic surfaces to produce lift and consequently follow a ballistic (free-fall) trajectory once their thrust is terminated. Some ballistic missiles are relatively simple weapons (such as the Scud used by Saddam Hussein during the Persian Gulf War). Others are highly sophisticated, such as the Navy’s Trident II, which is a submarine-launched ballistic missile (SLBM) that can deliver multiple warheads to different targets thousands of miles away.
Earlier missile systems had “dedicated” launchers—separate, magazine-loaded launchers for each type of missile. These took up valuable space on board ship, and they significantly increased topside weight. Later launchers handled more than one type of missile but still had to be individually loaded. The newest launcher, the Mark 41 VLS (vertical launch system), is a vast improvement. Missiles are carried in ready-to-launch tubes that are stowed below decks, permitting any needed mix of missiles to be fired directly from the tubes in quick succession without the delays that were involved in reloading topside launchers.
Missiles have become extremely sophisticated (and correspondingly expensive) and are a major component of the U.S. Navy’s weapons inventory, including Trident II ballistic missiles, Tomahawk land attack missiles, Standard surface-to-air missiles, and the Sidewinder air-to-air missile, to name a few.