A missile is an airborne ranged weapon capable of self-propelled flight aided usually by a propellant, jet engine or rocket motor. Historically, 'missile' referred to any projectile that is thrown, shot or propelled towards a target; this usage is still recognized today with any unguided jet- or rocket-propelled weapons generally described as rocket artillery. Airborne explosive devices without propulsion are referred to as shells if fired by an artillery piece and bombs if dropped by an aircraft. Missiles are also generally guided towards specific targets termed as guided missiles or guided rockets. Missile systems usually have five system components: targeting, guidance system, flight system, engine, and warhead. Missiles are primarily classified into different types based on firing source and target such as surface-to-surface, air-to-surface, surface-to-air and air-to-air missiles.
Terminology Missile is derived from Latin "missilis" meaning "that may be thrown". The first use of the word was in the early 1600s by Philemon Holland. Historically, 'missile' referred to any projectile that is capable of being thrown or a weapon that is shot or propelled towards a target. Later military definition refers to a missile as an airborne ranged weapon capable of self-propelled flight guided towards a specific target. Any unguided jet or rocket-propelled weapons are generally described as rocket artillery, and airborne explosive devices without propulsion are referred to as shells if fired by an artillery piece and bombs if dropped by a vehicle such as an aircraft.
History
Rockets were the precursor to modern missiles and the first rockets were used as propulsion systems for arrows as early as the 10th century in China. Usage of rockets as weapons before modern rocketry is attested to in China, Korea, India and Europe. In the 18th century, iron-cased rockets were used in India by the Kingdom of Mysore and Maratha Empire against the British which was developed into Congreve rocket and used in the Napoleonic Wars. In the early 20th century, American Robert Goddard and German Hermann Oberth developed early rockets propelled by jet engines. In the 1920s, Soviet Union developed solid fuel rockets at the Gas Dynamics Laboratory. Later, the first missiles to be used operationally were a series of rocket based missiles developed by Nazi Germany during World War II including the V-1 flying bomb and V-2 rocket which used mechanical autopilot to keep the missile flying along a pre-chosen route. Less well known were a series of anti-ship and anti-aircraft missiles, typically based on a simple radio control (command guidance) system directed by the operator. However, these early systems in World War II were only built in small numbers. After World War II, the advent of the Cold War and development of nuclear weapons necessitated faster, more accurate and more versatile missiles with longer range and missile development was pursued by multiple countries.
Proliferation restrictions Various attempts have been made to control the spread of long range missiles capable of carrying weapons of mass destruction, such as the Missile Technology Control Regime (1987) and the International Code of Conduct against Ballistic Missile Proliferation (2002). These were voluntary and not international treaties. Though not legally binding, more than 140 countries have been part of these agreements, and provide prior information on missile programs, expected launches, and tests. The gradual introduction of missile launched hypersonic glide vehicles since 2019, anti-satellite missiles, and the deployment of dual use missiles capable of carrying both conventional and nuclear warheads are proliferation concerns.
Components
Guidance, targeting and flight systems
A missile is most often guided by a guidance system though there are missiles that are unguided during some phases of flight. Missile guidance refers to methods of guiding a missile to its intended target. Effective guidance is important because reaching the target position accurately and precisely is a critical factor for its effectiveness. The missile guidance system accomplishes this by four steps: tracking the target, computing the directions using tracking information, directing the computed inputs to steering control and steering the missile by directing inputs to motors or flight control surfaces. The guidance system consists of three sections: launch, mid-course and terminal with same or different systems employed across sections.
The guidance and homing systems are generally classified broadly into active, semi-active and passive. In active homing systems, the missile carries the equipment needed to transmit the radiation needed to illuminate the target and receive the reflected energy. Once the homing is initiated, the missile directs independently towards the target. In semi-active systems, the source of the radiation is located outside the missile usually in the launch vehicle which might be an aircraft or a ship and the missile will receive the radiation to direct towards the target. As the source is located outside, the launch vehicle needs to continue supporting the missile till it is guided to the intended target. In a passive system, the missile relies solely on the information from the target. The homing system might use light such as infrared, laser or visible light, radio waves or other electromagnetic radiation to illuminate the target. Once the guidance system identifies the target, the target might required to be tracked continuously if it is in motion. A guidance system might use INS which consists of a gyroscope and accelerometer or might use satellite guidance (such as GPS) to track the missile’s position relative to a known target. The missile computers will compute the flight path required to steer the missile towards the target. In command guidance, a human operator may operate it manually or a support or launch system will transmit commands by using either optic fiber or radio to guide the missile. The flight system uses the data from the targeting or guidance system to maneuver the missile in flight which might be accomplished using vectored thrust of engines or aerodynamic maneuvering using flight control surfaces such as wings, fins and canards.
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