Missile defense

Missile defense operates across three flight phases: boost, midcourse, and terminal. Boost-phase interception occurs within minutes of launch, when the missile is slow and its exhaust is bright, but requires sensors near the launch site. Midcourse interception happens in space, where warheads and decoys separate, making discrimination challenging. Terminal-phase defense engages the warhead as it re-enters the atmosphere, offering the last chance to intercept but with limited reaction time.

Layered architectures combine these phases to increase probability of kill. For example, the US Ground-based Midcourse Defense (GMD) targets intercontinental ballistic missiles, while Terminal High Altitude Area Defense (THAAD) and Patriot systems handle shorter-range threats. Effective command-and-control networks fuse data from satellites, ground radars, and sea-based sensors to guide interceptors.

The first practical anti-missile efforts emerged during World War II with the German Wasserfall rocket, though it never became operational. During the Cold War, both superpowers developed nuclear-tipped interceptors, such as the US Nike Zeus and Soviet A-35, to destroy incoming warheads with blast effects. The 1972 Anti-Ballistic Missile Treaty limited these systems, but the US Strategic Defense Initiative (SDI) in 1983 revived research into space-based lasers and kinetic interceptors.

After the Cold War, focus shifted to regional threats. The 1991 Gulf War highlighted the vulnerability of Patriot systems against Scud missiles, prompting improvements. In 2002, the US withdrew from the ABM Treaty to deploy national missile defense, leading to the current GMD system. Other nations, including Israel (Iron Dome, David's Sling) and India (Prithvi Air Defence), have developed their own systems.

Contemporary missile defense employs hit-to-kill kinetic interceptors that destroy targets by collision, avoiding the fallout of nuclear warheads. The US Aegis system uses SM-3 missiles on ships to intercept short- and medium-range missiles in midcourse. THAAD provides high-altitude terminal defense, while Patriot PAC-3 handles lower-altitude threats. Israel's Iron Dome is optimized for short-range rockets and artillery, using a radar to prioritize threats.

Directed-energy weapons, such as lasers, are being developed for low-cost interception of drones and cruise missiles. The US Airborne Laser Test Bed demonstrated a megawatt-class laser in 2010, but was cancelled. Hypersonic glide vehicles pose new challenges due to their speed and maneuverability, prompting research into space-based sensors and advanced interceptors like the Glide Phase Interceptor.

Beyond headline systems, missile defense includes niche efforts like the US Army's Indirect Fire Protection Capability (IFPC) for cruise missiles and drones, and the European TWISTER program. The Soviet Union's A-135 system remains operational around Moscow, using nuclear-tipped interceptors. Countermeasures, such as decoys and MIRVs, have historically complicated interception; the US Safeguard system was deactivated after only 154 days due to doubts about effectiveness.

Critics argue that missile defense can provoke arms races, as seen in Russia's development of Avangard hypersonic glide vehicles. The 1983 'Star Wars' speech by Ronald Reagan, which launched SDI, was partly inspired by a 1979 film 'The Seduction of Joe Tynan' according to some accounts. Additionally, the 1996 'Rumsfeld Commission' highlighted the threat of rogue states, influencing US policy. International cooperation, such as NATO's missile defense, has been strained by Russian objections.

Boost phase

The initial phase of a missile's flight when its rocket engines are burning.

Midcourse phase

The phase of a ballistic missile's trajectory outside the atmosphere, where it coasts toward its target.

Terminal phase

The final phase of a missile's flight as it re-enters the atmosphere and approaches its target.

Hit-to-kill

A technique where an interceptor destroys a target by direct collision, without explosives.

MIRV

Multiple Independently targetable Reentry Vehicle; a missile carrying multiple warheads, each aimed at a different target.