Missile Defence, Deterrence and Arms Control - UNIDIR

TECHNICAL ASPECTS OF MISSILE DEFENCE
Missile defence systems are comprised of a broad array of technical
measures designed to target incoming missiles—either ballistic or
cruise—at some point along their flight trajectory. Short-range theatre
ballistic missile defences, such as the Patriot Advanced Capability (PAC-
3) system which the United States employed to protect its forces and
allies vulnerable to Iraq’s Al-Hussayn Scud-derivative missiles, were the
subject of much attention during the Gulf War. Since a short-range
ballistic missile is powered for most of its flight, and thus has a plume of
hot gases trailing it, missile interceptors have a relatively welldifferentiated
target to hit. In addition, short-range ballistic missile flight
trajectories are entirely endoatmospheric, which affords tracking,
sensory, and targeting advantages. As such, the United States has been
able to develop rather sophisticated, albeit debatably effective, shortrange
theatre missile defences for tactical wartime scenarios where its
troops or allies are at risk.
A natural technical extension of short-range ballistic missile defences
such as the Patriot system is intermediate and long-range ballistic missile
defence systems which, instead of targeting missiles in tactical situations,
aim to defend against an entirely different class of missiles that target a
State’s homeland. Lately, this class of ballistic missiles has received the
most attention, with the United States pledging to deploy some version
of ballistic missile defence by the end of this decade, if not sooner.
Unlike cruise missiles, which are powered for the entirety of their flight,
ballistic missiles are powered only for part of theirs—thereafter they
move under the influence of their own momentum and gravity.
Employed as the primary delivery vehicle of strategic nuclear weapons,
the flight path of a ballistic missile is divided into three distinct stages.
Boost Phase
The first stage is termed the boost phase, where the
warhead—which can be conventional, nuclear, chemical or
biological—is mounted on a single or multistage booster. Various types
of rocket boosters have been developed across the world, with more
advanced boosters employing solid fuel or cryogenic systems as opposed
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