BY JONATHAN MASTERS
U.S. ballistic missile defense systems are designed to protect the U.S. homeland, deployed military forces, and allies from limited attacks. The Pentagon originally sought development of ballistic missile defense (BMD) technology to counter the Soviet nuclear threat during the Cold War, but its focus in the twenty-first century has shifted to defending against potential strikes from regional actors, particularly Iran and North Korea. Proponents of BMD stress its role in the projection of U.S. power and its value as a deterrent, while critics question its reliability and high costs. In recent years, some military analysts have said that the planned expansion of U.S-NATO missile defense systems in the former Soviet bloc has unnecessarily frayed relations with Moscow.
How does ballistic missile defense work?
Ballistic missiles can be launched from a variety of platforms, including silos, trucks, trains, submarines, and warships. There are four general classifications based on the maximum distance the missile can travel: short range (less than 1,000 kilometers); medium range (1,000–3,000 kilometers); intermediate range (3,000–5,500 kilometers); and intercontinental (more than 5,500 kilometers)
Ballistic missiles have three stages of flight: boost phase, which begins at launch and lasts until rocket engines finish; midcourse phase, the longest stage, when the projectile is on its parabolic path to the target; and terminal phase, when the detached warhead reenters the atmosphere, often traveling less than a minute to impact. (Cruise missiles, by contrast, are jet-engine powered weapons that fly low and level to the ground, often avoiding enemy radar, before striking their target.)
Defeating a ballistic missile involves four functions: detection, discrimination (separating the missile from everything else), fire control (determining exactly where to intercept), and killing (hitting the missile with some type of interceptor). However, the effectiveness of BMD systems in test trials has been mixed, and critics continue to question their value in realistic battle conditions
http://www.defenseone.com/technology/2014/08/your-pocket-guide-how-us-missile-defense-works/91742/?oref=d-dontmiss
