Missile defense is a form of air defense that refers to systems concerned with the detection and interception of hostile missiles, particularly ballistic missiles.
Historically, missile defense was instrumental as a countermeasure against the threat of ICBM. Over the years, its scope has expanded to include the matter of dealing with any other types of missiles.
Different Types of Missile Defense
Like missiles themselves, missile defense can be categorized using a wide variety of terms of non-mutually exclusive criteria. They may be classed by what sorts of missile they can intercept, by what region of trajectory they intercept missiles, and by whether the interception occurs within the Earth’s atmosphere, and so on.
In terms of the type of missiles they deal with, there are three types of missile defense. The first is strategic, which deals with ICBMs. The second is theater missile defense which deals with medium-range missiles. Finally, there is the tactical missile defense that deals primarily with tactical ballistic missiles
Region of Trajectory
In regards to the region of trajectory, there are also three types of missile defense. The first is the boost phase, which intercepts enemy ballistic missiles during the short period wherein their motors are still firing and likely still in hostile territory. The second is the mid-course phase, which intercepts a ballistic missile after its rocket has stopped firing and is now presumably in space, and provides perhaps the best window of time for interception. The third is the terminal phase, which involves the interception of a missile during or after its reentry into the atmosphere following its mid-course phase.
Region of Interception
Whether interception occurs within or outside of the Earth’s atmosphere is also a criteria of classifying missile defense. Endoatmospheric defense usually deals with the shorter-range missile types, while exoatmospheric defense intercepts the larger, further-reaching missiles. Ballistic missiles have trajectories that bring them outside the planet’s atmosphere and back again, during which they can be intercepted at either location.
Sources: rafael website