This is the basic definition of a system that intercepts projectiles, whether they be bullets, mortar shells, RPGs, missiles, ICBMs, warheads, or any other type of projectile.
This definition deals with the science behind intercepting such projectiles using modern technologies such as radar to detect the projectiles, and kill vehicles to intercept and disable the projectiles in mid-air.
Bullet Interception System – acquire the originating direction of the bullet, it’s speed and trajectory, and subsequently fire an intercepting kill vehicle, such as a programmable bullet, to intercept and disable the incoming bullet.
Mortar Shell Interception System – acquiring the originating of the mortar shell is easier than with bullets, because the mortar shell must originate from a large canon that can be identified by satellite photography. Radar systems could identify the incoming trajectory of the mortar shell, and fire a kill vehicle to intercept the shell mid-air and destroy it.
RPG Interception System – for use on aircraft to intercept a fired Rocket Propelled Grenade, a projectile is fired at the RPG and uses heat tracking to intercept the RPG and destroy it a safe distance away from the plane. Alternatively, if the RPG is fired too closely to the aircraft, chaff made from burning thermite or similar material could be propelled in the opposite direction of the aircraft to create a heat signature that the RPG can follow if it is heat seeking, and then another projectile can intercept the RPG from the ground or from another aircraft to destroy it a safe distance from the aircraft.
Missile Interception System – such as for use to intercept cruise missiles, there are multiple ways to destroy the devices based on the systems that run their navigation. There could be radar jamming, or misinformation of GLONASS or GPS signaling to throw the missile off course. The missile could also be intercepted by a kill vehicle to destroy it before it reaches its destination.
ICBM Interception System – likely, it is possible to intercept an ICBM before it separates in the upper atmosphere. This process is described in other documentation.
Warhead Interception System – such as the interception of warhead(s) ejected from ICBM or other type of carrier vehicle, such as a cruise missile with independently targeted warheads or mini-missiles that break off from the main unit. Targeting these warheads uses the same processes as targeting missiles (that have a propulsion system) or mortar shells (that don’t have a propulsion system).