What is a ballistic missile - and will it stop a missile from North Korea?

The only system expressly designed to shoot down ICBMs is the US Ground-based Midcourse Defence

North Korea’s test this week of an intercontinental ballistic missile has reignited interest and debate on the feasibility of ballistic missile defence systems, and whether countries such as Australia should seek to acquire them.

But what are these systems, and how do they work? How effective would they be in providing a defence against a potential missile attack?

How do they work?

All ballistic missile defence systems consist of a network of tracking and guidance radars, and the interceptor launchers.

On detecting a ballistic missile launch, the radars track the missile’s trajectory, fire an interceptor to shoot it down, and prepare