Number of ABM Systems Required to Cover a Defended Area

(Created October 2009)

Reference:
The Missile Defense Equation: Factors for Decision Making by Peter J. Mantle

NumberSystems = (RadiusDefended / RadiusSystem)2

Where

NumberSystems = The number of systems needed to effect near complete coverage of the defended area.

RadiusDefended = Radius of the Area to be defended.

RadiusSystem = Effective Defense Radius of each single system.

EXAMPLE: We want to defend the United Kingdom from enemy ballistic missile attack.

From the center of the UK with a radius of 660 km, you can defend virtually all of the UK (with some exceptions like very remote areas like the Shetland Islands).

Our ABM system has an effective defense radius of 75 kilometers against the type of threat we'll face. How many sites will we need?

(660 / 75)2 = 77.4 = 78 (rounded up)

If you however increase the defense radiuses...

100 km Defense Radius = 44 Sites Needed
125 km Defense Radius = 28 Sites Needed

You can see how a trivial investment in a better, longer ranged missile pays off in spades in the reduced number of sites you will have to build and man.