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There are a limited number of ways to prevent a ballistic missile from detonating over one's territory.  A brief primer on nuclear attack will help explain the problems to be solved.

There are a limited number of ways to prevent a ballistic missile from detonating over one's territory.  A brief primer on nuclear attack will help explain the problems to be solved.

===The Problems===

===The Problems===

Missiles with nuclear payloads are launched in two primary ways: as ground based intercontinental ballistic missiles, and as shorter range missiles, such as submarine-launched ballistic missiles and submarine-launched cruise missiles.

Missiles with nuclear payloads are launched in two primary ways: as ground based intercontinental ballistic missiles, and as shorter range missiles, such as submarine-launched ballistic missiles (SLBMs) and submarine-launched cruise missiles (SLCMs).

*ICBMs are launched from the ground, travel into space, and return with the assistance of gravity.  Most contain "multiple independently targeted reentry vehicles" or MIRVs.  This means that a single ICBM can cause many nuclear warheads to detonate over multiple targets.  Problems involved include detecting the launch, and deciding on what level to intercept the target.  If the target is disabled before deployment of MIRVs, this obviously solves many problems.  Once MIRVs are deployed, many more targets must be eliminated.

*'''ICBMs''' are launched from the ground, travel into space, and return with the assistance of gravity.  Most contain "multiple independently targeted reentry vehicles" or MIRVs.  This means that a single ICBM can cause many nuclear warheads to detonate over multiple targets.  Problems involved include detecting the launch, and deciding on what level to intercept the target.  If the target is disabled before deployment of MIRVs, this obviously solves many problems.  Once MIRVs are deployed, many more targets must be eliminated.  Destroying an ICBM before it enters space is essentially impossible.  Interception in space requires a pre-placed infrastructure.  Interception after MIRV deployment involves ground-based systems.

*SLBMs and SLCMs present serious difficulties.  SLBMs have a shorter time available to intercept, as they can be launched nearer to target. SLCMs are basically a first-strike weapon, travel short distances quickly and close to the ground.

===The Solutions===

===The Solutions===