Story highlights A North Korean launch would be detected almost instantly

The president will be told and consulted but if the threat is imminent the US military has the right to self defense

(CNN) As tensions continue to ratchet up over North Korea's pursuit of a nuclear missile capable of striking the US, CNN has spoken to multiple officials with a detailed knowledge of how the US will determine if any North Korean missile launch poses a threat that requires the US military to shoot it down.

US satellites are constantly surveying North Korea looking at known missile launch sites and watching for any signs of launches from areas they may not know about.

Launches are detected almost instantly because the missiles pick up the infrared heat signature of the launch. Then other classified intelligence systems begin to quickly calculate the trajectory of the missile based on the telemetry or electronic signals it emanates. That allows US commanders to quickly calculate the path of the missile and the estimated target point.

The trajectory and estimated target point can be calculated within minutes of launch.

There is a full interagency communication process during a North Korean missile launch which would involve command centers from the Pentagon, the intelligence community and major US military commands overseas. Each quickly would weigh in with their calculation of the specific threat the missile may pose.

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