© US Department of DefenseA missile interceptor launches from California's Vandenberg Air Force base during a 2017 test.
At a Nov. 6 press conference with US President Donald Trump, Japanese prime minister Shinzo Abe was asked if Japan would respond to North Korean missile launches by shooting them down.
"I could just take a piece of the Prime Minister's answer," Trump interjected, "He will shoot them out of the sky when he completes the purchase of lots of additional military equipment from the United States. He will easily shoot them out of the sky, just like we shot something out of the sky the other day in Saudi Arabia."
But Trump was wrong:
The US can't easily shoot down missiles like the one North Korea tested yesterday, which are designed to launch nuclear weapons. The Saudi military did intercept a missile using a US-made Patriot missile defense system, but it was a medium-range missile moving at far slower speeds than a nuclear warhead launched
by an inter-continental ballistic missile.
Stopping a nuclear ICBM is a much more difficult challenge, one that the US has struggled with since the Cold War, spending hundreds of billions of dollars to come up with a system of sensors and missiles called GMD, or Ground-based Midcourse Defense.
The premise is simple: Once the US detects a missile launch with a variety of radar systems, it will shoot its own interceptor into the sky. After the enemy nuclear warhead separates from its rocket booster, a defensive interceptor, or "kill vehicle," separates from its own booster and attempts to crash into the warhead.
Executing this maneuver during a roughly twenty minute window against a warhead moving faster than the speed of sound is extremely difficult in practice.
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