Why Worry About ICBMs?

  • By Erin Dahlstrom
  • Posted 09.21.17
  • NOVA

North Korea has launched more than a dozen missiles this year, including ICBMs. What are ICBMs, and why are they so hard to shoot down?

Running Time: 02:59


News: By early next year, North Korea will have a missile capable of carrying a nuclear warhead to the American mainland. And the U.S. confirmed that the North Korean missile was a long-range ICBM.

Onscreen: What exactly is an ICBM? ICBM stands for InterContinental Ballistic Missile.

Tom Karako: An ICBM is in principle any missile that is over 5500 km in range, a distance that was really a metric between Russia and the United States during the Cold War for arms control purposes.

Onscreen: Ballistic: the motion of something launched through the air. When a country like North Korea launches a test missile…

Melissa Hanham: We want to know where it landed, how long it flew, and how high it went, and from those basic pieces of information, we can get a rough model of the range of that missile.

Onscreen: Launching an ICBM is like hitting a baseball. Both trace a parabolic path but with some key differences. A baseball is the same at the bat and in the glove. But a missile loses mass as it moves.

Hanham: Partly through flight, when it's finished its burn, the engine will separate and then the shroud comes off, and then the warheads will go to their final destination.

Onscreen: The lighter the missile, the farther it might go. A baseball's path on Earth is simple and predictable.

Hanham: An ICBM flies out through the atmosphere into space, and then comes back through the atmosphere. A missile launched from west to east can gain speed and distance, boosted by the Earth's rotation.

Predicting how far a real missile might travel requires some math. Missiles usually get launched at nearly 90˚. Over the next few minutes, the engines orient the missile. Once the engines cut out, the angle and speed are set for the missile's parabolic path. These initial conditions determine where the missile will land.

So how worried should we be about ICBMs?

Karako: What makes an ICBM dangerous is what it's got as its payload.

Onscreen: Nuclear weapons. No one has ever shot down an ICBM in actual warfare before. And it's harder than you might think.

Karako: Nobody said this was easy.

Onscreen: Once a missile is in the air, it's moving fast.

Karako: This is a problem of minutes.

Onscreen: Not to mention all the debris produced along the way.

Karako: You have nuts and bolts and just junk flying around in a cloud. And so the challenge is to look at that junk pile and say that this one thing right here is the warhead.

Onscreen: And if North Korea does decide to attack, it will likely launch not one, but multiple missiles into the air. So where does that leave us?

Hanham: [Our science measures] North Korea's capabilities. Much more difficult to measure is their intention.

Onscreen: And for now, intention is beyond our ability to calculate.



Erin Dahlstrom
Editorial & Production Assistance
Ari Daniel
Editorial Review
Julia Cort
Special Thanks
Theresa Machemer & Ian Williams
© WGBH Educational Foundation 2017


Animations, Imagery, and Videography
CSIS Missile Defense Project
Google Earth
West Ohio Sports Net
U.S. Department of Defense / Daniel Brosam
YouTube.com / Jesse Mason
The Noun Project /Artem Yurov


(main image: ICBM path)
U.S. Department of Defense / Daniel Brosam

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