North Korea launched an intercontinental-ranged ballistic missile July 28 that spent a whopping 47 minutes in the air, demonstrating a range that could easily strike the United States' West Coast but it failed critically in its last few seconds.

The missile's reentry vehicle, or where North Korea would put its warhead, burned up during the final seconds before touching down on the ground, Mike Elleman, the senior fellow for missile defense at the International Institute for Strategic Studies, said on press call organized by North Korea analysis website 38 North.

Elleman said that footage of the reentry vehicle showed it brightly streaking across the sky at 6 kilometers per second before going dim just a few kilometers above the ocean.

When a ballistic missile's reentry vehicle gets about 30 kilometers from earth, contact with air causes heat and friction that makes the incoming warhead glow. A successful warhead should then “continue to glow and increasingly glow until it impacts the ground, or in this case the ocean,” said Elleman.

The North Korean reentry vehicle, however, became “very dim,” according to Elleman, indicating that it went to pieces before impact.

While North Korea could have been using a lighter reentry vehicle to boost its perceived range, or purposefully designing the reentry vehicle to disintegrate to avoid the U.S. or Japan from recovering, Elleman said those scenarios are unlikely.

“The reentry vehicle sees its highest stress level at elevations above ten kilometers. They would need to test it in that environment. Purposefully destroying it before it has the opportunity to survive or fail would defeat the purpose of the test,” said Elleman.

North Korea can now range U.S. cities, but it can't expect to hit them with any reliability or accuracy, Elleman said, who added that the country would need two or three more tests to get the technology reliable.

Shooting a missile straight up and down, as North Korea has done in recent tests, doesn't have the same challenges as shooting one on a trajectory that could actually cover ground.

If North Korea shot a missile at the U.S., it would enter the atmosphere at a shallow angle and undergo longer exposure to intense heat and pressure, which could destroy the missile or knock it off course.

“The bottom line is if they want high reliability, they’re going to need to launch a missile on a flatter trajectory,” said Elleman. Overflying a country and not just shooting into the ocean would be politically more dangerous for North Korea, and could potentially look like a real attack on another country.

Reentry vehicles are not the only obstacle to a truly reliable system. North Korea must still master missile guidance and navigation. Despite these engineering challenges, North Korea gains a tremendous amount of knowledge from each launch, and the failure of the last stage does not mean the test was a waste.

Elleman concluded that North Korea could achieve its dream — a reasonably reliable ICBM — by the end of the year.

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