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A Terminal High Altitude Area Defense (THAAD) interceptor is launched during a successful intercept test, in this undated ...

Could the U.S. actually shoot down a North Korean missile?

On Tuesday, the Pentagon confirmed that after a two-month lull, North Korea fired another intercontinental ballistic missile over Japan. It flew about 620 miles and landed in the Sea of Japan.

While visiting Tokyo in November, President Donald Trump pledged that the U.S. would support Japan’s defense against North Korean missiles. Mr. Trump said that with U.S. technology, Japan could “easily shoot them out of the sky.”

While Trump has expressed confidence in the current system’s capabilities, the threat from North Korea has the U.S. reassessing missile defense and has prompted moves in Congress to boost funding. But does the current system really work? We got perspectives from two experts.

What is the U.S. missile defense program?

The $40 billion program is made up of four basic systems designed to protect U.S. bases, its allies and the United States itself, and “they all are about the North Korea threat,” said Thomas Karako, director of the Missile Defense Project at the Center for Strategic and International Studies. The four systems are:

  • Patriot air and missile defense system deployed by the United States, South Korea and Japan. It is the shortest-range system and is meant to defend small groups of troops.
  • Terminal High Altitude Area Defense, or THAAD, is in Guam and South Korea. THAAD is a land-based, mobile system designed to defend against short- and medium-range ballistic missiles.
  • Aegis Ballistic Missile Defense System, deployed by the United States, Japan and South Korea, is designed to intercept ballistic missiles post-boost phase and before re-entry. For Japan and the U.S., it includes ship-based missiles, and covers a wider area than the THAAD program.
  • Ground-based Midcourse Defense system, or GMD, is a global network of radar and sensors, along with surface-to-air missiles designed to intercept and destroy ballistic missiles from the enemy. There are 44 interceptors in silos in the ground — 40 at Fort Greely in Alaska and four at Vandenberg Air Force Base in California — and they are designed to protect all 50 states.

Does the U.S. missile defense system work?

Karako says yes. “The system has demonstrated a lot of capability. … You’ve seen the Patriot being put to good use on a weekly and monthly basis in the ongoing Yemen missile war.” Patriot missiles, operated by Saudi Arabia and the United Arab Emirates in the Gulf region, have intercepted more than 100 ballistic missiles since 2015, according to U.S. contractor Raytheon.

THAAD, in its current configuration, has had success in each of its 15 tests, Karako said. “That’s about as good as you can get.” The ground-based system, or GMD, has tested successfully fewer times — in 10 of 18 intercept tests — but those included earlier tests with configurations that no longer exist, he said, and the Missile Defense Agency deconstructs every failure to fix the problems.

But Philip Coyle, a senior science fellow at the Center for Arms Control and Non-Proliferation, gives the program an “F.” The failure rate of missile tests is more like 60 percent since 2002, he said. “It’s not effective, not only because the success rate has been so poor in flight-intercept tests, but because those tests are scripted for success.”

Coyle said the Pentagon doesn’t want to see its tests fail, which would make the system look bad. “I would hate to think what the success rate would be if they weren’t scripted for success,” he said.

“The Missile Defense Agency does everything they can to make the geometry of the test as realistic as possible within the limitations of range safety and other things,” Karako said. “We can’t fire the targets out of North Korea, so we fire from the middle of the Pacific from a testing range.”

The national missile defense strategy is supposed to defend the United States against attacks from a rogue nation like North Korea or Iran, or an unauthorized or accidental launch from Russia or China, said Coyle. “It is not expected to defend against an attack from Russia or China – they have way too many missiles for that – it would overwhelm the system.”

The U.S. also would have trouble dealing with North Korea launching decoys, such as balloons or radar-deflecting devices, which in space would look similar to missiles, Coyle said.

“No weapon system is perfect,” said Karako. “But it provides a very important capability for the defense of the homeland and therefore, for the overall deterrence and defense posture of the United States.”

What’s on the horizon?

In May, the Pentagon announced the start of a Ballistic Missile Defense Review, which is expected to result in a report describing the Trump administration’s plans for missile defense.

Meanwhile, the House and Senate this month passed a $692 billion National Defense Authorization Act for fiscal year 2018. The House and Senate appropriations committees still need to approve the actual spending.

The bill contains nearly $3 billion more than Trump’s budget proposal for the Missile Defense Agency, and authorized up to 28 additional ground-based interceptors. In addition, it would require the Missile Defense Agency to develop a space-based sensor layer for ballistic missile defense, according to a summary of the bill.

The two experts also had different views on whether a space-based anti-ballistic missile system would work.

“It would not only be horrendously expensive but loaded with all sorts of technical problems,” Coyle said. The system is supposed to be able to blow up the enemy’s missiles before they had a chance to travel into space, but satellites carrying the interceptors would have to be at such a low altitude that they would fall out of orbit, he said. And hundreds of satellites would be needed to guarantee constant coverage as they orbited over rogue countries, he added.

Karako, however, said a space-based senor layer would eliminate some of the gaps that the current ground- or sea-based system would miss. “Each of the last five presidential administrations has had a space-based sensor layer as a critical element of our long-range national missile defense effort on paper” though none has chosen to deploy it to date, he said. With North Korea acting as it is, “now’s the time to do it.”