How Missile Defense Works (and Why It’s Hard)

By Agnes Chang and Samuel Granados

June 23, 2025

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Iran fired missiles at an American base in Qatar on Monday in retaliation for U.S. strikes on three critical nuclear sites.

U.S. forces operating anti-missile batteries shot down the Iranian missiles, two Pentagon officials said. The officials spoke on condition of anonymity to discuss security matters.

Over days of conflict with Iran, Israel’s sophisticated and multilayered air defense system has intercepted most but not all of the incoming ballistic missiles that Iran has fired in retaliation for Israel's strikes on Iranian nuclear sites and other targets.

Here’s how missile defense systems work — and why it is hard to stop a ballistic missile attack.

Interceptor

Enemy missile

Kill vehicle

Re-entry vehicle

SPACE

ATMOSPHERE

Enemy missile

Re-entry vehicle

Interceptor

Kill vehicle

SPACE

ATMOSPHERE

Enemy missile

Re-entry vehicle

Kill

vehicle

Gimbaled

sensor

Rear

thruster

Enemy missile

Re-entry vehicle

Kill

vehicle

Gimbaled

sensor

Rear

thruster

Enemy missile

Re-entry vehicle

Warhead

Enemy missile

Re-entry vehicle

Warhead

Out of the

atmosphere

Upper

atmosphere

Medium range

Long range

Out of the

atmosphere

Upper

atmosphere

Medium range

Long range

Out of the

atmosphere

Upper

atmosphere

Lower

atmosphere

Short range

Medium range

Long range

Out of the

atmosphere

Upper

atmosphere

Lower

atmosphere

Short range

Medium range

Long range

Once a ballistic missile is fired into the air, a defender has only minutes to identify its precise trajectory and try to shoot it down.

Ballistic missiles escape the atmosphere and accelerate to great speeds as they fall back down to Earth. Within seconds, satellites must detect the heat signature given off by a missile launch. Radars must find the missile and try to calculate its exact course.

A defensive missile called an interceptor must be fired soon after that to reach the incoming missile in time.

Long-range interceptors operate in space, where ballistic missiles spend most of their time. They are the first chance to stop a missile, but high above the atmosphere, there is no room for error. Both an interceptor and an enemy missile shed the boosters that power them into space. Just two smaller vehicles remain, hurtling toward each other.

The interceptor seeks a direct hit to destroy the warhead. To home in, the interceptor carries sensors to track the enemy missile and thrusters to move toward it. But by the time an interceptor senses its target a mile away, it has only a split second to adjust.

That’s because advanced missiles like Iran’s latest are only about three feet wide at the base by the time they are in space, and they are traveling about two miles every second.

It’s unclear how often interceptions above the atmosphere actually work. If a missile succeeds in re-entering the atmosphere, often less than a minute remains before it strikes.Defenses that work in the upper atmosphere — like Israel’s Arrow 2 or the United States’ THAAD system — must fire their interceptors within seconds.

As the missile nears the ground, close-range defenses like the Patriot system from the U.S. provide a final chance to stop it. But these systems have a range of about 12 miles and can only protect limited areas.

For all of the technological sophistication of missile defense systems, they are not foolproof.

Israel has one of the world’s best defense systems, yet it could not stop all of the missiles Iran has been firing in retaliation of Israel’s continuing attacks, leaving civilians dead or injured.

And Israel has a limited number of anti-missile interceptors. The question of whether its interceptors will outlast Iran's missiles may shape the future of the conflict.

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