After Israel killed the military leader of Hamas early in November, militants in the Gaza strip responded by launching hundreds of short-range rockets into southern Israel, striking terror and killing at least three people and injuring several others.

The attacks, on pause since a cease fire was negotiated last week, highlighted the existence of Iron Dome, a system of missile-defense batteries developed with U.S. assistance that Israel began installing last year. Videos of Israeli missiles intercepting Hamas’s homemade rockets in midair appeared across the Internet and Israeli defense officials claimed that Iron Dome successfully intercepted around 300 rockets, or about 80 to 90 percent of those it fired on.

To assess these claims, MIT Technology Review spoke with Theodore Postol, an MIT physicist and missile-defense expert. In 1991, during the first Gulf War, Postol gained notoriety when he debunked claims by the U.S. Army that its Patriot missiles were successfully shooting down Iraqi Scud missiles (see “Postol vs. the Pentagon” and “Preventing Fratricide”). Postol believes this time that missile defense is working, but against a very different kind of threat.

How well did Iron Dome work?

It appeared to work very well—a lot better even than the people involved in building it expected. It’s an astonishing achievement—I think it’s even fair to use the word miraculous—to be able to hit these rockets with the reliability they demonstrated.

What is the system designed to do?

It’s supposed to defend relatively small populated areas against quite primitive short-range rockets that travel 16 to 25 kilometers, typically.  It’s like somebody in Wellesley Hills [a Boston suburb] trying to shoot rockets at MIT. 

Does this mean missile-defense systems may be more reliable than in the past?

Let’s say you are batting .750 against a fastball pitcher. That’s tremendously good. But a fastball pitcher can throw a pitch at only 160 kilometers per hour. So how well are you going to do against a pitcher who can pitch at 800 kilometers per hour? It’s not a minor difference.

The actual speed of these Hamas rockets is in the range of 500 meters per second. Scuds that can travel 600 kilometers are traveling at 2,200 meters per second. An ICBM [intercontinental ballistic missile] is traveling at 7,000 meters per second, so 13 or 14 times as fast. With ICBMs, the main weakness of missile-defense systems is that they can be fooled by decoys that can be released in the near-vacuum of space and travel with the ICBM.  

Were all the rockets launched by Hamas short-range rockets?

Two rockets were of longer range–of about 65 kilometers. That gets you to the outskirts of Tel Aviv. I understand from my contacts—I don’t have primary knowledge—that one of these rockets was shot down. The other one they didn’t try to shoot down because it was going to fall in a place that was not populated.

How does the Iron Dome system work?

They have fairly capable short-range radar that measures the locations of rockets as they are fired and some advanced methods for estimating their trajectory. They have to be fast, because it could be 90 seconds from launch to impact. 

Then they fire an interceptor toward the rocket. The radar guides the interceptor until it acquires the target with its infrared sensor. Then the infrared homes in. It has to be very rapidly maneuverable. The interceptor is trying to hit what is literally a piece of pipe with some fins welded on it. This thing could wobble around a bit. So the interceptor has to detect that, and make final adjustments.

This all sounds a lot like the Patriot system that you criticized so heavily. Is there anything new in Iron Dome’s technology?

They’ve made every effort to optimize the system to be as efficient as possible and not fire at rockets that pose no threats; they don’t shoot at rockets that are not going to land in populated areas. And there are some exotic features related to real-time adjustments. If there is an indication that an interceptor is going to miss—that it’s not on the optimum track toward the missile it’s trying to hit—they have computer programs that will launch a second interceptor.

Does Iron Dome save lives?

There were some news reports where they were talking about saving hundreds of lives, but that’s a total misunderstanding of the lethality of these weapons. Before the recent attacks, some 11,000 or 12,000 rockets and mortars were launched over six or eight years, and in total, 60 or 61 people were killed.  

So if you are saving lives, it would be “several” lives. Think of a mailed package bomb—it wouldn’t destroy a building, but would do a lot of damage in a room. One of these Hamas rockets wouldn’t go through the roof of a house and bring the house down.