Iron Dome -- Are The Critics On Target?

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In the aftermath of the latest Gaza conflict, long-time missile defense critic Theodore Postol has repeated his assertions that the Rafael Iron Dome anti-rocket defense system is ineffective, missing 95 percent or more of its targets, contrary to Israeli claims that “the 84 percent success rate achieved in the Gaza war of 2012 has improved to 90 percent in the current conflict.” Despite the fact that the rockets have indisputably caused little damage on the ground, Postol accuses the Israeli government of “extended deception.”

Postol’s most recent piece can be found here. The core of his argument is that the Tamir interceptor missile will not destroy the warhead of an incoming rocket except in a narrowly defined engagement geometry:

To have a realistic chance of destroying an artillery rocket's warhead, an Iron Dome interceptor must approach the rocket from the front—in fact, almost directly head-on. And for all practical purposes, an Iron Dome interceptor has no chance of destroying the warhead if the interceptor engages the rocket from the side or from the back.

Postol cites photography of contrails from Iron Dome intercepts that, he says, shows that “most of the system's interceptors have either been chasing Hamas rockets from behind or engaging those rockets from the side.” Therefore, he argues, the system cannot work, and he credits better warning rather than active defense with Israel’s low casualties.

The contrail analysis is problematical: In any photograph, the distance from the smoke trail to the camera, the difference between the viewing angle and the bearing of the fly-out path, the effective magnification (hence foreshortening), and the elevation angle of the view are all unknown, but all are factors in determining how a three-dimensional scene is projected onto a two-dimensional focal plane.  For example, if the camera is close to the launch point, the trajectory will be foreshortened and low-g spirals will look like tight loops.

There is one bigger problem, however. Although Postol calls the statements quoted above, about the Tamir’s effective engagement envelope, “two connected facts”, they are assumptions. They are not verifiable and if they are incorrect Postol’s argument falls apart, even if he has the trajectory right.

The detailed design of the Tamir missile is classified. Postol’s sketches in the Bulletin assume that the weapon has a laser proximity fuze that looks forward by a small angle (defining a wide cone around the centerline) and that the fuze instantly detonates a radial-pattern warhead.

But if the Iron Dome system uses ground radar tracks (giving the target’s velocity) and the missile seeker to compute the engagement geometry, it would be feasible to introduce a variable delay between detection of the detonation, which would deal with a number of Postol’s “no chance” geometries.

Postol bases his lethality estimates on the unverified  assumption that the warhead forms a uniform toroidal fragment pattern. Rafael has referred to a “special warhead” for Iron Dome. In a 2009 interview, a Rafael executive said that it was “not enough to hit the target, you have to totally destroy it.”

Rafael has developed a specialized kill module, designed to destroy a rocket-propelled grenade warhead, for the Trophy active protection system. It produces a cone-shaped salvo of explosively formed projectiles. Photos of the Tamir interceptor show that (like the Python and Derby air-to-air missiles) it has dedicated roll-control vanes and could in theory roll to aim a Trophy-type directional warhead at the target.

In a separate document, Postol says that “Rafael has made public 2 Iron Dome Warhead Arena tests and descriptions of the explosive weight and rocket types to be killed. This information reveals how the Iron Dome warhead was designed.” Postol provides no link to these revelations and Rafael says that it has not made any such information public.

Postol goes on to say that “it is clear that the Iron Dome radar tracking and guidance system is not working as it should work”, but (again) this is an assertion, not a fact: the system may just not work the way Postol thinks it should work. For many reasons (including wind and manufacturing irregularities), the system won’t be able to predict the trajectory of a rocket precisely, and will guide the interceptor into a “basket” where its seeker can detect the target and guide the endgame maneuver.

Postol’s imagery shows that the interceptor is powered all the way to impact and is capable of performing endgame maneuvers. Why is it not possible that this is how the system is designed to work? Postol does not consider this, nor does he attempt to explain why it would have such a capability, combined with a fuze and warhead that would be ineffective other than in a simple head-on engagement.

“If the IDF wants to make a public claim of a much higher intercept rate then it can and should provide the data to prove its claims,” Postol asserts. However, it’s hard to see what data would be considered convincing, without revealing so-far-classified details of truly sensitive system elements such as interception parameters and the design of the interceptor’s fuze and warhead.

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