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.

Discuss this Blog Entry 7

on Aug 26, 2014

Technicalities aside - which Postol admittedly is not privy to - he is probably frustrated that Iron Dome had been chosen over the Nautilus laser project that he was involved in.

His past is glorious. It really was. His present is less.

on Aug 26, 2014

Sour grapes. And while US towns and cities have no immediate worries of being showered by rockets, US financial support and partnership in Iron Dome means the technology also belongs to the US if ever needed.

on Aug 26, 2014

We can be grateful that in the United States we have not needed to check this out for ourselves. Those of us in Michigan are not having rockets rained down upon us from Canada. Imagine that.

on Aug 26, 2014

The man is making many mistakes as to the nature of the intercepts and the varying qualities of kill effector and fuzing.

On the AIM-120C7, we are looking at both the potential of very high rate terminal closure states between supercruise (F-22 @ 1.3 Mach) boosted weapons and threat jets that are at least at .9 Mach, and at very uncertain closure states against low RCS threats like cruise missiles where the need to see flank-side aspects to pull the targets from the clutter results in a low doppler shift for both primary tracking and warhead detonation. The variable PRF/PRI of the AIM-120s monopulse antenna can generate angular deflection states which indicate (via rate gains) the relative terminal closure threats, especially when it is as a result of a '3D' relative track state supplied by both onboard IMU and potentially, assisted TVM guidance updating from the APG-77 or similar.

At a given point -before- this happens, one or two things will occur: Either the weapon will initiate a sacrificial HPM mode where the TWT removes all limiters to create a maximum 300-500KW focussed output needed to disable the target's FLCS/Seeker through ungated apertures.

Or the weapon will straighten up from lead collision to direct-point and fire a directional warhead through the seeker mechanism to ensure a weapon+explosive equivalent fragment pattern that may well be over 3,000m/sec.

Such 'seeker linked' fusing systems have been with us for quite awhile, principally as a compensation for fusing limitations on aspect from simplistic fan-type laser or RF based fuses.

If you look at Trophy demonstrations on Youtube, you can see that a large component of the weapon function is to _knock down_ inbound RPG etc systems with a fuze defeat rather than a hardkill, for purposes of securing the immediate area around the vehicle which may be occupied by friendly forces. Indeed, the warhead casing is often recovered. This can only be if part of the wardet process is in fact based on some type of overload of the piezo-electric fusing (a surface detonation of a 'tipped' RPG warhead would otherwise still have serious blast and fragmentation risk to both vehicle chassis and tires and infantry in the protected zone of the APS).

Iron Dome likely has to pay a sophistication vs. saturation penalty in it's siting densities. Which is to say a fairly sophisticated IMU and RFCG steering system vs. the cost of a true seeker ala David's sling.

What this means is that the missile stays dumb and the guidance electronics remain attached to the ground unit which tracks BOTH threat and target, commanding the missile to a given point in space where it 'holds', via corkscrew orbits, until the threat comes into acceptable engagement geometries.

This will mean a bigger motor for an earlier/faster launch but even sophisticated motors are cheap compared to guidance chips.

Once the weapon is airborne and at speed/height, it has more options for trajectory mechanic to create a positive intercept geometry.

The big question then becomes whether the missile uses some form of spiral or conical scan laser dither as part of it's fuzing event or relies on the ground tracker (which will have the benefit of seeing a missile beacon in all likelihood to help discriminate position and IMU driven time synchs) to create proximal detonations.

EITHER WAY, if the warhead is in fact a shaped charge, sending a directional stream ahead of the missile, along with perhaps a pulsed microwave event to overwhelm the weapon fusing, weapon:target aspect and closure rates can be based upon the sophistication of the ground based tracking algorithm sophistication as as a function of signal and data processor scrubbing of the trackfiles from much earlier on in the terminal commit.

In such a case, you are more concerned with doppler and phase state crossing angles between what may well be MULTIPLE emitter sites using networked tracking to provide best possible lead solutions to include (yes) hard crossing angle and even overtake shots.

Where there are not physical launchers sufficient to address gaps in the coverage (this will in turn depend on whether you are trying for early or late intercept).

Now, imagine you have supersonic projectiles (1,210m/sec = Mach 3 though I personally would imagine this to be much more likely to be in the range of 1.5-1.8 due to manufacturing variables and zero-stabilization response to buffet increasing profile drag) falling to earth. If one hits a roof on a three story building with a slight delay in it's contact or electronic fuze, it's going to drill all the way to the basement which is the ONLY place an Israeli could possibly reach in the 10 second minimum time requirement for close in rockets. Without double A-frame roofs/floors with blast voids to slow and then redirect the projectile into harmless detonation channels, even a light Katyusha/Grad type rocket can thus be devastating simply because you have clustered all your targets into a contained area where there is no possibility of survival.

But what happens if you tumble that inbound rocket? First, if it's got a primitive fuze, it may mistake the sudden sidefore acceleration increment of missile body breakup as an impact event and go off in mid air. But even where it doesn't do so, the result is inevitably that it has MUCH LESS accuracy of ballistic flightpath and strikes with much less certainty of penetrating even low hardness, structural, targets.

This matches well with the few fatalities known to have occurred: One a man caught out in the open without time to reach a shelter and another a trio of casual voyeurs on a balcony hoping to see the Iron Dome in action.

Go ahead and blow the roof off the house. Even take out the upper stories as sacrificial 'spaced armor'. But so long as the warhead doesn't bus into multidart penetrators, every intercept by the Iron Dome is going to result in basically surface level detonations which do nothing to harm the people.

From my own perspective, the Israelis are making a simple mistake:

1. Use ID or similar, very high energy, randomly relocateable (vehicle mobile) interceptors to achieve fallback kills within the Palestinian territories. This means the need for a VERY high energy (Mach 6+) interceptor, and/or a dedicated UAV overwatch system to catch the preparations in play but it can be done. APWKS or similar light-SALH suppression might also be possible.

2. Back the mechanicals with DEWS based on MTHEL with slab SSL technology. Preferably from median/midcourse points which have sufficient coverage (5-7km reach in CAVU for MTHEL) to allow for individual 'laned' intercept coverage of major settlements from just a few sites. This is your guard against chemical or bussed warhead designs.

3. Use true APS, again on vehicle mounts to provide random massing capability but also potentially on rooftops of larger structures, to provide terminal destruction of warheads. Modern APS are not simply limited to subsonic ATR/ATGW they have increasing amounts of KE defense capabilities. And because they can be designed to detonate high angle threats without worries about collaterals or unintendeds, they can be _very densely populated_ through high risk areas.

The above will not remove the necessity for Israeli duck and cover + shelter seeking survival mechanisms. But it will greatly alleviate the structural loss economics and the potential of exotic warhead and UXE hazards.

on Aug 27, 2014

Apparently Israel has built a high turn rate aero-missile. This may be a world first for the aerospace people. Automobiles, trucks and tanks have been doing this for generations.

on Aug 27, 2014

Having spent a lot of time in a previous life in the world of missle acquisition and destruction, I very much appreciate the discourse provided by MandS - Thank you
And a hearty Thank You to everyone else for focusing on the technical aspects of this issue and leaving the political issues for a different forum.

on Aug 27, 2014

Israel needs to tip the Iron Dome rockets with Californium-254 so as to have a yield of only 10 kilotons and Hamas can chew on some radioisotopes in their beards.

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