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June 26, 2009

The devil is in them

Information Dissemination identifies an alarming technical detail of an anti-ship ballistic missile (ASBM) reported to be by mainland China; second stage control fins which would make this a ballistic missile without a fixed trajectory.

Why does this matter? Because open source information sources describing AEGIS ballistic missile defense note that AEGIS calculates intercept based primarily due to launch trajectory, and I'd bet your paycheck that when the PLA Strategic Rocket Forces realized that, they knew that if they could make a mid-course correction during flight, they would invalidate the AEGIS BMD capability.

You see, if the launch is accurately detected, trajectory can be determined based on the launch. When we shoot our SM-3, because ballistic missiles have a fixed trajectory, our interceptor knows where the missile is going to be and can intercept it.

But if a ballistic missile changes course in flight, our AEGIS BMD interceptor finds itself in the wrong place, because it calculated the intercept based on the initial trajectory, not the new trajectory following the mid-course change.

This technical detail is why I call bullshit with the Navy's suggestion that we have a critical need for more DDG-51s specifically for ballistic missile defense. The Burke is not capable of intercepting this ballistic missile, and we are going to need a new radar that can track the mid-course change accurately, and new software to very quickly do the math for identifying a new intercept point if we are going to defeat this weapon. That is going to be enormously expensive, which is why when I say I think the Navy is going to need $6 billion nuclear cruisers if they are going to evolve ballistic missile defense towards 21st century threats, I'm not kidding.

Update: Chris Taylor responds via email.

I am reading that Information Dissemination post and it is causing me to scratch my head... We've had gimbaled thrust since Goddard proved the concept in 1937, and they've been integral to US ICBMs since the 50s. Surely the idea of inflight course changes has ah, advanced a ilttle since then? It's not like other things (ships, airplanes, tanks) stay still when other sorts of warheads get lobbed at them. Granted, they go a little slower (Mach 3-6, vs Mach 10 for a ballistic booster).

We could always use that other integral part of AEGIS BMD, the ability to intercept targets in the terminal (i.e. final) phase, rather than an earlier phase (like midcourse). In other words, wait until after the second stage does it manouvre, then plonk the warhead. It just means you probably won't get a lot of second chances; the first volley has to matter.

Also, the missile doesn't have to do much in the way of target search. You can have some dopey trawler or sub shadow the target and give you a halfway-decent lat/long fix. In the sixteen minutes it will take for the ASBM to reach its target 3000km distant at mach 10, a carrier is not going to move a few hundred miles at 30 knots max speed. It will move 8 nautical miles at best. What are the odds you can develop a seeker/terminal guidance sensor small enough to fit into the 1.4m diameter of a DF-21 ASBM, but big enough to have a search range of say, 16nm? 1.4m is big enough to put a fullblown F-22-style AN/APG-77 AESA array (0.98m diameter) in there with a detection and targeting range of 125 nm.

I dunno what to make of it really. None of the concerns he has raised seem to be insurmountable technical challenges for either side.

Another update: I should explain my comments system appears to be having some sort of indigestion. Consequently, I am posting another response via email; this from Armored Facilities Manager.

From what I understand of the open source material, the Aegis system in fact relies on directing separate beams of Radar at the target which, by reflection cue the missile to the target terminally.

Initial trajectories will be off, but if the Ballistic missile is launched at the Surface Action group itself, then there will be very little ballistic correction to make.

I have to wonder whether SM-2 would in fact do the job neatly.

The other aspect is that the guidance is mostly software. I doubt that the folks at Hughes are sitting on their backsides NOT coming up with tweaks to effect positive intercepts of a maneuvering terminal ballistic missile were there a problem.

Note, SM-3 intercepted a satellite which was in effect maneuvering a touch due to atmospheric effects on it's irregular shape. They HAD to do final calculations to get the hit to kill warhead on the satellite.

Posted by Ghost of a flea at June 26, 2009 06:53 AM