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Science Matters: ABM (June 26, 2006) I have been planning to launch an occasional series called Science Matters on topics in which some very basic science can cut through the welter of uninformed opinion which clutters both Big Media and the Web. Today is the first entry. Armed with only high school chemistry and physics and a B.A. in liberal arts, my hope is to leverage a typically non-expert perspective into some fresh understanding of complex subjects. Our first topic: Missile Defense 
Wait--don't click to the next blog just yet. This is interesting stuff. Whatever
your political persuasion, hopefully you recognize the threat posed by rogue states ruled
by fanatics who view the death of thousands as a glorious spiritual victory
(Iran) or callous madmen who are capable of launching nuclear weapons as part of a political
calculation of survival (North Korea).
There is merit in at least examining anti-missile defense options. Let's start by de-politicizing the issue. Some feel having a defense will trigger an arms race (as if we're not already in multiple arms races anyway) while others feel no cost is too great to protect American cities from a potential catastrophe. The issue boils down to this: can such a system actually work in a shooting war, and can we afford it? First, a bit of background. Anti-missile systems have been in the research- and-development process for decades. The idea is an obvious offshoot of anti-aircraft missiles: if we can shoot down an enemy airplane, why not speed things up and shoot down a ballistic missile? Here are the problems. The first is speed, of course--ballistic missiles are traveling at very high speeds as they descend from the height of 1,000 miles: about five miles per second. Second, they are rather small targets. Hitting a city or a ship is easier than hitting a long, thin cylindrical object, and once the rocket body has been expended, all that's left is the warhead, which is not much larger than a car. (see photo below) 
Third, there are cheap and easy ways to confuse any anti-missile defense. The warhead
can separate in space into multiple warheads (called MIRV, multiple independently targetable
re-entry vehicle), and various decoy warheads can be dispersed as well.
These factors make locating and tracking the target difficult. This is called "target
acquisition." Trying to intercept a small, very fast-moving target is often summarized as
"hitting a bullet with a bullet."
In the Reagan-era "Star Wars" missile defense scheme, this problem would be saolved by deploying space-based lasers. Five miles per second is pretty pokey compared to light's 186,000 miles per second, and so the advantage of a laser positioned above the turbulance of the atmosphere looked like a solution. Alas, there are problems with lasers. The first is that such a laser would have to be extremely powerful. Where are you going to get a power source large enough to fire such a laser? (An extension cord to space would be very very expensive and very very thick.) About the only practical way to generate such high bursts of power is a chemical laser, which can only be fired once, or at best, at intervals. And then you have the problem of such a system sitting for years in the deep freeze of space, waiting for the moment when it must work flawlessly. A friend with a physics degree and a working knowledge of lasers pointed out a simple way to counter such a laser: put the missile into a fast spin. Lasers do need some time to damage the skin of the re-entry vehicle/warhead, and a spinning warhead would diffuse the laser's concentrated light. You might peel off some of the skin or etch the surface, but the laser would constantly be hitting a new section of the spinning warhead. For these reasons, space-based lasers are impractical (not to mention horrendously costly and of unknown reliability.) The physics of missile launch define its vulerability: a missile is vulnerable when it is large, slow and emitting a huge hot plume of heat which can easily be tracked--that is, right after it has been launched, in the so-called "boost phase." The physics of rocketry also limit how fast the rocket can reach high speed (the faster you accelerate, the more fuel you use, making your rocket bigger and heavier in the process, which requires even more fuel, etc.) To cut to the chase: any ballistic rocket is a big, fat, hot, easy to track sitting duck in the first moments after launch. Nice, you say, but the bad guys are over there and we're over here. How do we nail their missile in the first few moments of flight? The answer is geography: the planet is mostly ocean. And the U.S. has the world's largest blue-water (ocean-going) Navy. Pretty much the only terrestrial launch sites which couldn't be reached by a sea-launched anti-missile missile are the interiors of Russia and China, and we have to assume the leaders of those nations have little motivation to engage in a mutually unwinnable nuclear war with the U.S. OK, but do we have ship-launched missiles which can actually hit ballistic missiles in the boost phase? Answer: we do. The key to affordable high-tech weapons is to use existing ships ("platforms") and existing missiles. And since the Navy has been working for decades to provide anti-missile defense for its large capital ships, it already has such a system in place: the Aegis Cruisers, which were designed to track, acquire and destroy the small, fast anti-ship missiles of the sort which almost sank the U.S.S. Stark some years back. (The Stark was a small ship without any anti-ship missile defense. The fleet has 69 Aegis Cruisers.) Can such anti-ship technology be expanded into a ballistic missile defense? The answer appears to be at least a qualified yes. Tests of such a sea-launched anti-ballistic missile (ABM) missile in 2003 and 2005 were successful. Inter-service rivalry is a reality that must be dealt with politically. The Air Force, rather naturally, is very keen on using aircraft to shoot down ballistic missiles in the boost phase, and the Army sees an acute need to keep improving the land-based Patriot missile defense which saw action in the first Gulf War. While these systems may well have a part, when it comes to defending the nation against rogue-state missiles, it's very clear: only ships can be kept nearby indefinitely, and only ship-based systems are capable of detecting the launch and firing the anti-missile missile in time to catch the rogue-state missile in its early boost phase. The tests of the system referenced above took about 4 minutes from the launch of the target missile (the bad guy's missile) to its destruction. What about cost? In that the Aegis radars, launchers, ships and missiles are already in service, the cost of upgrading to ballistic missile defense is on the order of $300-400 million (at least initially), as opposed to $60 billion or even higher for some space-based system (clearly unaffordable, never mind the technical objections). The argument against sea-based ABM boils down to this: all the enemy has to do is sink the Aegis cruiser, and then they're home free. Yes, but easier said than done. Recall that the Aegis' entire purpose is anti-ship defense; firing a couple of cheap anti-ship missiles at an Aegis may not work as advertised. As for submarines--rogue states don't have submarines, and in any event the U.S. maintains a robust anti-submarine defense. getting close enough to an Aegis battle group to launch a torpedo will not be that easy. Possible, no doubt, but certainly not easy or guaranteed. Most obviously: do ya reckon firing on a U.S. Navy ship is an act of war which will draw a response? Trying to sink an Aegis cruiser would certainly alert the U.S. that someone was planning/hoping to launch a ballistic missile. But just trying to sink the ship would be a declaration of war. And the ships have multiple layers of anti-missile defense, so a "just sink the Aegis" plan might fail. If you don't have a "Plan B," then that is a very high-risk gamble. And convincing potential enemies that the gamble isn't worth taking is the entire point of a working ballistic missile defense. Here are some interesting articles for further reading: A good overview of missile defense by Gen Charles A. Horner, USAF (Ret.) ship-based ballistic missisle defense A White Paper on the Defense Against Ballistic Missiles For more on this subject and a wide array of other topics, please visit my weblog. 
copyright © 2006 Charles Hugh Smith. All rights reserved in all media. I would be honored if you linked this wEssay to your site, or printed a copy for your own use.
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