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The Patriot Missile Failure

152 pointsby AndyBakerabout 11 years ago

22 comments

dmouratiabout 11 years ago
In 1993, while in college, I wrote a paper about the fallacies of the Patriot Missile effectiveness. What I learned in writing it was that the so-called accuracy of the Patriot was grossly exaggerated. The mainstream media, and indeed the country, needed some symbol to rally around and the Patriot Missile became that symbol. The battery&#x27;s very name started the process.<p>The US touted a 95% accuracy.<p><a href="http://www.slate.com/articles/news_and_politics/war_stories/2003/03/patriot_games.html" rel="nofollow">http:&#x2F;&#x2F;www.slate.com&#x2F;articles&#x2F;news_and_politics&#x2F;war_stories&#x2F;...</a><p>In reality, a &quot;success&quot; didn&#x27;t mean disarming the scud. It meant flying on a trajectory sufficiently close to the scud to have disabled it if all else worked as designed.
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snacktimetodayabout 11 years ago
As an Israeli who lived through the Gulf War and served in the army, I can attest that the patriot missile was a success and massive failure at the same time. It was better than nothing, let me just say that.<p>The problem was that we knew it had issues, complained many times, but it was tied up in politics. We wanted to develop and deploy our own missile defence systems for a long time, but in many ways we were more or less blackmailed into spending the defence loans we receive to pay back the American defence establishment. The message was take what you are given and enrich private American companies, or else (btw for the haters, we must spend our &quot;aid&quot; with companies like Lockheed, Raytheon, Boeing, etc., it does not go to anything else at all, so really it&#x27;s your tax dollars shilling your military industry).<p>Anyway, I saw first hand Patriot misses and the fear after that, especially regarding chemical weapons. A huge part of the country spent time with gas masks and plastic in safe rooms during the gulf war. At the end of the war, we felt like our leaders failed protecting us sufficiently, especially when they knew there were issues.<p>The interesting outcome is this directly lead to various missile programs including kipat barzel, arrow, spider, and others. Before, missile defence was a much harder sell, but the aftermath of patriot failures raise the case that again as a country we had to be more self-sufficient regardless of the cost. The other reason of course is that the Americans never really had an offering that assessed needs such as short-range, low flying projectiles, rockets, shells, multiple-target tracking, etc. Today, we have arguably the most advanced short-range and tactical missile defence systems.<p>All of these systems are built heavily on targeting&#x2F;guidance and to run on cheap hardware that can fail massively. The interceptors and computers are not necessarily cost effective and super expensive, but much more practical. Additionally, redundancy in terms of overlap of targeting errors and misses is a heavy part of deployment. Resource-wise, it&#x27;s not always possible, but I know first-hand it is a combination of various operational failures of the Patriot combined with years of relentless attacks by our enemies using anything from glorified flying garbage to old Soviet tech.
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angersockabout 11 years ago
For most of the whiz-bang web apps being written today, this sort of thing doesn&#x27;t matter.<p>Every so often, though, working on embedded devices or medical software or finance stuff, it becomes really important that you remember that lives depend--in a non-trivial and quite real way--on your code being correct and on the implemented algorithms fitting the problem.<p>Something that&#x27;s very tricky isn&#x27;t just understanding that the code does what it says it does, but that the code implements a solution that is properly modeled to the problem at hand.<p>EDIT:<p>My background is in mechanical engineering, and I never forget this quote by Dr. Dykes:<p><i>&quot;Engineering is the art of modelling materials we do not wholly understand, into shapes we cannot precisely analyse so as to withstand forces we cannot properly assess, in such a way that the public has no reason to suspect the extent of our ignorance.&quot;</i><p>Software engineering in life-critical applications is serious business.
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jug6ernautabout 11 years ago
While Science Fiction and not directly related, one of the Tom Clancy novels went into the Science of missile intercept pretty extensively(was a very important part of the book.<p>This book brought to my attention the mathematics and for lack of a better term difficulty of having a missile intercept system. Not only the mathematics but the but the raw limitations of physics that must be dealt with. In the case of the book it was ICBM&#x27;s which travel much faster, 7 km&#x2F;s (15,700 mph)[1], compared to the 3749.11 mph of the skud missile.<p>For anyone interested the book is Tom Clancy - The Bear and the Dragon.<p>[1] <a href="http://en.wikipedia.org/wiki/Missile_defense" rel="nofollow">http:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Missile_defense</a>
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danbrucabout 11 years ago
This makes no sense in the way it is stated - the calculations involved are independent of the up-time. You do not aim at a target differently depending on how long the system is up. The correct way to think about this is probably the following - they noticed that the up-time drifted and tried to improve on that, but they failed to do so in all places. In consequence different parts of the system used different times that also advanced with differing speeds and this inconsistencies caused the calculations to go wrong. As mentioned in the article, would they not have made the &quot;improvement&quot; all parts would have used the same time and the errors would have canceled because the calculations are time-independent and the drift is probably to small to be important during the relatively short time a target approaches. This seems one of the rare cases where blaming math with limited precision is wrong.
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fiatmoneyabout 11 years ago
What&#x27;s interesting is that this is the kind of thing where a standard &quot;boot-and-test&quot; routine is likely to miss it (because the clock starts out in sync). Time-dependent bugs are always tricky.
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bradleyyabout 11 years ago
I was an 18 year old grunt, fresh out of basic training, when I went to Iraq in 1991.<p>After about 48 hours of living on tarmac at the airport (where I experienced the first of many MOPP-4 chemical warnings: let me tell you how fun it is to have a gas mask, charcoal suit and rubber accoutrements while laying on tarmac, psychosomatically creating the nerve agent symptoms they just taught us), I moved to the a high-rise apartment complex.<p>I was in a North-facing room, on the northernmost edge of the complex. Open desert as far as the eye can see to the North. I watched scuds get shot down (seems like every night, but memories are wont to be inaccurate).<p>Here&#x27;s the thing: I hear all this talk about the Patriot missle being inaccurate, and I seem to remember something like &quot;no patriot ever shot down a scud&quot;. That takes some serious parsing to arrive at-- because I saw patriots &quot;hit&quot; scuds, but of course they could have &quot;exploded in the vicinity of&quot; scuds, destroying them.<p>From what I hear, the Patriots were running on 100-mile-an-hour tape (you did know that the military has its own version of duct tape, right?!) and bubble gum, but I&#x27;m thankful for them nonetheless; you tend to take what defense you can when folks shoot at you.
madengrabout 11 years ago
Even if it didn&#x27;t fail (numerically), there is a decent probability it still would have failed to intercept the scud:<p><a href="http://en.wikipedia.org/wiki/MIM-104_Patriot#Success_rate_vs._accuracy" rel="nofollow">http:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;MIM-104_Patriot#Success_rate_vs...</a><p>The U.S. Army claimed an initial success rate of 80% in Saudi Arabia and 50% in Israel. Those claims were eventually scaled back to 70% and 40%. However, when President George H. W. Bush traveled to Raytheon&#x27;s Patriot manufacturing plant in Andover, Massachusetts, during the Gulf War, he declared, the &quot;Patriot is 41 for 42: 42 Scuds engaged, 41 intercepted!&quot;[28] The President&#x27;s claimed success rate was thus over 97% during the war.
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bronsonabout 11 years ago
The devops fix? Reboot every night. Works wonders. :&#x2F;
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briantakitaabout 11 years ago
Here&#x27;s a post mortem report sent to the House of Representatives:<p><a href="http://www.fas.org/spp/starwars/gao/im92026.htm" rel="nofollow">http:&#x2F;&#x2F;www.fas.org&#x2F;spp&#x2F;starwars&#x2F;gao&#x2F;im92026.htm</a>
boiler_up800about 11 years ago
We talked about this in my microcontrollers class today! Not this exact incident but about the problems associated with using the system clock in a micro for precise timing.<p>Our micro (Freescale HC9S12) is clocked by a 24 MHz crystal quartz oscillator and if you use the timing module to clock the micro, you cannot get exactly 1ms, 10ms, etc. This makes summing the time over a long period tricky.
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allochthonabout 11 years ago
I&#x27;m not that knowledgeable about hardware, but the fact that they were using a &quot;24 bit fixed point register&quot; sounds like they were not using a commodity processor, even for 1991. I assume that the error described would simply not arise today on a modern CPU running Linux?
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dicroceabout 11 years ago
If the time was in tenths, why would you multiply it by 1&#x2F;10 to get seconds? Shouldn&#x27;t you be multiplying it by 10 to get seconds?<p>update: Ahh, I get it. You&#x27;d need to divide it by 10 to get seconds.
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6d0debc071about 11 years ago
&gt; Ironically, the fact that the bad time calculation had been improved in some parts of the code, but not all, contributed to the problem, since it meant that the inaccuracies did not cancel.<p>-----------<p>I wonder what trade-off informed their decision not to have the time code in one place and pass it around as they needed it. Or at least defined in one place and then inserted where they needed it if there was some requirement that it be right there in the functions that wanted to know about time.<p>:&#x2F;<p>Just seems a danged odd thing to do.
singoldabout 11 years ago
And I didn&#x27;t want to take that Numerical Methods course...
adolgertabout 11 years ago
There&#x27;s an algorithm to deal with this kind of additive small error, the Kahan Summation algorithm. It keeps a second number to record the residual of an addition so that adding something small to something large doesn&#x27;t go awry. With modern floating point, it&#x27;s rarely an issue, but with a mere 24 bits, I guess it was a terrible problem.
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danbmil99about 11 years ago
I had a very similar bug in some software I wrote and used to perform in a band. The upshot was that everything worked fine at soundcheck; 6 hours later, the tempos were off by about 8%, and varied pseudo-randomly during each song.<p>The fix was to switch from float (24 bits precision) to a long int (32 bits), and to reset all the relevant vars between songs.<p>Fun times!
brucebabout 11 years ago
What is next? Iraqi soldiers didn&#x27;t take babies out of incubators as Congress and the American people&#x2F;world was told?<p>Oh yeah, that was a lie also. <a href="http://en.wikipedia.org/wiki/Nayirah_%28testimony%29" rel="nofollow">http:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Nayirah_%28testimony%29</a>
abruzziabout 11 years ago
Dumb question, but could you solve the problem by simply using 1&#x2F;16th of a second, not 1&#x2F;10th?
caycepabout 11 years ago
I&#x27;m impressed the GAO investigators got into pretty technical detail.<p>For a government agency, I know the GAO reports are generally considered objective, and nonpartisan. For politico experts - how has the GAO managed to not go, say, the way of the EPA
systematicalabout 11 years ago
Next time I have a &quot;bad&quot; bug I&#x27;ll try and remember this.
midas007about 11 years ago
So if one happens to own or operate an early Patriot battery, wait until the last possible moment to fire it up so accuracy doesn&#x27;t go to shit. Wow. Engineering maths fail.