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    The Proof is in the Pie

    0 תגובות   יום שבת, 16/8/14, 20:47

    לפני שבועיים התפרסם (שוב, יש לומר) מאמר של הפיסיקאי האמריקני Ted Postol, שחזר על טענתו (מ- 2012, בעקבות "עמוד ענן") ש"כיפת ברזל" אינה משיגה יותר מכ- 5% הצלחה. 

    מאמרו התפרסם הן ב MIT Review ושבוע אחר כך, ב-  The Bulletin of the Atomic Scientists. 

    שלחתי לעיתון מאמר תגובה משלי, אך לדאבוני - הוא נדחה על ידי העורך. 


    הרי המאמר - ככתבו וכלשונו (נכתב במקור באנגלית)


    Iron Dome – The Proof is in the Pie

     Yiftah S. Shapir


    As soon as a new round of heavy rocket fire began showering on Israel, and the media started reporting on Iron Dome's successes – we began hearing that Iron Dome is a fake. This time the Bulletin joined the choir with Prof. Theodor Postol explaining us why Iron Dome is not working. This is not new. Iron Dome had many opponents from its very humble beginning back in 2005. The IDF did not want it, and did not think it necessary.  Supporters of different systems were very vocal in denouncing the very concept behind Iron Dome – claiming, of course, the superiority of their proposed system. (Supporters of the THEL – The chemical high energy laser which was developed in Israel since the mid 1990s and abandoned in 2007 – are still very active in Israel). It needed the terrible experience of the Second Lebanon War, with a barrage of some 4000 rockets, and the strong will of Mr. Peretz – a minister of defense who resided in Sderot – a town in the south part of Israel which was under constant Qassam rockets from Gaza since 2001 – to initiate the fast paced development of the system. Iron Dome entered service in 2010, and soon announced its first successes – but the opposition was still vocal. Iron Dome's first real test took place in November 2012, during Operation Pillar of Defense” (November 14 to 22, 2012). According to the official announcement – during the operation 1506 rockets were fired on Israel. 875 fell in open spaces and were not engaged by the system. 152 were defined as “failed launches”. Iron Dome downed 421, and 58 rockets fell in built up areas, causing 245 casualties, of which 5 died. This meant that according to the official data Iron dome achieved a success rate of 84%.1Soon after “Pillar of Defense”, and the public hype over “Iron Dome” we began to hear that what we were deceived. Prof. Postol, who gained fame for exposing the failure of the “Patriot” air defense system in shooting down the “Al-Hussein” missiles from Iraq during “Operation Desert Storm” in 1991 – analysed the contrail of Iron Dome intercept (many of which were uploaded to the web by Israelis witnessing the intercepts), and came up with the conclusion that Iron Dome had a success rate of no more than 5%.  Prof. Postol's conclusions were published in Israel mostly by the late Reuven Pedahtzur – a journalist and researcher who was a harsh critic of Israel's missile-and-rocket defense systems for many years.2  A second critic was Dr. Mordechai Sheffer – a former senior engineer in Rafael (the producer of Iron Dome) who claimed that Iron Dome's rate of success in absolutely zero.  Both Prof. Pstol and Dr. Sheffer repeated their claims during the first weeks of “Defensive Edge” in July 2014. The critiqueProf. Postol's paper explains in detail why a rocket must be intercepted on a head-on trajectory – otherwise the rocket's warhead cannot be destroyed. He then goes on to his analysis of Iron Dome's contrails and comes to the conclusion that Iron Dome's interceptor usually tries to intercept the incoming rocket from the side or from the rear – geometies in which it has very low probabilities to destroy the warhead. Prof. Postol goes further as he has to explain the low number of casualties since Iron Dome entered service. Basically – he attributes it to Israel's alarm system that allows civilians to enter shelters. 

    It is true that Israel alarm system improved considerably. The country is now divided into several hundreds zones, and alarms are sounded only in the threatened zones.  And people do seek shelter whenever the alarm is sounded.  However – Israelis in general feel safe, even though the country was under repeated attacks.  By the time this paper is being written more than 2600 rockets were fired but there were only 4 dead civilians from them3 (but many more from short range mortar fire!!). The “standard procedure” for civilians in Israel, whenever the sirens are sounded is – go to the shelter, listen until you hear the boom – and go on with your business. (the homefront command recommends staying at least 10 minutes in the shelters. Very few civilians comply).  It is annoying but people feel safe. In particular – since there are hardly any reports about real damage. Not only there are hardly any casualties – there are very few cases of real damage to property reported.  Rockets have been fired on most major cities in Israel. But there was no damage in any of the major cities in Israel – and even in towns closest to Gaza (such as Ashkelon) there were very few damaged properties. Did Prof. Postol got it wrong? Apparently – yes. He did get it wrong. I can only guess where was his mistake. It is clear that most of his thesis is correct. Rockets must be intercepted head-on.  But analyzing the actual intercepts from video footage is very difficult. We are speaking of analyzing a 3 dimentional event from a 2 dimentional video footage. It is very easy to confuse actual directions.  Moreover – you cannot actually see the intercept itself. You can see the Iron Dome's interceptor's contrail – but you can't see the incoming rocket – since it is, at this stage, a motorless pipe in the sky. It is also very difficult to distinguish between the explosion of the rocket's warhead and the Iron Dome's warhead – they are seperated by a very short distance – and a very short time interval.  Assuming that Rafael's engineers are no fools, and assuming they understand the intercept probabilities in each intercept geometry just as Prof. Postol does – we can assume that Iron Dome does attempt to intercept the rockets from a head on geometry. Interestingly enough – trying to achieve this geometry would require a very similar sharp turn before the intercept – just as would be required for a chase geometry (but inverted, of course). 

    But all this is discussion is moot, as far as the Israeli public is concerned.  Whether Prof Postol's critique is founded or not – for the public the proof was in the pie4





    The official data did not say how many interceptors were fired at each rocket. This is important: if two interceptors are used against each rocket – the success rate would be 42%, not 84%. In fact just as the system chooses which roclet to engage – and which one not to engage – can choose how many interceptors should be fired – according to the value of the rocket's intended target. I would estimate the ratio to be somewhere between 1.1 – 1.2 interceptors per rocket. 



    Reuven Pedahtzur died last April in a highway accident. I was well acquainted with Reuven and although I opposed his views I always appreciated him as a sincere and serious writer. 



    During Pillar of Defense there were 3 oprerational Iron Dome batteries (and a fourth entered service during the operation. Defensive Edge began with 7 bateries, and two more were introduced hastily since the beginning of the operation. 


    A word should be added about the other critique – Dr Sheffer's. Dr. Sheffer is a distinguished engineer with a lot of experience in missile design,  and he is deeply convinced that the Iron Dome's interceptor just cannot intercept any rocket. However – he, too, had to explain away the results. He did so with an elaborate conspiracy theory, according to which 3 - 5 engineers inside the industries responsible for Iron Dome secretly introduced a computer code into the system's software which produces fake rocket tracks which are then intercepted by real Iron Dome interceptors – thus creating a large rate of success. According to Dr Sheffer – these few engineers fooled everyone – including the Ministry of Defense, the IDF, the system's operators, as well as the USA who funds the project. I would just say that it is extremely difficult to accept such a theory  seriously. 

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