Geoff FordenPCS #1: Jet Vane Hypothesis

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Iraqi destructive quality control test on jet vanes using two different imported batches of graphite. See UNMOVIC’s Compendium, Chapter IV, pp. 739-740.

As any regular read of my posts on ACW will know, I have a love/hate relationship with jet vanes. That is partly why I was so attracted to the hypothesis that the Iranian furnace that is the subject of this proliferation case study (or PCS; you have Theresa Hitchens to thank for my over-use of acronyms) is used for their production. Yesterday, I considered the hypothesis that the furnace shown in the video on the production of the Iranian Safir rocket was used for brazing together the inner and out shells of the Safir’s liquid propellant engines. Today, I want to take up the alternative hypothesis, that the furnace is used at some step in the production of graphite reinforced ceramic composite jet vanes. But first some background.

Historical Examples of Production Problems

The image above shows Iraqi fabricated graphite jet vanes used in a static test of the Al Samoud II, which uses a single SA-2/Volga liquid propellant engine. But they were not totally indigenous. In particular, Iraq was not able to manufacture the graphite but instead imported graphite blocks that it then machined into shape. This test, where vane material imported from one country were compared with vane material imported from another, was intended to show that the quality (density? purity? monolithic integrity?) from one source was not sufficient to allow them to be used for jet vanes. The two jet vanes of the acceptable batch survived the test while those from the country that exported the unacceptable batch completely failed. They could have failed for any number of reasons, all of which might fall under the heading of thermal shock or corrosion. The interesting thing, though, is that Iraq was apparently not able to test this quality nondestructively. That implies that they had not issued, and probably not able to issue, a specification that could have been used for the graphite manufacture and quality acceptance. We can conclude that Iraq’s pre-existing knowledge, to borrow a term from tomorrow’s posting, was not very great.

Jet vane suitable for use in solid-propellant rocket exhaust made from carbon-ceramic composites.


If, as rumored, Iran is using carbon-ceramic composite jet vanes, then they have opened the door to a material that is much, much more resistant to thermal shock and oxidation etc. than simple graphite jet vanes. In fact, they could be using the same type of jet vanes for both their liquid propellant rockets and the Sajil solid-propellant missile if they use what is know as Chemical Vapor Deposit (or CVD) using silicon and carbon, SiC. Jet vanes for solid propellant missiles operate in a particularly difficult environment considering the eroding effects of molten aluminum blobs hitting the vanes. If the Iranians are manufacturing their own, then they have almost certainly assimilated an important adjunct technological base. (Again borrowing terminology from tomorrow’s post.)

Details of Jet Vane Production Process

Let’s assume, for the moment, that they are using CVD-SiC. What would that production process look like? First, the vanes would not have to be manufactured in a single step. In fact, they almost certainly would be manufactured in two or more steps. The first steps could be grouped together as fabricating the fiber “pre-form,” which have essentially the final shape of the jet vanes. Since these vane pre-forms are fairly complex shapes, they are probably formed in high pressure/high temperature molds. This is not the step that is shown in the video. The next step could be to remove the pre-form’s temporary matrix, essentially burning it out by a process known as pyrolysis. This could be the step shown in the video but it is more likely that the video shows the next step, deposition of a ceramic matrix in the place of the temporary matrix removed in the last step. This step most likely involves, especially for complex shapes, placing the pre-form in a very low pressure atmosphere of methyltrichlorosilane (MTS or ) with hydrogen as a “carrier” gas. This is typically done with temperatures between 800 to 900 degrees C and pressures on the order of 0.1 atmospheres. This explains the cylindrical shape of the furnace “insert:” it supports the nearly one atmosphere pressure outside the cylinder. (See Chapter 6 of the Handbook of Ceramic Composites.)

The typical temperatures are lower than we determined yesterday for the furnace but not excessively so. Interestingly, based on the ribs on the end caps of the cylinder, it is clearly intended to support a pressure difference between the inside and outside. However, the outer rim of the cylinder, which has little reinforcement, indicates that the pressure difference is probably no greater than a single atmosphere, consistent with the vapor deposition parameters.

This doesn’t prove that the furnace is used for producing jet vanes; only that it is consistent with that use. We will continue this discussion on Thursday, when we talk about Iran’s pre-existing knowledge related to composites. However, we will need some theoretical background before that; background that I will present tomorrow as the theoretical underpinnings for how successful proliferators acquire the know-how to produce technologically sophisticated WMD and the means to deliver it.

This series of posts consists of:
0) Do You Know What This Thing Is?

1) Iranian Furnances

2) The Jet Vane Hypothesis

3) The How of Proliferation, Part 1

4) The How of Proliferation, Part 2

5) Iran’s Composites Infrastructure


  1. JR (History)

    Is there any chance that they could be using a less sophisticated jet vane composite — say, carbon with an evaporative/ablative copper matrix?

  2. John Blankenbaker

    I’m no expert, but when I looked at the before and after photos of the jet vane test what struck me was that the vanes that failed had a different mounting bracket than the ones that didn’t fail. Notice in the first photo that the top and bottom vanes are sitting in white (ceramic?) brackets, while the left and right vanes seem to be in black (graphite?) brackets.

    The after photo would seem to be rotated 45 degrees (notice how the golden flange thing has moved), which means that the white bracketed vanes are the ones that failed. But it could well be the brackets that failed, not the vanes.

    I’m not sure that my interpretation negates your analysis, but if the test was really comparing different mounting brackets, I might take issue with your statement “they had not issued, and probably not able to issue, a specification that could have been used for the graphite manufacture and quality acceptance”.

  3. Geoff Forden (History)

    I dont think that is the case. I think the white patina you see is paint or something else merely on the surface. Also, during static tests, Iraq would move the jet vanes around, simulating a pitch or correction program, so I wouldn’t put too much emphasis on the either the directions they appear in either the before or after pictures.


    I want to emphasize that I haven’t proved that Iran is using fiber reinforced ceramic composites for its jet vanes. At most, I’ve shown the video clip is consistent with indigenous production of that type of jet vane.

  4. Jochen Schischka (History)

    Hmmm, i don’t know, Geoff, maybe John Blankenbaker has a point here;

    Compare the position of the turbine-exhaust in both photos; it’s definitely the two jet-vanes with the lighter-colored brackets missing (and those brackets seem to be completely gone, not really the typical erosion-like type of failure i’d expect).

  5. Geoff Forden (History)

    What can I say? UNMOVIC has other pictures, not in the public domain, that show other tests of the “defective” graphite and this explanation was accepted by UN inspectors.

  6. nukeman (History)

    Sharif University researchers made carbon fiber composites by either hot pressing or infiltration. They do not use CVD in their manufacture. It should be noted that the Iranians are currently trying to manufacture PAN based carbon fiber and then infiltrate the performs using various pitchs and other related materials. All of this and more has been reported on in the open scientific literaure.

  7. Jochen Schischka (History)


    I hope you understand that i have problems to simply believe what some UN-inspector is willing to accept if there are clowns like these out there:

    They’re wondering about not being able to detect UDMH in Scud-kerosene-containers in Afghanistan! D’Oh! They should have tested for tricresol-residuals instead!

    Based on embarrassing affairs like this, i’d say that it depends a lot on which particular UN-inspector we’re talking about (thank god, there are competent ones out there, too)…

  8. Geoff Forden (History)


    You wont finding me defending the UN in general but I have to point out that these guys (that you link to) are NOT UN weapons inspectors; they are from some environment program. Finally, you (you in general, not necessarily you in particular) should not take anyone’s word for something simply based on their affiliation or even their degrees. However, the UNMOVIC inspectors were the last outside observers to take an independent look at the jet vanes and they were asking the right questions. If you do not accept their assessment, you wont arrive at a better analysis by simply arguing about the white patina seen on one image.

    I would also say, think in terms of “thermal shock” not necessarily corrosion.

  9. Jochen Schischka (History)


    Agreed, those were UNEP-guys, but aren’t they counseled by somebody else with more competence on the issues they’re tasked to analyze? All in all, faux pas like these are rather counterproductive for inspirating confidence…

    But back to (the jet vane) business:

    Yes, “thermal shock” would explain the breakup of those two brackets nicely; I hope we agree on a) all four jet vanes themselves seemingly having the same color in those two photos, b) two of the “brackets” (some sort of adaptor-piece between the actual jet vane and the flange of the actuator – quite an unusual configuration, unless you already have a working jet vane that doesn’t fit onto your new actuator flange) have lighter color than the two others (or the vanes) and c) these two lighter-colored “brackets” (not the jet vanes themselves, although due to their absence, we can’t really make substantiated statements about that issue) seem to have failed during that test (let me again advert to the position of the SA-2-engine tubine-exhaust-pipe in those two pictures) – perhaps indicating that that particular test was in reality about testing “brackets” from two different materials, not the jet vanes themselves?

  10. Geoff Forden (History)

    actually, I believe it is the quality of the graphite that is being tested. One foreign graphite supplier provided good graphite and one didn’t. Perhaps I cannot convince you of that with the publicly available information but that doesn’t mean I should change my opinion and not believe what UNMOVIC concluded.

    This hints at what is a major problem for UN inspections: how do you get the world to believe the conclusions. One thing UNMOVIC did was to convene conferences with experts from major powers to present the scientific evidence on which conclusions were based on. We did this for Iraq’s missile programs in February 2003 to backup our proscription of the Al Samoud II. I don’t remember anyone talking about the jet vanes because that was not relevant to the decision we made to require Iraq to destroy those missiles. However, I believe that if that issue had come up, UNMOVIC could have justified its belief in Iraq’s explanation.

  11. Anon.

    The “brackets” look to me about the same thickness as the base of the vane where it connects with the “bracket.” Perhaps this was the thickness of graphite received by Iraq, thus necessicating (sp?) a two-piece construction. If so, then maybe this particular pair of photos came from a test to see whether they could use some cheaper material, or perhaps the defective graphite batch (to get at least some use out of it) as the bracket?

  12. Jochen Schischka (History)


    Interesting idea. Unfortunately the UNMOVIC compendium treats the whole jet vane issue only rather cursory…