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Closeup of the cylinder removed from an Iranian furnace.

A while ago, I asked if anybody knew what the purpose of a furnace shown in an Iranian video covering the construction of the Safir-Omid space launcher was. Answering this question, as well understanding several other interesting scenes in the video, could help provide a better understanding of Iran’s indigenous production capabilities. This, in turn, has important implications for policy choices in such disparate fields as export controls and missile defense. Several interesting suggestions were made, which I list below as hypotheses:

1. Brazing (a form of soldering) together the inner and outer shells of a rocket motor. I had originally thought this might be for the smaller second stage engines but it was also suggested that it might be for the larger first stage engine; a Nodong engine.

2. Manufacturing fiber reinforced ceramic matrix composite jet vanes. Iran’s ability to manufacture jet vanes, for both liquid and solid propellant missiles, is important in understanding how sensitive they might be to targeted sanctions or the MTCR (Missile Technology Control Regime).

3. An as yet undetermined purpose. This catch all hypothesis is a logical necessity. As we shall see, it possible to rule out one of these hypotheses while not positively confirming the other.

Let’s now turn to each hypothesis in turn.

Engine Brazing Hypothesis
The cylinder, which in this hypothesis, could either be for forming a vacuum or supplying a special atmosphere (such as argon) for brazing the inner and outer shells together. In this hypothesis, the furnace has heated the cylinder with the engine inside it to a temperature above the melting (liquidus) temperature of the brazing filler material (the equivalent of the solder) but, of necessity, less than the melting point of the materials—the engine shells—being brazed together. Typical brazing temperatures for stainless steel are about 1100 degrees C.

Fortunately, the video can be used to estimate the minimum temperature of the furnace by gauging the color of cylinder’s metal. (See the image at the top of this post.) The cylinder has recently been removed from the furnace and allowed to cool for an indeterminate period of time. The cylinder has cooled off first at its outer radius, retaining a hot inner core while the support cylinder, presumably made of stainless steel, has not conducted much heat away from the cylinder. That, too, is a property of stainless steel. The cylinder’s lemon-colored inner core, surrounded by cooler cherry red fading to dark red metal, indicates the furnace’s temperature was at least 1000 degrees C, consistent with brazing stainless steel. Interestingly, it rules out the cylinder being used, at this time, for brazing the copper based second stage engines since that would melt the material. (See my post on missile development consortiums for a discussion, especially in the comments, of the material used for fabricating the second stage engines.)

An Iranian “Nodong” engine with an outline of the furnace cylinder with the correct aspect ratio shown in yellow.

However, brazing the first stage engine can also be ruled out as unlikely because of the relative dimensions, the aspect ratio, of the cylinder: it appears that the cylinder probably cannot fit an entire Nodong engine into its volume. That argument is somewhat too narrow and technical even for my techno-wonk posts so I have provided a link for the die-hard technical types here.

Tomorrow, I will consider the possibility of Iran using this furnace for producing carbon-fiber reinforced ceramic matrix composite jet vanes for thrust vector control of its missiles. Unfortunately, I cannot be definitive about that hypothesis the way I can with the brazing hypothesis and thus it still remains possible that the furnace is being used for something totally different. However, I want to explore the composite jet vanes hypothesis in more detail so there will several more posts in this series after that. I promise that the more political science types will (I hope) find these interesting as two days from now I will present a theoretical framework for understanding how states get the know-how and industrial infrastructure for producing 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