Are Iran’s Khorramshahr Missile and North Korea’s Musudan Missile the Same?

As we know President Trump will very soon, like October 09, either certify or refuse to certify that Iran is in compliance with the Joint Comprehensive Plan of Action (JCPOA) on its nuclear programme. According to the International Atomic Energy Agency, and most credible analysts, Iran indeed is verifiably complying with its JCPOA obligations.

If Trump declares that Iran is not in compliance the main talking point, one rather suspects, will be less gas centrifuges and uranium enrichment and more ballistic missiles. Under the terms of the broader understanding that underpins the JCPOA Iran is not to develop missiles “designed” to deliver a nuclear warhead.

Much may well trade on this in the coming days.

Now one could argue that North Korea’s Musudan (Hwasong-10) MRBM was designed to deliver a nuclear payload. Of course, the Musudan has been superseded by the Hwasong-12 IRBM and Hwasong-14 ICBM, both using an indigenously developed high thrust core engine, but the matter might come up in the coming days as many argue that Iran’s newest missile, the Khorramshahr MRBM is (a) for all intents and purposes the Musudan and (b) demonstrates continued Iranian and North Korean missile technology cooperation.

The Khorramshahr was recently shown in an annual military parade that marks the Iran-Iraq war, a war in which Iraq, supported by the United States, employed chemical weapons. The Musudan, we know, was derived from the Soviet R-27 (SS-N-6 “Serb”), see images below especially the warhead on the second R-27 image, sea launched ballistic missile and so an obvious distinguishing feature of the Musudan is the relatively wide diameter of the missile.

The Khorramshahr has, it appears, a relatively wide diameter. Furthermore, the exhaust plume is consistent with the use of UDMH propellant for the fuel (we return to the oxidiser later), also used on the R-27 and Hwasong-10, and video imagery, as pointed out by myself when released, appears to demonstrate the use of vernier steering engines (Iran’s other LPE missiles use jet vanes like the Scud and Nodong), and crucially just like the R-27 and Hwasong-10 the Khorramshahr employs a sunken engine.

That’s certainly enough information to draw an inference regarding the common design heritage of the Hwasong-10 and the Khorramshahr. No scientist would begrudge anybody drawing a working hypothesis from such data. There are obvious differences too. The Khorramshahr, unlike the Hwasong-10, does not have grid fins for stabilisation. Furthermore, the warhead is different. The RV on the Khorramshahr has a conic RV whereas the Hwasong-10 (below) has a baby bottle RV, as does the R-27 as shown above.

In so far as any debate on what the Khorramshahr is “designed” for that difference might be one that will attract a lot of discussion and analysis in the coming days. This might be a bit theological so do bear with me. Say the Minuteman III ICBM has a guidance package with an accuracy consistent with counter value targeting but then comes to be guided with an MX ICBM guidance package, giving it MX accuracy and so thus a hard target, counter force, kill capability. Is that same Minuteman III ICBM now “designed” for a different mission? I would say; yes.

Something like this did happen with the Minuteman III, it must be said.

A conic RV, as opposed to the baby bottle RV, of course does not negate a possible nuclear payload but one might argue that the different RV means that a common design heritage does not equate to a common payload. The conic RV could be a shroud concealing a baby bottle RV, but that is unlikely. Iran has flight tested baby bottle RVs before, and it did attract a lot of attention from analysts when first unveiled which I remember very well.

One interesting difference is the flight test history. North Korea had one successful lofted trajectory test of the Hwasong-10 followed by a string of spectacular failures before Pyongyang showed us the Hwasong-12. Iran has tested the Khorramshahr once, on a standard trajectory, and uncertainty exists as to whether the test was successful or not. The test did appear to fail 1000km into flight, but what is not known is whether that was because of failure or because of deliberate in-flight destruction. North Korea, as noted, was not able to launch the Hwasong-10 so far on a standard trajectory with catastrophic failures almost immediately after launch being the norm.

Ralph Savelsberg has a really interesting analysis on the Khorramshahr, like really interesting, arguing that it is not the Hwasong-10. He argues that the diameter of the Khorramshahr is 1.25 metres rather than 1.5 metres for the Hwasong-10. When you take his estimate for the acceleration, reasonable given You Tube and Tracker physics software is often employed for this, of 6 m/s^2 and his dimensional analysis you do get a thrust, using the relevant rocket equations, of 173kN. The thrust of the R-27 engine, the 4D10, is estimated at about 226kN and with the verniers that becomes 255kN (Savelsberg gives about 270kN. The 255kN comes from astronautix).

That strongly indicates the Khorramshahr engine is not the 4D10, so therefore the Khorramshahr and the Hwasong-10 do not share the same, North Korean, design heritage.

However, if you drop his key assumption, on diameter, and do your own volume, litres and propellant mass calculations using 1.5m instead with UDMH density and assuming 6 m/s^2 acceleration, and further assuming for simplicity everything else remains equal, you get a figure not too far off from the thrust of the 4D10. Savelsberg argues that, for geographical reasons, the Khorramshahr does not use N2O4 for the oxidiser. My propellant mass estimate from cylindrical volume is based on the density of UDMH alone. It’s just a rough getting a sense or guide calculation.

That means much rides on Savelsberg’s dimensional analysis. Notice that he uses the known parameters of the tyres of the transporter at the recent military parade to reach an estimate for the diameter. That’s something, and often employed, but can lead to error. My own considered view is that Savelsberg might be right, but dimensional analysis from the transporter tyres alone is not enough to be conclusive.

We’ll be in a much better position when we get a glimpse of the engine itself, but as the tale of the RD-250 engine and the Hwasong-14 demonstrates even that can lead one to go astray (the Hwasong-14 does not use the RD-250).

Either way, the world is a much safer place with the JCPOA than without it 1.25 m or 1.5 m doesn’t change that. Indeed, if the diameter is 1.5m and the engine is the 4D10 one might argue that the JCPOA becomes more important and building upon it to reach a comprehensive peace in the Middle East even more so still.

Let us see what Trump does.

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