Jeffrey LewisPostol and Wright on the Unha-2

A couple weeks ago, Benn Tannenbaum invited Ted Postol to come down to Washington. Ted gave a fascinating talk, in which he argued that the second stage of the Unha may be a re-purposed SS-N-6.

This is a plausible answer to the BM-25 — the North Korean bought kits to use as a second stage of the Taepodong series.

David Wright and Ted have a provocative article in the Bulletin suggesting that the Unha-2 “second stage appears identical to the single-stage Soviet R-27 sea-launched ballistic missile, called the SS-N-6 in the United States, which the Soviet Union first deployed in 1968.”

First the bad news: An SS-N-6 second stage massively increases the range-payload curve (doing away with the golf ball of death), putting CONUS within range of a 1 ton payload from North Korea.

Now, the good news: North Korea can’t indigenously manufacture the second stage, so if we can secure the rest of the SS-N-6 kits components (and cut off external assistance), the North Korea ICBM program is at a technological dead-end:

Analysis of the Taepodong-1 and Unha-2 launchers strongly suggests that they may be designed and built around components of Soviet missiles. The apparent lack of testing of these components by North Korea suggests that they aren’t indigenously produced systems but are existing components that North Korea has been able to combine to build multistage launchers. The Taepodong-1 appears to have used a modified Nodong missile for the first stage; a modified engine from a Soviet surface-to-air missile for the second stage; and the engine from a solid-fueled Soviet SS-21 tactical missile for the third stage. As noted above, the second stage of the Unha-2 appears to be a modified SS-N-6 missile, which was produced by the Makeyev bureau in the 1960s.

It’s possible that North Korea learned, with significant Russian assistance, to manufacture Scuds and Nodongs and is therefore not limited in its number of these missiles, assuming it can acquire the necessary materials. But this is much less likely for the SS-N-6, which is a far more advanced system due to its use of highly optimized rocket motors, very energetic propellant, and a complex airframe fabricated from aluminum alloy.

None of this evidence is conclusive, but because it has important policy implications, it should be a high priority for the United States to assess it and work with Russia to determine what technical assistance and components North Korea may have received.


  1. Andrew Tubbiolo (History)

    It sure would explain the lack of test launches. If Iran is using the same second stage they would suffer from the same problems. Is there a public source for how many R-27’s (SS-N-6) were sold? I’m sure quite a few were built. I don’t suppose there’s a public accounting for where these things are kept and in what condition?

  2. Murray Anderson (History)

    Two points, somewhat in conflict:
    1. We have to assume large-scale ongoing Iranian technical assistance. Iran has a large auto production industry, something like a million vehicles per year, so they have plenty of good production engineers.

    2. If the second stage is an SS-N-6, why use a three-stage rocket? The payload will increase, but the reward is much the same, so long as the satellite can broadcast revolutionary slogans.

  3. bradley laing (History)

    —is this important wonk news, or not?

    WASHINGTON – U.S. officials said Tuesday that a North Korean ship has turned around and is headed back toward the north where it came from, after being tracked for more than a week by American Navy vessels on suspicion of carrying illegal weapons.

    The move keeps the U.S. and the rest of the international community guessing: Where is the Kang Nam going? Does its cargo include materials banned by a new U.N. anti-proliferation resolution?

    The ship left a North Korean port of Nampo on June 17 and is the first vessel monitored under U.N. sanctions that ban the regime from selling arms and nuclear-related material.

  4. George William Herbert (History)

    They offhandedly continue the “warhead must weigh at least a thousand kilograms” assumption halfway through, which I find dissapointing.

    There should be a more serious look at the alleged 60 cm NK warhead, which matches the RVs we’ve seen on their missiles and is technically not particularly challenging.

    The stage match and performance analysis is useful, and insightful.

  5. Jochen Schischka (History)

    I must say that i am skeptical about the Eunha-second-stage simply being a R-27/SS-N-6/Serb.

    Sure, the diameter of ~1.5m is rather similar (and i personally think that it’s most likely identical due to the same production tooling), but the SS-N-6-engine was designed for a sub-surface underwater-launch at a depth of up to 50m and thus is anything but vacuum-optimized (i’d mark that as a quite important characteristic for an upper-stage-engine – otherwise the losses might outweigh the expenses)! What is more, i’m not sure to what extent the steering concept of the SS-N-6 with the two-chambered ZhRD 4D10 vernier-engine allows adding so much weight on top of the missile (a third stage in the range of at least 4 tons, probably even more); And i haven’t even mentioned the guidance system…

    In essence, to sufficiently work as a second-stage, the SS-N-6 would have to be at least heavily modified – and then, it’s not really a SS-N-6 anymore, but something only vaguely based on that missile.

    And i still haven’t seen any evidence that the North Koreans can produce (or were able to procure functional examples of) the high-pressure closed-cycle “NTO”/UDMH main engine of the SS-N-6 (the associated two-chamber open-cycle vernier-part obviously showed up in Iran in modified form as engine for the Safir-upper-stage – but that is arguably rather low-tech in comparison). BTW, the pressure ratio might be difficult to enhance by a simple radiation-cooled nozzle-skirt (i’d expect thermal problems in case of the main chamber) on that one…

  6. Left Flank (History)

    Now if only someone can convince the SOUTH Koreans not to use Russian components for ROK missiles!

  7. Allen Thomson (History)

    > They offhandedly continue the “warhead must weigh at least a thousand kilograms” assumption halfway through, which I find dissapointing.

    I agree. The initial version of the MTCR used a 500 kg throw-weight figure. And if you look at the weights, dimensions and yields of US weapons in the table at, there are a number of single-stage devices weighing < 1100 lb.

    Maybe the DPRKians can’t do better than 1,000 kg, but in the absence of real information to that effect, I’d go with 500 kg as a prudent threshold of concern.

  8. George William Herbert (History)

    Jochen –

    It’s not considered particularly challenging to extend a nozzle to higher expansion ratio, unless the whole existing nozzle is regeneratively cooled with propellant.

    Radiation cooled or ablatively cooled nozzles are fairly easy to extend.

    You end up with a possibly less optimal overall weight and length than a designed-from-scratch nozzle for the same expansion ratio and throat area, but those just affect interstage structure size and mass (which is typically down in the noise in overall mass impact), and to a tiny degree final stage performance.

    The flow is supersonic in the nozzle, so it doesn’t affect the chamber or nozzle upstream. If the expansion of the original nozzle is enough that the gas is cool enough that good stainless steel or titanium can take the operating conditions in the nozzle extension, which is not particularly unusual, it’s not a big deal at all.

  9. Azr@el (History)

    This SS-N-6 business makes no sense. It is as Herr Schischka says, high-pressure closed-cycle engines are not an easy bit of kit to turn out. But say that the DPRK has managed this coup; why in the name of Buddha and Marx haven’t they used it for their first stage? It would make much more sense to have this high performance NTO/UDMH engine in the first stage. It would make the overall rocket smaller and allow it to achieve it’s objective with only a two stage design. It’s like an aircraft using reciprocating engine propellers to get off the ground and then switching over to jets for cruise.

    As to the BM-25, hasn’t this been debunked yet? The story had no basis in reality. The authour is a known “leaker” of disinformation for Israel Intel. And Tel Aviv has been hard peddling the notion that the Iranian missile program is a threat to not just Israel but the whole world; mainly by drawing cute little pictures showing that Austria and Czech republic are within Iranian missile range and “leaking” info about mythological Iranian Wunderwaffen such as the BM-25 . Do we have to fall hook, line and sinker for this comical propaganda?

  10. Jodi (History)

    Thanks Jeffrey. I’d like to take credit for the Postol invite, though.

  11. Jodi (History)

    In fact, I ran the EWI study that Postol and David Holloway penned with the Russians. At least until I returned to DC last August.

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