Jeffrey LewisNew DPRK ICBM Engine

Yesterday, Melissa Hanham and I gave a talk to a meeting of US and Russian experts about North Korea’s growing nuclear and missile programs.  The presentation is part of a high-level dialogue that seeks to resume US-Russian cooperation on nonproliferation, even as relations are in the toilet.  Melissa tweeted some pictures from last night’s dinner, which gives a sense of some of the participants — including California Governor Jerry Brown and the Executive Director of the CTBTO, Lassina Zerbo.

The North Koreans kindly spiced up our meeting by testing a new engine for their ICBMs. It is not good news.

One of the conversations we had concerned North Korea’s new series of the road-mobile intercontinental-range ballistic missiles, known as as the KN-08 (Hwasong-13) and KN-14 (Hwasong-14, below).

epa04974362 A picture released by the North Korean Central News Agency (KCNA) on 12 October 2015 shows large missiles, believed to be KN-08 intercontinental ballistic missiles, appearing during a large-scale military parade at Pyongyang's Kim Il-sung Square, in Pyongyang, North Korea, 10 October 2015, to mark the 70th anniversary of the founding of the ruling Workers' Party of Korea. EPA/KCNA -- BEST QUALITY AVAILABLE -- SOUTH KOREA OUT

We’ve often wondered what to make of these missiles.

North Korea’s missile programs are largely based on engines derived from the small number of Scud missiles that North Korean imported from Egypt.  The Nodong is just a super-sized Scud engine, while the the first stage of the Taepodong-2 (aka Unha/Kwangmyongsong-series) is just a cluster of Nodong engines.  These rockets all use relatively simple propellants (IRNFA and Kerosene), which severely limits their performance.

When North Korea showed off the Musudan missile, analysts took notice.  The Musudan appears to be an enlarged version of a different Soviet missile — not a Scud, but the SS-N-6 (R-27) submarine launched ballistic missile.  The SS-N-6 engine uses a much more energetic propellants — nitrogen tetroxide (NTO) and UDMH — and is in general much fancier.   What if North Korea replaced its Scud-based missiles with a series of missiles based on this technology? This subject pops up in a paper the US distributed to MTCR adherents that is now available thanks to Wikileaks:

“Recently, North Korea has developed a new land-mobile IRBM –called the Musudan by the United States. The Musudan is a single-stage missile and may have a range of up to 4,000 km with a 500 kg payload. The Musudan is derived from the SS-N-6 submarine-launched ballistic missile (SLBM) and represents a substantial advance in North Korea’s liquid propellant technology, as the SS-N-6 had a much more advanced engine and used more energetic propellants — unsymmetrical dimethylhydrazine (UDMH) and nitrogen tetroxide (N204) — than those used in Scud-type missiles. Development of the Musudan with this more advanced propulsion technology allows North Korea to build even longer-range missiles — or shorter range missiles with greater payload capacity — than would be possible using Scud-type technology.”

In a different cable, the US raised the possibility that North Korea could “further develop the technology for an IRBM based on their new MRBM, in the same way the No Dong was a path to the Taepo Dong” as a path to an ICBM.

If you are interested, there is a nice discussion of early-generation Soviet propellants in a declassified CIA estimate from 1962.  For our purposes, the most interesting aspect is the chart showing the performance curves of different propellant types.  “Nitrogen tetroxide-UDMH” represent a significant improvement over Scud fuels.  (North Korea’s use of RFNA-Kerosene falls below the lowest curve in the chart, RNFA-UDMH).


That brings us to the KN-08 and the KN-14. The diameter of these missiles is not large — probably less than 2 meters.  That only leaves room for no more than two, maybe three, engines of types known in North Korea.  So do North Korea’s road-mobile ballistic missiles use Nodong engines or something more interesting?

On March 9, North Korean state media released a partial image of the back-end of the KN-08.  Although the image is obscured, it seems to confirm that the first stage comprises only two rocket engines.  There is a tantalizing hint, too.  The nozzle looks too small to be a Nodong engine. That would suggest that the KN-08 uses a pair of 4D10 engines from the SS-N-6.


But that seems — or rather, it seemed — like a technical stretch.  The 4D10 engine is a complicated piece of work, starting with the fact that it is submerged in the fuel tank.  My friend George Herbert sent along a pair of images that show how much plumbing needs to be rearranged.


Clustering a pair of engines like that would be quite a feat — not impossible, but perhaps rather more than we’ve seen the North Koreans do before.  Pulling off a stunt like that would represent an advance in North Korea’s engineering capabilities.

And now this.  Yesterday, North Korea announced that it conducted a static engine test of “a new type high-power engine of inter-continental ballistic rocket.”  From the images, it seems the most likely explanation is that North Korea tested a pair of 4D10 engines from the SS-N-6 for the KN-08 (and possibly KN-14).


Why do we say that?

First, the rocket plume appears to be exiting from two nozzles.  That would suggest a pair of engines.

Second, it is not possible to see the engines themselves.  Instead, the engines appear to be submerged in a large tank, which is the configuration of the 4D10.  It does seem that there are some vernier engines visible, which would tend to confirm the 4D10 hypothesis.

Third, the coloration of the plume looks much cleaner than Scud fuel.  Again, that would be consistent  with the more energetic propellant associated with the 4D10.  George and John Schilling happen to be a conference of rocket designers.  They’ve done a simple crowdsourcing exercise and the consensus seems to be settling around more advanced propellants.

We’ve previously considered the possibility that North Korea might cluster 4D10 engines in an ICBM, but clustering 4D10 engines implied a level of sophistication we had not previously observed in North Korea’s missile programs.  Well, I guess there is a first time for everything.

So what?

The KN-08 and KN-14 are far more capable than more conservative estimates that assume a pair of Nodong engines. The range/payload curve for these missile will jump. John is going to rerun his models, but I would expect the range of the revised KN-08/KN-14 family will now fall at the upper end of his estimates.  That means that, rather than simply hitting the West Coast, an operational North Korean ICBM could probably reach targets throughout the United States, including Washington, DC with a nuclear weapon.  In other words, the Map of Death is real.

We can stop laughing any time now.  The joke is on us.



  1. hblumenk (History)

    I’ve seen the estimates in Mr. Shillings projections, but even at the higher end they seem to be constrained by the size of the warhead. his “Max” variant can only carry a 1000 kg payload 8000 km. Which would place it in Seattle, not D.C. Do you believe the DPRK is on the verge of creating a more advanced warhead? like moving from the disco ball to something lighter?

    • Jeffrey Lewis (History)

      The disco ball probably weights a few hundred kilograms, plus the aeroshell. That’s pretty close to John’s estimate of a “heavier” warhead.

    • Carl DeHaven (History)

      The assumption is being made that the “disco ball” device is what may be arming either the KN-08, KN-14 or an “emergency capability” modified Unha-3/TD-2 initially in the ICBM role, or for that matter their SRBMs, MRBMs or IRBMs. The other warhead option, an HEU gun system, though cruder and less efficient, has the advantage of being a lot more robust. A W-33 type device could be well under the estimated weight of the “disco ball”.

      As to yield, the “high end” 40 Kt yield of the W-33 would be more than sufficient if the focus was on targeting major metropolitan areas, assuming the North Koreans can keep the CEP to within the blast and or flash radius of such a yield. That being said, since the volume available to work with would be a lot more than the 8″ diameter and the depth of a howitzer’s chamber and the 250 lbs of such shells, there would be room for more optimization.

    • Anon2 (History)


      “The disco ball probably weights a few hundred kilograms, plus the aeroshell.”

      Looking at the photos, the diameter of the discoball exceeds the width of “Little” Boy KJU by about 2x. I’m gonna guess it is 0.9m in diameter. That makes it internal volume around 0.38 m^3. Density of TNT is 1650 kg/m^3. Steel 8000 kg/m^3. That makes the weight of the nuclear explosive pit (perhaps hollow for boosting) de minimis, so if it is 10% steel and 90% explosive, the average density is around 2300 kg/m^3 giving the discoball a weight of around 875 kg. Fatman weighted 4600 kg. And then we have the nose shroud, the heat shield, and any guidance package. Am I missing something? This discoball weapon looks like it will barely make it out of their Il-28 bomb-bay, or hang under an SU-25, Mig-23, or Mig 29, let alone fly on a missile.

      Maybe they have something that is more miniaturized tested. Who knows.

  2. Michael (History)

    I have a question. In his most recent analysis John Schilling contends the new North Korean solid fuel rocket rocket motor is 1.25 meters in diameter ( This would be akin to, and perhaps sharing (although he explicitly and curiously rules this out) a lineage with Iran Sejil missile. How does he draw this this conclusion? Are the photos manipulated to misrepresent the diameter of the motor? My own analysis, and independently of mine, Norbert Brugge both reach a conclusion of a ‘missile with a maximum diameter of 1meter’ , perhaps slightly less ( The discrepancy is not insignificant. It would suggest the new North Korean solid motor that is roughly comparable to China’s M-9 in a two stage configuration and not as Schilling contends a missile that would ‘weigh 18 tonnes at launch and deliver a 1000 kg warhead to a range of roughly 1800 km. With a lighter 500 kg warhead, the range could be as high as 2600 km’, but instead would be an order less capable, perhaps being able to deliver a 500 kg warhead to cover most, but perhaps not all, of Japan . It would also suggest an incremental development based on the North Korean version of the SS-21 Tochka – the KN-02 rather than a technological leap or the acquisition of foreign missile components. I would welcome thoughts on this!

    • Jeffrey Lewis (History)

      Our measurements are a bit larger than yours — 1.2 m. This is worth discussing!

  3. georgewilliamherbert (History)

    Quick note – the images of the 4D10 were originally from Norbert Brugge’s website and I apologize for leaving source credit off when I sent them to Jeff during the discussion. Norbert’s site is an excellent detailed reference.

  4. xutianran (History)

    The new engine’s plume is indeed a little bit different from Scud engines. However,comparing the Rodong Sinsmun photos with other NTO-UDMH engine plume, the difference in coloration is apparent:

  5. xutianran (History)

    Some new pics. the first one does share similarities with NTO engine plume. But RFNA UDMH can also have similar plume coloration, such as the MGM-52 Lance. For a land mobile missile RFNA has clearly better handling qualities, whereas, please correct me if i’m wrong, there is no land mobile ballistic missile using NTO/MON.

    • George William Herbert (History)

      If we were discussing many other countries, a new engine / new propellant program would be a likely candidate.

      North Korea has the following history, slightly simplified:

      Bought some Scud-B missiles from Egypt ~1980.

      Reverse engineered those and produced more, and many variants. ~1984

      Scaled the motor for those up by 1.5x (and very few other changes) for Nodong from 1988-1993.

      And that’s it until R-27 parts start showing up.

  6. Steven Hayden (History)

    The DPRK 300mm MLRS had estimated range of only 100 km by Western experts. When tested however it reached 200 km. Western military industrial complex underestimates DPRK military capacity.Western military estimates are politically influenced. The Western estimates of DPRK nuclear weapons are grossly understated. Remember the devastation of Korean War and sanctions for sixty five years provided two choices to DPRK: surrender or resist . The West has relentlessly inflicted hardship onto DPRK .The DPRK might lose a third of population in nuclear war and have every building demolished. However despite such losses the DPRK maintained control of food distribution and leadership remained intact. DPRK society has already adapted to extreme hardship. It is the West that has not faced the same hardship as DPRK. It is destiny.

    • George William Herbert (History)

      Kim, baby! Glad you’re posting! How are the Wife and Generals?

    • keve (History)

      Yes, agree. For main stream media-experts, under-estimating has been a pattern for last 60 years; this only benefits the NoKorea. But what will over-estimating do??? There is not whole lot US can do to stop NoKorea from nuclear development to counter potential outside nuclear threat. For US mass population to worry and blaming/scorning the US politicians will not stop NoKorea. Ignorance is bliss… NoKorean nuclear threat is not any greater than those of China and Russia. What it is, is what it is….. Only tool/option US has against NoKorea is sanction which only agitate NoKorea to invest more on nukes with the support of its population, blaming US for taking action to sanction NoKorea, targeting companies that employee NoKorean workers. But thank informative sites like “armscontrolwonk”, “”, “”, run by scientists and scholars, keeping a “reality” check and balance for the technical society in US. Scientists and scholars have to speak louder than the under-estimating mass media-experts. This article is one good example.

  7. xutianran (History)

    to George,

    yes, i understand the approach to estimate new NK missile development by judging from what foreign engines they might have access to.

    but i’d like to add that neat NTO has quite high outdoor handling requirement. According to official Chinese literature the LM series launch tower and storage facility are equipped with warming/cooling machines and the Chinese see it safe for launch activities when the NTO/tower room temperature is between roughly -7 to 15 C, about 5C difference from theoretical upper and lower usage limits of neat NTO. The US Titan II, using almost pure NTO, sits in heated silos that keep the temperature at 15.5C.

    MON25 or 30 can not solve the problem due to their low “boiling” point (-9C for MON25, their military application in missiles has been very limited, almost none) . Besides, MON25 is an American invention in 1971, several years after the Russians put 4D10 into service, while credible Russian literature say 4D10 burns neat NTO. The engine cannot change to MON25 without major redesign due to MON-25’s own characters.

    I guess that’s why we don’t see land mobile missile using neat NTO or MON as oxidizer. The Chinese DF 3 and 4 use RFNA, so are the case of Russian R-14 and 16. When Russian designers changed to NTO the new missiles all lose the ability to be launched in outdoor, non-tower environment. As China developed its DF-16, 14/22 liquid land mobile missile, designers choose RFNA, while they have become well familiar with NTO through the development of DF-5. By the way, R-14,16’s plume coloration is quite similar to that of the new NK engine, while Chinese RFNA-UDMH plume is not transparent/clean, and seems very yellow/orange.

    Maybe huge, refrigerator like missile canisters and oxidizer tankers can satisfy the temperature requirement. But it would be messy and in the case of NTO no country has done that before, and there hasn’t been any indication that the KN08 TEL has anything like that on it.

    Secondly, it is an old topic, but there is really no concrete evidence showing the NK does have access to 4D10 main engine. As is clear now, the Unha-3 second stage has been proven to be at SCUD-tech level. Polaris-1 has only done several ejection and ignition tests. Even “parts of R-27” is not really proven: what we saw is Iranian copies of the small verniers. We made the connection ourselves. It is a reasonable guess, but not necessarily true. All we have is circumstantial, even for the small verniers.

    i admit NK is a very special country, but can they beat handling requirements? and can they really not develop new engines? The US govt says the NK is developing a new 80 ton booster.If true, and if the new engine is indeed the 80 ton booster, it needs a lot more thrust than two 4D10 can offer.

    The situation reminds me of early 90s, when many speculated that Ro-dong-1 is powered by a cluster of 4 SCUD engines. The single Ro-dong engine came as a surprise. Using submerged 1st stage engine in land-based missile is already an abomination. Just like Mr.Lewis said, the NK is pulling of a stunt, i personally would expect the stunt to be more in line with the the land-mobile missile role.

  8. Steve Hildreth (History)

    A single static engine test, while important, is just that — a data point, or maybe even a ‘show’. I’d want to see more testing by orders of magnitude to be impressed.

    What I’ve not seen in the DPRK test program is any sense of how much static engine testing they have conducted on the same engine or even the same engine design. Absent static engine testing on the order of perhaps 15,000-20,000 seconds or more over a long period of time doesn’t provide the kind of confidence that one would expect for their system to work as intended. I’d want to see extensive short bursts of the engine test under various conditions, longer burn times, and minutes long tests from start to burnout. I’d want to know whether they’re getting not just a single engine test like we’ve seen but significant number of tests showing they’re trying to figure out exactly what kind of thrust they’re getting and what kind of total impulse they’re striving for, etc.

    You don’t get those things without extensive static testing. If you don’t do those kinds of things, it tells me they’re just not striving for any serious confidence levels in their system or that this is for show.

  9. John Schilling (History)

    @xutianran: The orange color in the plume has little to do with the oxidizer; that comes mostly from the carbon in the fuel. US missiles like Titan used a blend called Aerozene-50, which is ~20% carbon by weight. Russian missiles like the R-27 used unsymmetrical dimethylhydrazine, ~40% carbon by weight. So we’d expect a dual 4D10 engine set to produce a plume similar to the Titan’s LR-87 but with a more pronounced red-orange color, and that’s what we see.

    And you’re right that NTO requires tighter controls in ground handling than IRFNA, but nobody has ever suggested that a lone KN-08 TEL is going to be headed into the countryside with a fully-fueled missile on top ready to fire. That’s not practical at this scale with any (liquid) propellant combination. As with e.g. the old US Jupiter, the KN-08 and KN-14 are going to be limited to road convoys with a dozen or more support vehicles including fuel tankers, and are probably going to spend most of their time in underground bunkers. You or I might use nitric acid if we were designing a system from scratch. The Russians, with different requirements, chose NTO, so that’s the system North Korea was able to buy.

    • xutianran (History)

      and another circumstantial link that might be often ignored: the Nkoreans are said to have involved in the project DF-61, which was meant to be sold to the NK. They knew the superiority of this combination (performance and outdoor handling quality) and might have known some of the engine design concept but they just couldn’t build it and had to bitterly switch to SCUD.

  10. ChrisV (History)

    It looks like the nozzle shown on the KN08 is surrounded by some kind of curved bulkhead. To me this suggests that the engine is submerged into the bottom tank.

    The SS-N-6 shown in this video seems to have a bright opaque exhaust plume as opposed to the semi-translucent ones seen on Titan launches. The plume shown in the DPRK test may match that for the 410D. (Unless this is a byproduct of the B&W technology used to film the launch). It would be nice to know if the visible length of the exhaust plume in the DPRK test matches that in the SS-N-6 video. (I’m sure that analysis is probably underway if not already completed).

    Both the engine test stand and launch gantry area have new fuel bunkers. To me, this means that the North Koreans intend to launch whatever they are testing and that this is not all for show. That they didn’t just expand the existing fuel bunkers suggests that the new bunkers are meant for a different propellant combination (not just IRFNA/Kerosene).

    As others have noted, the DPRK would probably deploy KN08 launchers in tunnels where temperatures are likely to be stable.

    • John Schilling (History)

      Some of us have been looking for literally years for a decent non-saturated color image of an SS-N-6 plume; if such a thing exists it probably is stuck on film in some ex-Soviet archive a mule cart ride away from any internet access.

  11. Douglas Ferrin (History)

    I’ll bet if we got rid of all of our nuclear weapons North Korea, China, Russia, and Iran would see the error of their ways and get rid of all of theirs.

  12. xutianran (History)

    @John Schilling
    yes, i don’t mean that KN08 should ever be transported when it is fueled. That would be disastrous. Structure wouldn’t hold. However, underground bunker/tunnel/cave storage could not solve the temperature issue. The DF-4 missile’s most popular deployment model is cave/tunnel storage and outdoor erect-fuel-launch. The Chinese managed to minimize the outdoor handling time to several hours, and DF-4 is a two-stage rocket. One would expect the KN08’s outdoor preparation time to be about the same. The oxidizer(NTO) needs to remain stable during this period. For very warm or cold weather, one would need tankers with warming/cooling functions and a huge missile canister/environmental protection cover that keeps temperature inside the canister safe, and remains closed when the missile inside is being fueled and only opens immediately before launch. In other words, one should offer the land mobile/movable NTO missile the same handling environment just as treating a silo or sub-based NTO missile.

    I too searched for R-27 inflight photos in vain. But there are numerous pics showing inflight missiles burning the same oxidizer and fuel combination, most of them Russian and Chinese. I looked at a lot of NTO-UDMH plumes, haven’t found a match with KN08. Here is a comparison, one of them is a UR-100. whose single engine thrust is identical to that of 4D10 main engine. I found the difference quite obvious:

    However, comparing the KN08 photos (plume and smoke) with Russian/Ukraine RFNA UDMH rockets, the resemblance is hard to ignore:

    For sure, Plume comparison is tricky and also circumstantial. But as of yet, the 4D10 engine theory is also backed by circumstantial evidences. Several years ago two NK spies are caught stealing materials of turbo pumps in Ukraine, where there are abundant infos on RFNA UDMH engines, which have satisfactory performance and perfect outdoor handling quality for a liquid missile. Rumor about a 80-ton NK booster has been ongoing for years. There are a lot of IFs here, but this might just be it. I loved you KN08 model, maybe this time you could also include the RFNA-UDMH scenario as well?

    p.s. an unrelated remark: the world has been guessing the KN08’s configuration for a long time, but actually the truth has been staring at us for years, we didnt look hard enough:

    • John Schilling (History)

      I’m not sure why you think refrigerated tankers and protective canisters would be required; could you elaborate? Summer high temperatures in Pyongyang are usually less than 30 deg C, , and lower still in the mountains where such a missile would be based. At 30 C, the vapor pressure of nitrogen tetroxide is only 21.6 psia (1.5 bar). The fuel tanks will need to be pressurized to roughly 30-50 psia to suppress cavitation and pogo instability anyway, so there will be no issue of the propellant boiling. Transporting liquids under modest pressure is a well-established industrial practice that does not generally require refrigeration. I am looking right now at the USAF Propellant Handbook for Nitrogen Tetroxide Oxidizers, which states that N2O4 is shipped “in cylinders, tank trucks, and tank cars”, goes on for several pages about the relevant specifications and procedures while making absolutely no mention of refrigeration or temperature limits except to note that high-pressure containers may be required at 60 deg C or above. At the low temperature limit, it freezes at -11.2 deg C. That’s not terribly difficult to deal with either.

      I have personally supervised the fueling of rockets with nitrogen tetroxide, and while I have some issues with the toxicity, those apply equally to IRFNA. In terms of temperature and stability, if you can handle e.g. water or propane in the field, you can handle nitrogen tetroxide. That’s why we chose nitrogen tetroxide for our rockets.

      As for the Ukranian connection, the UN report says the North Koreans were found with information regarding propellant tanks and feed systems, not turbopumps or engines. And Yuzhnoye hasn’t built a large rocket engine in several decades. They build missile and satellite launch vehicle airframes, including propellant tanks and feed systems, that use Russian-made engines.

      We have a great deal of circumstantial evidence that North Korea obtained R-27 missile technology, including engines, from Russia. We have no evidence to support any speculation that they have obtained any other high-performance engines. What we saw this weekend, looks almost exactly like what we’d expect a cluster of R-27 engines to look like, and a cluster of R-27 engines – yes, with nitrogen tetroxide oxidizer – is a technically sound approach to propelling an ICBM. If you are insisting that this must be something completely different, for which we have no evidence, simply because you read somewhere that nitrogen tetroxide is too volatile, you’re almost certainly wrong.

    • Steven Hayden (History)

      That is a very impressive picture.Where did it come from ?It looks like Kim Jong ILL. What year do you suppose it was taken?

    • George William Herbert (History)

      Following John’s comment – Up a ways, Flames in the Desert posted a video of Sineva SLBM launches ( ) yesterday, which shows a yellow flame. Sineva uses the RD-0243 engine with UDMH/NTO and a mixture ratio of 2.6. 4D10 uses UDMH/NTO at a mixture ratio es estimate around 2.0. So it’s got even more carbon-containing fuel per unit mass oxidizer, and should be yellower if anything.

      I think the yellow vs blue-pink-yellow is UDMH versus say 50/50 mixes of MMH/UDMH (Aerozine-50).

      I don’t know so; still looking to find quality color photos / film of R-27 Zyb launches…

    • George William Herbert (History)

      Also, regarding the missile behind the late Kim Jong-Il, I don’t think that matches the tested motor assembly. I tweeted about this, but to repeat that here…

      The tested assembly has two main motors and four verniers. The verniers are offset about half a main motor nozzle diameter from the sides of the main motors, 2 on each side of the mains and parallel to the axis the two mains line up on. You can see this looking at the two axies photos were taken from.

      Roughly this:

      That doesn’t match the RD-215 configuration, which is roughly half of this: (photo from FAS site)

      The base of a single 4D10 is this: (mangled but showing configuration) (photo from Norbert Brugge’s site)

      The configuration does line up with two 4D10s side by side, but would require a source for the verniers for RD-215, and a location where the turbine exhausts went.

      None of this is exhaustive proof but I think the two 4D10 theory matches better.

  13. Gregory Matteson (History)

    Accidentally stumbled on this while looking up something else entirely: Am I kidding myself, or is the flame on this western-designed missile a good match for the test pic under discussion?

    • Gregory Matteson (History)

      Oddly enough, the missile pic in the article I linked does not match the written description in Wikipedia.

    • xutianran (History)

      Geroge, isnt it a solid booster? Anyway, i received a photo from a friend yesterday, showing a LM-2 flame, gotta say it is kinda of a quasi match. but i have to beat the Great Fire Wall (also a first in the world, a GREAT Chinese invention) to upload the pic to Twitter and my VPN is not stable today….

  14. xutianran (History)

    @John Schilling
    Thanks for your explanation! I think refrigerator-like canister is required because missile ox tankers are closed space made of metal. After being transported in warm weather for a while and during the erect-fuel and launch preparation period, the inside temperature could quickly rise to over 50C, like one would expect when entering a car that has parked for a while under the summer sun.Heat insulation is not new technology but that would make the body heavier. As of weather, Pyongyang and some other places’ temperature could reach 36C in recent years, ground temperature would be higher, and when inside a closed metal space it would be much hotter.(Beijing summer sometimes reaches 38C, and media shows cooking eggs on a metal plate after it is put under the sun for a while). Could you please tell me, when you supervise the fueling of NTO rocket outdoor, what are your highest/lowest weather record?

    Road convoys with a dozen or more support vehicles including tankers is the DF14/22′ deployment model, and most certainly they will be hidden from view most of the time in bunkers. China is a vast land with many areas and different temperature conditions. Should be easy for designers to find a huge area favorable for outdoor combat NTO handling. And the outdoor preparation time is said to be shortened in comparison with the DF4.But they chose RFNA, and even chose a relatively rare formula, the AK40, to achieve maximum performance and had to make it a three stage design, where a two stage NTO missile would suffice.With much stronger technology base, intensive knowledge about NTO, richer outdoor combat handling experience and better geographic conditions, NTO was given up (by the Chinese, of course).

    So yes, my conclusion is largely based on previous liquid mobile missile attempts silo based missile temperature requirement. Then again, we are back to the theory that NK might have the 4D10, which is their only high performance engine at hand. Actually since i saw the submerged design and one of the plume photos i began to try embrace the idea of a land-mobile NTO missile, the first in the world. They might really dont have any alternatives but to make this invention. I also thought of some ways that it can be used:

    1. cooling/warming tankers and missile tube/canister (which you deem not necessary)
    2. Iranian style bunker, missile erected, fueled, launched inside the cave. TELs only carry them around into different bunkers. A lot of digging to do and is similar to silo mode, but maybe it is more confusing.
    3. find a region/some certain spots where the condition constantly remains favorable, or switch to different places according to seasons.
    4. only goes out of the cave when outside temperature allows. (i actually made this suggestion once in a piece for a Chinese magazine, the editor thought i was joking and cut it, but i was sincere)

    • John Schilling (History)

      For satellites we do actual propellant loading in a climate-controlled building, but the propellants are delivered by truck in non-refrigerated cylinders in Florida, which iwas probably about 30 deg C when I did it last summer. The only large rocket we have left using NTO is the soon-to-be-retired Delta II, in which case the propellant is loaded on the pad, again possibly in the Florida summer. And in at least one case I worked, left on the pad for more than a month before launch, so even if the propellant were cooled during the transfer it would have seen full local temperatures by time of launch. Looking at the payload planner’s guide, the maximum allowable temperature seems to be 54.4 deg C, and that is due to a limit on the solid kick motor rather than the liquid propellants.

      As for metal tanks getting hot in the sun, that depends very much on the surface coating. Ignoring convection for the moment, the equilibrium temperature for a steel surface with black enamel paint lying flat under the Pyongyang summer sun would be 110 deg C; clearly unacceptable(*). But white enamel paint would stay at a cool 2 deg C. Counterintuitively, bare metal is even worse than black paint – while shiny and reflective, it has an extremely low infrared emissivity. I don’t have figures for camouflage paints handy, but it is likely that if the North Koreans stick to lighter hues the tankers would not get above 30 deg C.

      If you do an image search for liquid propane tanks or tank trucks, you’ll see that they are almost never refrigerated but almost always painted white. NTO is somewhat more tolerant of high temperatures than propane and should be able to handle tan or khaki. From a military standpoint, I’d rather be able to use any sort of camouflage and so I’d rather have the still more forgiving nitric acid oxidizers, but if North Korea’s only high-performance engines are designed for NTO, they can handle that without too much trouble. I do suspect they will be spending most of their time in tunnels and bunkers anyway.

      (*) In reality, convection will keep any of these temperatures from getting too far from the local air temperature.

  15. xutianran (History)

    @Steven Hayden
    the pic is from , if i remember correctly, it was aired in 2012/13.

    • xutianran (History)

      sorry, from

    • xutianran (History)

      sorry, again….from documentary Kim Jong Il, the great military strategist

  16. xutianran (History)

    @John Schilling
    forgot one thing to ask: I noticed the pressurization argument before. But other NTO rockets are also pressurized to the same degree, if boiling point not an issue, why the temperature requirement at all? why the Chinese specifically say -7 to 15 for the sake of ox? (And the tower storage pre-cools the NTO in hot weather so that when it rises slowly to 15C inside the missile, which is inside tower, it is still okay for launch.)

    For freezing point i read in Ignition! that NTO is used in heated silos due to its high performance and freezing point. If that’s the case, wouldnt one need a tanker with warming function?

    • John Schilling (History)

      If you plan to operate in a very cold winter, which sometimes does happen in Korea, you’d need tank heaters or the like. That’s hardly an insurmountable problem; anyone who has to deliver liquid water has to be able to solve it, and any engine that can pull a tanker truck can generate enough heat to keep the contents above freezing, and at least in the United States such systems are commercially available for tanker trucks. Refrigeration is harder, but as already noted probably not necessary if you are careful in your choice of paints.

      And from your reference, it does look like the US and China have different standards. As far as I know, China never contemplated using NTO/UDMH missiles outside of fixed sites, and so presumably never developed the necessary procedures. The US Air Force, in the 1950s and early 1960s at least, was considering every option even though it never actually used NTO outside of silo-based missiles. Mostly because we developed good solid motors first; North Korea is still catching up in that area.

  17. xutianran (History)

    i now know why the different views on transport: China and the US may have different standards for propellant handling. This book named Liquid Propellant, published by China Aerospace Publishing House, written by Chinese propellant experts, says the temperature of neat NTO must be kept between -5 to 18C, carried by specialized container, and personnel must regularly check the temperature during the ride. It does not state much about pressurization though:

    • George William Herbert (History)

      That Chinese standard temp range may be to avoid vapor pressure buildup.

      But I am just guessing…

  18. xutianran (History)

    @John Schilling
    Thanks for your answers! It is interesting that the handling of the same ox can be so country-wise different. According to the same book (published in 2011) the storage temperature of NTO should remain between 5 to 21C. Maybe as you said, the Chinese didnt develop the procedures cos they never intended to use it outside silo/tower environment. Or they considered the option and thought it was not worth the trouble and chose AK40, whose vapor pressure is 8 psia at 20C.

    I didn’t give paint a serious thought before. Now it seems boiling point can be solved if the temperature inside the missile can be kept around/under 50C. For cold weather i still think a missile canister/tube is necessary, or tankers should pre-warm it to a higher temperature. But you are right, NTO land mobile missile is doable. And NKoreans might make this invention if they only have 4D10. Personally i would be more comfortable with the idea if they’ve flown it on Unha 3 or Polaris-1. Anyway, we will have a clearer idea should they really launch a Musudan tomorrow.

  19. Anon2 (History)


    May I politely ask for you to seed a (written) discussion here on the Musudan failed launch.

    Thank you,


    • George William Herbert (History)

      There is not much we actually know about the apparently failed apparently Musudan launch. No pictures, no useful intel tidbits leaked (other than “We think it was a Musudan”), etc.

      To review the background…

      In general terms, missiles and launch vehicles have a significant first-flight failure rate (good rule of thumb is 50% for first two flights, 25% for next four, dropping below 12% after that). Some factors can reduce that like a very long development team history of success, more hardware lineage to earlier designs, etc.

      With the Musudan, we have the opposite. NK’s development team flies infrequently, has only developed a handful of truly new things each decade, etc. Likely higher risks.

      The Musudan is thought (thought) to be a R-27 / SS-N-6 / Zyb derivative with a longer set of fuel tanks. We don’t know if the tanks are simplified (like the Unha tanks; one of which South Korea recovered not intact but in excellent condition a few years ago) or are the same Orthogrid structure as the Zyb structure uses. Orthogrid would offer potential to be lighter. But we don’t currently have a clue.

      It also would be the first flights of NTO/UDMH propellants (why do I keep typing that as UDHM?.. gah) for North Korea. They probably are ground testing with those (the pictures of the two-engine ballistic missile booster engine test from a couple of weeks ago seem to be that). But not in flight that we know of. So that’s another risk area.

      We shall see. We can hypothesize all we want, but evidence is scant so far. We can discuss the historical and background information but we don’t really know yet what this missile is, really. Skepticism is wise at this time.

    • Jeffrey Lewis (History)

      It is awfully scant. I can’t even nail down the launch site.

  20. Anon2 (History)

    Thank you Jeffrey. I was hoping someone had more data, i.e. did Musudan/R27 make it off the pad, how far did it fly, what was the mode of failure, could it have been (cough) laser intercepted.

    Without a DPRK working method of long distance special delivery of the Silver Orb (AKA Little Boy’s Fat Man), the current risk calculus is changed, i.e. if the current probability that DPRK can retaliate or first strike the United States or Japan with nuclear weapons is perhaps zero as evidenced by this failure. This implies there is a window for unilateral actions to neutralize the fielded nuclear weapons and the production facilities without a DPRK long distance nuclear response. (Defending against a quick one way DPRK mission across the DMZ by an attack fighter flying a low level penetration profile is another story.)

    Depending on the probability assessment that DPRK would actually follow through on their rhetoric and use a nuclear weapon after the development and flight testing is completed, it might be rational to remove that risk now rather than wait until DPRK deploys 25 or so Musudans on mobile launchers hiding in a cave network. The unpredictable and perhaps irrational nature of the aggregate KJU regime/military makes it difficult to accurately assess the future risk that they will unilaterally launch a first strike once they have capability.

    Once it is certain that DPRK can deliver a long distance working nuclear weapon, the calculus changes to something like MAD depending on the reliability of the U.S./ROK/Japan missile shield.

    I am worried. I’d like a negotiated peace. That seems improbable.

  21. ben reuter (History)

    I think it is visible on google earth (compare history layer for progress of construction). Sadly enough we have no images from April 2013 or April 2016 when they supposedly had two launchers at this site.
    Cheers from Ben Reuter

    • Chris V (History)

      According to an April 14 Yonhap article: “South Korea’s Defense Ministry said Wednesday that the North has deployed one or two Musudan intermediate-range ballistic missiles near the eastern port city of Wonsan for a possible launch…”

      Regarding the launch:
      “U.S. Strategic Command (USSTRATCOM) systems detected and tracked what we assess was a failed North Korean missile launch at 3:33 p.m. CDT (4:33pm EDT),” said Lieutenant Colonel Martin O”Donnell, a USSTRATCOM spokesman. -ABC News

      The words “tracked” seem to indicate that the missile did not explode on the launch pad but actually flew a short distance prior to failure. That is what I am inferring from this quote.

    • Jeffrey Lewis (History)

      I concur.