Analysis of North Korea’s Musudan Missile Test–Part 1

, co-director and senior scientist | June 24, 2016, 3:58 pm EST
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After four failed attempts to launch its so-called Musudan missile (called Hwasong-10 in North Korea), it appears to have had at least one success in a new sets of flight tests on June 21. That test tells us something interesting about the range of the missile.

The second of the two launches on June 21 apparently flew successfully, but followed an unusual trajectory. It splashed down into the Sea of Japan at a range of only 400 km from the launch site, but was highly lofted so that it reached an altitude of 1,400 km.

Using this trajectory allowed North Korea to test the missile from its military launch site on the country’s east coast without flying over Japan, since the Musudan’s range on a standard trajectory is about twice as great as the distance from North Korea to Japan (Fig. 1). A past overflight of Japan caused serious international tensions and it seems likely this launch was intended to test the missile while avoiding that.

Fig

Fig. 1 The red circle shows a range of 400 km from the launch site. (Source: Google Earth, with additions)

Range of the Musudan missile

Knowing the range and maximum altitude of the test flight allows us to estimate the range of the Musudan if it were launched on a standard trajectory.

I put together a computer model of the missile based on estimates of parameters like thrust, engine burntime, payload, etc. I then adjusted those parameters to give a range of 400 km with an apogee of 1,400 km. Using those same parameters, I then calculated what the maximum range of that missile would be if flown on a non-lofted trajectory. The result of that calculation is shown in Fig. 2.

That calculation shows that the Musudan’s range would be about 3,000 km on a standard “minimum-energy” (MET) trajectory, assuming the same payload as the lofted test.

Fig.

Fig. 2  The red curve shows the lofted trajectory that was reportedly used in the second test on June 21. The black curve shows the trajectory of the same missile flown on a standard “minimum-energy” trajectory (MET).

This is an interesting result because it is significantly shorter than many estimates of the Musudan range. For example, this WikiLeaks document gives an official US range estimate of 4,000 km with a 500 kg payload.

I have long been skeptical of those range claims. The Musudan is believed to be based on a Soviet submarine-launched missile, the SSN-6, which the Koreans have lengthened to carry more fuel and increase its range. My analysis based on the performance of the SSN-6 suggests instead a Musudan range of about 3,500 km with a 500 kg payload, and about 3,000 km with a 750 kg payload.

We don’t, of course, know what payload was used on the test. Maybe the missile carried a much heavier payload than 500 kg. But it would make sense for North Korea to conduct the test with the payload it would expect the missile to carry if it was actually used. For example, the reentry heating on a 4,000 km range missile would be nearly 40% higher than on a 3,000 km range missile, given the higher reentry speed. So the North would want to test on the equivalent of a 4,000 km range trajectory if it expected to fly the missile to that distance.

The 3,000 km range is also interesting since it is shorter than the distance to Guam, which is about 3,400 km (Fig. 3). Being able to reach Guam is seen as a key motivation for the Musudan since Guam has a US military base and is the next logical target for North Korea after its development of the Nodong missile to reach Japan.

If this test reflects the state of the art of North Korea’s missile and warhead technology it could mean that North Korea’s nuclear warhead is currently too heavy for the Musudan to carry it to Guam.

Fig.

Fig. 3 (Source: Google maps, with additions)

The “failure” of the first launch on June 21

Reports state that the first missile launched on June 21 broke up at a range of about 150 km and fell into the sea. That may have resulted from a simple mechanical failure, although it is not clear what would have caused it at that point in the flight.

There may be another possibility. It is unclear from press reports whether or not this missile was also flown on a lofted trajectory. If it was instead flown on a standard trajectory, it is interesting that 150 km range corresponds roughly to burnout of the Musudan engines (see red dot in Fig. 2).

Is it possible that Pyongyang launched the first missile on a standard trajectory to test the guidance and control system, and then intentionally terminated the flight following burnout to keep it from overflying Japan? That would allow them to test on a standard trajectory the guidance and control systems that operate in the early part of flight. The second test on the lofted trajectory would allow them to test the operation of the reentry heat shield in the later part of the flight. We discuss that more in Part 2 of this post.

So it would be very useful to know what trajectory the first missile followed.

Posted in: Missiles and Missile Defense, Nuclear Weapons Tags: , ,

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  • J_kies

    David
    The video from Youtube and associated captures have clearly shown the presence of 8 objects with strong similarity to grid fins. Given the stock propulsion system on the SS-N-6 Zydb provides plenty of guidance authority before someone decided to ‘stretch’ that optimized design, the presence of grid fins would indicate a need for additional base drag to acheive static margin. Since that margin argument exists, I expect that a near zero payload is the appropriate expectation for the early launch and the drag model applied needs to account for the ~ doubling of the vehicle area*Cd product.

    Incidentally – thrust termination at burnout ~ 100km altitude would propagate debris full range regardless.

  • jianyu

    Great scientific explanation. we are looking forward to the further research on the trajectory of the first test and other information.

  • nikkkom

    If it broke up on June 21 at a range of about 150 km, at burnout, it was already exoatmospheric and debris should follow approximately the same trajectory as an intact missile.

    • dwrightucsusa

      Yes. The assumption is that North Korea could have had the missile follow the normal flyout early on, but then use the guidance system before burnout to put it on a downward angle so the debris would fall at a much shorter range. Since that maneuver would change the vertical but not the horizontal component of velocity, burnout would still occur at about the same range.

      • J_kies

        Why make that assumption? Pulling a hard downward vector isn’t near the stock missile behaviors. Close to burnout fuel and oxidizer are cut off from the main engine at some close fraction of the intended state vector, verniers continue to achieve intended Vbo and then verniers stop. The maneuver you describe does not appear to have a military application so its value as a test protocol would be rather limited.

        • dwrightucsusa

          RIght, I don’t think they would do this maneuver because it was useful as a test protocol. The question is: If the DPRK wanted to test the missile on a standard flyout trajectory, how could they do that and avoid having the warhead, debris, etc. travel to long distances. They could do that by adding a nonstandard maneuver near the end of boost. The DPRK may not have tried an standard flyout, of course, but if it did it seems like it would need to have done something like this.

          • J_kies

            I suggest a shave with William of Okham. We invoke failure in the tested hypotheses and consider which mechanisms drop the missile at 150km. Main engine failure or fuel expenditure at about 1km/s is quite viable and plops the item near that range.

          • dwrightucsusa

            Yes, I expect you’re right. I was hearing some interesting things from some Japan reporters that got me wondering about other possibilities.