Saturday 27 May 2017

The range of North Korea's Hwasong-12

Hwasong-12 launch. Source: Rodong Sinmun

On 13 May 2017 at 20:58 UT (May 14 in local time, just after local sunrise), North Korea launched a new type of IRBM, the Hwasong-12. It is probably one of the surprise mobile launcher missiles seen during the April 15 parade. A North-Korean Rodong Sinmun communique on the launch is here.

Hwasong-12 on mobile launcher. Source: Rodong Sinmun
In this blogpost, I try to find the maximum range of this missile, going from released information about the missile's trajectory by Western and North Korean sources. I should ad that my analysis is not original: it is inspired by earlier similar analysis by David Wright on the All Things Nuclear blog and a later analysis by Ralph Savelsberg on the 38 North blog.

Hwasong-12 being erected. Source: Rodong Sinmun

My analysis was sparked by three things. One was that I wanted to see whether I could reproduce David Wright's results. The second was that I wanted to visualize the situation (I am a visually oriented guy).

The third was a recent exchange on Twitter between me and Dutch science journalist Martijn van Calmthout of the Volkskrant. He had written a newspaper piece on North Korea's recent missile and atomic activities that seemed to underplay the significance of the May 13 test, choosing wording to suggest North Korea could not reach Japan with this missile. I then pointed him to David Wrigth's analysis.

Van Calmthout is a good journalist, so as a result of our Twitter conversation he actually followed up with a new Volkskrant piece where he corrected himself later:

As pointed out by David Wright, the May 13 test missile was not launched on a standard trajectory but on a so-called 'lofted' trajectory: North Korea released info that the missile travelled a ground distance of 787 km and reached an apogee altitude of 2111.5 km. Western military sources quote similar figures, so I see no reason to doubt them.

Such a lofted trajectory brings the missile very high and shortens the ground track. Fired on a more normal trajectory, the same missile with the same impulse would fly a much larger ground distance. A more normal apogee altitude for a missile like this is 600 to 1300 km.

The reason that North Korea choose this 'lofted' trajectory, is in order to avoid that the missile overflies neighbouring countries, which could be mistaken for an attack and might evoke countermeasures. South Korea, Japan (for obvious reasons) don't like it when North Korea fires a missile over their territory.

The 13 May test missile was launched from Kusong in the western part of North Korea, into an E-NE direction overflying North Korea and then onwards over sea. As part of the photographs released by North Korea after the test, an image was released showing Kim Jong Un with a map of the missile's trajectory. Based on that map, I estimate the impact point of the missile to be near 41.64N, 134.27 E, which indeed is ~787 km from Kusong (I have taken the airport near Kusong as the launch location). This is a bit further away from Vladivostok than earlier reports suggested: about 250 km. Of course these could perhaps be the intended test results rather than  the true test results.

Kim Jong Un with map (click to enlarge). Source: Rodong Sinmun
blow-up of part of previous picture

I used these parameters (estimated impact point, 2111.5 km apogee altitude) as input in STK in order to model the trajectory. It suggests that the missile delivers an impulse of 5.59 km/s. The launch was towards azimuth 72.5 degrees under an angle of 81 degrees, almost vertically. The resulting time of flight would be 28 minutes, very close to the ~30 minutes reported by western sources.The resulting trajectory is (as it should be) very similar to that on the photographs above.

Next, I used the same parameters (in terms of impulse), but with the launch angle adjusted from 81 degrees to 45 degrees, consistent with a more normal trajectory optimized for maximum range. This is the visualized result:

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The red line shows the 'lofted' trajectory from the May 13 test. The blue line shows the trajectory the same missile with the same impulse would travel using a 'normal' launch angle.

The resulting maximum range I get is about 4200 km (with an apogee altitude at ~1300 km) - close to Wright's original figure of 4500 km, somewhat less than his later revised figure of ~4800 km, and slightly larger than Savelsberg's 3700 km. Given the uncertainties, all results mentioned are in the same ballpark figure.

A distance of 4200 km brings this area into range of the Hwasong-12:

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This range circle reconstructed for the Hwasong-12 includes Japan, almost the whole of China, east Russia and the Phillipines. The US bases in Guam would also be in reach, i.e. this means that in theory (and if North-Korea has developed a working re-entry vehicle to match the missile - interestingly, their Rodong Sinmun communique mentions that the test also verified "the homing feature of the warhead under the worst re-entry situation") North-Korea would have the power to strike US bases outside of South Korea with this missile.

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Outside of Hwasong-12 reach would remain Hawaii and the US mainland: the 4200 km range falls just short of reaching Alaska.

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Edit:  The actual range of a missile depends on several parameters. One of these is what you put on it, i.e. the warhead used.

The STK analysis is also slightly simplified as it treats it as purely ballistic and ignores atmospheric drag during initial launch phase and reentry.

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