North Korea’s September 15 Hwasong-12 Test: The Why and The Wherefore.

On September 15, at 627am Pyongyang time, North Korea test fired a Hwasong-12 IRBM that landed 3,700km into the Pacific Ocean. When you watch video footage of the launch you can see preparations, that is the placing of the Hwasong-12 on its accompanying mobile erector platform, at about dawn which would have been 5.23am Pyongyang time.

That gives us an hour from when *that* footage was taken and the actual launch of the Hwasong-12. In a press release KCNA stated that the Hwasong-12 launch was, in part, a combat readiness drill of the missile system. Given that the Hwasong-12 is powered by the Pektusan engine, just like the first stage of the Hwasong-14 ICBM, the propellants are N2O4 for the oxidiser and UDMH for the fuel.

The test was a standard, that is minimum energy, trajectory test of the missile. That is the second MET test of the Hwasong-12. The flight profile was awfully similar to the first, it being launched from the same Pyongyang location, overflying Hokkaido at the Cape of Erimo, and then heading out for the Pacific. The reported apogee of the September 12 test was 770km. For the first MET test, on August 29, the apogee was 550km. The range of the September 15 test was 3,700km which is the target range to US air assets at Guam.

David Wright calculates that the September 15 Hwasong-12 test launch was close to apogee when it passed over Hokkaido, hence it did not enter Japanese airspace over Hokkaido (the Karman line separating space from the atmosphere is at 100km). The Hwasong-12 certainly, therefore, could not have been intercepted by Japan’s PAC3 Ballistic Missile Defense system, which is deployed on the Japanese main lands, given that PAC3 is designed to intercept missiles warheads on a terminal trajectory.

However, a sea based Aegis SM3 intercept could have been attempted by either Japan or the United State as Aegis SM3 is a midcourse interceptor which could be used to strike a missile at or close to apogee. The launch location was the same as the August 29 launch. The launch trajectory was the same as the August 29 launch. The test was much anticipated, and reports in The New York Times suggest preparations for the launch were picked up by US intelligence.

The September 15 Hwasong-12 test could not have been better scripted by Kim Jong-un for Ballistic Missile Defense. However, again BMD was nowhere to be found. This test, like the August 29 test, meet Ashton Carter’s criteria for a BMD intercept test. The Bush administration intercepted a wayward satellite with an SM3 interceptor fired from an Aegis naval vessel, so eager were BMD proponents for positive publicity.

The Hwasong-12 re-entry vehicle is not like the Hwasong-14 ICBM re-entry vehicle. As you can see below it is more slender. Underneath the image of the Hwasong-14 RV is the hydrogen bomb that North Korea tested on September 3. The fourth image below is a better man to RV comparison of the Hwasong-12 RV. One must wonder whether that hydrogen bomb can be delivered by the Hwasong-12 IRBM. This might explain the difference in the dimensions of the Hwasong-12 and Hwasong-14 RVs, that is the Hwasong 14 RV was designed to deliver the hydrogen bomb (but not for the Hwasong-14 ICBM) not just the boosted fission weapon.

David Wright has also argued that the Hwasong-12 is quite inaccurate putting the CEP at 5 to 10km “and possibly larger.” The Hwasong-12 IRBM is widely credited with targeting Andersen Airforce Base at Guam. An airburst 5psi blast overpressure damage radius would be 3.7km for a 150KT warhead. That makes the Hwasong-12, even with a 5km CEP quite inaccurate in terms of single shoot probability of kill and at 10km CEP one has a single shoot probability of kill at less than 10%. Assuming that the Hwasong-12 is this inaccurate and that its payload is a 35KT weapon then its single shoot probability of kill for a Guam mission becomes even less.

However, there exists good reason to suppose that the hydrogen bomb tested on September 3 had a yield of at least 350KT, in which case at a CEP of 5km the single shoot probability of kill (assuming a 4.9km 5psi blast overpressure lethal airburst radius) becomes 48% and at 10km CEP SSPK becomes 15%. Notice none of these calculations are expressed in terms of two-on-one cross targeting, which increases the probability of kill. Notice also this all assumes that the Hwasong-12 has a hydrogen bomb payload, which is by no means a done deal as discussed above.

To increase the lethality of a nuclear warhead by a factor of 4 one can improve the accuracy by a factor of 2 (halve the CEP) or increase the yield by a factor of 8. Increasing accuracy is a more efficient means of increasing lethality than yield. This means North Korea, assuming rationality, will not necessarily seek to increase the yield of its nuclear warheads rather Pyongyang will work to increase the reliability of its missiles and the accuracy of its RVs, both important quantities for boosting the single shoot probability of kill. The big advances from this point onward would come in North Korea’s missile programme, less so in terms of nuclear weapons unless, of course, North Korea seeks lower yield battlefield tactical nuclear weapons. Although the RV for the September 15 Hwasong-12 test would not give North Korea any great added insight into the re-entry capabilities of the Hwasong-14 RV fired on an MET trajectory, it would give insight into a Hwasong-12 RV fired on an MET trajectory which of course is the point.

That all equates to more and more missile testing. The more North Korea tests its missiles the more reliable they will become. The more they test their RVs on MET trajectories the more data they have to learn how to improve guidance. I have seen a graphic animated depiction of a North Korean Hwasong-14 flight which includes retrorocket burn prior to RV separation and something depicting almost a post boost vehicle after separation. Both facets can increase accuracy. These are only animations, it is to be stressed.

The September 14 test was widely seen as a response to the September 11 UN sanctions passed by the Security Council in response to the September 3 hydrogen bomb test. I do not accept this interpretation.

A missile test, indeed a testing programme, is a complex scientific undertaking and missile tests are intricate scientific experiments. I suspect that North Korea is not, and will not, necessarily conduct missile tests as political demonstrations of resolve following UN sanctions and the like. Rather North Korea will, indeed I submit is, conducting reliability and accuracy testing of its missiles mostly for technical reasons. That is, North Korea will use, indeed is using, increasing sanctions and heated US rhetoric and military demonstrations as legitimatory cover, as it were, to further pursue the scientific and engineering requirements of its missile programme.

The goal standard for North Korea remains reliable solid fuelled road mobile IRBMs and ICBMs, as well as solid fuelled sea launched MRBMs and IRBMs. That remains a work in progress and that requires tests, tests and more tests.

The two Hwasong-12 MET tests, important scientific experiments, have all but normalised or routinised what just a few months ago was considered almost unthinkable. Namely, frequent MET testing over Japan into the Pacific. Just what North Korea needs to continue its missile programme, and a comatose BMD is a handy bonus.

The UN sanctions and Trump’s twitter account helps handily to normalise such tests.