Another hot test, I confess I can’t get enough of these ‘cause they’re so rad, of the RS-25 engine for the SLS core stage, which brings us closer to the first RS-24 four cluster hot test, and the recent hot test of the Blue Origin BE-4 engine came at a time when I was thinking about a seeming anomaly in the hot testing of North Korea’s missile and rocket engines.
I am, naturally, referring to three key hot tests prior to the test launches of the Hwasong-12 and Hwasong-14 missiles. Those three tests occurred on April 2016, September 2016 and March 2017.
Analysis, and North Korean statements, suggest that the April 2016 test and the two subsequent were hot tests of different engines. North Korea stated that the April 2016 test was that for an ICBM, then presumed to be the KN-08 (Hwasong-13). The September 2016 and March 2017 tests, according to North Korea, were for the space programme. Hello anomaly.
We know North Korea wants to send payloads into geosynchronous orbits, further confirming its economic status as a poor advanced country rather than a poor technologically stunted country, and for this it needs a bigger SLV than the Unha class which is reversed engineered from Scud technology.
So, both in its space programme and its missile programme North Korea is advancing beyond Scud technology.
Images of the three hot tests, in chronological order, appear below. The second image shows the April 2016 test juxtaposed with the September 2016 test. The final image is a closer view of the engine that powers the Hwasong 12 and the first stage of the Hwasong-14 on the static test stand.
As stated above the first static hot test came when all eyes were on the KN-08 as representative of the North Korean ICBM. When the KN-08, as a mock up, was first paraded the assumption was that the KN-08 first stage was based on 4 Nodong engines, assuming North Korea would seek to use technical capabilities at hand, or a cluster of 3 4D10 engines derived from the Soviet R-27 SLBM if Pyongyang was seeking to push beyond its production possibility frontier (which of course it was).
However, further modified versions of the KN-08 on parade later suggested the very real possibility that the KN-08 could employ a cluster of two 4D10 engines for the first stage. This was all but confirmed when Kim Jong-un showed off the disco ball boosted fission nuclear warhead next to a KN-08 and a KN-08 Reentry Vehicle. See the two images below. The third image is of the back end of a Musudan missile, showing of the 4D10.
When you look at the image of the April 2016 static hot test and the KN-08 and R-27 above you can easily see why analysts concluded that the test was a of a cluster of two 4D10 engines. The image shows what appears to be a sunken configuration, and the plume, upon closer inspection, also appears to show two different exhaust plumes. When you zoom in for further detail it’s possible to infer the presence of vernier engines. So, bingo, this must have been a 4D10 cluster for the KN-08 ICBM.
Then we had a series of flight test failures from April 2016 onward, interspersed with the one successful lofted trajectory, of the Musudan medium range ballistic missile. So, the assumption has tended to be goodbye KN-08 with the 4D10 and hello a new engine, and that new engine powers the first stage not of the Hwasong-13 but of the new Hwasong-14. Will it feature in North Korea’s space programme, and how so? Time will tell.
As we know the nature and origins of the Pektusan engine, i.e. the core engine of the Hwasong-12 and Hwasong-14, are controversial with two schools of thought; one that the Pektusan engine is sourced from the Soviet era RD-250 and the other that the Pektusan engine was largely indigenously developed. Both sides, however, concur on initial acceleration analysis of the Hwasong-14 giving it a booster acceleration 4-4.5 m/s^2 and both sides have cited a thrust based on that analysis, and assumptions regarding mass, of just under 40 tonnes of thrust. See here and here for the shared initial acceleration analysis. The latter focuses on the Hwasong-12, but the analyses match.
That’s pretty close to the thrust of two clustered 4D10 engines with four verniers. Now the Hwasong-12 and Hwasong-14 do not employ a clustered configuration, but the North Korean statement that the April 2016 static hot test was for an ICBM and the analysis that it was a pair of 4D10 engines is consistent with the thrust arising from the initial acceleration analyses on the Hwasong-12 and Hwasong-14 engine.
North Korea stated that the September 2016 static hot test was of an engine with 80 tonnes of thrust. Assuming that the North Korean statement is accurate, and the derivation of thrust from the Hwasong-12 and Hwasong-14 initial acceleration analysis is also accurate, then we have a clear anomaly.
A dimensional analysis of the September 2016 and March 2017 static hot test comparative to images of the Hwasong-14 core stage engine demonstrates that they’re the same. That analysis can be seen in the Elleman paper cited above (the first of the two initial acceleration analyses). The engine tested on September 2016, the same as the March 18 test, is bigger than the April 2016 test.
What I am suggesting is that external analysis of the static hot tests and North Korean statements with regard to them are anomalous. Of course, North Korean statements have hardly been gospel, so this wouldn’t be a terribly new development but when Pyongyang provides a clear measurement, such as 80 tonnes of thrust, it’s hard to dismiss so easily.
That anomaly kind of bugs me, but also has me intrigued. Just what did North Korea mean when it cited that figure, and why did it do so? Perhaps this post is much ado about nothing, North Korea has been given to exaggerating previously but why would North Korea exaggerate on so precise a figure when surely Pyongyang would have known of the spectaculars just around the corner?
See video below of the latest groovy RS-25 hot test.