By John Schilling
12 March 2015
The past year might seem to have been one of conspicuous inactivity in North Korea’s long-range rocket program. The last flight test was the December 2012 launch of an Unha-3 carrying North Korea’s first successful satellite. Since then we have seen only the usual Scuds and Nodongs and possibly an improved variant of the short-range, solid-fueled KN-02 “Toksa.” The Musudan and KN-08 missiles so proudly displayed in July 2013 have not been seen since, and neither has been flight tested. In short, one might be tempted to conclude that the regime has given up its pursuit of long-range weapons.
But conspicuous inactivity can mask quiet activity, visible mainly to the sort of people who spend their hours scrutinizing satellite imagery of obscure corners of the DPRK. I’m not one of them, but I am on their mailing lists. And these observers have seen interesting developments lately. Possibly most significant in the near-term have been reports of the continuation of the rocket engine ground testing that has been underway at the Sohae Satellite Launching Station since 2012, if not before. There has also been significant infrastructure construction at that facility, including a recently modified gantry tower sized for a space launch vehicle (SLV) much larger than the Unha-3. Most recently, a potential test facility for a submarine missile launch system was identified, which, while certainly not suited for long-range rockets, indicates active exploration by the North of possible new launch platforms. It is worth emphasizing, however, that such a development is likely far in the future.
The possibility that North Korea may have begun to move on from the Unha-3 SLV is not surprising; most nations retire their first SLV after one to three successful flights. After demonstrating basic spaceflight technology at minimum cost, a more sophisticated and capable design is usually developed for operational space missions. With a larger gantry waiting at Sohae, this appears to be the North’s plan, and it will be interesting to see what sort of space missions are on Pyongyang’s agenda. A North Korean astronaut may be far in the future but communications satellites in geostationary orbit or spy satellites may not.
That said, an intercontinental ballistic missile (ICBM) using the basic Unha design, does not appear to be part of Pyongyang’s plan. We first mistook that rocket (from grainy satellite photos) as an ICBM, and gave it the delightful name “Taepodong-2.” But the Unha is clearly not optimized for military use; it is too large and cumbersome, and its upper stages would have more thrust if they were meant to carry heavy warheads. If the plan were to evolve the Unha-3 into a capable ICBM, or even to use it for technology development for other ICBM-class systems like the KN-08, they would most likely continue testing the current design and eventually a more sophisticated but not larger system.
Still, it is possible that, in a pinch, the DPRK might deploy a limited number of these systems as a stop-gap measure to demonstrate an ICBM capability. Other countries, like China, have done just that. Moreover, there have been reports dating back to the 1990s about North Korea exploring building missile silos, most recently at Mt. Paektu, near the Chinese border. It is not clear that the Unha rocket—8 ft in diameter and nearly 100 ft tall—could even fit in those silos. And we have not seen the reentry vehicle testing that would be necessary to turn the Unha into a weapon. With large rockets, what goes up does not necessarily come down, at least not in one piece. However, we cannot rule out limited deployment of an Unha-derived ICBM as an interim capability.
Ground testing of rocket engines could give insight into what long-range missiles North Korea may build, and there is evidence of extensive activity since about 2012. Unfortunately, it is not always clear what engines are being tested. The most obvious possibility is the Isayev 4D10 engine North Korea is believed to have acquired from Russia along with a number of surplus R-27 submarine-launched missiles in the 1990s (that’s the SS-N-6 to all you old-school cold warriors). This is likely the only high-performance liquid-fueled engine available to North Korea, but in over 15 years, no North Korean rocket using this engine has been successfully flown. Without a high-performance engine in this class, North Korea cannot hope to build an ICBM smaller or less cumbersome than the Unha.
As indicated by the spectacular loss of a US Antares rocket in October of last year, ex-Soviet rocket engines that have been sitting in warehouses since the early 1970s are troublesome at best. It should be noted that four out of five Antares launches with the Russian NK-33 engine were successful; North Korea would likely be satisfied with missiles that can match that performance. However, requalifying the old Russian engines for US use required approximately 15 series of ground tests over a three-year period, with direct Russian assistance. If North Korea is getting serious about using its old R-27 engines, they are probably having more trouble than anticipated and may have another year or more of testing to do. Other possibilities for the observed testing include integrated clusters of North Korea’s demonstrated Scud and Nodong engines, and possibly new engines of North Korean design.
Of chief concern to the United States is the KN-08 road-mobile ICBM first spotted in April 2012 in a parade in Pyongyang. The availability of high-resolution imagery from the July 2013 parades allowed for a more refined assessment of the KN-08 missile than was previously available. The parade articles were mock-ups, but of a more advanced design than was seen a year earlier, with items like fuel ports and interstage structural reinforcement visible in consistent locations. Figure 1 shows an image from the parade, and Figure 2 the model derived from that image.
Figure 1: KN-08 mock-up from a July 2013 parade.
Figure 2: KN-08 external configuration.
Figure 3: Estimated KN-08 internal configuration.
The missile is slightly smaller than first estimated—only 1.9 m in diameter rather than 2.0 meters, and 17.1 m long. Figure 3 shows the current best estimate for the internal configuration of the KN-08. The fuel ports and interstage reinforcement limit the size of the engine bays, and the only known North Korean engines that would fit these bays while still providing adequate thrust are a cluster of four improved Scud engines for the first stage, a complete R-27 engine for the second stage, and a set of R-27 vernier engines for the third stage. The KN-08 also sports a triconic reentry vehicle at the business end. This is a simple and robust design well suited for novice rocket scientists, though not conducive to great accuracy. And, importantly, not tested in North Korea. There is no way to fit that test between the Yalu River and the 38th parallel; and no way to get the results back without a North Korean ship somewhere downrange. So any test with a North Korean ship parked near the impact zone is something we are going to want to look for.
The KN-08 (along with the North’s new Musudan intermediate-range and old Nodong medium-range missiles) is sized for a warhead of about 60 cm in diameter, consistent with a total warhead weight of 500 to 700 kg. It is plausible that North Korea’s nuclear testing to date has produced a low-yield (~10 kiloton) fission warhead in this class. With such a warhead, the KN-08 could achieve a range of 7000 to 9500 km, probably enough to reach parts of the west coast of the United States. (The Musudan, by comparison, would have a range of only 3000 to 4500 km, capable of reaching Guam but not the US mainland.)
It has been repeatedly suggested that the KN-08 parade models are simply fakes and that there is no real missile being developed. Indeed, until there is a test flight—even a failed one—there is no way to be sure. However, if they are fakes, they are now sophisticated and technically credible ones, representing a substantial investment of money and engineering talent. North Korea has in other programs (such as the Unha) demonstrated almost everything it would need to make a real KN-08 except the second stage engine and the reentry vehicle. They are also busy with ground tests of an unknown large rocket engine that they don’t need for any of their other programs. The safest assumption is that the DPRK is doing exactly what it looks like it is doing—building a real KN-08 ICBM. The question is whether, and when, they will succeed.
Without flight testing, the KN-08 will not be an operational weapon. Even under ideal conditions, flight tests of early ICBMs have a high failure rate; the probability of success if the first flight attempt is a combat launch is extremely small. In order to field the KN-08 as an operational weapons system, North Korea will need first to complete its engine ground test program and achieve reliable operation of the R-27 engine. Then, Pyongyang will have to complete a series of flight tests, with each incorporating design modifications based on what has been learned. At least one of these will need to include reentry vehicle testing with a downrange recovery ship. Only when the full test sequence is complete can the production of operational missiles begin.
The pessimistic scenario (from a US viewpoint) is that North Korea aggressively pursues these developments and encounters no major difficulties. Even in this case, the earliest plausible timeframe for operational deployment would be 2018 for the more complex KN-08 missile. North Korea might deploy as many as 50 of these missiles using stockpiled R-27 components, and eventually learn to manufacture equivalent systems themselves, allowing a second-generation KN-08 with improved performance to be deployed circa 2025. Foreign assistance could play a critical role, providing technical advice and maybe specialized parts and materials. A schedule this aggressive allows little room for mistakes, and that really calls for expert assistance. If the North Koreans are teaching themselves rocket science, they are likely to make quite a few mistakes before they get it right.
The most realistic scenario sees operational deployment of the KN-08 shortly around 2020. North Korea might choose to deploy a small force of Unha-derived ICBMs as an interim capability; these would be large and cumbersome weapons subject to preemptive attack. The number of KN-08 missiles would be limited to one or two dozen and no second-generation system would be seen before 2030. First-generation missiles would be transportable rather than mobile, limited to paved roads and prepared sites and requiring hours to ready for launch. They would be generally unreliable and inaccurate, incapable of targeting anything smaller than a large city, and equipped with low-yield fission warheads.
We could, however, see North Korea struggle with the challenges of developing long-range missiles for a decade or more. For example, domestic political, economic and technical constraints could all impede North Korea’s progress, as could more effective economic sanctions and other diplomatic efforts (that prevent further long-range tests). The North could still deploy a few Unha-derived ICBMs. And, of course, the substantial force of Nodong missiles—some almost certainly nuclear-armed—would pose a continued regional threat, along with shorter-range tactical systems. North Korea can certainly cause a world of grief if the regime is desperate enough, even if it can’t directly target American cities.
Which of these will come to pass is something we should expect to learn from North Korea’s long-range missile tests. The North will soon reach the point, if they have not already, where they can learn little more about missiles from ground tests or from satellite launches. If Pyongyang does not test long-range missiles, or if it does and the tests persistently fail, we should have little to fear. A pattern of success, including reentry vehicle tests with a downrange support ship, would be a clear warning sign of dangerous developments to come.
 Assumes 20-30 flight-worthy R-27 engines are available with an unknown split between KN-08 and Musudan missiles.