Continued from “A New ICBM for North Korea?”
The most important question is: “Does this change the threat posed by the KN-08 missile?” The simplest answer is: “not by much.”
There is very little performance impact. Figure 6, below, shows range-versus-payload curves for both the original KN-08 Mod 1 missile and the Mod 2 configuration discussed here. The new version offers slightly less range with the lightest warheads, though somewhat more with heavier loads. But the differences are small, within the margin of error of the calculations given how little we know about the Mod 2 design. And the use of a blunt-body RV will allow the North Koreans to reduce the warhead weight while maintaining adequate protection against reentry heating, which should recover some of the lost performance. So the KN-08 Mod 2 probably will not fly any farther than we expected the Mod 1 to reach.
Figure 6. Estimated performance of the KN-08 Mod 1 and KN-08 Mod 2 missiles.
This should not come as any surprise. The North Koreans have a fairly limited technology base for building long-range rockets, and they are further constrained by the need to carry this rocket on a heavy-duty truck. There is no magic to change the basic engineering realities here. However the North Koreans tinker with the shape of the missile or the number of rivets, any rocket they can fit onto a WS-51200 transporter using their existing engine technology will be a very marginal ICBM capable of reaching Pacific Rim targets out to the US west coast, but no farther, and then only with lightweight warheads. If they eventually develop better engines, we will have to reevaluate this estimate.
The KN-08 Mod 2 will probably be less accurate than we expected for the Mod 1. The error ellipse will be at least 5 km crossrange and 10 km downrange, and achieving even that level of performance will require multiple calibration tests of the RV. It will also be more vulnerable to interception, particularly if the intended recipient can deploy missile systems like Patriot or THAAD in the target areas. ICBM warheads are typically too fast to be shot down by such missiles, but blunt RVs slow quite a bit as they descend.
The biggest advantage of the Mod 2, particularly for the two-stage version we expect, will be increased reliability. We had previously estimated, based on the performance of other North Korean multistage rockets, that the KN-08 Mod 1 would work only 30-40 percent of the time in early operation. With the more robust design, the Mod 2 could have a 50-60 percent reliability at its initial operational capability. The North Koreans may have decided to trade a bit of performance to get a missile that is more likely to reach its target than to fall back on North Korean soil. It is even possible that the performance has increased slightly, though there is little room for major gains in this design.
But perhaps the most important change in the threat is that it has been postponed. While this may be a simpler and more robust configuration, and one which retains key elements of the Mod 1, it is also a substantial design change relatively late in the development process. This means that design work has not proceeded as far or as fast as we might have feared, and that some work already completed has been tossed out and will need to be redone. Just as telling is the lack of any flight tests for any version of the KN-08, or even of the related single-stage Musudan missile. North Korea seems to have been slow to resume their engine ground testing after an overhaul of their test facilities.
We had previously estimated that the KN-08 would enter very limited operational service no earlier than 2018 and most likely in 2021. It is now unlikely that the KN-08 Mod 2 could enter service before 2020, and most likely not until 2023. Given the major design changes on the missile flight testing will probably not begin for 2-3 years, and a substantial flight test campaign will be required before production can begin. North Korea appears to be making progress towards developing a road-mobile ICBM, but it is slow progress and the end result will likely be a missile of modest reliability and limited performance.
Return to last section: What’s “Under the Hood”
 The design of the KN-08 Mod 2 began in approximately 2013, and the changes are substantial enough to require more than two years of design work. Ground testing will also be required, and an upgrade of North Korea’s test facilities in 2014-2015 will have interfered with such tests until quite recently. Two to three years of additional development and ground testing is a conservative estimate. North Korea’s past record suggests that at least three flight tests will be required to demonstrate success on a vehicle of this complexity, with a year or so between tests to incorporate the lessons learned. With a proven design in hand establishing a production line and testing manufacturing processes will likely take another one to two years.