Resumed North Korean ICBM Testing: Possible Technical Objectives
On December 7, North Korea claimed to have conducted a “very important test” at its Sohae Satellite Launching Station that “will have an important impact on changing the strategic position of the DPRK.” The North Koreans did not describe what was tested, but prior open-source imagery suggests it was a static (ground) test of a large liquid-propellant rocket engine. It remains to be seen what rocket system the engine was associated with: a previously launched intercontinental ballistic missile (ICBM), intermediate-range ballistic missile, space launch vehicle, or a new system. In any case, the static test could be the precursor to a full-up flight test of an ICBM or one of these other systems. If North Korea decides or has decided to resume full-up ICBM launches, its decision almost certainly will be governed primarily by political objectives rather than programmatic factors, and tests will be conducted within parameters Kim Jong Un sets. North Korea’s rocket force developers and operators presumably would do the best they could to maximize value to the ICBM research, development and deployment effort within these parameters.
This article considers the possible technical objectives that North Korea might pursue if ICBM launches are resumed, within the political parameters set by the regime. Its principal conclusions are that North Korea is most likely to seek to improve the reliability and operational effectiveness of the Hwasong-15/KN-22 with a single warhead (rather than multiple warheads), that improving accuracy is unlikely to be an objective for a near-term ICBM test campaign, that the DPRK may not demonstrate missile defense penetration aids in flight tests (either because it cannot properly evaluate such tests or in order to conceal its penetration aid [penaid] capabilities) and that a next round of ICBM testing is unlikely to feature new types of ICBM systems.
Objectives of Renewed ICBM Testing
North Korea’s last launch of an ICBM was in November 2017. Starting with Kim Jong Un’s remarks in April 2019, and continuing through at least December 3, North Korea has been threatening dire consequences if the US does not change its approach to denuclearization negotiations by the end of the year. These threats have both implicitly and explicitly included a potential resumption of ICBM launches. The analysis of North Korean objectives for renewed ICBM testing is hindered by the fact that we do not know when the North might resume ICBM launches, how many times it might launch or what political parameters would govern those launches. Nor do we know much about what the DPRK’s 2017 ICBM tests achieved or what shortcomings in those systems remain to be addressed, much less DPRK plans for developing and deploying any further ICBM systems. Logically, however, it is possible to posit four broad technical objectives the North might seek to pursue in a next series of ICBM launches:
- improving the reliability of previously tested ICBMs and their single-warhead payloads;
- improving ICBM accuracy;
- testing new payload types, namely penetration aids or multiple-warhead payloads; and
- testing new types of ICBMs, most significantly solid-propellant missiles.
Improving Previously Tested Systems
The North conducted apparently successful launches of the 10,000 km range Hwasong-14/KN-20 ICBM on July 4 and 28, 2017, and of the larger, 13,000 km range Hwasong-15/KN-22 ICBM on November 28, 2017. This was a very small number of launches relative to the one to three dozen the US, USSR and China relied upon before deploying their first-generation ICBMs.
Based on its past practice with other ballistic missiles and reports of ongoing ICBM production and base construction, however, it is credible that North Korea could have deployed the KN-20 and/or KN-22 based solely on the limited flight testing to date. But these ICBMs almost certainly are not highly reliable at present, and the DPRK presumably understands that even a few more tests would improve their reliability and effectiveness. For example, all of the launches were on highly lofted trajectories to a much shorter ground range than a “minimum-energy,” full-range ICBM trajectory; thus, the missiles’ reentry vehicles (RVs) were not subjected to the thermal and mechanical stresses that would be created by a full-range flight.
Therefore, the most important and likely technical objective of a next round of ICBM launches would be to improve the reliability and operational effectiveness of the KN-20 and/or KN-22, particularly if some of these systems already have been deployed. Further launches would improve the North Koreans’ confidence that these systems will perform as designed, and would provide an opportunity to verify any modifications or improvements made to address whatever shortcomings they might have perceived in the 2017 launches. At least one or two more successful tests per system would substantially advance these objectives, but the more launches, the better (all other things being equal).
Even additional lofted-trajectory flights would be useful in building confidence in the performance of the KN-20/22’s launchers, booster stages, boost-phase guidance and stage and RV separation. But to address the very pressing issue of reliable performance at operational ranges and trajectories of the RV and the nuclear warhead it presumably is intended to contain, a successful full-range, “minimum-energy” trajectory flight using an operational RV and a “mock” nuclear warhead (with a stand-in for fissile material) would be ideal.
Such a launch would also, however, create the greatest political risks for North Korea, as an ICBM would probably overfly Japan in the general direction of the US and would telegraph the clear desire to increase the nuclear threat to the US homeland. Therefore, the North may stop short of conducting such launches, at least in the initial stages of a resumed ICBM launch campaign. It could avoid full-range testing if it used overdesigned (and, therefore, heavier) RVs and warheads and blunt-shaped (and, therefore, less accurate) RVs that would be highly likely to survive full-range flight, which probably would provide adequate confidence—based on likely historic North Korean standards—that an ICBM fired in anger would successfully strike targets in the US. (There also is a question about whether North Korea would be able to collect worthwhile reentry data from a full-range test without having a ship-borne collector—the existence of which currently is unknown—within line of sight of the impact area. But the North might test to full range anyway if its overriding purpose was political impact.)
A final aspect of launching previously tested systems is whether the North would launch the KN-20, the KN-22 or both. We have no real insight into the genesis or lineage of the two systems, or of how they might be related. From a purely military standpoint, however, the KN-22, with its substantially greater range/payload capability and larger-diameter payload section, would have greater military potential against the United States. Although this potential comes at the cost of greater length and weight that would make the road-mobile KN-22 harder to move around than the KN-20, the KN-22 would probably be given a higher priority for further launches.
Low accuracy is a traditional shortcoming of longer-range North Korean ballistic missiles. Because accuracy in inertially-guided missiles degrades as a function of flight time (and thus range), this shortcoming would be even more acute for the North’s ICBMs—particularly if, as is likely, it uses blunt-nosed RVs. One analyst has suggested such ICBMs would have accuracies of tens of kilometers.
Therefore, the North might seek to improve accuracy in resumed ICBM testing. It could try to reduce guidance and control errors during the boost phase of flight, and/or reduce reentry errors as the RV passes through the atmosphere.
- Boost-phase errors could be reduced by using higher-quality inertial instruments (if available), and/or by augmenting inertial guidance with satellite navigation updates (e.g., GPS) or stellar updates as in the 1970s-era Soviet SS-N-8 submarine-launched ballistic missile.
- Reentry errors could be addressed by moving to more slender, sharply-pointed RVs. But this would require using smaller-diameter and lighter nuclear warheads that are more technically challenging to build. Such RVs also are subject to higher atmospheric forces upon reentry than a blunt-nosed RV, increasing the need for successful long-range testing.
- Reentry errors also could be mitigated by using a maneuvering RV (MaRV) with terminal guidance. Doing so at ICBM range probably is beyond North Korea’s current technical capability, although it has apparently tested MaRVs on short-range ballistic missiles, which is much less technically demanding.
But given North Korea’s likely objective of using nuclear-armed ICBMs to threaten large US cities, extremely high accuracy would not be required. Even the currently-assumed accuracy of tens of kilometers would be sufficient. So for the DPRK, near-term accuracy improvement probably is a “nice-to-have,” allowing more efficient targeting of cities and the use of smaller (and smaller-yield) warheads once available, not a “must-have.” This is especially true if Kim Jong Un has political reasons to eschew full-range flights.
Testing New Payload Types
Analysts have readily noted that the KN-22’s greater range/payload capability and larger diameter open up the possibility for augmenting a single RV with other payload elements, such as penaids to confuse missile defenses or multiple warheads.
Given the existence of the US national missile defense system, which is specifically geared against DPRK missile attack, the North would have a clear motivation to deploy penaids. North Korea may also find penaids preferable to deploying large numbers of additional ICBMs in an effort to saturate US missile defenses, particularly if producing and deploying additional missile units and nuclear warheads is resource intensive. Penaids also could help mitigate the increased vulnerability to missile defenses of blunt-nosed RVs.
Penaids could take such forms as lightweight inflatable balloon decoys (and associated dispensers) that could be deployed from an ICBM in large numbers to confuse defenses about the location of the real RV during the exoatmospheric portion of flight, relatively lightweight chaff clouds (and associated dispensers) to confuse missile defense radars during exoatmospheric flight and small numbers of relatively heavy decoy RVs. Ideally, an attacker would want to thoroughly test penaids in simulated attacks against a replica of the missile defense systems’ sensors. There is no evidence that North Korea has developed such a test infrastructure or conducted such testing.
However, it would be consistent with North Korea’s historical missile development philosophy to deploy at least simple penaids on ICBMs without such testing—and consistent with its concealment and deception practices not to demonstrate penaids in flight testing at all to achieve surprise in wartime use (albeit at a lower level of reliability and effectiveness that would nonetheless probably be sufficient given historic North Korean standards). Thus, we may not see penaids tested in the next DPRK launch campaign even if they are to be deployed on ICBMs.
Use of a multiple RV payload (MRVs, warheads dispensed shotgun style without being individually targeted) or multiple independently targetable RVs (MIRVs) also would help combat US missile defenses. MRVs could allow better distribution of the destructive force of nuclear weapons against cities than a larger single RV, while MIRVs could permit striking several widely separated targets using a single booster. Either MRVs or MIRVs, therefore, could theoretically provide North Korea with operational advantages, as well as a big political splash if flight tested.
Based on past US/UK and Soviet practice, one might expect to see North Korea pursue less technically demanding MRVs before trying MIRVs. MIRVing also requires using substantial payload weight for the RV-dispensing post-boost vehicle (PBV, or “bus”) rather than for RVs, driving the use of smaller-diameter nuclear warheads and RVs with the technical and flight testing challenges noted above. MIRVing probably also would require substantially improved boost-phase ICBM accuracy to be cost effective. In addition, the North might consider the extent to which it wanted to put more relatively scarce nuclear warheads on fewer missiles and launchers that are potentially vulnerable to pre-launch attrition, launch failures and in-flight reliability problems.
Taking all of this into account, although multiple warheads have clear potential for the future, North Korea is more likely to focus a next ICBM launch campaign on single-warhead payloads than on multiple-warhead payloads.
Testing New Types of ICBMs
Just as there were no indications of the existence of the KN-20 and KN-22 before they were launched (although the US government reportedly may have known in advance about at least the KN-22), North Korea easily could be developing additional types of ICBMs that the US is unaware of. (The paraded but untested KN-08 and KN-14 ICBMs apparently have no better performance than the KN-20, much less the KN-22, and seem to use an inferior propulsion system based on that of the problematic Musudan intermediate-range ballistic missile. So North Korea is much less likely to continue to pursue these systems than the KN-20 and KN-22.)
A new liquid-propellant, road-mobile ICBM seems less likely at this stage given the KN-22’s performance and potential for improvement. The North might well be interested in having a smaller and lighter (KN-14-sized) system that would be easier to drive around than the KN-22, if such a missile could have enough range/payload capability to be worthwhile. But that may not be technically possible for the North in the near term, although it certainly cannot be ruled out. And North Korea’s long experience in road-mobile missile operations may allow it to manage KN-22 field deployments well enough that it has no urgent or near-term need to pursue a less balky liquid-propellant alternative.
More of a game changer would be the unveiling of a solid-propellant, road-mobile ICBM. Such a system could have many operational advantages, including faster reaction time, no handling requirements for toxic liquid propellants and no propellant storage and handling vehicles that make mobile missile operations harder to conceal. A solid also could avoid operational problems stemming from the relatively low boiling point and high freezing point of the liquid oxidizer used with the more powerful KN-20/22 propulsion system. And the launch of such a missile would be another powerful political statement.
But thus far, the most capable solid-propellant system the North Koreans have launched is the Pukguksong-3/KN-26 submarine-launched ballistic missile. The missile, launched for the first time only two months ago, is assessed to have a range of 1,900 to 2,000 km using two stages of some 1.4-1.5 meters in diameter totaling some 7.8 to 8.3 meters in length. This is a far cry from the US’s, USSR’s and China’s first solid-propellant ICBMs, which reached ranges of 7,000 to 10,000 km using three stages of some 1.8 to 2 meters in diameter, totaling some 13 to 21.27 meters in length.
We should not sell North Korean missile developers short. They may, for example, be able to use filament-wound motor cases in their first solid-propellant ICBM rather than the heavier steel cases these other countries used, allowing better range/payload performance. But the challenges of building larger solid-propellant motors should not be underestimated, either. While one should fully expect North Korea to seek solid-propellant ICBMs and to flight test them at their earliest combined technical and political opportunity, it is highly unlikely that such a system would be available for flight testing in a near-term DPRK launch campaign.
The Bottom Line
North Korea’s decisions about whether, when and how to resume ICBM launches almost certainly will be governed primarily by political rather than programmatic factors. Within whatever latitude they are given to shape a next series of ICBM launches, the North’s rocket force developers and operators are most likely to seek to improve the reliability and operational effectiveness of the KN-22, and possibly also the KN-20. Improving ICBM accuracy is unlikely to be an objective for a near-term test campaign, which is more likely to focus on single-warhead than multiple-warhead payloads. Although the North has a clear motivation to deploy missile defense penetration aids on its ICBMs, it may not demonstrate penaids in flight tests, either because it cannot properly evaluate such tests or because it wants to conceal its penaid capabilities from the US. Finally, a next round of ICBM testing is unlikely to feature new types of ICBM systems: new liquid-propellant ICBMs probably are unnecessary in the near-term given the KN-22’s potential, and North Korea probably is not technically capable of developing solid-propellant ICBMs so soon.
See: Min Joo Kim and Simon Denyer, “North Korea claims to have carried out a ‘very important’ test at rocket launch site,” The Washington Post, December 8, 2019, https://www.washingtonpost.com/world/2019/12/07/north-korea-claims-have-carried-out-very-important-rocket-test; and KCNA, “Statement of Spokesman for Academy of National Defence Science Issued,” December 8, 2019.
Because Sohae contains only a liquid-propellant rocket engine test stand (see Scott LaFoy, “It Takes a Village to Raze a Test Stand,” Arms Control Wonk, June 12, 2018, https://www.armscontrolwonk.com/archive/1205394/it-takes-a-village-to-raze-a-test-stand.), some press suggestions that the test was of a solid-propellant rocket motor (e.g., Hyung-Jim Kim, “North Korea Conducts ‘Important Test’ at Previously Dismantled Rocket Launch Site,” Time, December 8, 2019, https://time.com/5746075/north-korea-rocket-launch-test.) are almost certainly incorrect.
The DF-31 third stage was 1.5 meters in diameter compared to 2.0 meters for stages 1 and 2.