By Michael Elleman
27 January 2017
According to the New York Times, Kim Jong Un proclaimed to the North Korean people, during his annual New Year’s address, that the military is in the “final stages in preparations to test-launch an intercontinental ballistic rocket.” A North Korean intercontinental ballistic missile, or ICBM, would be capable of threatening the continental United States. In response, President Donald Trump tweeted: “North Korea just stated that it is in the final stages of developing a nuclear weapon capable of reaching parts of the U.S. It won’t happen!”
Not to be outdone, the Wall Street Journal published an opinion piece advocating for the US to employ its sea-based, missile interceptors to knock down the North Korean ICBM should Pyongyang conduct a test launch. However, contrary to the hopes expressed by editors at the Wall Street Journal, the US does not have a proven capability to intercept an ICBM using sea-based assets. The Pentagon may nonetheless attempt to shoot down a North Korean ICBM with SM-3 interceptors based on Aegis destroyers, should Pyongyang elect to test one in the near future. However, the likelihood of success is limited, if not improbable. In fact, the probability that the North Korean ICBM test will fail on its own is significantly higher than the probability of success.
Plausible ICBM Flight Paths?
Drawing from an excellent description of how North Korea might test an ICBM by John Schilling, it is easy to see that the most politically and technically feasible flight-test option would be to use an Unha rocket—possibly one modified to include higher-thrust engines for the upper stages—to evaluate warhead re-entry technologies. The test would likely succeed because the Unha is a relatively proven system, though using the satellite-carrier rocket as a military missile would throw cold water on Pyongyang’s claims that its space program is a strictly civilian enterprise. Further, relying on Unha technology would do little to address the development challenges associated with the KN-08 or KN-14 missiles, which appear to be optimized for the delivery of a nuclear weapon. As such, if North Korea’s primary objective is to develop an operational ICBM, Pyongyang would want to begin by conducting flight trials of the KN-08, KN-14 or both notwithstanding the strong probability initial test flights would fail.
How the missiles are tested will also take into account geographic, political and diplomatic constraints. To avoid the risk of a simulated warhead landing on the territory of another country, North Korea would likely fly the missile to the east; however, an easterly trajectory would necessarily overfly Japan. A test of the two-stage KN-14 offers the greatest likelihood that the impact of the first stage would fall well short of Japan (Figure 1). Use of the three-stage KN-08 would leave little room for error in missing Japanese territory (Figure 2). It therefore seems reasonable that if North Korea decides to launch an ICBM toward the Pacific Ocean, the KN-14 would be the preferred missile.
Figure 1. The KN-14, which has only two stages, can safely be launched to various ranges without risk of the first stage striking foreign territory.
Figure 2. Launching the three-stage KN-08 to the east risks having the second stage land on Japanese territory. This would likely deter North Korea from choosing the KN-08 for its initial ICBM test launch.
Can a Test be Prevented by Military Means?
The United States and Japan operate Aegis ships armed with SM-3 Block 1A and 1B interceptors in the East Sea. These ships are capable of intercepting short, medium and intermediate range ballistic missiles in the mid-course and terminal phases of flight. Tests to validate the performance of the SM-3 Block 1 interceptors are ongoing and to date have been largely successful. SM-3 interceptors have never been tested against an ICBM, nor have they been tested against any missile in the boost or ascent phase of flight. In other words, boost- or ascent phase intercepts using SM-3 interceptors are an unproven, hypothetical capability.
An Aegis ship armed with SM-3 Block 1A or B interceptors could, in principle, intercept a North Korean KN-14 ICBM under a limited set of circumstances. If North Korea flies a KN-14 on a minimum-energy trajectory, and the Aegis ship is located 500 km from the launch site, intercepts are kinematically possible. If, however, Pyongyang launches the KN-14 on steeper trajectories, the possibilities are reduced. For lofted trajectories roughly 18 degrees steeper than minimum-energy ones, no intercept is possible. In other words, North Korea can defeat America’s current sea-based capabilities by flying the ICBM to higher altitudes and shorter distances, while still gaining the necessary engineering information to support missile development. Though it must be noted, as stated previously, the KN-14 (or KN-08) is more likely than not to fail on its own during initial flight tests.
But even if the US was improbably fortunate, and North Korea launched a KN-14 directly over an Aegis ship, and the trajectory is not sufficiently lofted, it is doubtful that a successful intercept would occur. There are multiple operational reasons why an intercept is beyond current capabilities.
First, it is doubtful that an Aegis ship would be close enough (500 km or less from the KN-14 launch location) at the right time. The US or Japan would be placing their Aegis boats at considerable risk if either attempted to move closer than 200 km off North Korea’s coast while waiting for a launch. At the very least, good fortune would be needed to have an Aegis ship in the right place, at the right time to support the narrow circumstances under which an intercept could occur.
Second, it is unclear if the necessary tracking data can be acquired with enough precision when relying solely upon the Aegis’s on-board SPY-1D radar. Would other high-precision sensors be available to aid in developing a KN-14 track at the earliest possible moment? The answer today is likely to be no.
Third, can a fire-control solution be developed in just the required 10 seconds after the SPY-1 radar detects the KN-14 missile? This is likely an overly optimistic assumption, as command, control and communication limitations would likely delay the transmission of critical data, the development of a fire-control solution by the Aegis SPY-1D radar and battle management system and finally the decision and command to fire the interceptor. If it turns out that 30 seconds are required, then an intercept using SM-3 Block 1 interceptors is not possible, even when only the kinematics are considered.
Fourth, to reduce the chances of a successful intercept, North Korea could decide not to fly the missile to maximum range and to put it on a trajectory that is off-line from the Aegis ship. But even in the unlikely event that the KN-14 flies directly over an Aegis ship, the KN-14 would have already passed over and be moving away from it because a fire-control solution for the interceptor will likely require too much time. While it is still kinematically possible for intercepts to occur when the target is moving away from the SM-3’s launch position, such intercepts are not considered feasible because the interceptor is ‘chasing’ the target from behind. Therefore, the last possible intercept point is defined to occur when the target is directly over the Aegis ship.
In sum, current capabilities to intercept a North Korean ICBM using sea-based assets are lacking. However, when the SM-3 Block 2A interceptor becomes operational, the calculus changes dramatically. The Block 2A interceptor is projected to have a burnout velocity of 4.5 km/second, which is 50 percent faster than the current Block 1 interceptors. The added speed facilitates much greater possibilities. With this in mind, the Pentagon should be developing concepts of operations, procuring enabling assets and planning to test the Block 2 interceptors against ICBMs in the boost and ascent phases.
Preventing Kim Jong Un from developing an operational ICBM can be achieved if North Korea never tests prototypes of the missile. Without flight tests, Pyongyang will not know if the ICBM’s performance and reliability are adequate. However, sea-based missile defenses available today are not capable of reliably interrupting a North Korean ICBM test.