North Korea test fired a two-stage, liquid-propellant Hwasong-14 missile on July 4, 2017. The missile flew on a steep trajectory, reaching an altitude of about 2,800 km and impacting in the East Sea roughly 930 km from the launch site. A second flight test was attempted three weeks later, on July 28. It too flew almost vertically, peaking at an altitude of 3,725 km, while traversing a ground distance of approximately 1,000 km.
Based on available data from the two tests, analysists rushed to estimate the Hwasong-14’s reach if flown on a flatter trajectory intended to maximize range. The computed estimates for maximum range varied considerably, sparking vigorous debate among analysts about the Hwasong-14’s performance capacity. Media accounts, expert summaries, and reference sources generally favored the high-end estimates of the Hwasong-14, asserting it could reach a distance of at least 10,400 km, if not further.
A recent paper by James Acton, Jeffrey Lewis and David Wright, examines video recordings of what appears to be the Hwasong-14’s the upper-stage or re-entry vehicle (RV) plummeting toward earth during the July 28 test. Their analysis helps clarify the debate about the Hwasong-14’s capabilities. Armed with the new findings, one can reasonably conclude that the Hwasong-14 can deliver a North Korean nuclear weapon to Alaska, Hawaii, and perhaps Seattle. It cannot, however, reach Denver, Chicago, or New York, as is often stated. For these more distant targets, North Korea must rely on its larger, more powerful Hwasong-15, which has been flight tested only once.
Estimating Missile Range Based on Lofted-Trajectory Data
David Wright assessed that if flown on an optimal trajectory, the Hwasong-14 could reach a maximum range of 10,400 km. If the earth’s rotation is considered, the Hwasong-14 is, in principle, capable of reaching New York, though it falls just short of Washington, DC.
As explained by Wright, his methodology relies on Kepler’s Laws of Motion, the conservation of energy principle, and calculation adjustments to account for aerodynamic drag and gravity losses during the boost phase. It takes trajectory data from the July 28 test of the Hwasong-14 and calculates using fundamental physics the distance the missile would have traveled if it had been on a path that maximizes range. The maximum range Wright calculates is reasonably “insensitive to assumptions about the missile,” including details about Hwasong-14’s propulsion system, structural and propellant masses, payload size, and other characteristics that are difficult to determine from videos, photographs and available flight data. While providing a convenient model for estimating a missile’s maximum reach based only on the reported flight time, peak altitude and the surface distance traveled, this methodology assumes the tested Hwasong-14 was configured with a mock re-entry vehicle weighing the same as a prospective North Korean nuclear warhead. This is a reasonable assumption because Pyongyang’s engineers would want to test a configuration that closely replicates the real weapon system North Korea plans to deploy. Before Acton, et al., released their analysis, there was no independent method for determining the mass of the mock RV fitted atop the Hwasong-14 missile tested on July 28.
An alternative approach for evaluating performance begins by reconstructing the tested missile based on engineering fundamentals and the principle characteristics of missiles built and tested by other missile powers whose construction details are known. The reconstructed missile is then subjected to a mathematical, flight simulation model to compute its range as a function of several notional payload masses. This technique is subject to errors or uncertainties in the estimates used to reconstruct the missile.
However, in the case of the Hwasong-14, there is strong evidence that its first-stage is powered by a single-chamber engine derived from the RD-250 family of engines originally developed and used by the Soviet Union. Two pairs of steering engines originally designed for use on the Soviet R-27, submarine-launched ballistic missile, and North Korea’s Musudan (Hwasong-10) intermediate-range missile, operate in parallel with the modified RD-250 main-engine.
The performance parameters for these engines are well documented, thereby reducing key uncertainties that would otherwise compromise the fidelity of the range calculations. The reconstruction also relies on the missile’s external dimensions, acceleration at lift-off, propellant density, and other estimates based on engineering insights. Some of the assumptions are necessarily tweaked to establish a reconstructed missile that matches the known flight data. The missile’s range can then be calculated for different payload masses.
Several analysts used this methodology to calculate the Hwasong-14’s performance. Theodore Postol, Markus Schiller and Robert Schmucker estimate the North Korean missile has a range of just under 6,000 km when fitted with a 500-600 kg payload. To reach Seattle, about 8,000 km from the Korean Peninsula, the payload must be reduced to below 300 kg. John Schilling independently estimated that the Hwasong-14 could deliver a 500-600 kg payload to a range of 8,000 km. My calculations suggest the Hwasong-14 can reach 7,500 to 8,000 km when carrying a 500 kg payload, a performance estimate that falls between the Postol, et al., and Schilling findings. The minor discrepancies in the calculated range-payload curves generated independently are within the error-bandwidth of the assumptions applied to the missile’s external dimensions, structural and propellant masses, and measured acceleration at lift-off. It is also noteworthy that the Hwasong-14’s second stage employs low-thrust, long action-time engines, resulting in a missile whose maximum reach is quite sensitive to minor changes in payload mass. If, for example, the payload mass is increased from 250 kg to 300 kg, the Hwasong-14’s maximum range is reduced by roughly 1,600 km. Given this sensitivity, it is remarkable that the three independent calculations are reasonably consistent.
New Analysis of the Hwasong-14 RV
As mentioned at the outset, Acton, et al., conducted a detailed analysis of what appears to have been the final descent of the Hwasong-14’s RV and/or its second stage. Two video cameras perched on buildings located in Hokkaido, Japan captured the final moments of an object falling into the East Sea at rapid speed on July 28. The analysis concludes that the object seen on the videos fell at a time and location consistent with the reported landing spot of either the Hwasong-14’s RV, or the missile’s empty second stage. It is also possible that the Hwasong-14’s RV failed to separate from the second stage at the end of the boost phase, and that the RV and second stage descended as one until aerodynamic forces destructively separated the two components. Regardless, Acton, et al., conclude that the tested Hwasong-14 was likely carrying an RV weighing 200 kg or less. This finding, if correct, provides a solid foundation for determining the Hwasong-14’s reach when armed with a nuclear weapon.
Converging Range Estimates
David Wright correctly computes that the Hwasong-14 has a maximum range of about 10,400 km if flown on an optimal trajectory. If the earth’s rotation is considered, the Hwasong-14 could reach New York, which is almost 11,000 km from North Korea. Wright’s estimate assumes that North Korea’s operational, nuclear-armed Hwasong-14 will carry an RV weighing the same as the RV carried during the July 28, 2017 flight test. Findings by Acton, et al., indicate with reasonable confidence that the RV carried by the Hwasong-14 during the test launch weighed 200 kg or less. If one fits an RV weighing between 150 and 200 kg into the models used by Postol, et al., Schilling and myself, the Hwasong-14’s maximum range is the same as those calculated by Wright.
Remarkably, when all available data from the July 28 test are combined, the models and findings converge to create a consistent picture of the Hwasong-14’s capabilities. The Hwasong-14 could deliver a North Korean nuclear weapon to Seattle assuming an overall RV mass of about 500 kg, of which the nuclear bomb contributes roughly 300 kg. If North Korea wishes to target Chicago, New York or Washington, DC with a nuclear weapon, it will have to rely on the larger, more powerful Hwasong-15, which has only been flight tested once.