On Sunday, May 21, 2017, North Korea launched a two-stage, solid-fueled Pukguksong-2 (KN-15) ballistic missile. It was the second successful test firing of the medium-range ballistic missile, following the first in February. According to media reports, the missile traveled 500 km downrange and reached a peak altitude of 560 km, roughly replicating the performance of the February test. Pyongyang boasts that the Pukguksong-2 is now combat ready and will shortly enter into mass production. While it is certainly possible North Korea plans to deploy the missiles as they are roll off the manufacturing line, the military would be accepting a weapon with uncertain performance and questionable reliability. Many more flight tests over the next year or two would be needed before North Korea’s strategic planners would have confidence in the Pukguksong-2’s ability to fly to a target successfully.
Breaking from the Past
Prior to 2016, all of North Korea’s ballistic missiles relied on liquid-propellant engines, except for the solid-fueled KN-02 (Toksa). The KN-02 closely resembles the Soviet-era SS-21 short-range missile, which uses a small motor containing roughly 800 kg of solid propellant and is designed to support battlefield operations.
In March 2016, North Korea ground tested a solid-fueled motor substantially larger than the SS-21 motor. The new motor was more than one meter in diameter and likely housed a few tons of solid fuel. The following month, North Korean state television aired what it claimed was the launch of a solid-propellant missile from an underwater tube. The missile reportedly traveled 30 km. A second launch of the Pukguksong-1 was attempted on July 9, but according to South Korean military sources, the missile failed. A month later, on August 23, a two-stage, solid-fueled Pukguksong-1 was fired from either a submarine or underwater barge. It landed about 500 km downrange. The Pukguksong-1 is powered by a first-stage motor containing five to six tons of propellant; the smaller second stage holds two to three tons of solid fuel.
A land-based version of the Pukguksong-1, known as Pukguksong-2 (KN-15) was launched successfully from the Banghyon air base in February 2017. It reached a maximum height of about 550 km and travelled 500 km before landing in the East Sea. If flown on a standard trajectory, the Pukguksong-2 has a maximum range of about 1,300 km.
The second and most recent test firing of the Pukguksong-2 took place approximately 70 km north of Pyongyang. The missile’s trajectory closely resembled that of the first test, though it peaked at an altitude 10 km higher. It is not known if the additional 10 km height was intended; if it was not, the result indicates that the Pukguksong-2 may be wildly inaccurate. Had the two tests flown to maximum range, the second-test missile would have traveled roughly 20 km further than the first.
Soon after the test, North Korean media sources declared that the Pukguksong-2’s “tactical and technical data met the requirements of the Party, [and] this type of missile should be rapidly mass-produced in a serial way.” Officials further claimed that the test verified the missile’s solid-fuelled motor, stage separation processes and late-stage guidance for a nuclear warhead.” Pyongyang also released images of the earth taken from great altitude by a camera mounted on the missile’s warhead.
Transmitting images from the missile’s camera offers limited strategic value to North Korea. However, the ability to send large amounts of data from the missile to a ground station in real-time demonstrates North Korea’s capacity to collect invaluable data from the missile while it is in flight. These data provide the information needed to characterize fully the missile’s performance, and identify design or production flaws should a monitored component fail or underperform.
Nonetheless, despite North Korea’s boasts that the Pukguksong-2 is combat ready, and will soon be mass produced, important questions about the missile’s status remain. Two successful flights of a new missile should generate confidence in its fundamental design. But more tests are needed to characterize fully the missile’s performance and reliability under a range of operational conditions. Ballistic missiles, like any weapon, must meet their performance criteria (reliability, accuracy, etc.) when launched day or night, rain or shine, winter or summer. Typically, countries developing first-generation missiles designed to carry nuclear weapons conduct one to three dozen flight tests over the course of two to five years before the weapon is deployed with combat troops.
That the peak altitude reached during the most recent flight test was 10 km greater than that attained during the February test—despite both missiles flying to the same range—is a key indicator that the Pukguksong-2 is not ready for combat duty. As mentioned, the different altitudes reached by the two missiles translate into range inaccuracy of about 20 km when a standard trajectory is employed. The large difference in range suggests that the rocket motors powering the Pukguksong-2 do not generate a performance profile that can be reproduced from motor to motor.
One of the most pressing and difficult challenges to creating a solid-fueled missile is the manufacture of motors with reproducible performance. The challenge facing North Korea is even more difficult because its engineers and specialists have limited experience manufacturing large motors. The production of reliable solid-propellant motors is as much art as science. That art cannot be learned from books or classroom lectures. Instead, mastering the trade craft requires hands-on experience. This is why it takes dozens of ground and flight tests to demonstrate and validate the performance and reliability of first-generation, solid-fueled missiles.
In addition to validating the performance and reliability of the Pukguksong-2’s rocket motors, North Korea must also master other key elements of an operationally-viable ballistic missile. For example, engineers would have to develop an effective thrust-termination mechanism that activates when the missile reaches the pre-determined velocity and position in space that places the warhead on a trajectory to hit its assigned target. Neither test is believed to have included thrust termination.
Clearly, the Pukguksong-2 has not been subjected to the number of tests needed to validate its performance and reliability. But perhaps this is unimportant to North Korea’s leadership and military commanders. Maybe the regime is willing to accept the risk that its new missile will fail as often as it succeeds when used in battle, or that it could miss its target by tens of kilometers.
When armed with nuclear warheads, greater accuracy may not matter as much depending on the nature of the target and the damage expectancy criteria—for example, with counter-value or “city-busting” attacks. But if Pyongyang’s nuclear-armed missiles fail at a high rate, the odds that missile defenses in South Korea, Japan, Guam or the United States would block all of the missiles that fly successfully improve significantly. The possibility that a nuclear attack might not succeed would very likely weigh heavily on the minds of North Korea’s decision makers.
It is difficult to know how the Kim regime thinks about nuclear deterrence and the potential use of nuclear weapons. Pyongyang likely does not apply the same standards for performance and reliability demanded by the United States and other nuclear powers. However, North Korea’s strategic planners must have some sense of what is required, and it is reasonable the conclude that after only two successful flight tests, the Pukguksong-2 does not yet satisfy even their lowest operational standards. It is undeniable that deploying a missile that is only partially developed entails considerable risk. Consequently, the world should expect North Korea to continue flight testing the Puksguksong-2 over the next few years.