The Next Big Thing? North Korea Ground Tests ICBM-sized Solid Rocket Motor

North Korea reportedly conducted the first static (ground) test of a large solid-propellant rocket motor on December 15. This is the first direct indication it is developing a propulsion system usable in solid-propellant intercontinental ballistic missiles (ICBMs) or ICBM-range submarine-launched ballistic missiles (SLBMs). It also shows important progress toward these systems, which the Kim regime announced as a priority in January 2021. Solids are safer to handle in the field than liquids, and solid ICBMs are easier to conceal in land-mobile deployments.

The new rocket motor may be intended for an ICBM-range solid SLBM rather than an ICBM, or the same motor could be used in both types of systems. Subs carrying such missiles would be safer from attack than shorter-range systems that must deploy closer to anti-submarine threats, but still substantially less survivable and cost-effective than North Korean land-mobile ICBMs.

Kim Jong Un reportedly referred to developing a new system “in the shortest span of time,” suggesting we could see the flight testing of any new long-range solid missile relatively soon. We can expect the North to conduct more static motor tests in the near term, and probably to display any new ICBM at future military parades. It is unclear how many static tests would be needed before Pyongyang would be prepared to conduct the first full flight test or what political calculations will affect that timeline. However, based on North Korea’s history, one successful flight test may be sufficient for a new missile system to be deployed.

Information to Date

On December 17, North Korea issued a statement reporting a December 15 static (ground) test of a “high-thrust solid-fuel motor with a thrust of 140tf [metric tons]” at the Sohae Satellite Launching Station.[1] The accompanying photographs revealed a large-diameter solid propellant rocket motor mounted in a new horizontal rocket engine test stand, and the static test of such a motor underway.[2] The reportedly successful test included the motor’s “thrust vector controlling feature.”

The “test of strategic significance” was said to be “guided…on the spot” by Kim Jong Un, who was also featured in the photographs, and was explicitly linked to “the five priority tasks facing the strategic weapon field under the five-year plan for the development of defense science and weapon systems set forth by the Eighth Party Congress.” According to the statement, the test “provided a sure sci-tech guarantee for the development of another new-type strategic weapon system” that Kim reportedly expected “would be made in the shortest span of time.”

Analysis

The reported thrust level and apparent size of the motor seen in the photographs (about 2.2 meters in diameter[3]) are consistent with the first stage of an ICBM or a long-range SLBM. (The statement does not tie the motor to a specific type of missile system.) If the new motor does provide 140 metric tons of thrust, that would be greater than the first stages of the US Minuteman III (about 102tf) and Chinese DF-31 (about 120tf) ICBMs.[4] North Korea might need more thrust if the overall structure weight and/or payload weight of a new missile system is heavier than for these foreign ICBMs.[5]

Although the statement mentioned thrust vector control (TVC), which all ballistic missiles use to move or deflect the rocket exhaust to control the direction of powered flight, no TVC system was apparent in the photographs. There did, however, appear to be space around the rocket nozzle to accommodate key components (actuators) for the most modern TVC method, a gimbaled nozzle.[6] Such a nozzle is flexible at its base and moved by the actuators to change the direction of the rocket exhaust. The lack of any jet vanes or vernier engines at the aft end of the motor (other TVC methods previously used by North Korea), and the use of gimbaled liquid-propellant engines on the Hwasong-15 and -17 ICBMs, lend credence to the intention to use gimbaling with the new solid motor.

The horizontal rocket engine test stand depicted in the photographs matches the one built at Sohae starting only in early November 2022.[7] (This is the first horizontal test stand at Sohae, on the west coast, and is about the same size as the earlier one at Magunpo on the east coast.) The rapid construction of the test stand and its apparent use so quickly after completion suggest relatively recent decisions to give the rocket motor and its associated missile development and testing high priority. This is reinforced by Kim’s direct association with the motor test and its linkage to the “five priority tasks” of the Eighth Party Congress—which include solid-propellant ICBMs and ICBM-range SLBMs.[8]

Implications

North Korea is making progress in operationally advantageous solid ICBMs. This test is the first direct indication that North Korea is developing a propulsion system usable in solid-propellant ICBMs, and shows important progress toward that objective. Such ICBMs always made sense for Pyongyang, even prior to the parading of what appeared to be mock-ups of solid ICBMs in 2017 and the decision to “push ahead with the development of solid-fuel engine-propelled inter-continental underwater and ground ballistic rockets” at the January 2021 Party Congress. Solids are safer to handle in the field than liquids (especially if deployed on mobile launchers) and have a much smaller logistical footprint that makes field-deployed mobile missile units easier to conceal. Solids also could avoid operational problems stemming from the relatively low boiling point and high freezing point of the liquid oxidizer used with the North’s current liquid-propellant ICBMs.

Outside analysts often tout solids as being more survivable than liquids because the latter need to be fueled prior to launch, supposedly delaying launch and leaving liquids vulnerable to preemption during fueling. But this advantage of solids is overstated: North Korea would almost certainly have dispersed its mobile liquid missiles from garrison during the crisis period highly likely to precede a conflict, either already fueled or fueling them in “hide sites” prior to hostilities.

Reliable large solid motors are technically difficult to produce consistently, though, involving as much art as science. The extraordinary boost-phase success rate of the North’s new generation of smaller solid short-range ballistic missiles (SRBMs, the KN-23, -24, and -25) may indicate that Pyongyang has now acquired sufficient production experience—and perhaps also sufficient know-how from Russian and Chinese entities—to make ICBM-size solid motors a viable proposition. North Korea’s production capacity for large solid motors is unknown, particularly given its conventional warfighting requirements for hundreds of solid SRBMs.

The new engine could also be used for ICBM-range solid SLBMs. The new rocket motor may be intended for an ICBM-range solid SLBM rather than an ICBM, or the same motor could be used in both types of systems. The primary significance of such an SLBM would be the ability to strike targets in the US from North Korean waters (on either coast), farthest away from Allied anti-submarine warfare (ASW) assets, and potentially covered by some North Korean naval and air defenses. Such SLBMs would be much more survivable than shorter-range systems that would have to deploy closer to hostile ASW forces and without naval/air cover in order to strike the US—but still substantially less survivable than North Korean land-mobile ICBMs. It also would be difficult for the North to produce enough missile submarines to carry enough ICBM-range SLBMs to provide a meaningful capability; land-mobile ICBMs are much more cost-effective for Pyongyang.

Submersible lakebed launchers like the one North Korea used in September to launch a KN-23 SRBM might be more survivable and cost-effective than missile subs, but still appear inferior to land-mobile basing. For example, rail-mobile launchers, which North Korea has also used with the KN-23, would appear to be ideal for a solid ICBM—especially if the North is limited in obtaining or producing enough ICBM-sized road-mobile launchers. As with the USSR/Russia and India, rail-mobile missiles probably would augment rather than substitute road-mobile systems.

More testing soon…and possibly deployment. Kim’s reference to developing a new strategic system “in the shortest span of time” suggests we could see the flight testing of any new solid ICBM or ICBM-range SLBM relatively soon. At a minimum, we can expect the North to conduct more static motor tests in the near term, and probably to display any new ICBM at the military parade expected soon. It is unclear how many successful static tests of the new motor (not to mention the probable second and third-stage motors of any new strategic missile) would be needed before Pyongyang would regard the first full flight test as technically advisable. In any case, Kim’s political calculations would almost certainly drive the ultimate timing of a first flight test. Based on North Korea’s history, one successful flight test may be sufficient for a new missile system to be deployed.

1. [1]

   “Respected Comrade Kim Jong Un Guides Important Test of Strategic Significance,” Rodong Sinmun, December 17, 2022.

2. [2]

   By convention, solid-propellant propulsion systems are rocket “motors” while liquid-propellant systems are rocket “engines.”

3. [3]

   Tianran Xu, “DPRK Unveils Its Solid-Propellant ICBM Motor,” Open Nuclear Network, December 16, 2022. https://opennuclear.org/publication/dprk-unveils-its-solid-propellant-icbm-motor.

4. [4]

   Ibid.

5. [5]

   Taepodong, Twitter Post, December 15, 2022, 5:54 p.m., https://twitter.com/stoa1984/status/1603523862414622720.

6. [6]

   Ibid.

7. [7]

   Solid-propellant rocket motors are typically tested horizontally, and liquids vertically. This is the first horizontal engine test stand at Sohae. Past tests have been conducted at the Magunpo facility on the east coast. Both stands are about the same size.

8. [8]

   “On Report Made by Supreme Leader Kim Jong Un at Eighth Party Congress of WPK,” Korean Central News Agency, January 9, 2021.