North Korean officials said on Monday that the regime had test-fired an intercontinental ballistic missile powered by solid fuel. If confirmed, the latest test would be the third this year to boost capabilities for launching with little preparation, the goal being to have a mobile force of solid-fueled missiles ready at short notice. The nuclear-armed North unveiled its solid-fuel Hwasong-18 ICBM at a military parade in February and previously tested it during launches in April and July.
A solid-fueled missile can be loaded with reentry vehicles and warheads without additional truckloads of liquid fuel or oxidizer, allowing it to be prepared for launch with less warning. A canister holds the fuel, usually metallic powders, and the oxidizer, often ammonium perchlorate, a salt of perchloric acid and ammonia.
In addition to its convenience, a solid-fueled missile has the potential to be more reliable than one using liquid fuel. Liquid-fueled missiles can fail either at launch or during flight, whereas solid-fuel versions typically require no mechanical complexity to fire.
Analysts also note that a solid-fueled missile can be launched without trucks carrying fuel and oxidizer. This reduces its observable signature to overhead satellites, making it harder to intercept the vehicle before its launch.
While the reentry vehicles the North is developing could increase the range and payload capability of its future ICBM forces, it’s unlikely that they will entirely replace a road-mobile force of liquid-fueled missiles. The North likely will want a mix of both so that it can deploy the multiple-warhead Hwasong-18 and the super-large hydrogen bombs and hypersonic gliding flight warheads it reports are under development.
At the same time, a solid-fueled ICBM could provide an essential bridge while the North continues to develop its more advanced liquid-fueled rockets. The reentry vehicles required for long-range liquid-fueled ICBMs are more complex to build and have greater payload capacity than those needed for short-range solid-fueled ones. That means it will take longer for the North to have a full-scale liquid ICBM capability than a similar amount of time to establish a road-mobile solid-fueled force.
This is a project that Kim Jong Un personally oversees and has described as “a fundamental task for further enhancing the strategic offensive capabilities of our armed forces in the face of the grave and unstable security environment” and as “the enemies get more vicious in their military collusion and nexus.” The next milestone is expected to be the development of multiple reentry vehicles so that one ICBM can carry multiple warheads. A solid-fueled version of this capability is the most viable option. But the North must demonstrate that it can reliably eject these large and heavy reentry vehicles before achieving that.