How solid-fuel missiles give North Korea an edge

North Korea says it has tested a new solid-fuel intercontinental ballistic missile (ICBM), its first known use of the propellant in a longer-range projectile.

What is solid-fuel technology? Solid propellants are a mixture of fuel and oxidiser. Metallic powders such as aluminium often serve as the fuel, and ammonium perchlorate, which is the salt of perchloric acid and ammonia, is the most common oxidiser. The fuel and oxidiser are bound together by a hard rubbery material and packed into a metal casing.

When solid propellant burns, oxygen from the ammonium perchlorate combines with aluminium to generate enormous amounts of energy and temperatures of more than 2,700°C, creating thrust and lifting the missile from the launch pad.

Who has the technology? Solid fuel dates back to fireworks developed by the Chinese centuries ago, but made dramatic progress in the mid-20th century, when the US developed more powerful propellants.

The Soviet Union fielded its first solid-fuel ICBM, the RT-2, in the early 1970s, followed by France with the S3 (or SSBS), a medium-range ballistic missile. China started testing solid-fuel ICBMs in the late 1990s.

South Korea said on Friday it had already secured “efficient and advanced” solid-propellant ballistic missile technology.

Solid versus liquid: Liquid propellants provide greater propulsive thrust and power, but require more complex technology and extra weight.

Solid fuel is dense and burns quite quickly, generating thrust over a short time. It can remain in storage for an extended period without degrading — common with liquid fuel.

Vann Van Diepen, a former US government weapons expert who now works with the 38 North project, said solid-fuel missiles are easier and safer to operate, and require less logistical support, making them harder to detect and more survivable than liquid-fuel weapons.

Ankit Panda, a senior fellow at the US-based Carnegie

Endowment for International Peace, said any country that operates large-scale, missilebased nuclear forces would seek solid-propellant missiles, which do not need to be fuelled immediately ahead of launch.

“These capabilities are much more responsive in a time of crisis,” Panda said.

What next? North Korea said the development of its solid-fuel ICBM, the Hwasong-18, will “radically promote” its nuclear counterattack capability. South Korea’s defence ministry sought to downplay the tests, saying the

North will need “extra time and effort” to master the technology.

Panda said the North could face difficulties ensuring such a large missile does not break apart when the diameter of the booster becomes larger.

Though the Hwasong-18 might not be a “game changer”, it will most likely complicate calculations during a conflict.

“The most important interest the US and its allies have is to reduce the risks of nuclear use and escalation stemming from North Korea’s possession of these weapons.”