What are solid-fuel missiles, and why is North Korea developing them?

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Last Updated22/12/2023

North Korea recently test-fired an intercontinental ballistic missile (ICBM) powered by solid fuel.

Solid-fuel missiles do not need to be fuelled immediately ahead of launch.
They are often easier and safer to operate, and require less logistical support.
They are harder to detect and more survivable than liquid-fuel weapons.
Solid propellants are a mixture of fuel and oxidiser.
Metallic powders such as aluminium often serve as the fuel, and ammonium perchlorate is the most common oxidiser.
The fuel and oxidiser are bound together by a hard rubbery material and packed into a metal casing.

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.
Solid fuel can remain in storage for an extended period without degrading or breaking down - a common issue with liquid fuel.