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

By Hyonhee Shin SEOUL (Reuters) - North Korea's Hwasong-18 intercontinental ballistic missile (ICBM), launched for the second time on Wednesday, uses solid-fuel technology, giving it the capability to launch with little preparation. Here are some characteristics of solid-fuel technology, and how it can help the North improve its missile systems. 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. Th...