Explainer: What are solid rockets and why is North Korea developing them?

Hyunhee Shin

SEOUL (Reuters) – North Korea said it launched an intercontinental ballistic missile on Thursday, a move South Korean officials said could be linked to the development of new solid-fuel rocket engines.

South Korea’s defense minister said Wednesday the North could ask Russia for new intercontinental ballistic missile technology in exchange for deploying its troops to help Ukraine, but other military officials in Seoul said Pyongyang’s missile program was so far advanced that it was unclear what kind of help he needs it.

Here are some characteristics of solid rocket technology and how it could help the nuclear-armed North improve its missile systems.

WHAT ARE THE ADVANTAGES OF SOLID FUEL?

Solid-fuel missiles do not require refueling immediately before launch, are often simpler and safer to operate, and require less logistical support, making them more difficult to detect than liquid-fuel weapons.

“These capabilities are much more effective during a crisis,” said Ankit Panda, a senior fellow at the U.S.-based Carnegie Endowment for International Peace.

WHAT ARE SOLID FUEL TECHNOLOGIES?

Solid fuel is a mixture of fuel and oxidizer. The fuel is often metal powders such as aluminum, and the most common oxidizing agent is ammonium perchlorate, which is a salt of perchloric acid and ammonia.

The fuel and oxidizer are bound together by a hard rubber material and packaged in a metal casing.

When solid fuel burns, the oxygen in the ammonium perchlorate combines with the aluminum, generating enormous amounts of energy and temperatures of more than 5,000 degrees Fahrenheit (2,760 degrees Celsius), creating thrust and lifting the rocket off the launch pad.

WHO HAS THIS TECHNOLOGY?

Solid fuels date back to fireworks developed by the Chinese centuries ago, but made significant progress in the mid-20th century when the US developed more powerful fuels.

North Korea uses solid fuel in a number of smaller, shorter-range ballistic missiles, as well as its new Hwasong-18 intercontinental ballistic missile.

The Soviet Union fielded its first solid-fuel intercontinental ballistic missile, the RT-2, in the early 1970s, after which France developed the S3 medium-range ballistic missile, also known as the SSBS.

China began testing solid-fuel intercontinental ballistic missiles in the late 1990s.

South Korea also said it had acquired “effective and advanced” solid-fuel ballistic missile technology, although so far in much smaller missiles.

SOLID VS LIQUID

Liquid fuel provides greater thrust and power, but requires more sophisticated technology and additional weight.

Solid fuel is dense and burns quite quickly, creating thrust in a short time. Solid fuels can be stored for long periods of time without decomposing or breaking down, a common problem with liquid fuels.

North Korea has said the development of its solid-fueled Hwasong-18 will “radically enhance” its nuclear counterattack capability.

After the first launch last year, South Korea’s defense ministry tried to downplay the test, saying the North would need “additional time and effort” to master the technology.