What are Solid-fuel Missiles, and Why is North Korea Developing Them?

Hwasong-18 intercontinental ballistic missile is launched from an undisclosed location in North Korea in this image released by North Korea's Korean Central News Agency on July 13, 2023. KCNA via REUTERS
Hwasong-18 intercontinental ballistic missile is launched from an undisclosed location in North Korea in this image released by North Korea's Korean Central News Agency on July 13, 2023. KCNA via REUTERS
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What are Solid-fuel Missiles, and Why is North Korea Developing Them?

Hwasong-18 intercontinental ballistic missile is launched from an undisclosed location in North Korea in this image released by North Korea's Korean Central News Agency on July 13, 2023. KCNA via REUTERS
Hwasong-18 intercontinental ballistic missile is launched from an undisclosed location in North Korea in this image released by North Korea's Korean Central News Agency on July 13, 2023. KCNA via REUTERS

North Korea launched a suspected intermediate-range ballistic missile (IRBM) on Tuesday, in what South Korean officials said could be related to its development of a new solid-fuel hypersonic weapon.
The launch comes after North Korean leader Kim Jong Un oversaw a ground test of a solid-fuel engine for a new type of intermediate-range hypersonic missile to develop national defense capability, state media reported in March.
In January, North Korea test fired an IRBM that it said was equipped with a hypersonic maneuverable controlled warhead. State media did not immediately disclose details of Tuesday's launch.
Here are some characteristics of solid-fuel technology, and how it can help the nuclear-armed North improve its missile systems.
WHAT ARE SOME ADVANTAGES OF SOLID FUEL?
Solid-fuel missiles do not need to be fueled immediately ahead of launch, are often easier and safer to operate, and require less logistical support, making them harder to detect and more survivable than liquid-fuel weapons, reported Reuters.
"These capabilities are much more responsive in a time of crisis," said Ankit Panda, a senior fellow at the US-based Carnegie Endowment for International Peace.
WHAT IS SOLID-FUEL TECHNOLOGY?
Solid propellants are a mixture of fuel and oxidizer. Metallic powders such as aluminum often serve as the fuel, and ammonium perchlorate, which is the salt of perchloric acid and ammonia, is the most common oxidizer.
The fuel and oxidizer 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 aluminum to generate enormous amounts of energy and temperatures of more than 5,000 degrees Fahrenheit (2,760 degrees Celsius), creating thrust and lifting the missile from the launch pad.
WHO HAS THAT 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.
North Korea uses solid fuel in a range of small, shorter-range ballistic missiles, as well as in its new Hwasong-18 intercontinental ballistic missile (ICBM).
The Soviet Union fielded its first solid-fuel ICBM, the RT-2, in the early 1970s, followed by France's development of its S3, also known as SSBS, a medium-range ballistic missile.
China started testing solid-fuel ICBMs in the late 1990s.
South Korea has also said it has secured "efficient and advanced" solid-propellant ballistic missile technology, though in much smaller rockets so far.
SOLID VS 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. Solid fuel can remain in storage for an extended period without degrading or breaking down - a common issue with liquid fuel.
North Korea said the development of its solid-fuel ICBM, the Hwasong-18, would "radically promote" its nuclear counterattack capability.
After the first launch South Korea's defense ministry sought to downplay the testing, saying the North would need "extra time and effort" to master the technology.



Where Do Trade Talks Stand in the Rush to Avert Higher US Tariffs?

FILE PHOTO: A container is loaded onto a cargo ship while docked at Hai Phong port, after US President Donald Trump announced a 90-day pause on tariffs for many countries, in Hai Phong, Vietnam, April 16, 2025. REUTERS/Athit Perawongmetha/File Photo/File Photo
FILE PHOTO: A container is loaded onto a cargo ship while docked at Hai Phong port, after US President Donald Trump announced a 90-day pause on tariffs for many countries, in Hai Phong, Vietnam, April 16, 2025. REUTERS/Athit Perawongmetha/File Photo/File Photo
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Where Do Trade Talks Stand in the Rush to Avert Higher US Tariffs?

FILE PHOTO: A container is loaded onto a cargo ship while docked at Hai Phong port, after US President Donald Trump announced a 90-day pause on tariffs for many countries, in Hai Phong, Vietnam, April 16, 2025. REUTERS/Athit Perawongmetha/File Photo/File Photo
FILE PHOTO: A container is loaded onto a cargo ship while docked at Hai Phong port, after US President Donald Trump announced a 90-day pause on tariffs for many countries, in Hai Phong, Vietnam, April 16, 2025. REUTERS/Athit Perawongmetha/File Photo/File Photo

As a Wednesday deadline approaches for steeper US tariffs to hit dozens of economies ranging from the EU to India, trade negotiations with President Donald Trump's administration are coming down to the wire.

The levies taking effect July 9 were announced in April, with the White House citing a lack of "reciprocity" in trade relations. But they were swiftly halted, allowing room for talks.

Days before their reimposition, where do things stand?

EU: 'Ready' for deal

The European Union said it is "ready for a deal" with Washington, with the bloc's trade chief meeting his US counterparts Thursday.

European Commission president Ursula von der Leyen said the EU was targeting an "agreement in principle" when it came to the July 9 cutoff, AFP reported.

With no deal, the US tariff on EU goods doubles from the "baseline" of 10 percent to 20 percent -- with Trump previously threatening a 50 percent level.

Vietnam: A pact with uncertainties

Washington and Hanoi unveiled a trade pact Wednesday with much fanfare and few details, but it allowed Vietnam to avoid Trump's initial 46 percent tariff.

Under the agreement, Vietnamese goods face a minimum 20 percent tariff while products made elsewhere face a 40 percent levy -- a clause to restrict "transshipping" by Chinese groups.

But there remain questions on how the higher levy would apply to products using foreign parts.

There is also a risk that Beijing will adopt retaliatory measures, analysts warned.

Japan: Rice, autos at stake

Despite being a close US ally and major source of foreign investment, Japan might not escape Trump's tariff hike.

Tokyo's trade envoy Ryosei Akazawa has made numerous trips to Washington through the end of June.

But Trump recently criticized what he described as Japan's reluctance to open up further to US rice and auto exports.

"I'm not sure we're going to make a deal," Trump said, adding that the country could pay a tariff of "30 percent, 35 percent, or whatever the number is that we determine."

India: A good position

Indian manufacturers and exporters want to believe they can avoid a 26 percent tariff.

Negotiations between both countries have been going well for weeks, and Trump himself suggested at the end of June that a "very big" agreement was imminent.

Ajay Sahai, director general of the Federation of Indian Export Organizations, said the feedback he received "suggests positive developments." But he maintained that the situation was fluid.

Finance Minister Nirmala Sitharaman has stressed that agriculture and dairy products remain "very big red lines."

South Korea: Muted optimism

Seoul, which is already reeling from US tariffs on steel and autos, wants to avert a sweeping 25 percent levy on its other exports.

Cooperation in shipbuilding could be a bargaining chip, but "at this stage, both sides still haven't clearly defined what exactly they want," said new President Lee Jae Myung on Thursday.

"I can't say with confidence that we'll be able to wrap everything up by July 8," he added.

Indonesia, Thailand, Taiwan in the wings

Other Asian economies including Indonesia, Thailand and Cambodia, which faces a 49 percent tariff, wait with bated breath.

Indonesia has indicated willingness to boost energy, agriculture and merchandise imports from the United States. Bangladesh meanwhile is proposing to buy Boeing planes and step up imports of US agriculture products.

Taiwan, for whom Washington is a vital security partner, faces a 32 percent duty without a pact.

Although both sides have faced bumps along the way, Taiwanese Vice President Hsiao Bi-khim said "negotiators from both sides are working diligently" to find a path forward.

Switzerland: Hope for delay

Switzerland's government said Washington has acknowledged it was acting in good faith, and assumes its tariff level will remain at 10 percent on July 9 while negotiations continue.

But without a decision by the president as of the end of June, Switzerland did not rule out that levies could still rise to a promised 31 percent.