[Yang Nak-gyu's Defence Club] The Secret Behind Cheonmu Missile's 0.1% Failure Rate

[Company Visit] Inside KDI Gumi Factory
The Core Component of Missile Technology is the Fuze
Over 70% of Assembly Line Automated
More Than 7 Inspections After Each of the 3 Processes
Safer Than US Products with a 3% Misfire Rate

The origin of the word missile comes from the Latin word ‘mittere,’ meaning ‘to throw.’ It refers to an object that flies when something like a stone, arrow, or bullet is thrown or launched. The first missiles were Nazi Germany’s V1 and V2 rockets during World War II. North Korea has steadily developed missiles by adopting technology from Russia and China. On the 14th, it test-fired a medium-range ballistic missile (IRBM) into the East Sea.

Our military also succeeded in developing solid-fuel-based launch vehicles after the missile guidelines were abolished at the 2021 South Korea-US summit, removing restrictions on weight and range. Various missiles such as Cheongeom, Cheonmu, and Cheongung-II have established themselves as leaders in the ‘K-Defense’ industry. We visited a small and medium-sized enterprise producing core missile technologies.

[Image source=Yonhap News]

On the 11th of last month, at Korea Defense Industry (KDI)’s Gumi factory, production of the fuzes for the domestically developed next-generation multiple launch rocket system ‘Cheonmu’ was in full swing. A fuze is a safety device that prevents the warhead from detonating under normal conditions. However, it is also a critical device that ensures the warhead detonates at a predetermined time upon launch. Cheonmu can fire 239mm guided rockets, 227mm unguided rockets, and 130mm unguided rockets. The guided rockets can precisely strike targets up to 80 km away. The unguided rockets gained fame through the movie Steel Rain. When detonated in the air, the unguided rockets release about 500 submunitions, devastating an area three times the size of a soccer field in an instant.

The assembly area is an electrostatic control zone. Electronic cigarettes or lighters are prohibited. Visitors are no exception. Compared to the size of the factory, the number of employees seemed small, thanks to automation. Over 70% of the fuzes produced at KDI are made in automated facilities. Some processes still require human hands. Observing the workers, they were so focused that it was difficult to speak to them. They were assembling fuze components with tweezers, and the parts were tiny gears smaller than fingernails. It looked like assembling a mechanical watch powered by a spring.

More than 70% of the new components produced at KDI are made in automated facilities. Some parts require human hands. Employees assemble tiny gears smaller than fingernails using tweezers.

More than 70% of the new buildings produced by KDI are made in automated facilities.

The adjacent room is the potting room where the fuze surfaces are coated. Coating is necessary for the fuze to withstand gravity in the air. Humans experience 1G (G is the unit of gravitational acceleration, equal to Earth's gravity) in daily life, up to 2G on a Viking ride, and over 7.3G for fighter pilots. The fuze must endure 50,000G. If it cannot withstand this, all internal electronic components will be damaged during flight, rendering the missile ineffective. The testing does not end here. It must also pass the detonation test. Electrical signals are applied to check if voltage, electromagnetic waves, and other parameters meet the specified standards. In the adjacent assembly building, glass tubes resembling baby test tubes were lined up. This is the automated assembly system. The fuze undergoes three manufacturing processes, and after each process, more than seven inspections are conducted in real-time, including detonator inspection, resistance measurement, and detonating cord checks. Factory manager Park Ki-heum said, “One fuze is produced after various tests, and this facility alone can produce 12,000 fuzes per day.”

More than 7 inspections per fuze process to protect internal components

The completed fuzes are moved to another testing building for additional tests. One is the shock test. The Jolt tester looks similar to a mill wheel with a pounding machine attached. The fuze is fixed and slammed onto the floor more than 1,700 times. Passing this test is required for the product to be certified. The Jumble tester, which tests rotation, must also be passed. It rotates the fuze 3,600 times. The fuze is also submerged in water. It is placed inside a steel box filled with water, and pressure is increased. This checks whether water pushed by pressure enters the fuze.

Cheonmu’s unguided rockets detonate in the air thanks to the fuze’s self-destruct function. There are electronic and mechanical fuzes, with electronic fuzes increasingly used recently. Electronic fuzes automatically calculate and input values, making them more accurate with narrower error margins than mechanical fuzes, which require manual input. Mechanical fuzes are used in older weapons like 60mm mortars, while electronic fuzes are used in 155mm shells for the K-9 self-propelled howitzer.

Cheonmu unguided rockets self-destruct with electronic fuzes... 0.1% failure rate

KDI boasts a low failure rate for unguided rockets. The international community is concerned that unguided rockets can harm civilians due to unexploded ordnance. This is caused by submunitions failing to detonate. In September last year, KDI test-fired unguided rockets in Israel. The failure rate of submunitions was 0.1%. Considering that the failure rate of American unguided rockets is 3%, safety is guaranteed.

A KDI official said, “By reducing the failure rate of unguided rockets, we have proven that they are as effective as conventional weapon systems,” adding, “This will also contribute to ‘K-Defense’ exports.”