Is Nuriho a 'Russian Copy' and ICBM? [Reading Science]

Misunderstandings and Controversies After Second Launch Success on 21st
Should Be Seen as a Pure Space Launch Vehicle Using Liquid Fuel Rocket
"Never Reverse-Engineered Russian Engines"
Completed with Domestic Technology After Over 10 Years of Nighttime Research

The Korean launch vehicle Nuriho (KSLV-II), designed and manufactured entirely with domestic technology, is soaring into space with flames erupting from the launch pad at Naro Space Center in Goheung-gun, Jeollanam-do on the 21st. Unlike the first launch, which carried only a satellite mock-up with no actual functionality, the second Nuriho launch this time is equipped with a performance verification satellite and four CubeSats.
Goheung - Photo by Joint Press Corps

[Asia Economy Reporter Kim Bong-su] Since the successful launch of South Korea's first space launch vehicle Nuriho (KSLV-II) on the 21st, many questions and 'misunderstandings' have arisen. Controversies are rampant, such as claims that Nuriho is essentially an intercontinental ballistic missile (ICBM) or that it is a 'knockoff' reverse-engineered by disassembling Russian engines, thus not a domestically developed technology.

◇ Space Launch Vehicle for Peaceful Use of Outer Space

Nuriho is not an ICBM. An ICBM is the most powerful strategic weapon currently existing, carrying nuclear warheads and striking enemy countries by traveling over 1,000 km in orbit before descending. In contrast, Nuriho is a space launch vehicle developed for purposes such as satellite launches and space exploration.

Some argue that if a nuclear warhead is loaded instead of a satellite, it becomes an ICBM. However, most ICBMs use solid fuel. Solid fuel engines have a relatively simple structure, making development easier. They can be stored at room temperature with fuel loaded, allowing launch preparation in just a few minutes. Operational personnel and equipment can also be minimized. On the other hand, solid fuel engines cannot be reignited or have their burn time and thrust adjusted. Their propulsion is weaker compared to liquid engines, and their accuracy in placing payloads into target orbits is relatively lower. For this reason, solid fuel is mainly used for launching small satellites into low Earth orbit or as boosters for additional thrust in space launch vehicles. Incidentally, South Korea also announced in March that the Agency for Defense Development (ADD) successfully test-launched a solid fuel launch vehicle.

In contrast, space launch vehicles like Nuriho primarily use liquid fuel engines. These require complex components and are difficult to develop. Because they use highly volatile fuel and oxidizers, fueling must be done on the day of launch. Compared to solid fuel, liquid engines provide stronger propulsion, enabling launches into medium and high Earth orbits. Thrust can be adjusted and engines can be reignited, allowing multiple satellites to be deployed into different orbits in a single launch, and enabling the creation of reusable launch vehicles like SpaceX's Falcon 9, which reduce costs. Launch preparations also take a long time. For Nuriho alone, moving, erecting, and inspection took all day the day before launch, and fueling took 4 hours on launch day. If an ICBM were exposed externally for such a long time like Nuriho, it would likely be destroyed immediately by enemy bombardment.

Of course, some technologies such as stage separation, propulsion power, and flight technology are similar. It is not entirely impossible to build a base underground to conceal Nuriho, attach a nuclear warhead to its third stage, and use it as a missile. However, unlike countries that have developed ICBMs, which use solid fuel engines that allow much easier and faster launches, using a liquid engine launch vehicle like Nuriho that requires complicated and lengthy preparations as an ICBM is illogical. Moreover, South Korea does not yet possess atmospheric reentry technology, one of the core technologies of ICBMs.

Nuriho is a space launch vehicle created for peaceful space development, like the US SpaceX Falcon 9, the Space Shuttle, the European Space Agency's (ESA) Ariane 5, and Russia's Soyuz.

◇ Is Nuriho a Copy of a Russian Launch Vehicle? No!

Some cast doubt on whether Nuriho was developed with 100% domestic technology. In particular, they mention the Russian Angara engine (170t) that was 'accidentally' left at the Korea Aerospace Research Institute (KARI) during the 2013 completion of the Naroho (KSLV-I) development project, claiming it was disassembled and reverse-engineered to create a 'knockoff.' However, according to KARI, the Russian engine was never disassembled or reverse-engineered during Nuriho's engine development. A KARI official explained, "We observed the engine's exterior to reference the shape and position of parts like valves, but unlike the staged combustion cycle engine we are developing, it was a different type. It's like trying to make a diesel engine by looking at a gasoline engine?it was of no help, so we did not disassemble it."

KARI initially sought technology transfer for space launch vehicles from 'allied countries' such as the US and Japan during Nuriho's early development but was rejected, ultimately completing the project independently from A to Z. The primitive KSR-3 scientific rocket, which succeeded in its first launch in 2002, laid the foundation for liquid engine technology. At that time, KSR-3's liquid engine was a pressurized engine without a turbopump, with thrust reduced by its own weight, making satellite launches impossible at that basic level.

Subsequently, based on this technology, KARI succeeded in developing core components such as combustion chambers and turbopumps for liquid engines alongside the Naroho development project. This led to the full-scale research and development of Nuriho after 2010. The biggest challenge was the combustion instability phenomenon that occurred in 2015-2016. This phenomenon involved the engine being destroyed due to resonance between the frequency generated by fuel combustion and the combustion chamber's natural frequency. This was a common difficulty experienced during rocket engine development by space powers like Russia and the US. Notably, the US faced severe challenges with this issue during the development of the F-1 engine used in the Apollo project's Saturn V launch vehicle, investing huge sums to resolve it.

KARI engineers solved this problem within a year after 12 design changes and numerous experiments. A KARI official who participated in the research recalled, "We stayed up many nights conducting repeated experiments and identified that the injector spraying liquid oxygen and kerosene into the combustion chamber was the problem, so we modified it. Even now, we cannot theoretically explain the cause and solution; it was something we had to discover through trial."