Passion of 3300 Degrees Toward Space... Nuriho's '3 Major Domestic Core Technologies'? [Reading Science]

Successful Localization of 3 Core Components After 'Heading on Bare Ground'
Behind the Development of 75t-class Engine, Propellant Tank, and Payload Fairing.

[Asia Economy Reporter Kim Bong-su] The Korean space launch vehicle 'Nuriho,' set to soar on the 21st carrying the dream of becoming one of the 'world's seven major space powers,' is even more remarkable because it is a pure product of domestic technology. Even 'allied countries' like the United States and Japan refused technology transfer or cooperation, so it was purely independently developed over more than 20 years by the sweat and blood of domestic researchers. Among these, the three core technologies?rocket engine, propellant tank, and payload fairing?are fundamental technologies of space launch vehicles. Even advanced space countries like China and Japan initially succeeded only by adopting other countries' technologies.

◆ Making the Heart of Nuriho, the Engine

The flame temperature of the rocket engine that launches Nuriho into space exceeds 3300 degrees Celsius. However, the sweat and blood poured by the Korea Aerospace Research Institute (KARI) developers to complete it were hotter than the sun. The development of the 75-ton class engine mounted on Nuriho began with the Naroho project in 2002. At that time, Naroho used a first-stage (170-ton class) engine provided by Russia, but KARI developers simultaneously started developing a 30-ton class liquid engine independently. Publicly, it was a 'Plan B' in case cooperation with Russia failed, but in fact, KARI developers regarded it as the starting point for the Korean space launch vehicle program to develop an independent rocket engine.

However, 'heading into the unknown' was not easy. Especially, the space launch vehicle turbo pump is on a completely different level from cars or aircraft, and there was no manpower or experience at all. KARI formed a research team centered on engineers with experience in developing aircraft gas turbine engines, which are somewhat similar technically, then studied classic textbooks from the U.S. and Russia and examined old engines displayed in overseas museums to learn the technology and conduct experiments. After more than five years of research, they barely completed the design and made prototypes, but then they could not find a test site. Although the Naro Space Center now has rocket engine test facilities, back then it was out of the question. They rented Russian test facilities at great cost but suffered hardships such as being unable to conduct desired tests on desired dates and being monitored by armed soldiers. In the first combustion test conducted in 2007, the turbo pump exploded, posing a major challenge, but in a 2008 retry, they succeeded. At this time, KARI secured technology for core parts such as the turbo pump, combustor, and gas generator of the 30-ton class engine, which became the fundamental technology for developing the 75-ton engine starting in 2010.

Developing the 75-ton engine was also not easy. They had to solve challenges such as combustion instability problems arising from the larger engine size and system integration. KARI developers created a total of 33 prototypes and conducted 184 combustion tests totaling 18,290 seconds, shedding sweat and blood to develop the 75-ton engine. Rocket engines require the creation of devices that precisely supply fuel and oxidizer by coordinating hundreds of valves down to 0.01-second intervals, a difficult task. Completing this with their own hands means they have secured technology that can be upgraded to any desired performance in the future.

◆ The Science of 2mm - Propellant Tank

The propellant tank, which makes up 80% of the 47.2-meter length, may seem simple at first glance, but it is not. It must be thin and light to minimize rocket weight, yet strong enough to withstand internal and external pressures.

The rocket's propellant tank must withstand internal pressure six times atmospheric pressure, engine thrust, and wind forces. Also, since it uses cryogenic liquid oxygen at minus 183 degrees Celsius, materials that can endure extreme cold must be used. Accordingly, Nuriho's tanks are made of thin special aluminum alloy sheets 2 to 3 mm thick. The challenge is processing these thin materials into huge structures up to 10 meters high and 3 to 5 meters in diameter. This process requires much higher precision, advanced welding technology, and excellent concentration than computer simulations. Therefore, KARI developers completed the propellant tanks through manual work, using spinning technology and developing special welding techniques. The first-stage propellant tank was verified through a pressure burst test in 2018, and the second-stage propellant tank development was completed with a successful test launch in November 2018.

KARI said that being seen as a 'world-leading shipbuilding powerhouse with the best welding technology' was actually a burden. Unlike shipbuilding, which uses thick steel plates, processing thin aluminum plates without deformation or defects to make tanks is a completely different technology. Also, because the material is so thin and the process so demanding, even a small mistake would require repeating the 10-month manufacturing process, a burden they had to overcome. It was a process requiring high concentration and extreme technology.

◆ The Finishing Touch, 'Payload Fairing'

The satellite protection cover located at the top of the space launch vehicle is called the 'payload fairing.' It protects the internal payload satellite from extreme external environments during launch, such as intense heat, vibration, noise, wind, and gravity. After breaking through Earth's atmosphere, it separates at a precisely designed altitude and timing to place the satellite into its proper orbit, playing a crucial role. Although it seems simple, it requires lightweight and strong materials and sophisticated technology, so space powers classify it as 'top secret' advanced technology.

After many trials and errors, KARI succeeded in developing it independently. First, they spread carbon composite fibers as thin as paper and applied heat and pressure to achieve strength comparable to metal and aluminum. They also succeeded in designing a structure where two identical-shaped components enclose and combine around the payload. The core was the separation technology. When explosives detonate to break the locking device, built-in springs push the halves apart sideways to separate. The key challenge was to mitigate the shock wave from the explosive, called pyro shock, because it must not adversely affect electronic payloads or satellites. They also manufactured springs capable of exerting one ton of force each and placed them precisely. Through over 200 separation tests, KARI repeatedly improved and modified the system, and in January 2013, during the third Naroho launch, they successfully separated, finally securing the technology. No matter how well the rocket operates, if the payload fairing fails, the primary mission of launching the payload fails. This is why the payload fairing is the 'finishing touch' of space launch vehicle technology.

This content was produced with the assistance of AI translation services.