3300-Degree Flames of Nuriho... The Door to South Korea's Space Exploration Opens [Reading Science]

[Image source=Yonhap News]

[Asia Economy Reporter Kim Bong-su] In October 1957, the former Soviet Union launched Sputnik 1, the world's first artificial satellite, leading humanity into space. Some 64 years later, in June 2022, the Republic of Korea embarked on completing its first indigenous space launch vehicle, Nuriho. This project involved nearly 2 trillion won in funding, over 20 years of time, and the blood and sweat of highly skilled personnel. In the era of the 4th Industrial Revolution, where 21st-century advanced technology flourishes, space has become deeply embedded in humanity's economy, security, and environment. Having a domestically made launch vehicle place a satellite into orbit and explore the Moon, Mars, and asteroids signifies that a nation has independently established its survival foundation.

◇What is the significance of Nuriho?

During the Cold War, the United States and the Soviet Union competed in rocket development, satellite launches, and lunar exploration, but beyond intercontinental ballistic missile (ICBM) weapon technology development and defense and security-related espionage and communications, it held little broader significance. Although the U.S. conducted the Apollo project, achieving humanity's first manned lunar landing, it gained little tangible benefit. Since the 2000s, the situation has changed. Numerous private companies have emerged aiming to profit through space mining, space solar power plants, and lunar and Martian exploration using advanced technologies. SpaceX, led by Elon Musk, and Blue Origin, led by Jeff Bezos, are representative examples. Earth's resource depletion and environmental destruction have also expanded the horizons of space exploration. The U.S. Artemis project, which involves lunar exploration, base construction, and terminal (Lunar Gateway) establishment, is driven by these reasons. China and Russia have formed a bloc through joint lunar exploration and space station construction in response. Korea had little presence until now. Although its satellite development since the 1990s earned recognition in communication and observation satellite manufacturing technology, its position in the international space development cooperation system was limited without an independent space launch vehicle.

Especially as space has become an essential domain in the 4th Industrial Revolution era's advanced technologies, competition among countries has intensified. Currently, nine countries can launch space launch vehicles independently: Russia, the United States, Europe, China, Japan, India, Israel, Iran, and North Korea. Among these, Israel, Iran, and North Korea are evaluated to have payload capacities under 300 kg. If Nuriho's final launch succeeds, Korea will secure a 1.5-ton payload capacity, becoming the seventh country worldwide capable of launching practical satellites over 1 ton.

[Image source=Yonhap News]

◇What is different about the second launch?

During Nuriho's first launch last October, all operations such as ignition and separation of each stage engine and fairing separation proceeded normally. However, the 7-ton class liquid engine in the third stage shut down about 46 seconds earlier than expected, resulting in failure to enter the target satellite mock-up orbit. Investigation revealed a crack in the oxidizer tank of the third-stage engine, causing fuel leakage. The Korea Aerospace Research Institute (KARI) conducted about two months of cause analysis and successfully completed component design changes and verification work starting in January.

Unlike the first launch, which carried only the satellite mock-up, the second launch will include four CubeSats along with a performance verification satellite. The performance verification satellite, specially made weighing about 200 kg, will separate first when Nuriho reaches an altitude of 700 km, followed by the satellite mock-up. Maintaining a speed of 7.5 km/s and successful separation will mark the 'mission success.' Additionally, the performance verification satellite will maintain continuous communication with the ground station for two hours after separation, and four hours later, the South Korean Antarctic King Sejong Station will verify the satellite's attitude information. Ko Jung-hwan, head of KARI's Korean Launch Vehicle Development Project Group, explained, "Launching a domestically made launch vehicle from our own launch site into orbit means we have the capability to deploy anything we make into space."

◇All four core technologies independently developed

The flame temperature of Nuriho exceeds 3,300 degrees Celsius. However, the blood and sweat of our engineers who completed Nuriho with indigenous technology without external help burned even hotter. First, developing the rocket engine to guarantee launch vehicle propulsion was the top priority. Especially, the core component, the turbo pump, had to be manufactured without prior knowledge, experience, or know-how. It is an ultra-precision device that controls hundreds of valves to supply fuel and oxidizer accurately within 0.01-second intervals. KARI researchers passionately studied classic textbooks from the U.S. and Russia and referred to old rockets in museums. Centered on experts with experience in aircraft gas turbine engine development, KARI succeeded in development after about five years of research in 2008. The development of the 75-ton class liquid engine for Nuriho, which began in 2010, was also full of challenges. As the engine size increased, combustion instability issues arose, which were barely resolved after several design changes and experiments over about six months starting in 2017. Until just before the first launch last year, 33 prototypes were produced, and combustion tests were repeated 184 times for a total of 18,290 seconds.

Additionally, the 'clustering' technology, which bundles multiple engines into one stage, was also independently developed. The first stage of Nuriho combines four 75-ton engines to produce 300 tons of thrust. The engines must be precisely aligned and produce identical thrust for the rocket to fly along the intended trajectory. A KARI engine development official said, "Flame heating analysis and insulation technology, thrust imbalance countermeasures, and assembly, alignment, and gimbaling (direction control) technologies for the four engines were necessary," adding, "Due to the high technical difficulty, precise design and high-level ground testing were required."

Seemingly simple, manufacturing the propellant tanks was also a challenging task. They had to be robustly made from thin special aluminum sheets 2?3 mm thick to withstand enormous internal and external pressures during launch. Nuriho's propellant tanks are designed to endure internal pressure six times atmospheric pressure and strong external forces from engine thrust and atmospheric resistance. Materials capable of withstanding the cryogenic temperature of minus 183 degrees Celsius for liquid oxygen, used as the oxidizer, were also employed.

Another high-difficulty technology for space launch vehicles, the 'payload fairing,' was a formidable challenge but was successfully overcome. The payload fairing, a protective cover for the satellite, must act as a shield and separate at the correct timing and force upon reaching the target altitude. Lightweight and strong material technology and detailed know-how are required, and even space powers keep these technologies highly confidential. KARI engineers made the fairing by thinly layering carbon composite fibers, applying heat and pressure to achieve high strength, and independently developed technology to mitigate separation shock (pyro shock).

◇Nuriho is a 'primer'

The 2 trillion won Nuriho project will conclude with this second launch but serves as a primer for Korea's independent space exploration. The government plans to continue verifying and upgrading Nuriho's performance and increase reliability by conducting four more launches in the future. In 2023, it will carry the second next-generation small satellite into orbit. In 2024, 2026, and 2027, repeated launches will verify reliability and place the first ultra-small satellite and others into orbit. The government also plans to invest an additional approximately 3 trillion won to develop next-generation launch vehicles. A preliminary feasibility study is underway to significantly upgrade Nuriho's performance to compete in the international space launch vehicle market and to utilize it for deep space exploration such as the Moon, Mars, and asteroids.

A KARI official stated, "Through the continuous advancement of Korean launch vehicle technology, we will expand space transportation capabilities," adding, "We will discover and nurture system integration companies and establish a self-sustaining industrial ecosystem that grows together."