On the 25th, when the whole country was covered in fine dust, the sky observed from the Naro Space Center launch pad in Goheung, Jeollanam-do, was clear. It was the kind of weather that seemed suitable for launching the Korean launch vehicle Nuri (KSLV-Ⅱ) at any moment. The Korea Aerospace Research Institute (KAI) successfully completed the third launch of Nuri here on May 25, 2023. Unlike the first and second launches, the third launch carried a practical satellite into space for the first time.
The Naro Space Center has experienced nearly a year and a half of calm since the third launch of Nuri. There were no additional launches of Nuri in 2024. In the meantime, the first-generation 'Rocketmen,' who led the development of Nuri, have stepped down from their positions and retreated to secondary roles. Ko Jeong-hwan, the former head of the KAI Advanced Launch Vehicle Development Project, is now assisting the Nuri launch as a senior researcher at KAI.
The Naro Space Center has started to bustle again, breaking the silence. The Korea Aerospace Administration and KAI are preparing for the fourth launch of Nuri this November. Following that, the fifth and sixth launches are scheduled to take place in 2026 and 2027, respectively. Since October of last year, the assembly of Nuri's fourth unit has started, bringing vitality back to the Naro Space Center. Notably, this time, the private company Hanwha Aerospace is taking charge of the launch operations in partnership with KAI as one team.
◇KAI·Hanwha Aerospace, working as one team on-site
On this day, at the comprehensive assembly building of the Naro Space Center, the Nuri 4 unit, which is set to launch in November, was being built. All major components of the Nuri 4 unit had arrived, and assembly work had commenced. The first thing visible was the first stage of Nuri, with four 75-ton engines consolidated into one.
Lee Chang-bae, a senior researcher at KAI, noted, “Last week, we just finished the work of attaching all four engines, and now we are proceeding with the remaining pipeline assembly work. This process, which began in October of last year, was the longest and technically most challenging, but we have successfully completed it in five months.”
Inside the assembly building, the first and second stage bodies were separated. Researchers were working on filling the internal electronic equipment into each body. Tanks for oxidizer and fuel were also waiting to be consolidated in the assembly building. This senior researcher stated, “We plan to finish the separate assembly by August this year, and afterward, we will complete the ground equipment for the launch site according to the launch operation process, ensuring that preparations for the November launch go smoothly.”
As I ventured further inside the assembly building, dozens of people were gathered in front of the Nuri second-stage engine. They were checking whether the second-stage engine moved correctly at the desired angle. This experiment involves adjusting the engine to a specific angle and verifying how well it follows commands. This senior researcher explained, “Although it doesn’t ignite, we input kerosene fuel to check the engine's movements and control capabilities. If the engine's angle adjustments are not carried out correctly, the launch vehicle cannot ascend along the predetermined trajectory and is bound to fail.”
While working on the same tasks at one location, the researchers wore different jumpers. Some wore KAI clothes, while others were seen in Hanwha Aerospace jumpers. KAI and Hanwha Aerospace are the two pillars of the Nuri advancement project. Although there has been tension outside regarding intellectual property rights for Nuri and the next-generation launch vehicle, a one team approach has already been established at the Naro Space Center.
This senior researcher stated, “Hanwha participated in the third unit as well, but since they are responsible for assembly this time, there are more Hanwha engineers involved. While there are still issues regarding intellectual property rights, concerning assembly, KAI and Hanwha are fully collaborating and working together.”
◇Production of the 5th unit has also begun… Strengthening the launch pad
As I exited the assembly building, where the assembly of the Nuri 4 unit was in full swing, I headed towards the launch pad and spotted the engine testing facility. Although all engines for the 4th unit had been moved to the assembly building, a single 75-ton engine was present here as well. Jeon Jun-su, a senior researcher at KAI responsible for ground combustion testing, stated, “The first engine for the Nuri 5 unit has arrived this month, and we are preparing for the engine acceptance combustion test.”
The engine acceptance combustion test is a procedure to verify whether the core engine system of Nuri is functioning properly, marking the beginning of rocket manufacturing. Nuri will contain a total of six engines, including five 75-ton engines and one 7-ton engine. The acceptance combustion test is conducted for each engine over a period of one to two months. Jeon noted, “Engines that finish testing are thoroughly cleaned and then moved to the assembly building. The testing for the engine that will be used in the 5th unit is expected to be completed around October this year and will be moved to the assembly building.”
Eight months later, reinforcement work was also being conducted at the launch pad where the Nuri 4 unit would stand tall. Construction was in full swing next to the umbilical tower, a key facility of the launch pad. Yang Seon-il, a senior researcher at KAI, explained, “We are improving the water spray system to protect the launch vehicle from flames generated during the launch process.”
The umbilical tower is a device that supplies electricity and propellant to Nuri. It is named the 'umbilical' as it breathes life into Nuri. This umbilical is the only passage that connects various ground equipment and Nuri.
The launch pad began preparations for the 4th unit launch shortly after Nuri's assembly started in October of last year. Just like how a car may not operate correctly if it hasn't been used for a long time and is suddenly started, the major equipment of the launch pad that had been inactive for nearly two years also required maintenance for the 4th unit launch.
In particular, during the third launch, a communication issue between the helium storage tank and the ground equipment controlling system led to a one-day delay in the launch, necessitating inspections of the related equipment. Yang noted, “We have completely resolved the issues that arose with the launch pad equipment during the third launch.”