[Nuriho Launch] South Korea's Space Launch Vehicle Development History: 'Top 10 Decisive Moments'

[Image source=Yonhap News]

[Asia Economy Reporter Kim Bong-su] The Korean-style space launch vehicle 'Nuriho (KSLV-2)' was successfully launched on the afternoon of the 21st. Although it safely reached an altitude of 700 km and successfully separated the satellite mock-up, it failed to enter orbit, so it is not a 100% perfect success. However, the success of the space launch vehicle itself has been sufficiently proven.

The development of Nuriho is the result of dedicated effort over 11 years and 7 months since March 2010, with an investment of 1.9572 trillion won. With this, Korea has risen to become the world's 7th space power. Until the 1980s, Korea lacked economic power and was overshadowed by major powers such as the United States' missile guidelines, making 'space development' an unattainable dream. Starting with a small scientific rocket in 1993, Korea now possesses a 300-ton thrust space launch vehicle capable of launching a 1.5-ton practical satellite to an altitude of 700 km in just 30 years. It was not a simple process.

Space launch vehicle technology is directly linked to national security, and existing space powers such as the United States and Japan ignored Korea and refused technology transfer even if money was offered. The Korea Aerospace Research Institute (KARI) engineers, who started from 'scratch,' had no place to learn from, so they visited places like the National Air and Space Museum in Washington DC to sketch the displayed rocket engines. Let's look at the 30-year history of Korea's space launch vehicle development, which rose from the ground to become the 7th space power, through 10 decisive moments.

1. The first step was humble.

Korea began its space launch vehicle history by successfully launching the first-stage scientific rocket KSR-I on June 4, 1993. This was four years after the establishment of KARI in 1989. In 1997, the thrust doubled and the maximum altitude increased fourfold with the successful launch of KSR-II. In 2002, Korea successfully launched KSR-III, the country's first liquid-propellant rocket. Although it was a small 8-ton rocket, Korea secured the foundational technology for space launch vehicle development through this.

2. Establishment of the 1st Basic Plan for Space Development Promotion

All plans require 'dreams' and goals to be realized. Above all, government projects must have laws enacted and systems established to be properly implemented. Until the 1990s, 'space development' was a distant topic for Korea. However, in May 1996, the mid- to long-term basic plan for space development was finalized. In May 2005, the Space Development Promotion Act was enacted, completing the institutional foundation. Especially during the Roh Moo-hyun administration in June 2007, Korea secured core technologies for space development. The '1st Basic Plan for Space Development Promotion' was established, including the principle of launching domestically made satellites with independent launch vehicles.

3. Birth of Naro Space Center

The Korean government is one of 13 countries worldwide that have a 'space center' as an outpost to independently conduct space development. In 2001, Oenaro Island in Goheung-gun, Jeollanam-do was selected as the final site, and the center was completed in 2009. The space center is not just a place to erect and launch rockets but a complex facility where rocket manufacturing and testing are conducted. Especially, the second launch pad built for the recent Nuriho launch incorporated advanced technologies. Korea independently developed technologies such as ultra-high pressure, cryogenic, clean technology, strict control of moisture and dust content and size in the air, and ultra-high pressure generation of nitrogen and helium. Korea perfectly secured launch pad operation technology during the Naroho launch process in 2013.

4. Naroho Launch

January 30, 2013, was the day Korea launched a space launch vehicle from its own soil for the first time. Naroho was developed in cooperation with Russia to acquire technology. The first stage was made by Russia, and the second stage by Korea. After two failures and four launch delays, it was finally successful. Korea was able to start developing independent space launch vehicle technology such as Nuriho based on the technology acquired during the Naroho development process. All technologies necessary for space launch vehicle development, from design to manufacturing and testing, were accumulated through Naroho development.

5. Start of Nuriho Development

Nuriho development began in March 2010 after passing a preliminary feasibility study in accordance with the 1st Basic Plan for Space Development Promotion. At that time, the technology gap with advanced countries was over 10 years, and the number of specialized personnel was less than half. However, the conclusion was that "it is worth challenging." Ultimately, Korea embarked on developing a three-stage space launch vehicle capable of launching a 1.5-ton practical satellite into a 700 km low Earth orbit using domestic technology.

6. Liquid Engine Development Starting from 'Scratch'

The engine, the 'heart' of the rocket, is the core of space launch vehicle development. The KARI engineers who acquired 30-ton liquid engine development technology during Naroho development started developing a 75-ton liquid engine based on that. As a result, they succeeded in a 1.5-second combustion test in May 2016 and a 145-second combustion test in July 2016. Rocket engines are complex and sensitive, supplying and combusting an enormous amount of propellant at 1,000 kg per second. KARI completed the development of a 'turbopump-type' liquid engine that uses a rotating machine to increase propellant pressure and discharge high-pressure gas. This was the result of working day and night for 10 months to overcome the biggest technical challenge, combustion instability.

7. Success in Manufacturing Propellant Tanks 'Unmatched on Earth'

Propellant tanks account for about 80% of the rocket structure and are very important. They must withstand the enormous weight of the propellant, but the aluminum alloy thickness is only 2-3 mm. Using such thin and lightweight material for tanks does not exist on the ground. KARI engineers repeatedly welded, encountered defects, researched process improvements, and welded again countless times, eventually developing a special welding method that minimizes deformation, completing the propellant tanks for Nuriho. Of course, all work was done manually, requiring the spirit of a potter.

8. Success of Test Launch Vehicle

After completing the development of the 75-ton engine, KARI succeeded in launching a test launch vehicle in November 2018, finally completing the rocket engine, the 'heart' of the space launch vehicle. It was the moment Korea became the world's 7th country to develop a medium-sized liquid engine. Although there were twists and turns, such as a delay due to an anomaly found during the final inspection before launch, the Korean-developed space rocket safely soared into the sky.

9. Conquering the Most Difficult 'Clustering'

This was the most technically challenging part in developing Nuriho. To launch a 1.5-ton satellite into low Earth orbit as planned, a rocket with 300 tons of thrust had to be made. This required clustering four 75-ton engines to create a first stage with 300 tons of thrust. However, this was not easy. The four engines had to be precisely aligned and produce the same thrust. Thermal insulation technology to prevent engine overheating, precise directional control, and assembly were essential. KARI engineers faced difficulties including several test delays, which postponed the first launch from May to October this year. However, in January 2021, they finally succeeded in the clustered first-stage combustion test, and by March, they achieved three consecutive successes, perfectly completing it. This verified the performance of Nuriho's propulsion system.

10. Appearance of the Three-Stage Nuriho

On June 1st, the fully assembled three-stage Nuriho appeared at the Naro Space Center and was mounted on the launch pad (umbilical tower) for the first time. For the developers, it was a moment when the hardships of the past 10 years flashed before their eyes. A total of 370,000 parts were assembled after tens of thousands of hours of extreme space environment testing, finally reaching the last moment before launch. KARI conducted certification tests to check the functions of the launch pad that day, and at the end of August, they again placed Nuriho on the launch pad and completed the final inspection procedure called WDR (Wet Dress Rehearsal). WDR is the final preparation step that checks for abnormalities by injecting and discharging liquid propellant. Like a 'wedding dress rehearsal' that a bride and groom do just before the wedding, it means wetting the rocket with liquid fuel before launch.

On the 21st, as the Korean launch vehicle 'Nuriho' (KSLV-II) soared powerfully with flames from the 2nd launch pad at Naro Space Center in Goheung-gun, many citizens watched it from the Seoul Station concourse. Photo by Dongju Yoon doso7@

For the KARI and private company developers who have been developing rockets for over 10 years, Nuriho is like a child. Their passion, hotter than the 3,300-degree Nuriho engine, has finally led Korea to the path of 'space independence.'