"Ignoring Great Powers, Overcoming with Sweat and Passion"…10 Decisive Moments in Nuriho Development [Reading Science]

KARI Releases Retrospective Video on Major Development Processes Over the Past 30 Years

[Asia Economy Reporter Kim Bong-su] It is the Chuseok holiday. However, some are anxiously concerned about a major event ahead. These are the developers at the Korea Aerospace Research Institute (KARI) preparing for the first launch of the Korean space launch vehicle 'Nuriho' scheduled for the 21st of next month. If the Nuriho launch succeeds, South Korea will become the world's seventh space power. Until the 1980s, South Korea lacked economic strength and, overshadowed by major powers like the United States with its missile guidelines, could not even dream of 'space development.' Starting with a small scientific rocket in 1993, South Korea has acquired a 300-ton class space launch vehicle in 30 years. Established space powers like the U.S. and Japan ignored South Korea and refused technology transfer even when money was offered. Starting from 'scratch,' KARI engineers had nowhere to learn from, so they visited places like the Air and Space Museum in Washington, D.C., sketching rocket engines on display. Only Russia provided limited technical training at a high cost, and the conditions were harsh, but through determination, passion, and challenge, they overcame these obstacles. KARI summarized the major events in the space launch vehicle development process over the past 30 years into the 'Top 10 Decisive Scenes,' which were revealed on the 18th.

1. The first step was humble.

South Korea began its space launch vehicle history by successfully launching the first-stage scientific rocket KSR-I on June 4, 1993. This was just four years after KARI was established in 1989. Subsequently, in 1997, the KSR-II was successfully launched, doubling thrust and reaching four times the maximum altitude, and in 2002, the first domestically developed liquid-propellant rocket, KSR-III, was successfully launched. Although it was a small 8-ton class rocket, South Korea secured foundational technology for space launch vehicle development through these efforts.

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

All plans require 'dreams' and goals to be realized. Government projects also need laws enacted and systems in place to be properly executed. Until the 1990s, 'space development' was a distant concept for South Korea. However, in May 1996, a mid- to long-term basic plan for space development was finalized, and in May 2005, the Space Development Promotion Act was enacted, completing the institutional foundation. Especially during the Roh Moo-hyun administration in June 2007, the '1st Basic Plan for Space Development Promotion' was established, including principles to secure core technologies for space development and to launch domestically made satellites with independent launch vehicles. KARI explained, "Although this was later than other advanced countries, our passion for development was stronger."

3. Birth of Naro Space Center

The South Korean government is one of 13 countries worldwide that have their own 'space center' as a forward base for independent space development. In 2001, the site of Oenaro Island in Goheung County, Jeollanam-do, was selected as the final location, 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. Notably, the launch pad built for the Nuriho launch incorporates advanced technologies. Technologies such as ultra-high pressure, cryogenics, clean technology, strict control of moisture and dust content and size in the air, and the domestic development of ultra-high-pressure nitrogen and helium production were all developed independently. South Korea fully secured launch pad operation technology during the 2013 Naroho launch process.

4. Naroho Launch

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

5. Start of Nuriho Development

Nuriho development began in 2010 after passing a preliminary feasibility study in 2009, according to the 1st Basic Plan for Space Development Promotion. At that time, the technology gap with advanced countries was over ten years, and the number of specialized personnel was less than half. However, the conclusion was that "it is worth challenging," and the project to develop a three-stage space launch vehicle capable of launching a 1.5-ton class practical satellite into a 700 km low Earth orbit with domestic technology was initiated.

6. Development of Liquid Engine Starting from 'Scratch'

The rocket engine, the 'heart' of the rocket, is the core of space launch vehicle development. During the Naroho development, KARI developers acquired technology for a 30-ton class liquid engine and then began 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 devices that supply and combust an enormous amount of propellant?1,000 kg per second. KARI completed the development of a 'turbopump-type' liquid engine that uses a rotating device to increase propellant pressure and discharge high-pressure gas. Overcoming the biggest technical challenge, combustion instability, was the result of ten months of relentless day-and-night effort.

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

Propellant tanks constitute about 80% of the rocket structure and are crucial components. They must withstand the enormous weight of the propellant, yet the aluminum alloy thickness is only 2 to 3 mm. Using such thin and lightweight materials for tanks is said to be unmatched on Earth. KARI developers repeatedly welded, encountered defects, improved processes, 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 to be infused into the process.

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. South Korea became the world's seventh country to develop a medium-class liquid engine. This moment also confirmed the possibility of Nuriho's success. Although there were twists and turns, such as delays due to anomalies found during final checks before launch, the domestically developed Korean space rocket safely soared into the sky.

9. Conquering the Most Difficult 'Clustering'

This was the most technically challenging part during Nuriho development. To place a 1.5-ton satellite into low Earth orbit as planned, a rocket with 300 tons of thrust had to be built. This required clustering four 75-ton engines to create a first stage capable of 300 tons of thrust. However, this was not easy. The four engines had to be precisely aligned and produce identical thrust. Thermal insulation technology to prevent engine overheating, precise directional control, and assembly were essential. KARI engineers faced several test delays and even postponed the launch schedule from May to October. However, in January 2021, they finally succeeded in the clustered first-stage combustion test, and by March, they achieved three consecutive successes, perfectly completing the process. This also marked the completion of performance verification for 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 for the first time and was mounted on the launch pad (umbilical tower). For the developers, it was a moment when the hardships of the past decade flashed before their eyes. A total of 370,000 parts were assembled after tens of thousands of hours of extreme space environment testing, reaching the final moment before launch. KARI conducted a certification test to check the launch pad's functions that day, and at the end of August, Nuriho was again placed on the launch pad to complete the final inspection procedure called WDR (Wet Dress Rehearsal). WDR is the final preparation step that involves loading and unloading liquid propellant to check for abnormalities. Like a bride and groom's 'wedding dress rehearsal' just before the wedding, it means soaking the rocket with liquid fuel before launch.

For the KARI engineers who have developed rockets for over ten years, Nuriho is like a child. We hope that Nuriho, which will lead South Korea into the space era, will safely pierce the blue sky over the South Sea and soar. The sorrow of being a small country that has oppressed the Korean Peninsula for the past 5,000 years will also be somewhat alleviated.