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Nuri’s launch was a bad dream dispelled for this rocket scientist.
Han Young-min, who developed the liquid-fuel engines for Korea’s first domestically-developed rocket Nuri (KSLV-II), poses in front of the first stage engine of Nuri at the Korea Aerospace Research Institute in Daejeon on June 24. [KIM SUNG-TAE]
“A week before each launch, I used to have a dream every night,” says Han Young-min, “that the engine exploded on the launch pad.”
Han was the brains behind the development of liquid-fuel engines for Korea’s first domestically-developed rocket, Nuri.
“It happened during the test launch in 2018 and the first launch last October,” Han recalls.
But ahead of the launch on June 21 — the first fully successful one — Han’s subconscious cut him some slack.
“This time, I only had one dream two days before the launch — maybe that was a good omen.”
The 54-year-old aerospace engineer was head of the engine development department at the Korea Aerospace Research Institute (KARI). The first stage booster engine that Han’s team made thrust the Nuri rocket into space on June 21, a major milestone for Korea technologically and in terms of space development.
The JoongAng Ilbo sat down with Han for an interview at KARI headquarters in Daejeon on June 24, three days after the successful launch of Nuri, whose full name is the Korea Space Launch Vehicle-II (KSLV-II).
The excitement of the launch had not faded, and no wonder. It had been 22 years since KARI started developing rocket engines, starting with the KSR-3, the first liquid rocket with a thrust of 13 tons.
The interview with Han was done in his laboratory at KARI. A huge 2.9-meter (9.5 feet) engine is set up looking towards the sky.
Q. How did you feel about the successful launch of Nuri?
A. I was so happy. When the first and second stages went up, it was so tense in the Naro Space Center’s Mission Direction Center that you couldn’t hear a single sound. And 876 seconds after the launch, at an altitude of 700 kilometers, when the third stage engine stopped and the performance verification satellite was separated, shouts erupted from everywhere, including myself. We hugged each other, clapped hands and cried.
I didn’t realize one thing at the time, but later I saw a video recording of that moment. I drew a big heart with my hands at at my colleagues. My wife later complained that I had never given her such a gesture. I feel guilty about saying this but I think it was the happiest day of my life.
Q. The launch was initially scheduled for June 15. How did you feel when it was delayed twice?
A. On June 15, the first scheduled date, we had to delay the launch because of the wind. It was a weather problem so I was calm. The next morning, in still cloudy weather, we took the Nuri again from the assembly building and the sunlight shone on the launch pad. I thought that was a good sign.
So I was expecting that everything would be fine that day. But when we checked the electric signals, a sensor error signal appeared. It was a sensor in the oxidizer tank. A month or two could pass if we had to separate the first and second stages to fix the sensor. I was frustrated at the thought that we couldn’t fire the rocket because of that sensor.
At a meeting the next day, someone suggested that if it was a sensor problem, a person could go into the rocket and fix it without having to separate the first or second stages. Suddenly the mood changed. We could actually fit a person inside and we were able to replace the sensor. So the launch on June 21 was finally decided upon.
Q. Did you sleep well the night before the launch?
A. The Naro Space Center dormitory is located south of the launch site, about 700 meters from the assembly building. An engineer shouldn’t do this, but while walking around the assembly building, I prayed, “God, Mother, Buddha, please make sure this launch succeeds safely.”
I’m not religious, but I’ve been to a Catholic church before, and my wife is Buddhist. I wanted to lean on something. The night before the launch, I didn’t dream of the engine exploding.
Q. That was obviously a big worry?
A. Since the booster engine we use is a high-energy device, an explosive reaction occurs when liquid oxygen and kerosene fuel meet. The first ignition is the most dangerous. If the reaction gets out of control during the first ignition, not only the first stage but also the second and third stages will explode in a chain reaction, causing great damage.
Q. Has the engine ever actually exploded?
A. This hasn’t been disclosed to the press before, but there was an explosion.
It was in May 2020, when we conducted a two-stage engine high-performance combustion test. The second-stage engine burns at an altitude of 50 kilometers or higher, so the test was conducted in a vacuum chamber, and an explosion occurred and damaged the engine and the chamber equipment.
Fortunately, the development team was far away from the engine, about 1 kilometer away, so no one was hurt. SpaceX experienced a similar explosion in the second stage for a similar reason. For us, it was a valuable lesson.
Q. Were there any other difficulties?
A. Of course there were.
Among all the obstacles, the distrust people had in KARI was the most difficult. When we launched a test projectile equipped with a 75-ton engine in 2018, we ourselves were worried about whether it would fly properly. It goes without saying that those on the outside were even more skeptical. There were a lot of doubting views from domestic space engineering professors as well as foreign professors as to whether KARI could develop an engine and fly it successfully. One professor even said that he would chop off his hands if KARI ended up developing a successful 75-ton engine.
Q. You received a lot of help from Russia on the development of the rocket.
A. It’s true that we cooperated with Russia during the development of Naro-1 and received a lot of help from Russia, both formally and informally. We also signed an agreement for space technology cooperation with Russia. Until then, we had never put together an entire projectile rocket, nor did we ever build a launch pad or an assembly building.
Q. Russia left behind an Angara engine with a thrust of 210 tons after the launch of Naro-1 in 2013, right?
A. At first, we thought it was just a model, but it turned out to be a real rocket engine. To be honest, I was jealous as an engine developer. The Angara engine is the world’s best multi-state combustion cycle engine, so I thought about it a lot.
In the past, if you went to Russia, you could see Russian space rocket engines such as the RD-170 or 180 in space museums. These were 800-ton thrust engines with four combustors tied together.
Q. We heard that you will also be in charge of engine development for next-generation rockets after Nuri.
A. Yes. The engine thrust for the next-generation projectile is 100 tons, and like the Russian Angara engine used in the first stage of Naro-1, it is a multi-stage combustion cycle.
Five of these are mounted on the first stage, and two 10-ton engines are used in the second stage. The engine output can be adjusted from 40 percent to 100 percent, and re-ignition is also possible. It will have a basic structure that can descend upside down like the engines used by SpaceX.
This does not mean, however, that next-generation projectiles are being developed for the purpose of reuse. To do that, we need a lot of other technologies. Perhaps with future projectiles, after the next-generation ones, we can try that.
Q. The Angara engine used in Naro-1 seems like it would be of great help.
A. They haven’t taken the engine apart (to analyze) it yet. We did go inside the rocket and comprehend the engine system configuration as a whole. We figured out the layout of the engine, such as the size of the engine, value position, and piping configuration. However, the Angara engine has a thrust exceeding 200 tons. There is a big difference in thrust and pressure from our next-generation projectile engines.
Therefore, it is not what we can call reverse engineering. The Angara engine does help, but we have to design our rockets ourselves anyway. We have already started developing a 10-ton multi-stage combustion cycle engine from 2016 on a basic research level.
Q. The United States gave space rocket technology to Japan. Why does it not help Korea?
A. At the time of the development of Nuri, there was no test facility for a 75-ton engine in Korea, so we looked to Russia as well as the U.S. But the U.S. State Department did not give us a response. After waiting for a response for more than three months, we found out that no response was close to a refusal.
From what I know, the U.S. doesn’t want the spread of space launch vehicles or rocket technology in other countries. Back in the 1970s when Japan received help from the U.S., I think it was a strategic decision on their part to support at least one country in East Asia to try and contain China and Russia.
Q. Now that Korea has developed our own space rocket, would the U.S. respond differently?
A. There is a precedent for the U.S. letting a country into their inner circle if a country developed their own rockets without help from the U.S. That case is India.
Currently, satellites with U.S. components cannot be launched in space vehicles developed by Korea. This is because of the U.S. strategic material control policy. However, as in the example of India, I think the U.S. will eventually recognize Korea. Who knew that the Korea-U.S. missile deal would be resolved so quickly?
BY CHOI JOON-HO [lim.jeongwon@joongang.co.kr]
‘News of the Day’ content, as reported by public domain newswires.
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