[Reading Science] Next-Generation Launch Vehicle to Catch Up with Falcon 9 through a 'Quantum Jump'

Essential Technologies Like Rocket-Specific Fuel, Thrust Control, and Staged Combustion Cycle Already Significantly Advanced
KARI "Challenging but Not Overambitious"
Large, Reusable Rocket Expected to Rival Falcon 9 Performance

The Korean launch vehicle Nuriho (KSLV-II), designed and manufactured entirely with domestic technology, is soaring into space with flames erupting from the launch pad at Naro Space Center in Goheung-gun, Jeollanam-do on the 21st. Unlike the first launch, which carried only a satellite mock-up with no actual functionality, the second Nuriho launch this time is equipped with a performance verification satellite and four CubeSats. / Goheung = Photo by Joint Press Corps

[Asia Economy Reporter Kim Bong-su] "Once completed, it will immediately catch up with SpaceX's reusable launch vehicle Falcon 9, which boasts the highest efficiency with world-leading cutting-edge technology."

This is an evaluation of the "specs" of the "next-generation launch vehicle," which passed the government's preliminary feasibility study on the 29th. The Nuri rocket, successfully launched in June, laid the "fundamentals" as the first Korean-type space launch vehicle. The next-generation launch vehicle aims to achieve a quantum leap by quickly catching up with existing space powers by incorporating all the necessary functions for an advanced and high-efficiency space launch vehicle. Some even express concerns that this goal might be overly ambitious. What are the specific technologies of the next-generation launch vehicle and South Korea's readiness? In fact, the Korea Aerospace Research Institute (KARI) has already made significant progress in researching and developing core technologies required for advanced launch vehicle development, expressing confidence by stating, "It is a difficult task, but not an excessive ambition."

Staged Combustion Cycle Engine, Small-Scale Development Already Completed

The 75-ton class liquid engine used in the existing Nuri rocket employed a gas generator cycle. The gas generator engine expels the combustion gases used to drive the turbopump through the turbine exhaust to the outside. The next-generation launch vehicle will be developed using a staged combustion cycle. The combustion gases used to drive the turbopump are fed back into the main combustion chamber for combustion, enabling more efficient fuel utilization. Think of it as a "reverse-burning" boiler. Total fuel efficiency increases by more than 20%, and the internal combustion pressure of the engine is also higher. While the combustion pressure of the Nuri rocket was 60 bar, the next-generation launch vehicle is expected to reach about 165 bar. Designing the engine to withstand such high pressure and developing appropriate manufacturing manuals and processes are key tasks.

Although somewhat challenging, KARI believes it is entirely feasible. The Nuri rocket also went through a process of first developing a small 30-ton engine before scaling up to 75 tons, and the staged combustion cycle engine has already been developed, tested, and verified in small scale, leaving only the R&D to scale up. Moon Yoon-wan, head of KARI's launch vehicle engine development team, explained, "Through prior development research on small staged combustion cycle engines, we have accumulated experience up to near-flight levels," adding, "We are currently entering system design to scale up to 100 tons."

Thrust Control and Multiple Ignition Technologies Secured

One of the core concepts of the next-generation launch vehicle is to drastically reduce costs by reusing it multiple times. To compete with SpaceX's Falcon 9 launch vehicle, which dominates the global launch vehicle market by lowering launch costs to around $1,500 per kilogram, this specification has become essential. One of the most critical technologies for this is thrust control for rocket recovery. It is necessary to slow down the falling speed and guide the rocket body to a designated point by leaving some fuel unused, allowing the rocket to be recovered intact. In this regard, KARI has already secured rocket engine thrust control technology during the Nuri rocket development process. Although thrust control technology was secured during engine testing, it was not used in the actual development process to simplify the electronic control system as much as possible. KARI has secured technology capable of controlling rocket thrust up to 40% and has completed a certain level of verification.

The multiple ignition technology is similar. The key to multiple ignition is designing and configuring the system so that it operates smoothly when the engine is turned off and then restarted. KARI has already completed the design and conducted substantial experiments. Team leader Moon said, "The reason for choosing five engines for the next-generation launch vehicle is to consider reuse. If there were four engines, it would be difficult to balance the center because all engines' thrust would need to be controlled to about 10% during descent. With five engines, it is much easier to control speed and direction by keeping only the center engine alive during descent," revealing, "We conducted experiments with 2 to 3 re-ignitions while developing a small staged combustion cycle engine."

Dedicated Rocket Fuel Development Completed

To efficiently design, operate, and enhance the reusability of rockets, the use of high-density clean fuel with minimal residue is essential. Most space powers develop and use dedicated high-density kerosene for rockets, removing impurities such as sulfur and aromatic compounds. The United States developed RP-1 in the 1950s and recently upgraded to RP-2. Recently, liquid methane is being developed as a propellant. However, South Korea used regular aviation fuel for the Nuri rocket. As the rocket structure grows larger, more residue is generated, which can cause engine rupture. Especially, even when using reusable engines, residue limits the number of uses. To address this, KARI recently completed the development of dedicated high-density rocket fuel and is currently testing it.

Team leader Moon said, "The biggest feature of the next-generation launch vehicle is a significant improvement in engine performance and the addition of reuse capability," adding, "Originally, two launches were planned, but one more was added to increase the success probability of lunar landing exploration."

If the next-generation launch vehicle development plan is successfully completed, South Korea will possess a high-efficiency, large reusable launch vehicle with performance equivalent to SpaceX's Falcon 9 much earlier than expected. Earlier, KARI released a research report in September stating that it would take about 20 years for South Korea to secure launch vehicle reuse technology. KARI predicted that technologies such as ▲return flight guidance control ▲grid fin landing devices for directional control and stability during landing ▲reusable engines ▲thermal protection ▲fairing reuse ▲landing support ground systems and operations ▲re-ignition and thrust control are necessary for reusable launch vehicle development.

Meanwhile, President Yoon Suk-yeol announced a future space economy roadmap on the 28th, declaring lunar landing exploration by 2032 and Mars landing exploration by 2045. The government immediately announced the next day that the next-generation launch vehicle development budget of about 2.0132 trillion won passed the preliminary feasibility study and will begin in earnest. The next-generation launch vehicle will be composed of a first stage with five 100-ton engines and a second stage with two 10-ton engines. The first stage's maximum thrust of 500 tons will be used for Earth high orbit, lunar, and Mars exploration. The Nuri rocket (thrust 300 tons), capable of placing about 1.5 tons of cargo into low Earth orbit (500?600 km), is expected to be mainly used for launching small and medium-sized satellites.