From a technical standpoint, the full-flow rocket engine, which leverages the advantage of using all cryogenic fuels and cryogenic oxidizers for cooling the gas turbine and the main combustion chamber wall, represents the current limit of staged combustion rocket engine development. Since all cryogenic fuels and oxidizers can be used for cooling the gas turbine, the limit of the turbine's driving power can be increased, allowing for a higher chamber pressure in the rocket engine. Currently, only the full-flow rocket engine can achieve a chamber pressure of 35 MPa. The full-flow liquid oxygen methane rocket engine is a theoretical low-cost, low-carbon-accumulating full-flow rocket engine, making it highly suitable for use as an engine in reusable rockets.
Recently, SpaceX announced the third generation of the Raptor rocket engine, referred to as the Raptor 3 engine. This is the world's first full-flow liquid oxygen methane rocket engine. It is reported that SpaceX began developing the Raptor engine in 2009 and successfully tested it for the first time in July 2019, becoming the world's first full-flow liquid oxygen methane staged combustion rocket engine. Currently, the third-generation Raptor full-flow rocket engine has begun mass production.
The Raptor 3 engine has undergone a transformation compared to its initial version, which can be described as a complete metamorphosis:
Advertisement
1. The appearance has been greatly simplified. The exposed pipes above the nozzle have been significantly reduced, making the exterior extremely streamlined.
2. The overall weight has been reduced by 26.7%. The weight has decreased from the initial 2.08 tons to 1.525 tons.
3. The thrust has increased by 51%. The sea-level thrust has been increased from 185 tons to 280 tons.
4. The thrust-to-weight ratio has nearly doubled. It has been increased from 92.5 to 183.6.
5. The estimated cost has been reduced by 87.5%. It has been reduced from $2 million to $250,000.6. Chamber pressure is increased by 40%. It is raised from 25Mpa to 35Mpa, which is considered the best in the world.
In short, the Raptor 3 full-flow liquid oxygen methane rocket engine is the most advanced, highest performance, and highest cost-performance ratio full-flow staged combustion cycle rocket engine to date, which is a complete transformation compared to the Raptor 1.
The first stage of the Starship uses 33 Raptor engines. If the first-generation Raptor engine is replaced with the third-generation Raptor engine, only 22 are needed to exceed the original thrust. A simple calculation can be made, and theoretically, after the Starship adopts the third-generation Raptor engine, its first stage weight reduction can reach 35.4 tons! This is a very astonishing indicator. If the weight reduction of the second stage is added, the weight reduction effect will be even more astonishing.
Can our country make a Chinese version of the Raptor 3 full-flow rocket engine?
The Raptor 3 full-flow rocket engine is developed based on the Raptor 1 full-flow rocket engine through two iterations, which took about 5 years. Therefore, as long as we can make a full-flow liquid oxygen methane rocket engine, making a Chinese version of the Raptor 3 rocket engine is just a matter of time.
The technical difficulties of the full-flow rocket engine are mainly concentrated on the three major parts of the rich oxygen pre-combustion chamber, rich fuel pre-combustion chamber, and main combustion chamber. The current high-pressure regenerative hydrogen-oxygen rocket engine uses a rich fuel pre-combustion gas turbine drive, while the high-pressure regenerative liquid oxygen kerosene rocket engine uses a rich oxygen pre-combustion gas turbine drive. At present, our country has mastered the technology of high-pressure regenerative hydrogen-oxygen rocket engines and high-pressure regenerative liquid oxygen kerosene rocket engines. By integrating and testing existing technologies, a full-flow liquid oxygen methane rocket engine can be made.
It can be seen that our country making a Chinese version of the Raptor 3 full-flow liquid oxygen methane rocket engine is just a matter of time.
Research and development progress of China's full-flow liquid oxygen methane rocket engine
Public information shows that China already has two 200-ton full-flow liquid oxygen methane rocket engines in the research and development stage.1. The 200-ton class full-flow liquid oxygen methane rocket engine YF215 of the National Aerospace Department has completed technical verification.
The YF215 full-flow liquid oxygen methane rocket engine, developed by the Sixth Academy of Aerospace of China, successfully conducted a gas generator ignition test on May 15, 2023.
In April 2024, Academician Long LeHao, an authoritative expert on China's launch vehicles and aerospace engineering, mentioned in a lecture that China's full-flow regenerative cycle methane engine YF-215 with a sea-level thrust of 200 tons has completed technical verification and has undergone a test run for as long as a thousand seconds. According to the "eight years and nine engines" plan, this engine will be completed by 2028 at the latest. Judging from the current progress, it is expected to be completed ahead of schedule by 2026.
2. Blue Arrow Aerospace plans to develop a 200-ton class full-flow liquid oxygen methane rocket engine by 2027.
Public information shows that at the end of 2021, Blue Arrow Aerospace initiated the demonstration and research work of a 200-ton class full-flow staged combustion cycle liquid oxygen methane engine, with the engine codenamed "Blue Flame" (BF-20), having a sea-level thrust of 2200kN and a chamber pressure of 26Mpa. Currently, the technical scheme for this model has been determined, and it is expected to conduct a full engine test in 2025 and complete the engine development by 2027.
Looking at the progress milestones, the gap between China's 200-ton class full-flow liquid oxygen methane rocket engine and the United States is no more than 8 years. It should be emphasized here that this is only a progress gap, not a technical gap, because China has mastered all the key technologies required for full-flow rocket engines at this stage. It is only because China started the research and development of such engines relatively late, which led to a lag behind the United States' SpaceX company.
Objectively speaking, SpaceX's "Starship" is indeed very powerful, but it does not have an essential difference compared to existing rockets, and there is no essential difference in the launch method and power.
In order to overtake by changing lanes, China should focus on the development of spaceplanes.The rocket engines that can be produced with current technology have a maximum vacuum specific impulse that does not exceed 470 seconds. Even the most powerful full-flow liquid oxygen methane rocket engines still cannot match the specific impulse of high-pressure staged combustion hydrogen-oxygen rocket engines or expander cycle hydrogen-oxygen rocket engines. The theoretical specific impulse of a full-flow liquid oxygen methane rocket engine can only reach 390 seconds, and essentially, it is still a rocket engine. No amount of praise can change the fact that it is just a rocket engine.
Our country has already built the JF22 super wind tunnel, which is at least 20 years ahead of the United States. With this black technology equipment, our country's research and development progress in hypersonic vehicles is leading the world. This includes the spaceplane with epoch-making significance.
The spaceplane is called an epoch-making equipment mainly because it uses a new concept engine with a specific impulse far higher than that of rocket engines, and will eventually achieve single-stage-to-orbit. This space equipment does not rely on rocket launchers and can take off and land independently at airports. In the future, it is expected to achieve flight scheduling like civil aircraft, and the cost of entering orbit is expected to be lower than that of reusable rockets. Therefore, our country should not just follow the development of full-flow liquid oxygen methane rocket engines and reusable rockets behind the American SpaceX company. Instead, we should take advantage of our country's wind tunnel technology advantages and focus on the development of new concept engines, striving to achieve a change of track in space transportation tools through the spaceplane technology route.
It is gratifying that the current decision-making departments of our country's space industry seem to have realized this point and are trying to replicate the successful experience of "changing track to overtake" in the automotive field through the new energy vehicle technology route.
Previously, I also posted an article introducing the research and development progress of our country's spaceplane, and the conclusion is that it is leading the world. Interested parties can search for "spaceplane" to learn more.