Long March 9 - 2019 Iteration

By 2019 the specific indicators of Long March 9 were more detailed, and the data has been clarified. The maximum LEO carrying capacity has been changed from 140 tons to 180 tons. The core diameter is clearly 9.5 meters, and the booster diameter is clearly 5 meters and two plugs. A double-chamber kerosene engine, the height of the whole rocket is clearly 103 meters, the name of the 480-ton kerosene engine is clearly YF130, and the name of the 220-ton supplemental combustion hydrogen-oxygen engine is YF90.

By early 2019 China made significant progress in the development of the key technologies of the heavy-lift carrier rocket, the Long March-9, which was expected to make its maiden flight around 2030. The development of the heavy-lift rocket would greatly improve China's capacity of entering outer space. The Long March-9 rocket would support China's space industry development, utilization of space resources and deep space exploration, said experts from the China Academy of Launch Vehicle Technology.

The rocket would have a core stage with a diameter of 9.5 meters. Its total length would be about 100 meters. the LEO design load of the three configurations of the Long March 9 has spanned from 50 tons to 180 tons (and according to some calculations, the maximum LEO load of the Long 9 can even reach 200 tons), according to China's classification of rockets. Standard, Long March 9 has covered the range of heavy and super heavy rockets. The carrying capacity of the Long March-9 would be five times that of the Long March-5, currently the largest carrier rocket of China. The heavy-lift rocket was expected to help China realize manned lunar exploration, taking samples from Mars back to Earth, and other deep space explorations.

The YF130 does refer to many design concepts of RD180, which use one pump to drive two combustion chambers. However, the design thrust of YF130 is higher than that of RD180. Although RD180 is modified from the legendary rd170 with a vacuum thrust of 806 tons However, the vacuum thrust of the RD180 with dual combustion chambers is only 423.4 tons, which is much lower than the 500 tons vacuum thrust of the YF130 with dual chambers.

Kerosene engines are generally divided into two types: gas generator cycle and staged combustion cycle. The gas generator cycle is represented by the kerosene engines in the United States. The more well-known gas cycle engines include: the Merlin 1D installed on the Falcon 9 by Spacex, and the F1 engine used on the Saturn V. The gas generator generates insufficient combustion gas to drive the turbo pump to deliver the fuel to the combustion chamber.

The structure of the gas generator cycle is relatively simple, generally divided into two types, one is rich combustion (excess kerosene), the other is oxy-fuel combustion (excess oxygen). Among them, because oxygen-enriched combustion would produce gas up to 3000 degrees Celsius, few materials can withstand it, so the fuel-rich combustion scheme is generally adopted for the gas generator cycle. Rich combustion has one of the biggest drawbacks, that is, insufficient combustion of kerosene would produce a lot of black smoke, which can easily block the pipes and cause accidents. Therefore, after the gas passes through the turbo pump, the gas is generally discharged directly, and is not input into the combustion chamber for secondary combustion. Therefore, the specific impulse of the gas generator cycle engine is generally relatively low.

The staged combustion cycle means that part of the oxygen and all of the fuel, or part of the fuel and all of the oxygen are burned in the pre-combustion chamber (that is, oxygen-enriched and fuel-rich), and fuel gas is generated to drive the turbo pump, and then all the fuel is input into the combustion chamber for two Times burned. The staged combustion cycle structure is more complicated, but due to the black smoke produced by kerosene rich combustion, oxy-fuel combustion is generally selected for staged combustion. In addition to the higher specific impulse of staged combustion, because there is no too much black smoke at the pre-combustion chamber and the turbine disk, it is also more advantageous for recycling.

Americans abandoned the staged cycle and chose a lower-efficiency combustion generator cycle, largely because of this reason. But it is said that after Soviet scientists practiced oxygen-enriched combustion, they found another solution to this problem: inject more oxygen into the pre-combustion chamber, and use the low temperature of oxygen to dilute the high temperature of the fuel gas.

The SSME used by the American space shuttle and the RD120 of the Soviet Union are hovering around 200 tons of thrust. The Vulcan engine of Europe and the LE7 engine of Japan are only hovering around 100 tons of thrust. Generally speaking, the oxyhydrogen generator is also divided into a gas generator cycle and a staged combustion cycle, in which the over-oxygen combustion temperature of hydrogen is much higher than that of kerosene, and rich combustion does not produce black smoke. Therefore, whether the hydrogen-oxygen engine is a gas cycle or a staged cycle, the fuel-rich combustion method is generally adopted.

Due to the large differences in the density, volume, and quality of hydrogen and oxygen, hydrogen-oxygen engines use two pre-chambers/gas generators to drive two turbopumps to work in most cases. Single gas generator/pre-combustion chamber + coaxial double pump was once followed by the Soviet Union, and only by the Soviet Union in the RD120. This combination has good starting performance and can put the hydrogen pump in the pre-chamber and Between the oxygen pumps, the high-temperature fuel-rich hydrogen and oxygen would never come into contact, so that the turbo pump does not need to be filled with a large amount of helium for isolation and can continue to work stably. However, this combination limits the fine-tuning of the hydrogen-oxygen ratio and is likely to cause incomplete combustion of part of the fuel. The specific impulse is fixed by the coaxial turbo pump, and it is difficult to increase it in the future.

China’s 220-ton hydrogen-oxygen engine chose the third route: single pre-chamber + parallel double pumps. Of course, this scheme has its own problem, that is: the gas distribution problem in the pre-combustion chamber. The mixed combustion of hydrogen has a certain ratio. This ratio is respectively responsible for the speed of the hydrogen pump and the oxygen pump. However, it is impossible to install a transmission on the hydrogen-oxygen engine to adjust the speed, so the best way to control the speed of the turbo pump is to control the gas. The amount of production. If there is more gas, the speed would be faster, and if there is less gas, the speed would be slower.

However, in this scheme, the size of the hydrogen and oxygen distribution pipes is fixed. In other words, after determining a rough ratio range in the early stage, it would be difficult to adjust the hydrogen-oxygen mixing ratio in the later stage. Eventually, it would also face a situation like RD120, causing some fuels to not fully burn and continue to increase the specific impulse. If the gas volume is forcibly adjusted, the working conditions of the hydrogen pump and the oxygen pump would interfere with each other, and eventually fall into the vicious circle of "add more water to the surface, add more water to the surface".

The fine adjustment of the amount of gas in the pre-chamber is based on the amount required by the hydrogen turbo pump. Oxygen controls the amount of oxygen input into the combustion chamber by adjusting the size of the pipe valve that transports fuel back and forth. Finally, a relatively good hydrogen-oxygen mixing ratio is achieved. To put it simply, "put as many noodles as you can eat. After adding water, if there is too much water, scoop it out until the ratio of noodles to water reaches the best."

The 25 ton YF79 upper-level hydrogen oxygen engine was the slowest part of the progress. Some speculate that it is because it is the most technically difficult, and some speculate that there are still many key projects in Changjiu, and there is no time to deal with it.

In fact, compared to the first and second level engines, the technical difficulty of this engine is not very high, but it can be said to be the most mysterious. The development plan of this engine does not seem to be started with the Long March 9 project, but started as early as 2015, and would not only be used in the upper stage of the Long March 9 in the future. The expansion cycle engine does not produce gas during the cycle, and the hydrogen is heated along the pipe around the nozzle, and then the turbo pump is driven to circulate, and it can also cool the combustion chamber.