The three-stage rocket that launched Chang 'e 1 to Phase IV is a liquid oxygen liquid hydrogen engine, that is, a high thrust cryogenic engine. To launch a high-orbit load, such as launching a synchronous communication satellite with an apogee of more than 40,000 kilometers, or launching a lunar or planetary probe out of the gravity of the earth, it is necessary to use a low-temperature high-energy engine and a combination of liquid hydrogen and liquid oxygen. The same is true of the American Apollo spacecraft, the third stage.
Without low-temperature high-energy technology, it is impossible to launch high-orbit satellites, and few countries in the world have mastered low-temperature high-energy rockets. Only a few big countries, such as China, the United States and Russia, and second-rate space countries, basically all low-temperature and high-energy engines are purchased directly.
Launching a high-orbit satellite requires low temperature and high energy, because the engine itself is small in size and mass, but the specific impulse and thrust are the largest, and the satellite spacecraft and other payloads, plus the third stage, are very heavy. If the total weight of the two is about 20 tons, including: synchronous transfer orbit 5 to 6 tons, lunar transfer orbit 3 to 4 tons, plus the third stage rocket, the total mass is about 20 tons. Then the total mass of the rocket at take-off is required to exceed 500 tons. So far, only the long March bundled rocket can do it in China. Before the Long March 5 became stable and reliable, the maximum capacity of our rocket was so large. Only when Long March 5 is put into practical use can China's synchronous transfer orbit capacity reach 8 to 10 tons, and its ball orbit reach 7 to 8 tons.
What is the difference between the launch of Chang 'e 1 4 and the launch of Chang 'e 5?
The mission of Chang 'e V is the last step of a three-step detour. To sample the moon and fly back, the mass of the soft landing on the surface of the moon must be more than 5 tons, so that there is enough fuel to take off and return to the earth. Therefore, the current progress of the Long March 5 rocket will directly affect the last key step of the Chang 'e project.
It is more demanding to return to the moon with men. After the manned soft landing on the moon, the remaining mass of the lunar lander should be at least 15 to 20 tons, so that there is enough fuel for manned take-off again, and the mass for starting to run to the moon should be at least 80 tons to 100 tons, and the take-off weight of the launching rocket should be at least 3000 tons! This is not the current five-step project, but a new manned moon landing plan, which requires newly developed super-large rockets such as Long March 9.