The content of this article is written with authoritative information combined with personal opinions, and the source of the literature and screenshots have been marked at the end of the article, please be aware.
Preface
On May 8, Chang'e-6, which was launched for about 112 hours and 30 minutes, finally turned on the orbiter at the perilunar point for "deceleration and braking", and then entered the fourth stage - the circumlunar flight stage.
Chang'e-6 will have to fly around the moon for 20 days before it can land on the moon, while the United States will be able to land on the moon in one day.
Why is there such a big gap?
Chang'e-6 mission
As the "key point" of the fourth phase of the mainland lunar exploration project, Chang'e-6 will help mankind complete the acquisition work on the far side of the moon for the first time.
On May 3, Chang'e-6, carrying the Long March 5 carrier rocket, was successfully launched, accelerating and entering the Earth-Moon transfer orbit.
Later, Chang'e-6 glides along the Earth-Moon elliptical orbit at a speed of 10.9 kilometers per second, and no longer needs to use any power to provide acceleration, and it also needs to gradually decelerate.
After more than four days of flight, Chang'e-6 has reached the vicinity of the moon and successfully "braked" under the precise control of the Beijing Aerospace Flight Control Center.
After applying the brakes, Chang'e-6 will be traveling at a speed of less than 2.38 kilometers per second, so that it can be captured by the moon's gravity, which cannot capture Chang'e-6 without "braking".
If it can't be captured, Chang'e-6 will follow the elliptical orbit of the "Earth-Moon Transfer" and then return to the Earth's orbit.
After completing the brakes, Chang'e-6 was successfully captured by the moon's gravity, and then returned to orbit around the moon, but this time Chang'e-6 is very different from the previous Chang'e-5.
In the retrograde orbit adopted by Chang'e-5 and the retrograde orbit adopted by Chang'e-6, all the planets in the solar system are moving in "anterograde orbits" along the direction of rotation of the sun.
The "retrograde orbit" adopted by Chang'e-6 this time seems to be "unsafe", because other planets and probes are "smooth", and Chang'e-6 is the opposite, focusing on a "rebellion".
Therefore, the retrograde orbit of Chang'e-6 is completely opposite to the direction of the moon's rotation, and the reason why it adopts the retrograde orbit is "safety".
According to experts, in fact, Chang'e-6 adopts this method because the retrograde orbit will increase the "relative speed" between the probe and the moon, so that Chang'e-6 can fly more stably in lunar orbit.
Chang'e-6 will have to complete its 20-day "flight around the moon", during which it will need to constantly adjust the altitude and inclination angle of the orbit around the moon, and choose a suitable landing site.
When the landing is confirmed, the "orbiter and returner combination" will be separated from the "ascender and lander combination", and after landing on the moon, a 48-hour lunar sampling will be carried out, and after the acquisition is completed, the lander and ascender assembly and the orbiter assembly will converge.
After that, the "lunar soil" will be returned to Earth through the returner, and the rest of Chang'e-6 will continue to work in lunar orbit, a process that will take 53 days to complete.
Therefore, we found a problem, the time of the Earth-Moon transfer is inevitable, and the time damage to the lunar acquisition and return to the lunar orbit is also unavoidable, but in the entire 53-day mission, Chang'e-6 spent 20 days "flying around the moon".
However, why can the U.S. lunar exploration mission land on the lunar surface in 1 day?
Reference: Guangming Network "Intelligent Sampling on the Back of the Moon! Chang'e-6's 53-day space "business trip" is interlocking, and the key step by step is "2024.5.8
Guangming Network "Intelligent Sampling on the Back of the Moon! Chang'e-6's 53-day space "business trip" is interlocking, and the key step by step is "2024.5.8
U.S. lunar exploration mission
One of the most classic U.S. missions to the moon was achieved during the Cold War's "Space Race," when World War II had just ended, and the United States and the Soviet Union, the world's two most powerful forces, were in opposition.
As a result, the United States and the Soviet Union began the famous "space race", and the two sides exerted their fists in the military and aerospace fields, which greatly accelerated the time for human exploration of space.
The two most critical stages were that the Soviet Union had developed the "first artificial satellite" before the United States, so the Soviet Union became the first country to send spacecraft into space, which had a huge international impact and seemed to become the "talker" of the earth.
Of course, the United States also began to develop satellites early, but because the progress was slightly slower than that of the Soviet Union, after the Soviet Union successfully launched the satellite, the United States produced the first American satellite "Explorer 1" on January 31, 1958.
However, at this time, the Soviet Union had already seized the opportunity and lost the initiative in the space race, and three years after the United States launched its satellite, the Soviet Union made a feat that shocked the world.
In 1961, the Soviet Union sent the 27-year-old cosmonaut "Yuri Gagarin" into space, successfully stayed in space for 2 hours, and successfully returned to Earth.
At this time, the Soviet Union was already ahead of the United States for the second time, and the United States was already in a hurry to do it, so it decided to make a big one, that is, to launch the famous "Apollo Program".
In that world, the Soviet Union's lunar exploration program was frequently frustrated, while the American Apollo 8, 9, and 10 were all successful, and also developed the "Saturn V" series of launch vehicles, with a thrust of up to 3,400 tons, which could realize the American Apollo program.
So, on July 16, 1969, Apollo 11 was ready to launch at the Kennedy Aviation Center, and more than a million people gathered to watch the Apollo 11 launch site.
At 9:32, the Saturn V rocket was successfully ignited, and twelve minutes after launch, the Saturn V carrier rocket sent the Apollo 11 spacecraft into space and successfully entered the Earth's orbit.
After orbiting the Earth for about 150 minutes, the spacecraft's third-stage rocket ignited, accelerating the spacecraft to 10.5 kilometers per second and heading to the moon for a transfer orbit.
After Apollo 11 entered the Earth-Moon transfer orbit, the command module separated from the Saturn V rocket and connected to the lunar module of the third stage rocket.
After nearly 4 days of flight, Chang'e-6 took about 4 days to travel to the moon and relied on the gravitational pull of the Earth and the Moon.
Apollo 11 passed by the far side of the moon on July 19 and ignited a rocket that slowed to less than 2.38 kilometers per second, allowing Apollo 11 to successfully enter lunar orbit.
After that, Apollo 11 and Chang'e-6 began to "fly around the moon", but unlike Chang'e-6, the astronauts of Apollo 11 recognized the planned landing site in less than a day of flight around the moon.
The landing was successfully completed on July 20 in the southern part of the Moon's Tranquil Sea, 20 kilometers southwest of the Sabine D crater, which was much flatter than the other sites.
So Apollo 11 landed successfully, in which Commander Amsterdam successfully landed on the moon, and came up with the classic famous phrase: "This is a small step for me, but a giant leap for humanity".
It is of great significance to human civilization that human beings have set foot on a planet other than Earth for the first time, and it is also officially because of the success of the Apollo 11 moon landing that the United States has taken the lead in the space race and won the "space race".
Not only that, but the mission to the moon also carried out a "global live broadcast", with more than 600 million people around the world watching the Apollo 11 moon landing in front of their television sets, setting a historical record.
After the moon landing, the three astronauts dug up 21.55 kilograms of lunar soil and successfully returned to Earth in just eight days.
It is inconceivable that the first landing of the United States on the moon 55 years ago could land in a single day of flying around the moon, and it also successfully walked the moon and brought back lunar soil.
Why is there such a big gap between China and the United States in lunar exploration missions?
Reference: Douyin Encyclopedia "Apollo 11 (Man's First Mission to the Moon)"
Douyin Encyclopedia "Apollo 11 (Man's First Mission to the Moon)"
Why is the gap so big?
This is really incomprehensible, because we all know that aerospace technology is a multi-disciplinary discipline, covering dynamics, thermophysics, propulsion principles, combustion, applied materials, manufacturing technology, flight control, medicine, electronics, mathematics and other disciplines.
Therefore, space technology gives a "complex and rigorous" process, and the Apollo 11 mission, everything seems so "simple", and the moon landing does not seem too difficult.
Chang'e-6, on the other hand, needs to fly around the moon for about 20 days to adjust its attitude and landing site in the "flight around the moon", so it makes people feel that there is a big gap.
But in fact, these two missions cannot be compared, because Chang'e-6 is an unmanned lunar exploration, and it is also the most complex and final probe of mankind so far, weighing 8.2 tons.
And the mission of Chang'e-6 is not only to "collect lunar soil", but also to carry a number of international scientific payloads to the moon this time, so there are many side tasks.
And unlike Apollo 11, there were three astronauts on Apollo 11, so Apollo 11 was operated by astronauts, so the fault tolerance rate of the mission was much higher than that of Chang'e-6.
The control center of Chang'e-6 is 380,000 kilometers away from the earth, and it also needs to consider the problem of signal transmission, so many operations will become more rigorous.
Moreover, the environment of the Chang'e-6 moon landing site is very harsh, there are a large number of dark areas of the "moon sea", and there are meteorite impact craters and cosmic radiation and dust from outside the moon, so the difficulty of the mission will be more difficult.
The landing site is also the most severe area of the "lunar sea", the south pole of the moon - the Aitken Basin, which is currently the second largest crater in the solar system, with a diameter of 2,500 kilometers, a depth of 13 kilometers, and a drop of 16 kilometers.
And the proportion of craters and impact craters on the far side of the moon reaches 97.5 percent, which is much higher than the 69 percent on the front side, so the environmental complexity is much higher.
In addition, during the flight around the moon, other international and organizational scientific payload missions were completed, such as the French radon gas detector, the ESA lunar surface negative ion analyzer, and the Italian laser corner reflector, all of which were lengthened.
Resources:
Beijing News, "The World's First Lunar Sampling Mission, Chang'e-6 May Find Clues for the Origin of Life on Earth" 2024.5.3
Beijing News, "The World's First Lunar Sampling Mission, Chang'e-6 May Find Clues for the Origin of Life on Earth" 2024.5.3
epilogue
Therefore, the reason why China can only land after 20 days of flying around the moon is that the Chang'e-6 mission is indeed very difficult, the landing environment is complex, and it also carries the scientific payloads of many international organizations and also needs to allocate mission time.
Therefore, in the whole process from circumlunar to lunar landing, the flight time of Chang'e-6 around the moon will be greatly extended, which further illustrates the importance and difficulty of the mission.
Resources:
"The world's first lunar sampling mission, Chang'e-6 may find clues for the origin of life on Earth" 2024.5.3
Guangming Network "Intelligent Sampling on the Back of the Moon! Chang'e-6's 53-day space "business trip" is interlocking, and the key step by step is "2024.5.8
Douyin Encyclopedia "Apollo 11 (Man's First Mission to the Moon)"