At 4:30 am Beijing time today, the Chang'e-5 lunar probe was launched at the Wenchang Space Launch Site in Hainan by China’s strongest rocket, the Long March 5 Yaowu carrier rocket.
This is the sixth mission of China's lunar exploration project and the most complicated mission in China's aerospace history. For the first time, China will "dig earth" on the moon and bring it back to earth .
Chang'e 5 has gathered almost all the top technologies of China's aerospace at present, and this launch will also be an advance preview of China's manned moon landing, and will be a technical verification for the manned moon landing ten years later.
The Martian rover "Tianwen-1" launched four months ago has flown 300 million kilometers in space. The Chang'e-5 spacecraft has once again opened a new chapter in China's spaceflight.
The most complicated mission in China's space history
With the successful launch of Chang'e 5, the first phase of China's lunar exploration project has come to an end. According to China's lunar exploration project plan established in 2004, the Chang'e project is divided into three phases: "unmanned lunar exploration", "manned lunar landing" and "establishment of a lunar base" .
The unmanned lunar exploration is further divided into three steps of "orbiting, falling, and returning", that is, flying around the moon, landing for exploration, and sampling and returning. Among them, Chang'e 1 to Chang'e 4 have completed the first two steps, and Chang'e 5 will Completing the final "back" is also the most complex and technically difficult mission in the Chang'e series so far.
Because of this, the structure of the Chang'e-5 lunar probe is also the most complicated, consisting of four main components-orbiter, lander, ascender and returner, while the previous four Chang'e probes have only 1-3 components. composition.
Chang'e-5 will achieve four "firsts" in China's space history:
- Automatic sampling on the lunar surface for the first time;
- Take off from the moon for the first time;
- For the first time, unmanned rendezvous and docking on the lunar orbit beyond 380,000 kilometers;
- For the first time, the lunar soil returned to Earth at a speed close to the second universe.
Why is it said that Chang'e-5 will be the most complicated mission in China's space history? It is basically reflected in these four "firsts."
▲Picture from: Space Craft
Automatic sampling on the lunar surface for the first time
The last time humans took samples on the moon and brought them back to the Soviet Union in 1976, Lunar 24th, 44 years have passed.
▲ Soviet Lunar 24th.
It is not difficult to make the probe softly land on the moon and dig a handful of soil. The Chang'e series have already been able to do it. What is really difficult is to properly encapsulate the lunar soil.
After the Chang'e-5 probe collects lunar soil samples by drilling and robotic arms, they will be sent to the ascender and need to be packaged for the first time to prevent the samples from being lost and contaminated when they leave the moon.
When the "Apollo" spacecraft manned the moon to collect samples, there was a problem with the sealing of the samples, which caused the lunar soil to be contaminated.
According to Yu Dengyun , deputy chief designer of the lunar exploration project, since the gravity of the moon is only one-sixth of that of the earth, the requirements for sampling and packaging technology will be higher to ensure that the retrieved samples are valid. This has never been tried before. of.
Take off for the first time from the moon
In the past few lunar exploration missions, only one launch was required. In addition to being launched on the moon's surface, Chang'e-5 has to rise above the earth, which has raised several levels of difficulty at once.
Readers who have paid attention to rocket launches should also know that launching missions on earth require a complete guarantee system at the launch site. In addition to the fixation of the launch tower, there are also a large number of engineers who perform real-time maintenance and adjustments to ensure a smooth launch.
However, on the moon, these safeguards are almost impossible to provide, and uncontrollable factors have greatly increased. Whether the launch platform is stable and the angle is accurate, engineers on Earth cannot monitor it in real time.
All of this needs to be done by Chang'e 5 itself. Therefore, Chang'e 5 adopts a more advanced artificial intelligence system . From the selection of the landing site to the adjustment of the latitude and longitude, slope, and elevation of the launch site, all will be carried out by Chang'e 5. After collecting data, let the AI brain complete it autonomously.
The first time an unmanned rendezvous and docking in lunar orbit than 380,000 km
According to the plan, this time Chang'e 5 will return to Earth with at least a 2kg lunar soil sample. The Soviet Union brought back about 330g of soil samples in the past 3 lunar sampling missions.
Why can Chang'e-5 bring back so many samples at once? This is mainly due to the lunar orbit unmanned rendezvous and docking technology used in this mission.
More than 40 years ago, the Soviet lunar probes took off directly from the surface of the moon and returned to the earth after sampling. Naturally, the ascender needed more power, so more fuel must be loaded, leaving space for lunar soil samples. Will be greatly compressed.
Not only that, in order to load more fuel, the weight of the riser will also increase accordingly, which also increases the pressure on the launch vehicle during ground launch, so it may not even be able to support China's strongest launch vehicle, the "Fat Five".
The lunar orbit unmanned rendezvous and docking technology solves this problem. The probe does not directly fly back to the earth after sampling. Instead, the ascender transfers the soil samples to the returner flying on the lunar orbit, and then the returner brings it back to the earth. .
In this way, the distance that the ascender needs to fly is greatly shortened, and only a small amount of fuel is needed, which can give more space to soil samples.
However, this process will also face two major technical challenges, one is how to make the ascender and returner autonomously meet and dock, and the other is to complete the packaging during the sample transfer process.
In fact, similar space autonomous intersections and dockings have been used in my country’s past Shenzhou series, but they are all carried out in earth orbit. Ground stations and artificial satellites can provide accurate ranging, positioning, and navigation services, but these resources are scarce in lunar orbit. Much.
The packaging of samples is also critical, because whether the samples can be brought back intact is the criterion for judging the success or failure of the Chang'e-5 mission. If it is not tightly sealed, the sample may be burned in the process of returning to the atmosphere.
So just like taking off on the moon, the artificial intelligence system of Chang'e 5 will play an important role in these processes.
For the first time, the lunar soil returned to Earth at a speed close to the second universe.
In addition, when the returner returns to the earth with the sample, the speed will reach the second cosmic speed close to 11.2km/s, which is much faster than the first cosmic speed when the Shenzhou series spacecraft returns to the earth. If it directly rushes into the atmosphere, it will produce more Great heat.
In order to protect the return device, a thicker heat shield must be installed. As a result, the weight of the detector will increase and fewer samples can be brought back.
Therefore, Chang'e-5 enters the atmosphere in a way similar to "drifting", first ejects out by the lift of the atmosphere, and then enters the atmosphere again after slowing down.
In fact, as early as 2014, the Chang'e 5 T1 tester first tested the "drifting" and reenter the orbit, and took a photo of the earth and the moon.
China's strongest rocket "Fat Five"
It is also worth mentioning that this time the carrier rocket "Fat Five" that carried the Chang'e-5 to the sky. Four months ago, "Fat Five" sent Tianwen 1 into space .
It is called the "Fat Five" because it is the largest rocket in China with a core diameter of 5 meters. In addition, it is bundled with 4 3.35 meters boosters. It is a "big fat man" weighing 869 tons.
It is precisely because it is too fat that the "Fat Five" can no longer be transported by rail like rockets in the past, because this has exceeded the diameter of the railway bridge hole, and only two transport ships can reach the launch site by sea.
"Fat Five" is not only improved in size, 8 liquid oxygen kerosene engines and 4 hydrogen oxygen engines, giving it the most powerful power of domestic rockets, the thrust can reach more than 1,000 tons during takeoff.
▲ YF-100K engine.
In addition, the two propellants of liquid oxygen and liquid hydrogen must be stored at minus 183 ℃ and minus 253 ℃ respectively. This rocket is also called "ice arrow".
Such power and size gave the "Fat Five" the strongest carrying capacity in my country's history. It has a carrying capacity of 25 tons in low-Earth orbit, which is directly increased by more than 2.5 times on the basis of active domestic rockets.
Although this is not as good as the Falcon Heavy, the most powerful transport rocket currently in service, it has already entered the international ranks. At present, the main rockets of the United States and Russia have transportation capabilities mainly at the 20-30 ton level.
Without a rocket of this magnitude, not only would Chang'e-5 not be able to launch smoothly, and the subsequent manned moon landing and space station plans would not have to be thought of at all.
Why go to the moon to "dig earth"
If all goes well, in a while, Chang'e 5 will land near the Rumke Mountains in the northern part of the Moon Sea Storm Ocean, the largest on the front of the moon, a region of the moon that humans have never visited before.
Why do we travel all the way to the surface of the moon to "dig earth"? Because this not only allows us to understand the evolution of the moon, it is also of great significance for studying the 4.5 billion-year changes of the solar system.
For example, in the area where Chang'e 5 landed, there are basalts about 1.3 to 2 billion years ago. The lunar soil formed after meteorite impact, solar wind bombardment, cosmic ray radiation and other space weathering effects on the lunar rock contains a lot of information about solar activity.
A study published by a team of Chinese planetary scientists in the journal “Nature·Astronomy” not long ago found that the impact of the Earth-Moon system had changed about 3.5 billion years ago based on the evolution of the lunar soil. It also revealed that the giant planets in the early solar system The turbulent history provides new ideas and clues.
The lunar soil is the soil of the moon. Although it is readily available on the moon, it contains great scientific value for the people on the earth.
However, since only the United States and the Soviet Union had the ability to sample from the moon in the past, it is not easy for China to study. At present, the only 1g lunar soil sample in China was given to China by the United States after the establishment of diplomatic relations between China and the United States in the 1970s.
Moreover, most of the lunar samples brought back by the Apollo were concentrated in the lunar sea area in the middle and low latitudes on the front of the moon. The age was concentrated between 4.2-3.2 billion years ago, which is not comprehensive enough for lunar research. After Chang'e-5 brings back lunar samples, China will be able to conduct further research on the moon.
In addition, Ouyang Ziyuan, chief scientist of the lunar exploration project, also mentioned in an interview why the moon should be explored . In addition to studying the evolution of the moon, the moon has abundant energy.
Ouyang Ziyuan believes that the lunar soil also contains a very important ultimate energy raw material, which is needed by our current chemical energy and nuclear power plants, which will provide important support for the sustainable development of human society.
In the next ten years, the Chinese will go to the moon
After the successful completion of the Chang'e-5 mission, the next stage is the manned moon landing .
Wu Weiren, chief designer of China's lunar exploration project and academician of the Chinese Academy of Engineering, once revealed that China's manned moon landing will be realized around 2030, and an international lunar research station will be established in the lunar south pole. Before that, Chang'e 6 and 7 will go to the south pole. Conduct exploration.
In fact, this Chang'e-5 mission can also be seen as a preview of China's manned moon landing ten years later . The lunar orbit of Chang'e 5 has been separated and docked many times. In fact, it is similar to the technology of the American Apollo plan for manned landing on the moon. The United States also did a lunar orbital rendezvous and docking test before the manned moon landing.
As the aerospace science blogger "Space Craft" said , the only difference between the Apollo spacecraft and Chang'e 5 is manned and non-manned. When several major components of Chang'e-5 are upgraded to "cabins" and equipped with manned space systems and lunar landing equipment, manned moon landings can be realized.
Yu Dengyun, deputy chief designer of China's lunar exploration project, also stated that the Chang'e-5 mission is to make technical reserves for future manned moon landings.
In addition to China, NASA in the United States has also launched a plan to return to the moon, and it will conduct another manned moon landing as early as 2024. However, after ten years, the United States may not be the only country to achieve a manned moon landing.
Whether it is China or the United States, manned moon landing will not be the end of space exploration. Musk hopes to use the moon as a transit point for Martian immigration, and Ouyang Ziyuan also believes that the moon is just a springboard for humans, and humans may eventually go to Mars .
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