This article is from WeChat official account:Love Faner (ID: ifanr), author: Lee extraordinary, original title: “just, Chang-e V toward the moon! China has taken another big step towards manned landing on the moon”, title picture from: Visual China

At 4:30 a.m. 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 space 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 advanced 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 4 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.

1. The most complicated mission in the history of Chinese spaceflight

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 landing on the moon” and “building a lunar base”.

The unmanned lunar exploration is divided into three steps of “orbiting, landing, and returning”, namely orbiting the moon, landing exploration, sampling and returning, of which Chang’e-1 to Chang’e-4 have been completed After the first two steps, the Chang’e-5 will complete the final “back”, which is also the most complex and technically difficult task of 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-the orbiter, the lander, the ascender and the returner, while the previous four Chang’e probes only have 1～ It consists of 3 main components.

Chang’e-5 will realize four “firsts” in the history of China’s spaceflight:

  • Automatic sampling on the lunar surface for the first time;

    li>

  • First take off from the moon;

  • The first unmanned rendezvous and docking on the lunar orbit beyond 380,000 kilometers;< /strong>

  • 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 Crafts

First automatic sampling on the lunar surface

The last time humans took samples from the moon and brought them back to the Soviet Union Luna 24 in 1976, 44 years have passed.

Soviet Moon 24

It is not difficult for the probe to make a soft landing on the moon and dig a handful of soil. Chang’e series have already been able to do it. The real difficulty is to properly encapsulate the lunar soil.

After the Chang’e-5 probe collects lunar soil samples through drilling and robotic arms, it will be sent to the ascender and needs to be encapsulated 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 sample sealing, which caused the lunar soil to be contaminated.

According to Yu Dengyun, the 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. Haven’t tried.


First take off from the moon

In the past few lunar exploration missions, only one launch was required. In addition to being launched from the earth, Chang’e 5 must launch on the surface of the moon, which raised several levels of difficulty at once.

Readers who have paid attention to rocket launches should also know that launching missions on the earth require a complete guarantee system at the launch site. In addition to the fixing of the launch tower, there are also a large number of engineers who maintain and adjust in real time to ensure the 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 this needs to be done by Chang’e 5 itself, so Chang’e 5 adopts a more advanced artificial intelligence system. From the selection of the landing point to the adjustment of the latitude and longitude, slope, and elevation of the launch site, Chang’e After the sensors on No. 5 collect data, let the AI ​​brain complete it autonomously.

The first unmanned rendezvous and docking in the lunar orbit 380,000 kilometers away

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 three 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.

Forty years ago, the Soviet lunar probes all took off directly from the surface of the moon and returned to the earth after sampling. Naturally, the ascender needed more power, so it was necessary to load more fuel for the lunar soil samples. The space 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 launches, so it may not even support China’s strongest launch vehicle “Fat Five” .

The lunar orbit unmanned rendezvous and docking technology solves this problem. The probe does not fly back to the earth directly after sampling, but the ascender transfers the soil sample to the returner flying on the lunar orbit, and then Brought back to Earth by the return device.

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 for soil samples.

However, this process will also face two major technical challenges. One is how to make the ascender and returner meet and dock independently, and the other is to complete the packaging during the sample transfer process.

Actually, 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 precise ranging, positioning and navigation services, which can be used in lunar orbit. Resources are much scarce.

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 rushes directly into the atmosphere, Will generate more heat.

In order to protect the returner, 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”.It ejects using 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 had already tested the “drifting” and reenter the orbit for the first time, 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 Chang’e-5 to the sky. Four months ago, “Fat Five” sent Tianwen-1 into space.

It is called “Fat Five” because it is China’s largest diameter rocket, with a core stage of 5 meters in diameter, in addition to bundled with 4 3.35 meters boosters, which is a weight 869 tons of “big fat man”.

Because of being too fat, “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.

The “Fat Five” is not only improved in size. The 8 liquid oxygen kerosene engines and 4 hydrogen oxygen engines give it the strongest power of domestic rockets, and the thrust at take-off can reach more than 1,000 tons.

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 give 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 strongest transport rocket currently in service, it has already entered the ranks of the world. At present, the main rockets of the United States and Russia, the transportation capacity is mainly concentrated in the 20-30 tons level.

Without a rocket of this magnitude, not only would Chang’e-5 not be able to launch smoothly, and there would be no need to think about future manned missions to the moon and space station plans.

2. 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, which is 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 years of changes in the solar system.

For example, in the area where Chang’e 5 landed, there are basalts about 1.3 to 2 billion years ago. On the other hand, the lunar soil formed by meteorite impact, solar wind bombardment, and cosmic ray radiation in the lunar soil formed by space weathering, contains a lot of information about solar activity.

The Chinese planetary scientist team recently published the