Article reprinted from "Gezhi Discourse Forum"
The strong friction makes the temperature of the surface of the spacecraft as high as 2000 degrees,
The entire onboarding process takes 530 seconds.
But there are astronauts in the Shenzhou spacecraft.
So the temperature inside can't exceed 30 degrees,
This requires an efficient thermal protective material.
Luo Lijuan· Senior Engineer, China Academy of Launch Vehicle Technology
Gezhi Dao No. 24 | March 31, 2018 Beijing
Hello everyone, I am Luo Lijuan, from the Institute of Aerospace Materials and Technology of China Academy of Launch Vehicle Technology. Today I want to introduce you to a material - low-density ablation heat-proof material, what is this material used for? I would like to invite you to watch a video first.
As you can see, this is the Shenzhou spacecraft. What I have introduced to you is its heat-proof material. This material can withstand a high temperature of 2,000 degrees, protecting the Shenzhou spacecraft from returning home safely.
The heat-proof material of the Shenzhou spacecraft
Completed: 10%///////
The speed of the spacecraft when it re-enters the atmosphere is 7.8 km/s, how fast is this speed? We travel from Beijing to Tianjin, and it takes 30 minutes to take the high-speed train, but if we are on the Shenzhou spaceship, it only takes 15 seconds.
Our materials end up using honeycomb-reinforced low-density materials. As shown in the picture, is it particularly honeycomb-like? That's where its name comes from.
At very high speeds, the surface temperature of the spacecraft will be very high, and the atmosphere and the surface of the spacecraft will produce a very strong friction. The strong friction caused the temperature on the surface of the spacecraft to reach more than 2000 degrees, and the entire loading process took 530 seconds.
However, there are astronauts in the Shenzhou spacecraft, so the temperature inside cannot exceed 30 degrees, which requires an efficient thermal protective material, which is this material.
This material decomposes, resists, and sublimates a series of endothermic reactions in the process of high temperature, thereby taking away a large amount of heat and protecting the internal structure.
Doesn't that sound particularly like a candle? Burn yourself and illuminate others. In fact, our material is much more tragic.
According to the astronaut's recollection, the high temperature burned the porthole red, and then outside the red window, red and white debris kept sliding by, which is what we look like when the material is working.
So this material is so good, can it be used for civilian use? At present, there is none, but my brother-in-law is particularly dare to think and dare to do it.
He called me one day and said, "Little sister, I saw your spaceship in the museum, and the surface of your spaceship burned like a black pot." But I saw a brand logo below that said it could be used at temperatures of more than 2,000 degrees. Recently I just took over a project to do boiler heat protection, your material is so good, can you use it on me? ”
After listening to it, I thought that this boiler was too different from the spacecraft, but I still wanted to answer this question.
I said, "I don't think this material is very suitable for you, our ablative material, it's disposable, only 530 seconds." Your boiler is used for many years, how can you change the material once a few years. Besides, our material is quite expensive, 8,000 yuan a kilogram. ”
He said, "What? Your material is so expensive, you can only use it in such a short time? Then hurriedly interrupted me.
I felt very uncomfortable in my heart and wanted to cry foul for my material. This material is clearly leading the world and has won many awards. But I thought about it, this may be an individual case, and I didn't go too far into my heart.
After some time, I attended a coordination meeting that included many departments. My department is a material forming department, responsible for the production of materials, components, and products.
My upstream is a structural system department, which is specifically responsible for converting a general condition into a material indicator requirement to us, which is our party A.
So in between meetings, I asked, "What did you study in college?" "He said he was studying thermal energy and power engineering, and he saw that I didn't react to this, and he added that this specialty was boiler burning.
Since this is the case, I think it is necessary to carefully compare the heat insulation material used in the boiler with the heat-proof material used by the Shenzhou spacecraft.
Generally speaking, when we receive any heat-proof product task, we must look at its use environment requirements.
For example, this boiler, its use environment is 550 degrees of steam temperature, it wants to use insulation materials is to reduce heat loss, then you can use some lightweight thermal insulation felt materials.
I searched on Taobao, this material is quite a lot, the cheapest is only 5 yuan a kilogram, no wonder my brother-in-law heard the offer of 8,000 yuan is very stunned.
One of the biggest benefits of this boiler is that it is placed on the ground and it is not limited by weight and space. That is to say, if I want it to be more heat-proof and more insulating, I can paste several more layers of heat-proof material.
For example, we feel very cold in winter, if the economic conditions are not very good, wearing more layers can also withstand the cold, not necessarily have to wear light and warm, but very expensive clothes.
But the Shenzhou spacecraft is different, it uses an ambient temperature of more than 2,000 degrees, it is very demanding on weight. Why?
Space X, the civilian space company that won the price, offered $54 million for its Falcon 9 rocket, and $133 million for the Dragon spacecraft.
The spacecraft's heat-proof materials account for 45% of the weight of the entire system structure, and if we reduce the density of this heat-proof material by 10%, we can save 58 kilograms of weight, equivalent to the weight of an astronaut. So weight loss is very necessary, even if its cost is 8,000 yuan per kilogram, it is still very cost-effective.
In addition to weight reduction, we also need to consider some of the environmental issues of the spacecraft's other application space. Although the final use of this material is only the last 10 minutes, the early stage has to experience a space environment, that is, in orbit.
We humans are very lucky to stay on the earth, because of the protection of the atmosphere, so the temperature difference between the four seasons of the year, that is, more than 20 degrees below zero to 30 degrees above zero, the temperature difference in a day will not be particularly large.
But not so lucky on track. The temperature of the orbit ranges from minus 120 degrees to 120 degrees above zero, and every 90 minutes above the Shenzhou spacecraft, it has to go through such a cycle of high and low temperature alternating.
Any material will undergo thermal expansion and contraction, and the expansion and contraction rate of each material is different. If the heat-proof material and the inner bearing structure material are hard-bundled together, and no treatment is done, the stress is enough to crack the heat-proof layer, and unimaginable consequences will occur when the subsequent return.
How did America's Apollo spacecraft solve this problem? It adds a sliding truss between the heat barrier and the bearing layer to compensate for the mismatch between the two.
But the Shenzhou spacecraft does not do this, it is to glue the heat barrier directly to the housing of the bearing layer. In this way, the structure is simpler and the weight is lighter, but the problem is that the pressure of the two matches all falls on the development of the heat protection layer.
▲ A photo of the earth from the porthole of Shenzhou
The beautiful photo in the photo above is a photo of the Earth taken by the astronaut through the porthole. The porthole is a very important window for astronauts to observe the state of the spacecraft and conduct a series of space science experiments, but the volatile points will make this window invisible, just like the fogging and icing of car glass.
Water is liquid on Earth, but in the vacuum of space, it vaporizes. That is to say, many of these liquid low molecular weight compounds on Earth will vaporize in space, and we, the heat-proof materials, must avoid this phenomenon.
The molding process of heat-resistant materials
Completed: 40%/////////
As mentioned earlier, our material is a honeycomb reinforced form, so how is this material formed?
The United States is a single-hole perfusion technology. This method has been used since the Apollo spacecraft and until the new Orion outsole in 2010.
In the picture above is the orion base, which is 5 meters in diameter and only 6 mm in diameter for each honeycomb.
This outsole is densely covered with 330,000 honeycombs, when it is formed, a circle of people stands in the picture, surrounds this outsole, one person takes a perfusion gun, one by one for perfusion, and finally this outsole took almost 5 months to complete the perfusion.
But we didn't use such a method, we used a autoclave equipment. With this device we place the material neatly stacked on the upper part of the honeycomb lattice and paste a vacuum strip on it.
The whole system is vacuumed inside, and then it is pressurized by the equipment outside, and through the internal and external pressure difference, the material is pressed into the honeycomb as a whole.
The process is very simple, and it has one more benefit. That is, no matter how large the size of this product is, only a corresponding size of autoclave needs to be selected, and it can be molded at one time, and the whole process will not exceed 8 hours before and after.
Seeing this, you may think that the Americans are still quite stupid, so much behind us Chinese.
In fact, no, the process itself is not unusual, the key is how to make the material meet the requirements of the process, such as before infusion can be neatly stacked, after infusion can be evenly filled in the honeycomb lattice.
We combed through conditions like this, there are more than 20, and it is very difficult to meet these more than 20 conditions at the same time, and finally the two materials of H88 and H96 used by the Shenzhou spacecraft.
Do you think H88, H96, the naming of these two materials is strange.
Although there are many theoretical and research bases, the formulation of this material still needs a lot of experimentation to be derived.
We researchers have to number these materials, the abscissa is a letter like ABCD, and the ordinate coordinate is a number like 1 to 99. In this way, an orthogonal matrix has almost eight or nine hundred formulas. With so many formulations, H88 and H96 meet all performance requirements.
When I first received this speech task, everyone asked me to tell the story behind the Shenzhou spacecraft, but in fact, I was not very confident. Because we developed this material very early, we began to develop it in 1986.
In 1986, we did an 863 project, and then in 1992, we passed the special technical research of the manned spacecraft, and then after ten years of technical accumulation, we achieved the first flight success in 1999. Then, in 2003, after the successful debut of the Shenzhou manned spacecraft, our material was basically finalized, and there was no change.
It was not until 2011, under the guidance of the lunar exploration project, that we began to develop new materials, and the first flight of the return module was successful in 2014.
What am I doing for so long? In 1986 I was still an embryo and was not born. From 1992 to 1999, when the development of the Shenzhou spacecraft was in full swing, I was in elementary school.
I started working on new materials, and I just went to ph.D. in 2011. It was hard to wait until I joined the work, and our new small spaceship flew successfully again, so I was embarrassed to tell the story behind the Shenzhou spacecraft here.
Fortunately, I was studying for a doctorate in chemistry at the time, and I had accumulated a long period of scientific training. What I'm best at is digging into data, doing in-depth analysis of that data, making up a story, and posting an article. So I analyzed this timeline and found a story.
In 1986, our material was like a baby that had not yet been born, and it was being conceived.
By 1992 to 1999, it was also as vibrant as a schoolboy. After the process of development and finalization from Shenzhou 1 to Shenzhou 11, this material gradually matured.
When the lunar exploration project was pulled in 2011, it was just like a doctoral student, summing up and accumulating its previous basic knowledge, and digging deeper and more cutting-edge places to dig for research.
It is a great honor for me to have such a connection between my life and this material. Below I would like to share a story of my own experience with you.
In 2014, when I was just starting to work, I was suddenly informed that the ablation of the return module test piece for the third phase of the lunar exploration we delivered had been abnormal. Our research group and the relevant departments in the institute immediately entered a state of tension.
Why the tension? First of all, I will explain to you what is the stove. With the furnace, for any product, we want to prove that it is qualified when we finally return from the flight. But you can't directly use this product to experiment, so you have to use the same raw materials to make it with the product of the return capsule, and go through the same process and the same environment. Some are simply burned from a stove, so it is called a stove.
The performance of the furnace represents the performance of the product. At that time, there were three ablation anomalies with the furnace, which basically can be said that the ablation of our products is also abnormal.
If ablation is abnormal, what are the serious consequences?
There is a particularly famous accident in our space history. On February 1, 2003, the Space Shuttle Colombia disintegrated and exploded during its return, killing all seven astronauts.
The reason for the accident analysis is that there is a defect in the thermal insulation tile on the left edge of the shuttle's left wing. Now everyone understands why we are so nervous, so what to do? We'll go back to zero.
Zeroing is very aerospace- and it is a shortcut to solve problems and deal with problems quickly. Zeroing means finding the cause from scratch. We start from the raw materials, from the raw materials of the raw materials.
Later, a lot of processes were sorted out, and two anomalies were finally locked.
One is that the autoclave equipment suddenly broke on the day of perfusion, and after emergency repair, it was also perfused 6 hours later than the normal time. It was also summer, and it just happened to rain, even if the factory is air-conditioned, it is still a high temperature and high humidity environment.
What happens when two questions stack up together?
We conducted a mechanism analysis and established a system, from the temperature and humidity environment to the viscosity of the resin, the rheological behavior of the material, the perfusion time, the micromorphology of the material, and then to the macroscopic ablation behavior.
After this whole set of work, I think the problem can be ended like this, but no. I've always felt that the next part of this process is particularly unique.
Now that the problem has been found and the mechanism has been thoroughly analyzed, it should be possible to reproduce the same fault using this wrong method. Therefore, only after the problem is reproduced, we can say that the problem is indeed accurately positioned and the mechanism is recognized. Only in this way can we judge what should be done with the current product and what to do with future products.
So we did other experiments to prove that this product can actually be used, but due to the relationship between professionalism and time, I will not expand here.
So is zeroing over? No. Here's its second best, called the Second Proof. We say that this problem occurred in one material on the bottom, so is there a problem with the other four materials?
It has no problems and does not mean that there are no hidden dangers, so it also has to do the same work as before, and even the two materials with the Shenzhou spacecraft have done the same work.
I think this is particularly head-burning because the logic is too rigorous and the workload is also very large. How long will it take me to do this job? 1 month? A little too long. 3 days? It will exhaust me.
In fact, we have 3 people doing this work, it took 3 weeks to do it, and our daytime work cannot be interrupted. At that time, the rhythm was to do experiments during the day, coordinate experiments, hold meetings, make up experiments at night, and write various test reports.
We felt particularly tired and often came home after 11pm, no weekends, and occasionally stayed up all night. Physical pain is nothing, the key is that mental pressure is also very large.
Because at that time, our products had already been finalized, did the launch mission of the country have to be postponed because of us? Or can this product be used in the end? Many people are waiting for this zero report to make a decision.
I had just started working, and the situation frightened me.
In fact, I thought about it for a while, a material from the material development to the initial sample, specimen, stereotype stage of the product, to go through the development of many materials, but also through the multi-level quality review, in fact, to go through the hands of many people. The work I've done is just one of those very, very small points.
Astronauts stick to it
Completed: 80%/////////
So the longer I've been here, the more I know, the more I do, the more I feel very small and humble. Plus compared to my predecessors, I'm nothing at all.
In the picture is my master Ling Ying, who came to the group when she was 22 years old, and in 1988, she caught up with the 863 project and has been associated with Shenzhou ever since.
Immediately after that, from Shenzhou No. 1 to Shenzhou No. 11, she was the main craftsman of this product, and she stayed in this position for more than 30 years, which is actually an incredible thing.
Because from the perspective of any person's career planning, it is not normal to stay in one place and not be promoted.
And even if she doesn't get promoted, she shouldn't stay in the most bitter place on the front line, she often laughs at herself because she doesn't have the ability to change jobs, in fact, we all know that this is her personal choice.
The two people on the right next to my master in the picture above are skilled personnel, the one on the left is Qin Dehui, the one on the right is Jiang Shuping, and the spaceship is a hard-working, inseparable from such a lovely big country craftsman.
The molding process of the spacecraft is very complicated, although there are many process documents handed down, but it is difficult to achieve accurate inheritance without their hands-on teaching.
It is the three of them who are willing to dedicate themselves silently on the front line all the time, which has achieved the high reliability of the heat-proof materials of the Shenzhou spacecraft.
The above two pictures have witnessed the 30 years of the Shenzhou spacecraft, and the years have also left traces on the three of them, and I want to pay tribute to them here!
The Russian-German archives in the picture above are archives of material development, I just took an archive box and unfolded everything, and there are more than 30 file boxes like this.
Open each archive and you'll find that many of them are handwritten.
The picture above is drawn on coordinate paper.
The picture above is taken with a card camera and then pasted onto the report. At that time, the research and development task was already very tight, but the scientific researchers still had to spend time and energy to sort out these reports.
At that time, computers were not very popular, not as convenient as pasting and editing now, so they needed to copy the report from beginning to end every time they revised a draft.
This is also a reason why sometimes I ask my master the details of what he was working on at that time, and she remembers it very clearly, because she copied each manuscript many times.
Every time I look at these files, I have some different feelings in my heart. Because these archives not only objectively recorded this material, the purpose and results of the development of more than 900 formulas at that time, but also silently told the hard work of scientific researchers.
Therefore, this is not only a scientific and technological archive, but also a valuable spiritual wealth.
Finally, I would like to conclude with a poem, "The sky is broken, and the Kyushu universe shines; the wind burns out, and the guardianship of the god boat returns."
According to the routine, my speech should end in this magnificent verse, but I want to explain to you what this poem means.
The first half of the poem refers to a phenomenon when the material is working, and the second half explains the principle of the work of the material and the purpose of the work.
At the same time, this poem is pun-curated, the first half of the sentence shows the boldness of our aerospace, and the second half shows the persistence of our astronauts and the significance of the persistence of astronauts.
Thank you.
- END -