Jia Yang | How to make a beautiful Mars rover

"Outside Longlou Town, Zibei Dong is not a general but a scholar. With a hundred-foot arrow and a ten-thousand-pound bow, Yunxiao is about to reach the fifth level."

Jia Yang

Researcher of the General Department of China Academy of Space Technology

Hello everyone, I am Jia Yang, an aerospace engineer and the author of the popular science book "Lunar Rover and Mars Rover". Today I want to talk to you about how to make a beautiful Mars rover.

In fact, we are not the first country to go to Mars. Earlier, some countries' spacecraft had orbited Mars and landed on the surface of Mars, sending back many pictures.

This is my favorite. By processing the images of different spectrums into pseudo-color, a picture of the Martian landscape is formed.

In winter, the carbon dioxide on Mars also feels cold and is unwilling to fly in the air, so it condenses on the surface of Mars. My hometown is in Jilin, Northeast China, where there is a kind of scenery called rime, which we locals call tree hangings. There are no trees on Mars, so dry ice can only be hung on the ground.

Sometimes there are severe sandstorms on Mars, which will form various wind erosion landforms.

Mars also has four seasons. The temperature in the crater is sometimes higher and sometimes lower, which causes the condensation of carbon dioxide and water ice in the crater to vary, reflecting the change of seasons on Mars.

On the surface of Mars, there are valleys that seem to have existed in the past. I wonder if we can transform Mars one day, can we make this place a tourist attraction for rafting?

Completed: 10% //////////

Make a beautiful Mars rover

Mars is so beautiful, so we also need to make a beautiful Mars rover to match it.

There are many countries that have orbited Mars, including the Soviet Union, the United States, Japan, India, etc., so the outer circle around Mars shown in the picture below is relatively large. China's "Tianwen-1" orbiter is just above and slightly to the left of the picture.

Mars Family

There are several probes on the surface of Mars in the picture, some of which are stationary after landing on the surface, and some are rovers that can drive on the surface of Mars. All of them are American, with the exception of the "Zhurong" in the upper part.

We are the second country to have carried out patrol and exploration on the surface of Mars. The driving of the Zhurong Mars rover also has another significance, that is, we are now the only country in the world to carry out patrol and exploration on both the moon and Mars at the same time. We have personally experienced and witnessed the rapid development of China's space industry.

So, how was this probe, including the Mars rover, designed and what did it look like?

Tianwen-1 probe

The Tianwen-1 probe is divided into two floors. The lower floor is called an orbiting probe, which only flies in the orbit of Mars and will not land on the surface of Mars; the upper floor, which is like a flying saucer, will actually enter the atmosphere of Mars and then land on the surface of Mars.

During the landing process, the arc-shaped bottom and the upper back cover of the probe were thrown away. When it reached the surface of Mars, the landing platform and the rover in the middle were the only parts that landed steadily.

In July 2020, the Long March 5 series launch vehicle, also known as the "Fat Five", took off from Wenchang, Hainan, and sent the Tianwen-1 into the orbit towards Mars.

The probe's orbit - Hohmann transfer orbit

The process of flight is actually to revolve around the sun. The orbit of the probe is an elliptical orbit, which intersects with the earth and Mars. This orbit has a very famous name, called the Hohmann transfer orbit, which is the most energy-saving orbit.

After reaching Mars, the probe flew around Mars for another three months. What was it doing? We had two purposes: one was to see if the place we chose was right and to make further confirmation; the other was to wait for time. If we landed immediately, it would be close to dusk after landing, and we would not have time to charge the rover before entering the Martian night.

We waited for three months, one hour per month, and finally landed at 2 p.m., which was relatively sufficient sunlight, ensuring that the rover was fully charged when it entered the Martian night.

The probe's entry, descent, and landing (EDL) process

The landing process takes about 9 minutes in total and is divided into four stages. The initial landing speed is between 4 kilometers and 5 kilometers per second, close to 5 kilometers. The first stage is the aerodynamic deceleration stage, and the air resistance will basically reduce its speed by 90% or 99% of its energy.

The second stage is the parachute deceleration stage, which will further decelerate, and finally the speed will become constant, that is, 60 meters per second.

The third stage is the power deceleration stage, when the engine starts working and selects a more precise landing position above the surface of Mars. If this point is suitable, it will land directly. If it is not suitable, it can make limited position changes and maneuver laterally to another relatively safer position before landing.

The fourth stage is the landing buffer section, which relies on the four legs under the landing platform to buffer the last bit of energy and land steadily on the surface of Mars.

The entire entry, descent and landing (EDL) process is relatively complicated, so we need to conduct sufficient tests on the ground.

This is the experimental equipment. Many journalists and foreign envoys visited here, and most of them took a photo from the front. I wanted to be creative, so after the journalists and envoys left, I went under this rack at night and took more than 200 photos facing the top. Then I selected a part of them, about 89 photos, and put them together to form this picture.

Do you like to shoot star trails? If so, you may wonder why the star trail is not continuous. But I did it on purpose. The star trail is: dash, dot, dash, dash, dot, dot, dash, dash, dash, dash, dash, dash, and the corresponding Morse code means "Tianwen-1" after translation.

I gave this photo two names. The more common name is "The Stars in the Sky Can Talk", and the more elegant name is "Secret Language of Stars", which can be regarded as a blessing before departure.

Finally, our probe successfully landed on the surface of Mars. This is the corresponding video.

This is an imaginary picture of our Mars rover at work. It was originally designed to travel 7 meters in 3 days, but due to sufficient energy and good communication conditions, it actually traveled 20 meters a day. It has traveled more than 1,000 meters so far and has been running for 100 days.

How was the Mars rover Zhurong designed? At first, we thought we needed a relatively large solar wing, because Mars is farther from the sun than the moon. So we made the solar panels into a roof-like shape.

The evolution of the solar panels on the Mars rover Zhurong

After analysis, we found that it was not possible, because there would be violent vibrations during rocket launch, and the solar wing could not withstand it. So we compressed it, but after compressing it, we found that the area was not enough, so we divided it into 4 pieces and unfolded it backwards.

If the rover reaches the surface of Mars and drives forward away from the landing platform, there will be no problem. But if it moves backward, the two rear solar panels will touch the ground. Therefore, we made further adjustments, which is to adjust the two rear solar panels to a certain angle to the side and rear.

Various solar wing designs

During the entire design process, we designed many solar wing options, including one disc shape, or two disc shapes, and even one that resembled bat wings.

At the end of the whole evolution process, we found that the Mars rover we designed looked like a butterfly, a blue Morpho butterfly. To prove that our inspiration came from butterflies, I bought a butterfly specimen online and put it on my desk.

Completed: 30% //////////

Five magic weapons of Mars rover

So, what are the capabilities of the Mars rover? What difficulties are waiting for us on Mars? There are at least four difficulties, and we have prepared five magic weapons to deal with them.

The first difficulty is that there are many rocks on the surface of Mars and the terrain is complex, which can easily puncture the wheels of the Mars rover. In order to deal with this difficulty, we prepared an active suspension for the Zhurong. This is like the chassis of a car at home cannot be raised, but some off-road vehicles can raise the chassis when encountering specific terrain. This is called active suspension.

Different working modes of active suspension (left) and active suspension diagram (right)

In fact, the Zhurong has more capabilities than that. If it encounters a sinking, that is, most of the wheels are already stuck in the sand, then the Mars rover has a skill that can be used to deal with it.

Its front wheels move forward, while the middle and rear wheels do not move, and the vehicle body is lowered during the whole process; then the front wheels do not move, while the middle and rear wheels move forward again, and the vehicle body is raised again during the process. This process is like a small insect crawling. The advantage of this is that it can easily get out of the sunken sand, because there are no 4S stores or rescue vehicles when the Mars rover is working on Mars.

The second difficulty to be concerned about is the sandstorm. Sometimes on Mars there will be dust that covers the sky and sun, causing the solar cells to fail to generate electricity. After a lot of sand and dirt accumulates on the cells, the Mars rover may not be able to continue working.

To deal with this problem, we first thought of using windshield wipers, which are the windshield wipers on the front of the car. Later, we thought of a simpler solution that is also lighter, which is to cover the battery cells with five layers of plastic wrap. When the dust accumulates to a certain level, we inflate the space between the first and second layers of film, so that the first layer of film can be removed with the dust, and the fresh second layer can be exposed to continue working. Later, we found that this did not work. If the dust fell on the other battery plate after the first layer of film was removed, it would become a disaster.

Finally, the method we really adopted was to imitate the lotus leaf. If it rains, water drops will gather on the lotus leaf, but it will not wet the lotus leaf. When the breeze blows, the leaves will shake and the water drops will fall off.

Imitation lotus leaf battery

We also put a similar process material on the cell. From a microscopic point of view, we turned the glass of the cell into a needle bed with many sharp points. The dust does not fall firmly on the surface, but on the needle bed. During the movement of the solar wing, the dust can easily slide off, and the surface of the cell will be cleaner. The picture on the right shows the effect of the experiment. We can see that with this process, as long as the cell is stood up, it will become cleaner.

The third difficulty is that the temperature on Mars is lower than on Earth because Mars is farther from the sun. To solve this problem, we used two methods: one is to increase revenue, and the other is to save money.

Collector

The so-called open source means that we designed two telescope-like windows on the top of the Mars rover. A layer of film is stretched on the windows, which allows sunlight to shine in during the day, but is opaque to infrared rays at night, which means that energy can only enter but not exit. In fact, this is similar to the principle of vegetable greenhouses.

How to store energy? If the sunlight heats the equipment, won't it cool down again at night? Therefore, it has a storage capacity. We put ten "wine bottles" under this membrane. When they absorb sunlight during the day, the solid in the "wine bottles" will turn into liquid. At night, in order to ensure that the temperature of the equipment does not drop, the working fluid in the "wine bottles" will turn from liquid back into solid, releasing heat in the solidification process to ensure that the temperature of the Mars rover does not drop.

Another method is to use a special cotton coat. We put a layer of aerogel cotton coat on the Mars rover. This material has two major characteristics: one is light, and the other is good heat insulation effect.

The properties of aerogel (left, center) and the aerogel actually used on the Mars rover (right)

To prove that it is light, they often put it on top of flowers. To prove that it has good heat insulation effect, they burn it with an acetylene gun in another direction, and the flowers will not wither.

It is summer on Mars now, when the temperature is the highest and the weather is relatively clear, so the Zhurong rover will feel a little hot. But it doesn't matter, because it will be autumn and winter in a while, and by then, the effects of our methods will be apparent.

The last difficulty is the long distance. The distance between Mars and Earth is nearly 400 million kilometers. One circle around the Earth's equator is 40,000 kilometers, and 400 million kilometers is exactly the distance of 10,000 circles around the Earth's equator. It takes 22 minutes for the radio signal to be transmitted from Mars to Earth, so it is impossible for the ground master to manage the Mars rover in a timely manner. Our working method is that the ground master talks to the Mars rover once a day and receives data once a day. That is, tell the Mars rover what work to do in the next 24 hours, and report the work results of the previous 24 hours to the ground.

During this process, what work to do, or if difficulties arise and the work needs to be stopped, or if it needs to go into hibernation and sleep, etc., all of these depend on the rover's own judgment based on the energy usage. This is an autonomous spacecraft.

Completed: 50% //////////

100 Days in Wenchang

After we finished the Mars rover, we sent it to Wenchang, Hainan, because it can launch relatively large rockets. In April 2020, during the pandemic, we took a special plane to Wenchang. The plane did not go directly to Haikou, but turned west. After discovering this, I took a picture of the plane's display.

What is so special about this point? I can recite the longitude and latitude coordinates of the place where Tianwen-1 will go this time. If these longitude and latitude coordinates are converted to the earth, the corresponding location is Yangshuo, Guilin, Guangxi, China. When the Air China plane was sending us off, it happened to fly over Yangshuo. I think it was a blessing from fate that we would accomplish our mission.

After arriving in Wenchang, we have to be quarantined for 5 days and cannot leave the room. In order to express our determination to work here for the next 100 days, I wrote a poem "South China Sea, North China Sea":

Outside Longlou Town, Zibei East,

He is not a general but a scholar.

Hundred-foot arrows, ten-thousand-pound bows,

Yunxiao wants to reach the fifth level.

Why do we need to go to the fifth heaven? Because I wrote classical poetry, I did not use modern scientific theories, but the ancient geocentric theory. The earth is located at the center of the universe, and outside are Mercury, Venus, the moon, the sun, and Mars. Mars is located in the fifth heaven, so I said "the clouds are about to reach the fifth heaven."

What did we do during the 100 days in Wenchang, Hainan? We had to do the final test of the rover, move all the related mechanisms, confirm that they were normal, and then tighten it. In addition, we also had to clean equipment such as cameras to ensure that we would not be unable to see the surface of Mars clearly due to dust when we got there.

Mars rover ready

Another very important task is sterilization, because at least for now, we have not completely denied the possibility of life on Mars. We cannot bring microorganisms from Earth to the surface of Mars, so we have to disinfect it, especially the wheels.

In this way, the preparation work for the Mars rover was completed. At night, I should have been able to take a rest, but I couldn't sleep, so I took a photo outside the window sill.

The road in the photo is actually where we walk every night. The blue light is a light left by farmers who raise geese and ducks. I think it represents a kind of hope in our hearts. That night, I left a poem that was not too strict to express our blessings:

Martian wind on Martian rocks,

The ground is frozen and the weather is cold, but there is love.

But when the sun sets,

I am also looking forward to the artifact parade.

On July 23, 2020, the rocket was launched, and we certainly had to express our joy. But we didn't use the standard rocket launch pictures taken by Xinhua News Agency. Instead, we worked with a Fortune 500 company to produce the above picture, which can also be regarded as a photographic work.

Completed: 60% //////////

Mars, here we come

After 10 months of flight, the rover reached the surface of Mars, 7 months of which were spent on the way to Mars and 3 months of which were spent orbiting Mars.

The left picture proves that the rover has landed on the surface of Mars, and the right picture proves that the rover has driven onto the surface of Mars, which is a landmark point for us.

We also took a photo of the landing platform. Just like when we travel, we also take commemorative photos, as if we were here. It took me a little time to take this photo, because the brightness of different scenes in this photo is very different.

Finally, I decided the parameters. First, I used the camera's automatic exposure to make the sky look right, and the surface of Mars was also relatively suitable. Another exposure parameter I chose was 10 milliseconds, which made the national flag brighter and more vivid. Finally, I used a 15 millisecond exposure parameter to make the shadow part under the landing platform, that is, the darkest part, look appropriately bright. Then I used an HDR high dynamic technology to synthesize this photo, which I named "Mark of Mars".

During the display, some netizens were more careful and saw a little secret we hid in the wheels of the Mars rover. If you look closely, you will find that the word "中" can be seen in the wheel tracks in the photo below.

The left picture is a photo taken when we were doing experiments on the ground, and the middle picture is what the Chinese character "中" looks like on the wheel. We put two Chinese characters "中" on the wheel, and some people asked me whether I put them in the front or the back. Of course I put them in the back, otherwise the mark would not be visible when the wheel moves forward.

Is this idea for publicity? Not really. I used to work on a lunar rover, and we were more concerned about whether the rover was running normally or sinking when it was on the surface of the planet. But the wheel tracks were not very clear in the past, so I came up with this idea.

If we find that the distance between the two characters is 1 meter, it means that the rover is driving normally on the relatively hard ground of Mars; if the distance between the two characters is only 0.5 meters, it means that the rover is slipping, and it is likely to be accompanied by a relatively large sinking, which is quite dangerous. The main purpose is actually to measure the slip rate of the vehicle.

I once wrote a short article about this and published it on a public website, which received many compliments. I looked carefully and found that the most likes came from Henan, followed by Chengdu and Yangzhou.

During the design process of the Mars rover, there was more than one such careful consideration, and there was another one that took even more thought.

After our Mars rover was rigorously tested on the ground, we found that it was not beautiful enough, especially the part on the mast that looked like a forehead. It was the size of an A4 paper and had three holes for cameras, which looked a bit like a walk on the 15th of July. So we wanted to design some beautification solutions.

At first we wanted to put a Chinese knot, but then we thought it wasn't right to put a Chinese knot on the forehead. Another kid said, "How about we draw a character for king?" Then I thought it would be better to use calligraphy, and write the character for fire in Mars. We wrote a lot, probably thousands of them, and we selected a few of them for voting.

At first, our attention was focused on the third character in the first row, which is the oracle character for "fire". This represents the beginning of the origin of writing, with a 5,000-year history of civilization, and is very meaningful.

But my colleagues always asked me, "Mr. Jia, what does '山' mean?" In oracle bone script, there is a horizontal line under the character 山, and there is an arc under the character 火. The difference is really small. We are not all scholars of ancient characters, so I just said forget it, it is too difficult to explain, so we just used the first one in the second row.

This idea was taken from a seal unearthed in Hailin County, Heilongjiang Province, now Hailin City. This seal is called Huanshu Huocangzhiji, and it is the seal of a relatively low-ranking official. It contains the word "fire". We took it out and processed it to form the logo of the Mars rover, and carefully placed it on the forehead of the Mars rover.

The logo on the Mars rover (left) and the backup logo (right)

When we do space work, we always consider backup, so we made an extra one when we actually did it. This one is in a photo frame, signed by the relevant designer, and now it is on my desk. So, there are two of this logo, one on Mars and one on my desk.

This is a selfie of the Mars rover from Mars. How to take a selfie? We put a camera on the Mars rover, and it moves forward about 5 meters, releases the camera and drops it to the ground, and then moves back. When it moves back to more than 5 meters, this selfie of the Mars rover is formed.

Then, when the rover moved further back, it took another photo with the landing platform. We put a lot of thought into this. The photo below is the photo.

Of course, some naughty netizens further processed these photos. The netizen who took the left picture below should be a foodie, and the one on the right should also be a foodie. Relatively speaking, I prefer the one on the right, and posted it on WeChat Moments with the caption "The Farthest Reach of Chinese Agricultural Civilization".

The rover has now been working for 100 days and has traveled 1,000 meters. In the middle of the rover's journey, we also took a look at the back cover and parachute that landed on Mars.

At 90 days, the rover had completed its three-month lifespan requirement. That night I wrote a doggerel-level poem:

Three thousand feet in March,

Adding miles every day.

The suspense finally came to an end.

Talking and laughing began loudly.

I am also expressing the feeling of our designers after they have been released from great pressure.

Completed: 80% //////////

Why do we want to go to Mars?

Finally, why do we want to go to Mars? Different people will give different answers.

For example, when answering questions from Western reporters, an Indian government spokesman once said: If we don’t have a great dream, we will always be lumberjacks and water carriers.

Tsiolkovsky, the Russian "Father of Rocketry"

Tsiolkovsky once said a famous saying: The earth is the cradle of mankind, but people cannot live in the cradle forever.

What scientists are more concerned about is: Has there ever been life on this red planet? Is mankind alone in the universe?

Science fiction writer Liu Cixin once said: Mars is the first choice for human beings to migrate to space. The most likely scenario is that when a crisis comes, humans will devote all their efforts to the exploration and development of the extraterrestrial world. In fact, it will take a long time for humans to migrate to Mars.

Another philosopher once said: If you ask what is the significance of going to Mars, then please ask what is the significance of marine life first crawling onto land several hundred million years ago?

Why do we go to Mars? Today I will try to give my answer. Mars rotates once in 24 hours and 40 minutes, and the Earth rotates once in 24 hours. So every 37 days, the Zhurong Mars rover and Beijing on the ground will experience the same moment.

I made it into a picture and named it "Sharing the Moment Across the World". In the past three months, there were three moments when the Zhurong shared the same moment with us.

At sunset, the surface of Mars is not bright red, but light blue.

Mars also has a moon, but it is a little small, so it is impossible for it to block the sun completely and form a solar eclipse on Earth. However, the transit of Phobos by the sun, which lasts for tens of seconds, is also spectacular.

There is also a once-in-a-century astronomical spectacle. Compared to Mars, the Earth is an inner planet, so a rare spectacle is to see the Earth-Moon system transiting the Sun. Two small dots slowly slide across the surface of the Sun, taking about three hours. Sometimes they are far away, spanning the entire surface of the Sun (above), and sometimes they are relatively close (below).

The blue dot on the picture is our home, and the gray dot is the moon. I can't help but recite an ancient poem: People say that the sunset is the end of the world, and I can see the end of the world and my home again.

What I want to express through these pictures is that the significance of exploring Mars is to add a perspective for mankind, from which we can look at Mars, the Earth, the solar system and even the entire universe, including examining mankind itself.

Thank you everyone!

The articles and speeches only represent the author’s views and do not represent the position of the Gezhi Lundao Forum.

"Gezhi Lundao", formerly known as "SELF Gezhi Lundao", is a scientific culture forum launched by the Chinese Academy of Sciences, co-sponsored by the Computer Network Information Center of the Chinese Academy of Sciences and the Bureau of Science Communication of the Chinese Academy of Sciences, and hosted by China Science Popularization Expo. It is committed to the cross-border dissemination of extraordinary ideas, aiming to explore the development of science and technology, education, life and the future in the spirit of "Gewu Zhizhi".