(China Focus Face to Face) How many hurdles will the Tianwen No. 1 "fire detection" pass? Why is Mars exploration difficult?
China News Service, Beijing, October 29th, title: How many passes will the Tianwen No. 1 "fire detection" pass?
Why is Mars exploration difficult?
——Interview with Liu Tongjie, Deputy Director of China National Space Administration's Lunar Exploration and Space Engineering Center
Author Guo Chaokai
On October 28, the Tianwen-1 probe successfully completed the third midway correction of its orbit.
On the way to Mars, why did Tianwen-1 make a midway correction of its orbit?
What is the difficulty of Mars exploration?
How many hurdles will Tianwen-1 have to pass before successfully landing on Mars?
Liu Tongjie, deputy director of the China National Space Administration's Lunar Exploration and Space Engineering Center and spokesperson for China's first Mars exploration mission, recently accepted an exclusive interview with China News Agency "Focus on China" to give an authoritative interpretation of the Tianwen-1 mission.
Excerpts from the interview are as follows:
China News Agency reporter: Tianwen No.1 successfully completed the third midway correction of orbit on October 28. Can you explain to us what is midway correction of orbit? On the way to Mars, why do we need to make a midway correction of the orbit?
Liu Tongjie: When the rocket launches the detector, the detector will have a deviation in orbit, and there will also be a flight control deviation during the flight control process.
If these two deviations accumulate over time, they will deviate from the point where they meet Mars in space or time.
In space, that is, on the orbital plane, if it is not on the same plane as Mars, it will fly away from Mars and will not be captured by Martian gravity.
In terms of time, if Tianwen-1 misses the time node of its rendezvous with Mars, it will pass by, so it needs to be corrected midway through its orbit.
Another function of the midway correction of the orbit is to check the engine on the probe and let it work, so as to avoid being out of work in space for too long.
Liu Tongjie, deputy director of the China National Space Administration's Lunar Exploration and Space Engineering Center and spokesperson for China's first Mars exploration mission, accepted an exclusive interview with China News Agency "Focus on China".
Photo by China News Agency reporter Jiang Qiming
China News Agency reporter: After the third midway correction of the orbit, Tianwen-1 will fly in its current orbit for about 4 months to rendezvous with Mars. How many hurdles must Tianwen-1 pass if it is to successfully land on Mars?
Liu Tongjie: It has been flying for about 3 months since its launch on July 23, and it will be flying for another 4 months.
It takes nearly 7 months from launch to Mars gravitational capture, and it will take at least three passes to complete the detection.
The first difficulty is to capture near fire within the gravitational range of Mars.
It is necessary to make Mars capture very accurate, and allow the rover to brake within the gravitational range of Mars, and the speed should not be too high; it can also circle around to prevent the rover from flying out or hitting Mars.
The second difficulty is to look for a very good small window after orbiting Mars for 2 to 3 months to allow it to enter the Martian atmosphere.
Mars has an atmosphere, and the density of its atmosphere is about 1% of the earth's atmosphere.
In the process of deceleration, it has atmospheric deceleration, aerodynamic deceleration, parachute deceleration, and reverse thrust engine deceleration. Finally, it lands on the surface of Mars by landing legs and absorbs the energy of impact. This process is very difficult.
Just like the space (return) capsule enters the earth, it will have a black barrier (communication interruption) for about 8 minutes during the deceleration of the atmosphere. Its entry speed is quite high, and communication cannot obtain a signal.
Due to the considerable distance, there is also a long time delay from Mars back to the earth control ground station, and real-time control is impossible.
Therefore, the process of entry/deceleration/soft landing relies on (Tianwen No. 1) to complete a series of actions autonomously, not by ground control.
The third difficulty is the soft landing on the surface of Mars. The work is not completed yet, and the rover must be released on the surface of Mars, let it go and explore.
It is also very difficult for the six scientific instruments on the Mars rover to function, because we still have very little knowledge of the environment on the surface of Mars.
If the soft landing on the surface of Mars is not flat enough or the posture is not correct enough, how can the rover drive down?
You can go down from the front of the track or from the back, depending on the posture and terrain of the fall.
To successfully complete the Mars exploration mission, these three difficulties must be overcome.
Liu Tongjie, deputy director of the China National Space Administration's Lunar Exploration and Space Engineering Center and spokesperson for China's first Mars exploration mission, accepted an exclusive interview with China News Agency "Focus on China".
Photo by China News Agency reporter Jiang Qiming
Reporter from China News Service: As you said, Tianwen-1 will have to go through three hurdles to successfully land on Mars. This also shows that Mars exploration is not easy. In fact, there have been more than 40 Mars explorations in human history, but the success rate is less than 50%. Can you explain to us the difficulty of Mars exploration?
Liu Tongjie: Mars exploration has started in the 1960s. At that time, due to the lack of awareness of Mars and the initial stage of aerospace technology, there were slightly more failures at the beginning, but later failures and the difficulty of Mars exploration technology It matters a lot.
For example, there must be a huge launch vehicle to transport the probe to orbit so that it can explore Mars or even softly land on the surface of Mars.
Rocket (in terms of) We now have the Long March 5 rocket. This is the first step-to realize the development of a large rocket.
We have overcome many technical difficulties over the years.
In the second step, there is still the issue of the launch window when designing the detector.
Because Mars and the earth are so close, there is only one opportunity every 26 months, and each opportunity lasts from half a month to a month or so, and there are about 30 minutes of launch opportunities for rocket launchers every day. This is the launch window.
The launch window is very limited, which is another major difficulty.
In addition, Mars is 400 million kilometers away from the earth. Everyone knows that the moon is only 400,000 kilometers away from the earth.
This causes a delay in deep space telemetry and control communications.
When the distance between the Earth and Mars reaches 400 million kilometers, the time delay can reach more than 20 minutes. Send a command from the (earth) side, and more than 20 minutes have passed by the time it is received on Mars.
This brings about a problem. The autonomous detection capability of the detector must be strong, which is another difficulty.
Another difficulty is to capture near fire, let Mars capture the probe.
In addition, the process of entering, decelerating and soft landing on the surface of Mars is also very difficult. These are the major difficulties in Mars exploration.
Liu Tongjie, deputy director of the China National Space Administration's Lunar Exploration and Space Engineering Center and spokesperson for China's first Mars exploration mission, accepted an exclusive interview with China News Agency "Focus on China".
Photo by China News Agency reporter Jiang Qiming
China News Service: By May next year, Tianwen-1 is expected to land on Mars. Which region of Mars will Tianwen-1 choose to land?
Liu Tongjie: The location chosen now is in the northern hemisphere of Mars. There are international Mars exploration missions with landing plans. Most of them choose to be in the northern hemisphere of Mars.
Because the southern hemisphere is full of mountains, it is even more bumpy, and the northern hemisphere has plains.
The area we chose for soft landing happened to be a plain called Utopia Plain, (landing location) in the southern part of Utopia Plain.
Geologists say this is probably the location of an ancient ocean.
At the junction of ancient oceans and ancient land, scientists believe that the place has high scientific value and is likely to obtain unexpected scientific results. This is the reason why this place was chosen for soft landing and inspection.
China News Agency reporter: After successfully landing on the Utopia Plain, what scientific research missions will Tianwen-1 carry out?
Liu Tongjie: After landing on the surface of Mars, the rover will carry out scientific research and exploration.
There are 6 instruments on the rover.
For example, the navigation terrain camera is the multiplexing of two functions, which can not only navigate the Mars rover, but also look at the topography and landforms in front, visually letting scientists know if there is more detection value in the front.
The subsurface radar (on the rover) can detect shallow structures.
The Martian surface meteorological instrument can measure temperature, air pressure, wind speed, and wind direction.
There is an atmosphere on the surface of Mars, and there is no atmosphere on the surface of the moon, so the instruments of the Mars Rover and the Lunar Rover are also different.
The rover can also measure the magnetic field and surface material composition, which are all things that scientists care about.
There are medium-resolution cameras and high-resolution cameras on the orbiter to detect the surface topography of Mars.
There are also magnetometers, mineral spectrum analyzers, ion and neutral particle detection and energy particle detectors on the orbiter.
If enough scientific data is obtained, I believe it will produce influential results.
Data map: At 12:41 on July 23, 2020, China successfully launched the first Mars exploration mission Tianwen-1 probe using the Long March 5 Yaosi carrier rocket at the Wenchang Space Launch Field.
Photo by Luo Yunfei
China News Agency reporter: We also wish China's Mars exploration can achieve good results. This year the UAE, China and the United States have launched three Mars probes, opening a new chapter in human Mars exploration. What are the similarities and differences between the Mars exploration programs of these three countries? Where is the focus?
Liu Tongjie: It is precisely because of the launch window that these three countries concentrated on launching in July this year.
In fact, there was also the ExoMars (Mars exploration) project that ESA and Russia cooperated before, but they were delayed due to technical reasons.
These three probes have their own characteristics. The UAE’s "Nozomi" is an orbiting probe, equivalent to an orbiting satellite of Mars. It focuses on the exploration and research of the Martian atmosphere.
The US "Perseverance" is a patrol device, equivalent to a Mars rover, which is suspended on the surface of Mars.
We have both orbiters to orbit Mars, as well as Mars rover (landing on the surface of Mars) for patrol and exploration, combining heaven and earth for exploration.
But the three tasks have their own merits, after all, the technical route of each country is different.
Reporter from China News Service: You mentioned that the Tianwen-1 mission will complete the three major goals of "circumnavigation, approach and patrol" in one mission. This should be the first time in the world. If the mission can be successful, it will be for China Aerospace. What does it mean?
Liu Tongjie: First of all, I think that the development of deep space exploration and planetary exploration projects is a manifestation of the spirit of human exploration.
If our first mission to Mars is successfully completed, it shows that the Chinese have made great progress in this area and made more contributions to the peaceful use of space by mankind.
For example, we have the ability to detect planets in the solar system including Mars, carry out related scientific research, and obtain some original results; we can draw further scientific results on the evolution of the solar system and the earth, and in fact provide more knowledge for human survival on the earth. .
This is the role of technology and ethics.
If we can complete such a difficult science and technology project well, it can inspire young people’s enthusiasm for science and devote themselves to the construction of the country. Everyone can look up at the starry sky and work down-to-earth to stimulate everyone’s enthusiasm for exploration, especially young people.
So we are willing to go to colleges and middle schools to give them some engineering introductions.
For ordinary people, aerospace is still a relatively mysterious field.
For us, this is our job. It’s just that there is relatively little contact with this job. We have a responsibility to let more people understand the process, knowledge and spirit, so that we can make more contributions to the peaceful use of space by mankind. .
No matter from the perspective of science and technology, talent training, or worldview training and establishment, they all play a big role.
Data map: On October 1, 2020, China National Space Administration released the flight images of China's first Mars exploration mission Tianwen-1 probe. The five-star red flag on the map is dazzling, showing a bright Chinese red.
This is the first deep-space “self-portrait” of China's Tianwen-1 probe.
China News Agency issued photos courtesy of China National Space Administration
China News Agency reporter: China chose Mars as the first stop for planetary exploration. Why do we want to conduct Mars exploration?
Liu Tongjie: Why did you choose Mars exploration?
(This is because) Mars is a terrestrial planet and has many similarities with the earth's environment. The international community also chooses Mars as the focus of exploration.
We also have a lot of attention to Mars, so we choose Mars to explore.
As a terrestrial planet, Mars has an atmosphere and a surface. Let’s see if its evolution is the future of the earth’s evolution.
Life on Mars may have existed before, but now its atmosphere is thinner and life does not exist anymore.
If mankind develops and destroys the earth indefinitely, will the earth develop into Mars one day? This is a question raised by scientists.
We have great curiosity about Mars, and we also have great hopes for detecting Mars. This is the main reason for detecting Mars.
China News Agency reporter: Tianwen-1 has taken the first step in China's planetary exploration. What plans and arrangements does China have in the field of deep space exploration in the future?
Liu Tongjie: The planetary exploration program has planned 4 missions. The first mission to explore the Mars Tianwen-1 is the first time it has been launched and other missions are currently being demonstrated.
The second plan is the asteroid exploration mission, which is expected to be implemented around 2024.
There will be Mars sampling and return missions thereafter, which is around 2030.
Around 2030, there will be another Jupiter and interplanetary crossing detection, that is, after the detection of Jupiter and Io 4, it will fly to farther deep space.
(Finish)