On May 15, China's first Mars probe "Tianwen-1" successfully landed on the utopian plains of the northern hemisphere of Mars, and will lead the Zhurong rover to carry out the Mars exploration journey. China's first Mars exploration mission landed on Mars and achieved a complete success. China has become the second country in the world after the United States to successfully land a rover on the surface of Mars.
In the process of successful firefall, in addition to withstanding the test of "9 minutes of terror", what kind of "struggle history" does "Tianwen-1" have? The reporter specially invited Professor Wen Xin of the School of Astronautics of Nanjing University of Aeronautics and Astronautics to interpret the technical content of "Tianwen-1" and "punch-in" Mars.
About Mars, there are these "whys" -
Why should we explore Mars?
Maybe it's the next habitat for humans
With the successful landing of "Tianwen-1", "why should we explore Mars" has quickly become a hot topic of discussion among Weibo netizens. Netizens even began to discuss future travel plans: If you travel to Mars in the future, will you go?
Why we choose to explore Mars, Professor Wen Xin gave the answer: due to the disharmony caused by the consumption of earth's resources and the rapid growth of population, Mars may be the next habitat for human beings.
Wen Xin told reporters that among the planets in the solar system, the potential "habitability" of Mars is unique. "After space exploration, people have found that Mercury is the closest planet to the sun, but its daytime temperature is as high as 430 degrees Celsius, and worse, the temperature difference between day and night is nearly 600 degrees Celsius; while Venus is not only severely hypoxic, the atmosphere is also covered with sulfuric acid clouds, and the surface temperature is 460 degrees Celsius all year round." Wen Xin told reporters that in addition to Mercury and Venus, other solar system planets such as Jupiter are gas planets, and there is no external crust as a landing point, and standing up will fall directly like stepping on a huge marshmallow. In this comparison, Mars is more like a gentle and amiable star of hope.
How can Mars have an environment for human beings? At the very least, there must be plenty of oxygen and water. There is evidence that Mars was likely to be a habitable "paradise" like Earth. For example, in 2008, NASA's Phoenix lander dug water ice into the shallow underground near the North Pole of Mars; radar data from the ESA Mars Express probe in 2018 suggested that there was likely to be a saltwater lake under the south polar ice of Mars. Scientists therefore feel that it is not impossible to modify Mars and make It once again have a suitable atmosphere and water.
【Why do you have to fly for 10 months to explore Mars】
The farthest distance from the Earth is more than 400 million kilometers, and it is not yet possible to fly in a straight line
Since the first failed launch of a probe to Mars on October 10, 1960, for 60 years, human beings have never stopped exploring Mars. Compared with the distance of 380,000 kilometers between the moon and the earth, the distance between Mars and the earth is 55 million kilometers, which is more than a hundred times that of the earth and the moon. "If we use the length of flight to calculate, it takes 2-3 days to fly to the moon; and even if it is the best flight, it will take more than half a year to fly from Earth to Mars." The furthest distance between the Earth and Mars is more than 400 million kilometers, but the real difficulty of Mars exploration is not in the distance. Since the Earth and Mars orbit the Sun at the same time, it is not possible to fly in a straight line from the Earth to Mars. Wen Xin told reporters that from the earth to Mars, intuitively how to go can be seen. But in order to save costs, most of the current Mars probes fly according to the "Homan transfer orbit", which is the most economical way to change the orbit, but it also involves more times and higher precision orbit correction.
In the long journey from Earth to Mars, the probe also needs to experience the interference of three gravitational fields, which first break away from gravity, leave the Earth and enter the orbit around the sun, at this time the probe will use the sun as the near focus to do elliptical orbital motion, and then enter the orbit of Mars, that is, enter the gravitational field of Mars and be captured by Mars.
What has the "Tianwen-1" "Long March" done in the past 10 months -
【Obtained China's first image of Mars】
The launch of "Tianwen-1" dates back to 12:41 on July 23, 2020, when China launched the first Mars exploration mission "Tianwen-1" probe with the Long March 5 Yaosi carrier rocket at the Wenchang Cosmodrome in China on the northeast coast of Hainan Island, and after flying for more than 2,000 seconds, successfully sent the probe into a predetermined orbit, opened a Mars exploration journey, and took the first step in independent planetary exploration.
The Tianwen-1 probe, which weighs about 5 tons, consists of an orbiter, a lander and a Mars rover. It will achieve "orbiting, orbiting, and touring" of Mars. According to the scheduled plan, the probe will reach the vicinity of Mars after flying in the ground fire transfer orbit for about 7 months, complete the Mars capture through the "brake", enter the ring fire orbit, and choose the opportunity to carry out landing, inspection and other tasks to carry out Mars scientific exploration.
At about 2.2 million kilometers away from Mars, Tianwen-1 also obtained China's first image of Mars.
【Modified halfway through four orbits】
According to the information released by the China National Space Administration, after 9 days and 17 hours of flight work and more than 3 million kilometers from the earth, "Tianwen-1" successfully completed the first orbital midway correction at 7 o'clock on August 2, 2020 and continued to fly to Mars. Since then, "Tianwen-1" has successively carried out three halfway corrections in its orbit, which has led to the smooth progress of today's "orbiting" Mars.
Why do I need to make a halfway correction? Geng Yan, director of the General Department of Deep Space Exploration of the Lunar Exploration and Aerospace Engineering Center of the China National Space Administration, introduced that during the flight of the ground fire transfer orbit, the probe will be affected by factors such as orbit entry deviation and control accuracy deviation. Since the detector is in unpowered flight for a long time, small position speed errors gradually accumulate and amplify.
Therefore, when performing the flight mission, researchers need to complete the corresponding probe attitude and orbit control according to the deviation between the actual flight trajectory and the design orbit of the detector determined by the measurement and control system to ensure that the detector always flies on the predetermined orbit. The key to the correction of the mid-course track lies in the choice of the timing of the correction and the accuracy of the implementation of each correction.
[One foot "brake" orbits Mars for three months]
Chinese New Year's Eve this year, "Tianwen-1" "stepped on" a "brake" and carried out close-fire braking, starting a journey around Mars. Professor Wen Xin told reporters that this foot "brake" is related to the "life and death" of the detector. The closer "Tianwen-1" is to Mars, the more "exquisite" the speed of flight, and it can no longer be a state of "burying one's head and flying bitterly". "Unlike the Moon, Mars still has a thin atmosphere, which will put the spacecraft in great resistance." Tianwen-1 'Only by successfully being captured by the gravitational pull of Mars and entering the orbit can it lay the foundation for the subsequent landing on Mars. If it is still the original state of "flying vigorously", "Tianwen-1" will not be able to fly away from Mars. However, it should be noted that if the foot "brake" is not good, the ignition time of the probe brake is too long, which will lead to too much speed drop, and at that time, there will be a collision with Mars.
Some readers have noticed that "Tianwen-1" took three months from entry to landing. Experts told reporters that in the past three months, "Tianwen-1" is not idle, it is conscientiously carrying out scientific exploration, and conducting a wave of "bottoming" in the landing area first, which can not only enrich scientific data, but also make the future landing work more secure. "Tianwen-1" is equipped with medium and high resolution cameras, and carries spectrometers, with which it is possible to understand the landforms of the landing area and even observe the meteorological conditions of the landing area.
What is it like to experience the horror of "falling fire" for 9 minutes?
["Lost contact" with the earth, everything "on their own"]
Weibo "Tianwen-1 Mars Rover Zhu Rong" has an anthropomorphic description of the difficulty of landing on Mars:
The biggest difficulty in landing on Mars is the fully automatic soft landing, there is no ground signal during the landing process, and it is completely "out of touch" with the earth, which depends on myself. According to historical data, I entered the atmosphere at a speed of about 4.9 km/s and a maximum temperature of 2100 °C. For the next 9 minutes I'm going to slow down 90%, then start the variable thrust engine and start dropping power. I finally hovered at an altitude of 100 meters on the surface of Mars, at which point my vertical descent should be 0. Then enter the panning phase, observe and then determine the landing position. The whole process, I must be calm and focused, adaptable, can not panic!
This journey is known as the "9 Minutes of Terror" of the spacecraft. Some scientists have figuratively compared the difficulty of a probe entering the orbit of Mars as if playing a golf ball from Paris is exactly falling into a hole in Tokyo. Many Mars rovers failed at this stage.
This time, the "falling" fire is the most difficult step in the three target tasks of Mars exploration" of "orbiting, falling and touring". Of the 21 mars landing missions that have been conducted worldwide, only 9 have been successful. Professor Wen Xin told reporters that the terrain of Mars is complex, the air flow is not calm, and the biggest threat is sandstorms. The movie "The Martian" vividly describes the bad weather on Mars that is dusty and shady. "On the one hand, you have to confirm that any one of the detector's devices and devices will not fail in this environment. On the other hand, the technology of the probe landing on Mars is very complicated, and there can be no missing at every link. ”
"The reason why it is called 'Terror 9 Minutes' is because the whole process of Tianwen-1 requires autonomous control, and due to the long distance between Earth and Mars, the communication delay during May is more than 10 minutes. That is to say, an instruction is issued from the ground, and "Tianwen-1" cannot be received until 10 minutes later, and it is impossible to give instructions on the ground. At this time, the spacecraft in what attitude to fly, what time to ignite, how long to work, when to shut down, how to deal with problems, manual can not directly intervene, all need the probe to "arrange itself."
Wen Xin introduced that the landing process of Mars probes is very complicated, for example, in the first deceleration problem, supersonic landing is the most difficult link, it is necessary to overcome a series of problems such as parachute parachute opening difficulties, instability, etc. In addition, because China is the first time to implement a Mars exploration mission, it is equivalent to a completely unknown environment, and the difficulty can be imagined.
In general, throughout the process, Tianwen-1 reduced the speed of about 20,000 km/h to 0 m/h in 9 minutes, and each link must be accurate, and the difference of one second may cause the failure of the entire mission.
According to the information released publicly, at about 1:00 a.m. on the 15th, the "Tianwen-1" probe de-orbited in the mooring orbit and maneuvered until Mars entered the orbit. At about 4 o'clock, the landing rover "said goodbye" to the orbiter. The EDL journey of "Tianwen-1" starts here. (The process of landing on Mars by the ranger is divided into three steps: the first step is "entering", the second step is "descending", and the third step is "landing", which is called "EDL" by connecting their initials.)
The distance between Earth and Mars is too far, and the landing process is too short, which makes the mission more difficult.
【Why did the landing site choose the utopian plain】
The landing site of Tianwen-1 on Mars is the largest plain on Mars, the Utopian Plain. In addition to the good name, there are multiple reasons why the Utopian Plains are suitable for landing:
The first is because of the low engineering risk. The topography and geological formation of the northern and southern hemispheres of Mars are very different - the southern part of Mars is an ancient highland, with many craters, and 60% of the area is spread throughout the craters; while the northern part of Mars, where the utopia plain is located, is a low plain filled with Martian lava, with gentle terrain, fewer craters, and a younger geological age and thinner crust.
Not only that, but the utopian plains have high scientific value. For a long time, the biggest concern was whether there was life on Mars. According to the analysis of researchers, the utopian plain is likely to be the location of the ancient Martian ocean, and the landing site of "Tianwen-1" is at the junction of the ancient ocean and the ancient land. The latest scientific exploration has found that below the shallow bottom layer of the Martian utopian plain 1-10 meters above the ground, there is a large amount of groundwater ice, which stores water equivalent to the largest freshwater lake on Earth. Wondering if there's life on Mars, the Utopian Plains are an excellent place to explore.
How will Tianwen-1 work in the future?
[Matryoshka landing, will work on Mars for 90 days]
When it comes to Mars, what does Tianwen-1 need to do? Professor Wen Xin told reporters that the lift-off process of "Tianwen-1" is similar to a "nesting doll", and the flight after entering space is completed by the orbiter, and once the instruction to "land" is received, the lander "hidden" in the orbiter will be separated from the orbiter, release the parachute, and land at a fixed point according to the preset location of the researchers. After that, the Mars rover carrying the ground-penetrating radar will slide out of the lander and work on Mars for a full 90 days.
The long flight of "Tianwen-1" is precisely the long "paving" for the work of these 90 days. On Mars, the Mars rover transmits back relevant data, and scientists will analyze the Martian atmosphere and soil, study the composition of Martian rocks and soil, and look for water and signs of life. Of course, taking pictures is certainly indispensable, and by capturing the latest photos of Mars, we can better study what Mars "looks like".
Link: Why is the Mars rover called "Zhu Rong"
At the opening ceremony of the 2021 China Space Conference, the name of China's first Mars rover was officially announced. After the national name, expert review, online voting and other layers of selection, the final "Zhu Rong" stood out. Zhu Rong is revered as the earliest fire god in traditional Chinese culture, symbolizing that our ancestors used fire to illuminate the earth and bring light. The first Mars rover was named "Zhu Rong", which means to ignite the fire of China's interstellar exploration, and guide mankind's continuous exploration and self-transcendence of the vast starry sky and the unknown universe. The "Zhurong" rover has a height of 1 meter 85 and a weight of about 240 kilograms. The design lifespan is 3 Martian months, which equates to about 92 Earth days. The "Zhurong" rover will carry out exploration work on Mars such as surface composition, material type distribution, geological structure and Martian meteorological environment.
On the evening of May 15, @Tianwen-1 Zhurong Mars Rover released the first Weibo to say hello to the earth, the full text is as follows:
Mars arrives!
Hello friends on Earth: I am the Zhu Rong rover, and today, I arrived at the surface of Mars with the "lander", landing in the southern pre-selection area of the utopian plains of the northern hemisphere of Mars. This moment, let everyone wait for a long time!
At about 1 a.m. today, the Tianwen-1 probe de-orbited in the berthing orbit and maneuvered to Mars into orbit. At about 4 o'clock, the landing rover separated from the orbiter, and after about 3 hours of flight, it entered the Martian atmosphere, and after about 9 minutes of deceleration, hovering obstacle avoidance and buffering, it successfully soft-landed in the pre-selected landing area at 7:18 a.m. today. After the two devices are separated for about 30 minutes, the orbiter ascends the orbit and returns to the berthing track to provide relay communication for the landing rover.
At present, only 9 of the 21 Mars landing missions that have been carried out around the world have been successful, and the difficulty coefficient is extremely high! To land on Mars safely, in addition to choosing a landing area with flat terrain, you must also choose the right weather conditions to avoid being disturbed by the huge dust storm on Mars. After more than three months of flying around the fire, I finally found the best landing spot. Geologists say my soft landing area is likely to be a site of ancient oceans with high scientific value and is likely to achieve unexpected scientific results. But how can the impact of Martian dust storms be minimized? Of course, I can't afford to hide it! According to the past Martian meteorological data, Mars dust activity is concentrated in the second half of the year, the northern hemisphere is the most tranquil in the spring and summer, and choosing to land in mid-May is also the safest for me!
At present, I am still in the landing rover, carrying 6 scientific payloads such as terrain cameras and multispectral cameras, sub-surface detection radars, and magnetic field detectors, and after a short adjustment, I am out of the warehouse and carry out patrol detection. Looking forward to learning about Mars in all directions, and sending back valuable data and photos to everyone!
Love you guys, good luck!
Source: Xinhua Daily