[ad_1]
Enter the parking lot orbit and start scientific exploration
Tianwen No. 1: get ready to go to Mars
Our reporter Liu Yao
“People’s Daily Overseas Edition” (09th edition on February 25, 2021)
On February 24, China’s first Mars exploration mission, Tianwen-1, sent another piece of good news. At 6:29 a.m. that day, the Tianwen-1 probe successfully deployed the third near fire brake and entered the mooring orbit of Mars with a near fire point of 280 kilometers and a distant fire point of 59,000 kilometers. , with a period of two Martian days. .
In fact, during the Spring Festival holidays, Tianwen No.1 was quite “busy”. On February 10, the probe reached the orbit of Mars and became China’s first artificial Mars satellite; On February 12, the image of the Tianwen-1 Mars capture process was released, and the Chinese New Year blessings were returned from a distance of 190 million kilometers from the earth; February 15 On Sunday, Tianwen-1 successfully carried out the maneuver of the plane to capture the orbital far fire point …
After entering docking orbit, the Tianwen-1 probe will operate here for about three months, and the orbiter’s seven payloads will power up, begin scientific exploration, and prepare to land on Mars.
Brake catch
After a long-distance flight, how the Tianwen-1 probe will brake in time and be finally captured by Mars is one of the most risky and difficult links in the mission, which is directly related to the success or failure of the mission.
Why is the capture process difficult? When the rover came close to the orbit of Mars, it was only 400 kilometers from Mars, but its relative speed was as high as 4 to 5 kilometers per second. Therefore, the detector must be turned on and braked and “braked” in time. Otherwise, if the braking time is too long and the brake is hit early, the probe will head to Mars; if the time is too short and the brake is applied late, the probe will drift away from Mars due to too fast a speed. and it cannot enter orbit.
During this process, the rover has only one chance of being captured by Martian gravity, and the “window period” is only half an hour. To achieve a perfect catch, Tianwen No.1 must rely not only on instructions from the ground, but also on his own “wisdom” to make decisions at critical moments.
In Chang’e’s previous missions to the moon, China has successfully implemented multiple brakes lasting nearly a month. Although it also brakes, braking near the fire is more difficult than braking near the moon. The average distance between the Earth and the Moon is about 380,000 kilometers, and the delay of one-way communication is only 1 second. In most cases, the ground can directly control the lunar probe movements. But when the Tianwen-1 rover was captured by Mars, the Mars rover was about 190 million kilometers from Earth and the delay in one-way communication was more than 10 minutes. The ground cannot monitor the braking process in real time, and can only rely on the detector to execute the capture strategy autonomously, placing extremely high requirements on autonomous navigation and monitoring of the environment.
Experts said that to precisely control the engine’s on and off timing, the orbiter’s orbit must be precisely radio-determined by the ground before nearby fire is captured. In addition to radio communication navigation, Tianwen-1 also used the optical navigation sensor as a backup navigation tool for the first time to observe the precise position of the orbiter and Mars in real time through a pair of “eyes” on the probe. . The ground team can use this to more intuitively confirm the flight’s orbit and attitude, and calculate the geometric center and apparent radius of Mars in the image. Tianwen-1 can independently obtain real-time velocity and position information through the optimal estimation algorithm and rely on a reliable capture strategy to ensure it enters the orbit of the firing ring.
It is understood that this is the first time that China has applied autonomous optical navigation technology in the interplanetary transfer process, thus becoming the second country in the world to master and verify the autonomous optical navigation technology of Mars in orbit.
Additionally, during the braking process, the orbiter must autonomously complete the corresponding processing in the event of an emergency, to maximize the success of capturing Mars. To solve the problem of ultra-long-distance communication, the Mars Orbiter is also equipped with an integrated data transmission, control and measurement system, achieving the objectives of light weight, high communication efficiency and reliable communication links.
Multi-dimensional “stop before you hit” detection
After being successfully captured by Mars and completing the first step of “orbit, land and patrol”, Tianwen-1 has many new missions, not only to conduct a multidimensional exploration of Mars, but also to prepare for the next landing on Mars. . .
On February 15, Tianwen-1 carried out a plane maneuver toward the distant fire point, and the probe’s flight changed from around the Martian equator to around the north and south poles of Mars. On February 24, the probe entered Martian orbit after the third near-fire stop. The experts said that the adjustments to the trajectory of these times are to allow Tianwen-1 to “visit” the previously selected landing site.
The Tianwen-1 probe consists of two parts: the orbiter and the landing patrol. From launch to near-fire braking, the orbiter is primarily responsible for flight tasks; after Mars is captured, the orbiter will make a landing prediction for the landing patrol; After the landing patrol is released successfully, the orbiter will act as a communicator for landing patrols. The orbiter establishes a relay communication link with the ground; After the three-month work of the Mars rover is complete, the orbiter will continue to conduct deep exploration for one Martian year and nearly two Earth years.
According to experts, to “make a frontal stop” for the Mars rover and landing pad, the orbiter will carry out a multidimensional exploration of Mars with its medium and high resolution cameras, magnetometers and mineral spectrum analyzers, including the planned landing area. Carry out detailed terrain and geomorphological surveys, conduct sand and dust storm detection over a large and wide area near the landing area, provide forecasts for the second step of the Mars exploration mission, and choose the opportunity to land In mars .
While the Tianwen-1 probe is on its way to the fire, China’s first 1: 1 replica test vehicle of the Mars rover is still undergoing ground verification in preparation for possible situations after landing. After the landing patrol has successfully landed on the surface of Mars, the rover will explore the topography, soil structure, water ice distribution, surface material composition, and the space environment of Mars in the science mission orbit, and will eventually form a global map of Mars. .
Kirin, Nezha, Chasing Dream, Xinghuo … Although the name of the Chinese rover has not finally been published, its “various martial arts” have long been popular. The rover is equipped with a panoramic camera that can avoid obstacles, implement real-time forward detection, and a multispectral camera that can identify mineral components. At the same time, the rover is also equipped with 4 “wing” solar panels. In addition, the rover is also equipped with a detection radar, a magnetic field detector and a time measuring instrument, which can detect Mars in all directions. The underground detection radar installed on the rover will “observe” the internal structure of Mars at a depth of 10 meters or even 100 meters below the surface of Mars. Polarization echo data, and it will detect the subsoil structure of the inspection area, and get the data of the subsoil geological structure.
The lifespan of China’s first Martian rover is 90 Martian days. Since a day on Mars is slightly longer than on Earth (the rotation period of Mars is approximately 24 hours and 37 minutes), the rover will operate on Mars for 92 Earth days.
As in the orbiter’s capture of Mars, due to the Earthfire’s long-distance data transmission delay, the Mars rover must have a high degree of autonomy. At the same time, the low intensity of light on Mars, coupled with the reduction of sunlight by the Martian atmosphere, makes the rover’s power supply more difficult than that of the lunar rover; These factors make the Mars exploration mission more difficult and complicated. .
Link
What is the difference between China, the United States and the Arab states during the same “fire” exploration period?
During the Mars rover launch window in July 2020, China, the United States and the United Arab Emirates successively launched the Mars rover. Today, probes from three countries have successfully reached Mars.
On February 9, the UAE’s first Mars probe, “Hope”, successfully entered the orbit of Mars and began monitoring and investigating the Martian atmosphere. “Hope” leads 3 teams to study the Martian atmosphere and monitor climate change. The main task is to take pictures of the Martian atmosphere and study the daily and seasonal changes of the Martian atmosphere. It is expected to continue to orbit Mars for at least two years.
The US rover “Perseverance” touched down in Jezero crater north of the Martian equator on February 18. The US exploration mission will look for signs of life that may have existed on Mars within two years. At the same time, “Perseverance” will also explore the geological and climatic features of Mars and explore the path for future human exploration and landing on Mars.
“Perseverance” is NASA’s ninth probe to visit the surface of Mars, and it will also be the first probe to sample Mars to return to Earth. Rock and soil samples collected by Perseverance from Mars will be returned to Earth on other Mars exploration missions in the future. According to the plan, after 2026, a “van” will go to Mars and take the Perseverance. Recover the remaining samples.
Pang Zhihao, chief science communication expert of China’s national space exploration technology, said that the mission objectives and technical solutions for the exploration of Mars between China and the United States are different. The goal of Perseverance’s mission is to find life. The United States is familiar with the landing site through previous explorations, so it chose to “get straight to the point.” China’s first Mars exploration mission is to “circle, patrol and patrol” three steps in one step, and carry out detailed studies of the landing area during the orbit process, which is unprecedented in the history of human exploration. from Mars. China’s space exploration technology is constantly accumulating and improving day by day, and the conditions for exploring Mars are now ripe.
