Tianwen No. 1 "textbook-style" landing on Mars-

  China's Wentian road to a new level

  On May 15, 2021, after 295 days of space travel, my country's first Mars probe Tianwen-1 successfully landed on Mars.

China's first Mars exploration mission was won in a single battle and was accomplished in one go.

Ye Peijian, an academician of the Chinese Academy of Sciences, said excitedly: "This is a textbook landing, and it's a very beautiful result."

  This fall is the crystallization of Chinese wisdom, Chinese solutions and Chinese power.

  On this day, China's road to the heavens has reached a new level, and the Chinese nation has taken another big step into the more distant deep space.

  Wang Chuang, the overall chief designer of the Tianwen-1 probe of the Fifth Academy of the Aerospace Science and Technology Group, said that the successful landing of the Tianwen-1 was a victory with comprehensive preparations and adequate plans.

  How difficult is it to land on Mars?

  Before the Tianwen-1 Landing Patrol successfully landed on Mars, countries around the world carried out 44 Mars exploration activities, and only 19 completely successful exploration missions, with a success rate of less than 50%.

  Landing is the most risky link in Mars exploration.

So far, only 9 probes have successfully landed on Mars.

The successful landing of Tianwen-1 marked the first time that Mars left a Chinese mark.

  Landing is difficult, and the difficulty lies in the complexity of the landing process.

  In just 9 minutes from separation to landing, the operating speed of the Tianwen-1 Landing Patrol dropped from about 20,000 km/h to zero, during which it had to go through multiple links such as aerodynamic deceleration, parachute deceleration, power deceleration, landing buffer, etc. .

As the main engine of the landing patrol, the 7500N variable thrust engine is the main tool for the power deceleration link, enabling Tianwen No. 1 to achieve the "last kick" and steady braking.

This "space brake" method has been successfully implemented three times in a row during the landing of the Chang'e 3, 4, and 5 probes. The 7500N variable thrust engine of the Tianwen 1 Landing Patrol is the 2.0 version of the variable thrust engine used by the landing patrol. .

  Landing is difficult and difficult due to the uncertainty of the Martian environment.

  Unlike the approximate vacuum on the surface of the moon, the surface of Mars has a thin atmosphere, which is very unstable, with wind or sandstorms from time to time.

During the landing process, the lander and the atmosphere on the surface of Mars will violently rub against. In order to prevent it from being "burnt", a heat-resistant outsole was added to the lander, and the engine that could have been "stretched out" was "pocketed up".

Limited cabin space limits the size of the engine. The height of the Tianwen-1 variable-thrust engine is more than 60% smaller than that of the Chang'e-3 variable-thrust engine, but the main performance indicators such as thrust remain unchanged. "Big energy", which means that the engine must be stronger.

  Landing is difficult, and it is also difficult that the probe can only be controlled autonomously throughout the entire journey.

  Mars is far away from the earth, the signal has not yet reached the earth, and the probe has "closed".

For Tianwen No. 1 in a remote and foreign land, the measurement, judgment, and execution of all action trigger conditions are autonomous measurement, autonomous judgment, and autonomous control.

During the landing process of the landing patrol, radar and other detection equipment will stare at the Martian ground like eyes, measuring its distance from the ground and other parameters. These parameters enter the guidance, navigation and control system, and this wise "brain" calculates the engine The thrust requirements.

The engine will complete the variable thrust adjustment according to the preset timing and real-time commands, slow down the landing patrol, and finally land steadily on the surface of Mars at a very low speed.

  It is reported that after the Tianwen-1 Landing Patrol Rover lands, the Zhurong rover will start its work in a cycle of three Martian days in seven or eight days.

  The Zhurong rover carries a total of 6 payloads.

  The navigation terrain camera used for the terrain and landform detection of the Mars inspection area is mainly used to take images of the surface of Mars and plan the patrol path of the Mars rover; the subsurface detection radar is used to detect the soil structure of the Mars inspection area and whether there is water or under the soil The presence of ice; Mars surface composition detector and multi-spectral camera are used to detect the types of elements, minerals and rocks on the surface of the Mars patrol area.

  In addition, there are two instruments for detecting the environment: the Martian surface magnetic field detector and the Martian meteorological instrument.

Some scientists believe that Mars has no global magnetic field, only a local magnetic field.

The Mars surface magnetic field detector can find out the magnetic field in the inspection area.

The Mars weather measuring instrument is mainly used to measure the physical characteristics of the atmosphere such as wind speed, wind direction, air pressure, and temperature in the inspection area.

  Five years have passed since the first Mars exploration mission was established in January 2016.

In the past five years, China's aerospace industry has made great strides.

The path of the Chinese nation to ask for heaven may be full of twists and turns, but it is always full of courage and hope.

  (This paper, Beijing, May 15th)

He Yishu