"Not in the service area" for a month, what did Tianwen No. 1 experience?

　　Xinhua News Agency, Beijing, October 22 -

　　Xinhua News Agency reporter Hu Zhe

　　The earth and Mars move to both sides of the sun and the three are almost in a straight line. This phenomenon is called solar transit.

Beginning in late September 2021, the communication between Tianwen-1 and the earth was disturbed by solar electromagnetic radiation, which was unstable or even interrupted.

During the transit period, Tianwen-1 and Zhurong entered autonomous operation mode and suspended scientific exploration work.

　　Tianwen-1's every move to detect Mars has attracted much attention.

According to the latest news from the National Space Administration on the 22nd, the solar transit phenomenon has recently ended, and the measurement and control communication between the probe and the earth has returned to normal. According to the telemetry data, the Tianwen-1 spacecraft was in normal condition during the solar transit and passed the first solar transit safely.

The orbiter will enter the remote sensing mission orbit in early November to carry out global remote sensing exploration of Mars to obtain scientific data such as Mars morphology and geological structure, surface material composition and soil type distribution, atmospheric ionosphere, and Martian space environment, while taking into account the development of the rover mission Phase of relay communication.

So, what is Riling?

How did Tianwen No. 1 spend Riling?

What is Ri Ling?

　　Riling in the traditional sense was proposed for communication satellites.

Communication satellites are generally located in the geosynchronous orbit above the equator and at an orbital height of 36,000 kilometers from the earth.

In the vernal and autumnal equinoxes of each year, the sun also hits the earth's equator directly.

Therefore, from the perspective of the earth, the sun coincides with the communication satellite.

　　The sun emits a large number of messy radio signals all the time, and the antenna used to receive satellite signals actually receives signals from the sun.

In front of the powerful sun, satellite signals are like candlelights that are not worth mentioning.

Although the current antenna pointing accuracy is very high, but the radio signal from the sun will inevitably interfere with the signal of the normal communication satellite, which will cause abnormal ground reception.

　　When detecting Mars, the rover orbits Mars. From a macro point of view, the space position of the rover coincides with Mars.

Then, when Mars is blocked by the sun, or completely submerged by sunlight, the probe will naturally be blocked by the sun.

According to the laws of the movement of celestial bodies in the solar system, from late September to mid-October in 2021, Tianwen-1 is in the transiting phase.

What impact does Riling have on the Mars Rover?

　　Tianwen-1 is currently about 400 million kilometers away from the earth, and it takes more than 20 minutes to reach it even if it flies at the speed of light.

Tianwen-1 is so far away from the earth that people can only know its status through radio signals.

In the event of a solar transit, the connection between the probe and the earth will be significantly affected by the sun, and signal interruption may even occur.

Once the radio signal is interrupted, the ground will not be able to communicate with Tianwen-1, and will not be able to direct Zhurong to conduct scientific research.

　　In short, the sun is a huge source of radiation. When it appears on the communication link between the ground station and the probe, it will affect communication. Therefore, the Tianwen-1 and Zhurong “lost contact” for a month. .

How did Tianwen No. 1 spend Riling?

　　During the solar transit, the ground didn't know anything about the status of Tianwen-1, which put forward higher requirements for Tianwen-1's autonomous control capabilities.

Because the ground control personnel have accumulated data and experience, the external environmental conditions experienced by Tianwen No. 1 during the "lost connection" period are predictable.

　　In order to ensure the safety of flying in orbit, the Tianwen-1 orbiter team adjusted the working mode of the orbiter in mid-September 2021.

After completing the comprehensive state inspection, the orbiter is set to an autonomous safe and steady-state management mode through ground instructions, that is, the "sunlight mode", in order to deal with the loss of connection between the device and the ground.

During the transit period, the ground receives telemetering of the orbiter's status every day. On the one hand, it determines the status of the orbiter, and on the other hand, it determines the interference of the sun to the device-ground communication.

　　As the relative positions of Mars, the earth and the sun move, the orbiter-to-earth wireless communication has experienced a process of interference, interruption, and gradual recovery.

In mid-October 2021, the device-to-ground communication resumed, and the task team began the state assessment work.

After careful analysis and confirmation, the orbiter is in good condition.

A few days ago, the mission team officially set the on-board status to "out of the sun" through the form of ground issuing orders.

This marks that the Tianwen-1 orbiter has successfully completed its fully autonomous flight for more than one month, and has successfully passed the Riling test.

　　Chu Yingzhi, deputy commander of the Tianwen-1 orbiter of the Eighth Academy of China Aerospace Science and Technology Corporation, said that the detection of solar transit on Mars is a natural phenomenon, and solar transit has also accumulated certain experience for planetary exploration technology.

The Tianwen No.1 and Zhurong No.1, which spent the first day safely, made everyone more confident.