The results of the "Xihe" solar exploration mission were released! What achievements did my country's first dedicated "photographer" of the sun make?

Xinhua News Agency, Beijing, August 30th , Title: What achievements has been made by China's first exclusive "photographer" of the sun - "Xihe"?

Xinhua News Agency reporters Hu Zhe, Chen Xiyuan and Song Chen

"Follow the example of Xihe, who drove the celestial horse and aimed to herd the stars in the sky." my country's first solar exploration scientific and technological experimental satellite "Xihe" has been attracting attention since its successful launch. On August 30, the "Xihe" achievement press conference was held in Beijing. What important achievements has "Xihe" made? What is its significance? The reporter interviewed relevant experts.

The world's first "CT scan" of the sun's lower atmosphere

The sun is the most important environmental factor affecting the development of human civilization and economic and social development on Earth, and is the source of growth for all things. The sun is the largest celestial body in the solar system, the star closest to the Earth and the one that has the closest relationship with humans. The sun plays an indispensable role in the evolution of the Earth and the development of human civilization.

At the same time, the sun's influence on the earth is also omnipresent. Humans have established a ground-based solar monitoring network, but because the earth's atmosphere is opaque to electromagnetic waves such as ultraviolet rays, X-rays, and gamma rays, the visible light band on the ground is also affected by factors such as atmospheric absorption, disturbances, and rainy weather. To detect interplanetary plasma and magnetic field information, we must go into deep space.

Zhao Jian, chief designer and deputy commander of the GF project and director of the Major Project Engineering Center of the State Administration of Science, Technology and Industry for National Defense, introduced that in the past year, the National Space Administration has organized engineering task teams from the China Aerospace Science and Technology Corporation, Nanjing University and other institutions to carry out more than 300 technical tests on ultra-high pointing accuracy and ultra-high stability of satellite platforms, and more than 1,000 solar spectrum imaging tests. It has successfully completed the in-orbit testing and experiments of the "Xihe" satellite, and achieved important scientific research results, including five international firsts.

"We have achieved the first spectral scanning imaging of the solar Hα band in space in the world, recording the response process of solar activity in the photosphere and chromosphere." Zhao Jian told reporters that through one scan, "Xihe" can obtain solar images at 376 wavelength positions, and different wavelengths correspond to different levels of the solar atmosphere in the photosphere and chromosphere.

Zhao Jian said that the Hα spectral line is very important for solar physics research. "Because it is the spectral line with the strongest response to solar activity in the lower atmosphere of the sun. By detecting this spectral line, we can obtain information on the activities of the photosphere and chromosphere at the same time, which greatly improves our understanding of the physical mechanism of solar eruptions."

It is reported that the resolution of the Hα imaging spectrometer used by "Xihe" this time is about 10 times higher than that of the ground filter, reaching the international advanced level.

Ding Mingde, chief scientist of the "Xihe" satellite and professor at Nanjing University, said that "Xihe" was the first in the world to obtain the solar Hα spectral line, SiⅠ and FeⅠ spectral lines in orbit, and obtained a complete spectral line profile. These data will help scientists calculate the temperature, density and speed of the solar atmosphere, and conduct more in-depth research on the solar atmospheric structure, understand the triggering causes and propagation process of solar flare activities, so as to better carry out space weather forecasts and ensure human life safety.

Ding Mingde introduced that the scientific data of the "Xihe" satellite has been opened to the world for sharing and can be queried and downloaded through the Solar Science Data Center of Nanjing University. It has been widely used by solar physics researchers in the United States, France, Germany and other countries.

Space "magnetic levitation" allows accurate and stable photography

As a "photographer", the camera must be accurate and steady. "Xihe" is the first in the world to use a non-contact magnetic levitation satellite platform based on the concept of "dynamic and static isolation, master-slave coordination", just like a "pan-tilt platform".

Chen Jianxin, the general commander of the "Xihe" satellite system of the Eighth Academy of China Aerospace Science and Technology Corporation, introduced that traditional satellites all use a design method of fixed connection between the platform cabin and the payload cabin. The vibration of the platform cabin's flywheel, gyroscope and other active parts will inevitably be transmitted to the payload cabin, affecting the camera's observation quality. "Xihe" adopts a new overall design method of "dynamic and static isolation and non-contact", which physically isolates the platform cabin from the payload cabin, effectively isolating the interference of the satellite platform, and through a large-bandwidth, ultra-high-precision magnetic levitation actuator, the camera's pointing accuracy and stability indicators are improved by one to two orders of magnitude compared to traditional satellites.

At the same time, in order to realize the energy supply from the platform cabin to the payload cabin and the information transmission between the two cabins, "Xihe" also verified in orbit a number of new satellite platform technologies such as wireless energy transmission between cabins, laser communication, and wireless communication. In the future, the new platform will also be used in new generation space missions such as space astronomical exploration and high-resolution ground surveys to effectively complete high-precision observations.

Exploring new solutions for space speed measurement

How can a satellite accurately obtain its position and speed when flying in the vast space? Zhao Jian told reporters that compared with near-Earth space missions, deep space exploration missions can only rely on traditional radio ranging and speed measurement navigation methods due to the lack of assistance from navigation satellites. However, the accuracy of radio navigation will drop significantly as the distance the satellite flies increases. This time, the "Xihe" is equipped with an atomic frequency discrimination solar speed measurement navigation instrument to try to overcome this difficulty.

When a satellite moves in space, the light emitted by the sun will produce a frequency change when it reaches the satellite, which is called Doppler frequency shift. The magnitude of the frequency shift is proportional to the apparent velocity of the satellite relative to the sun. Therefore, if the frequency change of sunlight can be measured, the apparent velocity of the satellite relative to the sun can also be known.

Zhao Jian told reporters that Xihe was the first in the world to adopt the atomic frequency discrimination principle in orbit, using the hyperfine spectrum of sodium atoms as a frequency standard to accurately determine the frequency changes of sunlight in real time, and then obtain the satellite's apparent velocity relative to the sun. After on-orbit measurements, the navigator's velocity measurement accuracy is better than 2 meters per second, providing a new velocity measurement technology for autonomous navigation in future deep space exploration missions, and consolidating my country's original technological accumulation in the field of deep space exploration.

In addition, relevant scientific and engineering departments have jointly proposed a series of mission plans for future solar exploration at the Sun-Earth L5 point, solar polar orbit exploration, and solar close-in exploration. These missions will conduct all-round, three-dimensional exploration of the sun, further deepen our understanding of the origin and evolution of solar activity, monitor the interplanetary propagation and earth response of solar flares, and contribute to the development of human scientific civilization.