Unveiling the secrets of "Xihe"! my country's first solar exploration satellite was successfully launched!

At 18:51 Beijing time on October 14, 2021, my country successfully launched the Solar Hα Spectrum Detection and Dual Super Platform Science and Technology Experiment Satellite with the Long March 2D carrier rocket at the Taiyuan Satellite Launch Center. The satellite entered the predetermined orbit smoothly and the launch mission was a complete success.

The sun rises in the east, darkness dissipates. The sunlight shines through the cracks, sacred and warm, and people call it hope.

With hope in mind, people travel further and further in the journey of time, from eating raw meat and drinking blood to cooking dragons and roasting phoenixes, from slash-and-burn farming to intelligent automation. People began to wonder what the sun, which spreads hope, looks like? It is red in the morning and evening, and dazzling at noon. These are all its appearances, and they are not its appearances. I don't know when people began to think, it would be nice if they could "go up" and take a look.

So, on October 14, "Xihe" set off. As the first messenger sent by China to observe the sun, it wanted to help people see who lives in the sun.

(Video source: Eighth Academy of China Aerospace Science and Technology Corporation)

Check in the sun

In the 517-kilogram sun-synchronous orbit at an altitude of 517 kilometers, the 510-kilogram "Xihe" satellite is observing the sun. "Xihe" is the name given to my country's first solar exploration satellite by netizens after a naming campaign. From then on, the mythical sea of ​​stars has gained a touch of legendary color.

Through the dual super-platform with ultra-high pointing accuracy and ultra-high stability, the "Xihe" equipped with the Hα imaging spectrometer can better observe the sun in two ways: white light continuous spectrum imaging and spectral scanning imaging.

In white light continuum imaging mode, a full solar image can be obtained, as easy as pressing the shutter button on a mobile phone to take a photo.

⬆️Simulation image of the Xihe satellite

In the spectral scanning imaging mode, the Hα imaging spectrometer carried by "Xihe" can obtain more than 4,600 spectra by scanning the entire solar disk in about 46 seconds. Each spectrum can be restored into an image of the solar disk.

The Hα line is a visible red emission line of hydrogen in astronomy and physics. The Hα band line in the solar spectrum is the strongest chromospheric line in response to solar explosions, and can directly reflect the characteristics of the source region of the explosion.

As for why the Hα spectrum was chosen for detection and research, Chen Jianxin, chief commander of the Xihe satellite of the China Aerospace Science and Technology Corporation, explained, "Xihe is the first satellite in the world to realize spectral imaging detection of the solar Hα band from space. By analyzing the Hα spectrum data, we can obtain information about the solar lower atmosphere from the photosphere to the chromosphere, thereby deducing the changes in physical quantities such as atmospheric temperature and velocity during solar eruptions, and studying the dynamic process and physical mechanism of solar eruptions."

Chen Changya, executive manager and deputy chief engineer of the satellite, pointed out that "if the solar magnetic field changes dramatically and the corona erupts, it will affect the Earth's magnetic field and satellites on Earth, causing interference in many fields, including communication signals."

He also explained the significance of the Xihe satellite's solar exploration. "Our country's existing space weather forecasts are all obtained from abroad. The data obtained is relatively delayed, and the authenticity is difficult to guarantee, which is very passive. After solar exploration satellites such as the Xihe are sent into space, my country will be able to independently control relatively accurate space weather forecasts without being constrained by others."

5mm to a new era

"Xihe" is a solar double super satellite. The "double super" refers to ultra-high pointing accuracy and ultra-high stability.

The payload of traditional satellites is often fixed to the platform, but when the satellite is in operation, multiple devices work at the same time, and the satellite body will inevitably experience slight vibrations, and the working environment of the payload is not stable. As the executor of high-precision detection missions, "Xihe" needs a stable environment.

If the combination doesn't work, then let's separate. Guided by the new overall design method of "dynamic and static isolation and non-contact", the R&D team has successfully developed a magnetic levitation actuator with high precision, large bandwidth, and no interference. The payload cabin is connected to the platform cabin through magnetic levitation to form physical isolation. Without contact, the vibration on the platform cabin cannot be transmitted, and the payload cabin is quite stable.

However, such a design places higher demands on the satellite's attitude control.

When the Hα imaging spectrometer on the "Xihe" conducts solar observations, the satellite's attitude will change due to the needs of different working modes. Sometimes it is necessary to calibrate the sun through 9 observation points, sometimes it is necessary to control the satellite's attitude to conduct continuous swing observations of the sun, and sometimes it is necessary to perform dark field calibration on the satellite to control the satellite's attitude to point to a specific area in space. When the payload cabin changes its attitude, the platform cabin must also change immediately to avoid collision. This new master-slave collaborative control decoupling method of "active control of the payload cabin and slave control of the platform cabin" makes the detection of satellite payloads more stable and accurate.

⬆️"Xihe" satellite

Chen Changya said, "Unlike the overall attitude control of traditional satellites, the attitude control of the payload cabin, platform cabin and the relative position of the two cabins of 'Xihe' forms a three-loop control."

The adjustment distance of plus or minus 5 mm between the payload cabin and the platform cabin seems to be the distance for the satellite to rush into a new era.

Wireless charging in space

The payload cabin and platform cabin are separated, and the traditional power supply method cannot meet the energy transmission needs and becomes a thing of the past. Therefore, "wireless charging" is here.

If you take a different route, the distance between “is it easy to go” and “can it go” is often not far. Wireless energy transmission is simple in thought but difficult in practice.

As early as the mid-to-late 20th century, NASA had proposed space magnetic induction wireless transmission technology and successfully applied it on satellites. So far, my country has only carried out related experimental work in ground laboratories. Being able to apply high-power, long-life wireless energy transmission technology on satellites has been the wish of several generations of Chinese astronauts.

To carry out high-power wireless energy transmission on satellites, it is necessary to overcome the complexity of the space environment and deal with the ever-changing temperature and unknown magnetic field changes. Unlike wireless charging of mobile phones, "wireless charging" in space not only has high power, but also needs to undergo multiple conversions. Both solar panels and batteries provide direct current. In the process of wireless energy transmission between the payload cabin and the platform cabin, it is necessary to go through a conversion process from direct current to alternating current to magnetic field, and then from magnetic field to alternating current to direct current.

The research and development team of the 811 Institute of the Eighth Academy and the team of Liu Yanming of Xidian University worked together, and after many demonstrations and comparisons, they successfully solved the technical problems of joint power supply of the platform cabin and the payload cabin, power supply of the cabins, and energy transmission in space in more than a year, ensuring the effective supply of energy to the satellite under various conditions.

Chen Jianxin introduced that "'Xihe' is the first satellite in China to use high-power and long-life wireless energy transmission. Through the wireless energy transmission system, the energy of the platform cabin is continuously transmitted to the payload cabin."

⬆️"Xihe" satellite

Face-to-face fast data transmission

The special dual-cabin separation structure of the "Xihe" also has higher requirements for data transmission, so space laser communication technology "volunteered". The inter-cabin high-speed laser communication unit developed by the Laser Center Team of the 802 Institute of the Eighth Academy was turned on after the "Xihe" entered orbit smoothly. From then on, it will be responsible for the task of inter-cabin data transmission without interruption.

Unlike other observation data, the intensity of sunlight is strong enough, so the amount of data generated is very large. Therefore, how to quickly transmit and store data is the guarantee for the timely and effective development of scientific research.

Chen Changya introduced that "when the solar flare is at its peak, the amount of data from long-term observations will be very large. At that time, in addition to being transmitted to the ground satellite center, some of the data will be temporarily stored in the satellite's memory."

The laser communication subsystem is equipped with a high-speed laser transmission interface, which can significantly increase the data transmission rate of scientific payloads and greatly improve the intra-satellite data transmission bandwidth.

Chen Changya said, "The transmission distance of laser communication between cabins is short, but the deflection angle is large. When the payload cabin and the platform cabin do not need to be aligned straight, data transmission can be achieved." At the same time, the single machine has 10 various interfaces, which can meet the special requirements of various transmission speeds of the platform, process data quickly, and realize "face-to-face fast transmission" more smoothly.

In the future, my country will also launch a comprehensive solar exploration satellite, the Advanced Space-based Solar Observatory (ASO-S). Chen Jianxin introduced, "The satellite will carry more space telescopes to focus on observing the state of the upper atmosphere of the sun, and will effectively complement the Xihe satellite in terms of observation levels and observation bands."

Chen Changya said, "The verification of the dual-super platform is of great significance. In the future, we can even make Xihe into a series of satellites, large or small. Solar exploration is of great significance. In the future, we need to launch more solar exploration satellites to obtain more solar information in a timely manner and improve the precision and accuracy of my country's space weather forecast."

The future is now.

"Xihe" looked at the sun again and pressed the shutter.

(China Aerospace News)