Today is space with you [No. 1431]
On the afternoon of March 23, the second class of "Tiangong Classroom" was successfully started. Three "space teachers" Zhai Zhigang, Wang Yaping and Ye Guangfu demonstrated a number of experiments on track at the China Space Station, and interacted with teachers and students in the ground classroom in real time through video calls.
You may often see in the space news that there is a place marked "Sky Chain" on the screens of the various ground accusation halls. This standard represents that the "Skylink" series of relay satellite systems are transmitting data in both directions with spacecraft. Seeing this target in the "Tiangong Classroom" means that it is silently providing data relay guarantee for the wonderful "space" lecture.
So what is the "Sky Chain"? What role can it play? Let's start at the beginning!
For data on the space station to be transmitted to the ground, a communication link must be established. Our "Tiangong" is located in a low-Earth orbit about 400 kilometers from the ground, and the time to circle the earth is about 90 minutes. In those 90 minutes, a ground station can only observe and talk to it for about 2%-3% of the time.
▲ Yang Liwei talked to his family
When Shenzhou 5 entered space in 2003, astronaut Yang Liwei spoke to the ground several times, but each time there was a very strict time window. At 19:58 on October 15, Yang Liwei had a phone call with his family. This call, full of worry and reluctance, lasted only 4 minutes and 50 seconds due to technical limitations.
If you want to achieve longer calls, you need to use many observatories and probe ships in different locations. Moreover, with the change of the position of the spacecraft, these ground stations are also required to continuously capture dynamically, and the operation will also consume a lot of manpower and material resources.
In order to change this situation, relay satellites came into being. Shan Changsheng, chief engineer of the Beijing Space Information Transmission Center, told reporters that unlike ordinary low- and medium-orbit satellites, relay satellites operate in a geostationary orbit more than 30,000 kilometers above the equator. The orbit has a period equal to the Earth's rotation period and is like a fixed "beacon" for ground-based observers. Moreover, compared with the ground measurement and control station, the relay satellite "stands higher", naturally "sees farther", a satellite can cover about 40% of the earth's area, only three are needed to achieve global coverage, effectively solving the problem of data transmission between spacecraft and the ground, spacecraft and spacecraft.
▲At 23:35 on April 25, 2008, the mainland's first data relay satellite "Tianlian-1 01 Satellite" was successfully launched at the Xichang Launch Site of xichang satellite launch center. Photo by Xinhua News Agency reporter Li Gang
In 2008, China's own relay satellite project embarked on a long journey from scratch and had an intuitive name, "Tianchain". The Beijing Spatial Information Transmission Center, which controls the "Sky Chain" on the ground, has also given itself a romantic code name "Tianlu", and it is they who have built a high-speed communication link between heaven and earth.
On September 27 of the same year, astronaut Zhai Zhigang's sentence "I have left the capsule and feel good!" "From the outside of the Shenzhou VII in distant space back to the ground, this is the "debut" of the "Tianlian" series relay satellite system in the manned space mission.
The reporter learned that in the Shenzhou VII mission, the "Tianlian" relay satellite system completely and accurately and with high quality received and recorded the data of 7 circles and nearly 200 minutes during the flight of Shenzhou VII, and handed over a perfect answer sheet. Since then, while witnessing the development of manned spaceflight on the mainland, the relay satellite system has also been continuously optimized and improved, providing more and more high-quality services for space missions.
▲The network operation of 3 Skylink satellites has officially achieved nearly 100% orbit coverage for medium and low orbit spacecraft
On July 11, 2011, the Tianlian-1 02 satellite was launched, marking the construction of the continental relay satellite system into the multi-satellite networking stage; on July 25, 2012, the Tianlian-1 03 satellite was launched. So far, the three skylink satellites have been networked and operated, officially achieving nearly 100% orbit coverage of medium and low orbit spacecraft, and making the mainland the second country in the world with a relay satellite system with global coverage capabilities for medium and low orbit spacecraft.
▲ Astronaut Wang Yaping in the Shenzhou 10 manned mission gave a space lecture
In 2013, after the completion of the three-star networking of the first generation of Tianlian satellites, it guaranteed for the first time that General Secretary Xi Jinping and the Shenzhou 10 astronauts had a space-to-earth call. It also successfully guaranteed astronaut Wang Yaping's first 51-minute space lecture.
▲For the first time, astronauts watched the news broadcast simultaneously in heaven and earth
By the time of the Shenzhou 11 mission in November 2016, astronauts Jing Haipeng and Chen Dong watched the "News Network" in sync with the ground in the Tiangong-2 experimental module, which has become a routine activity that can be carried out every day during the 33-day flight period. In addition, in the manned missions of Tiangong-2 and Shenzhou-11, the "Tianlian-1" satellite also provides space-based measurement and control services for automatic rendezvous and docking, hand-controlled rendezvous and docking, spacecraft evacuation, return and search and rescue recovery.
▲ Day and core cabin
It is precisely because of this more mature communication support technology that the picture and sound of the call between heaven and earth are clearer and smoother. The space station Tianhe core module launched on April 29, 2021 is equipped with multi-channel high-definition cameras and voice processors, which can not only shoot the beauty of space in an all-round and multi-angle manner, show the status of the space station, but also ensure that astronauts can achieve two-way high-definition video calls with the ground, and correspondingly, higher requirements are also put forward for data transmission rates.
Of course, this is not a problem. In the 2021 Shenzhou 12 mission, the second-generation relay satellite "Tianlian-2" 01 satellite independently developed by the mainland made its debut in a manned space mission.
▲ On June 23, 2021, Xi Jinping, General Secretary of the CPC Central Committee, President of the People's Republic of China and Chairman of the Central Military Commission, came to the Beijing Aerospace Flight Control Center and spoke cordially with Shenzhou 12 astronauts Nie Haisheng, Liu Boming and Tang Hongbo, who were on a mission in the Tianhe core module. Photo by Xinhua News Agency reporters Ju Peng (left) and Yue Yuewei (right) (imposition photo)
Engineer Qin Mingchen told reporters that the second-generation relay satellite system has a higher rate of transmission speed, stronger ability of multi-target support, space data from the ground station received, transmitted to the Beijing Aerospace Flight Control Center, to automatic distribution according to different logos, the signal running distance of nearly 100,000 kilometers, plus the processing and reception of the time, the delay is only seconds. Although the "Sky Road" is busy, it is not congested.
▲Scientific and technological workers of Beijing Spatial Information Transmission Center
It can be said that the accurate and stable communication guarantee of the Tianlian satellite has set up an "information sky road" for people to travel back and forth between heaven and earth, and has also "escorted" generations of Chinese astronauts to make the "heavenly end of the world next to each other" that has been chanted for thousands of years become a reality! Whether it is at this moment or in the future, the "Skylink" relay satellite system will better provide these spacecraft with high-speed, wide-area, and stable space-based measurement and control and data relay services, and an overwhelming sky road information network is extending farther and wider.