Screenshot of CCTV's video

The three taikonauts aboard China’s Tianhe space station core module some 400 kilometers above the Earth received the first video call from Chinese President Xi Jinping at the control center in Beijing on Wednesday morning, impressing many with the high-resolution images, loud-and-clear voices, and a ground-space connection with almost zero time delay. What empowered such a smooth connection?

A “space network” composed of three homegrown Tianlian satellites guaranteed the unimpeded communication between the ground and space, according to China Space News, the newspaper co-hosted by two state-owned space giants, the China Aerospace Science and Technology Corporation and the China Aerospace Science and Industry Corporation.

Tianlian satellites are China's data tracking and relay communication satellites that fly in geostationary orbit. They are mainly tasked to provide data relay, measurements and control, and transmission services for the in-orbit spacecraft on a global scale.

The downlink rate of the station’s network is 1.2G, which is equivalent to the ground’s 5G communication speed. Its time delay is within merely one second, the system developer told CCTV News. 

Yi Yusheng, chief designer of the space station’s measurement, control and communication subsystem at the China Academy of Space Technology, introduced that the taikonauts could hold video calls, receive e-mails, and even watch online TV programs via the station’s telecommunication network during their three-month stay. 

“They can also have private phone calls with their families using a special telephone, which will not be heard by any of the ground control staff,” Yi said. 

Jing Zheng, deputy commander in chief of the space station, further added that the Wi-Fi in space feels the same as the ground, supporting taikonauts’ daily communications on WeChat and video calls. 

Over 10 cable and wireless network cameras, Bluetooth headsets, mobile phones, PADs, and laptops had been brought to the Tianhe core cabin to guarantee its connection with the ground through various means. 

These terminals will upload the images and voice messages to the space station’s Ethernet switcher, which will then transmit the data to the ground via a high-speed relay antenna. 

A major breakthrough has been made for the relay antenna in that the updated version could be repaired and maintained, with the aim of extending its lifespan to support the space station’s operation needs for 15 years, a system developer said. 

Yi added that the ground-space connection will not be interfered with, as the three Tianlian satellites and the space station’s relay antenna could achieve a coverage rate of more than 90 percent, meaning that the telecommunications signals can reach the craft for over 90 percent of its time in orbit. Once the two other laboratory modules are docked with the core cabin and the three-module complex is formed, there will be another two relay antennas that will realize a 100 percent coverage rate of ground-space connection.