Relay Satellite

by Li Zhuoxi

The word “relay” in “relay satellite” refers to expanding the distance of network transmission by sending or forwarding data signals.

A relay satellite， sometimes referred to as “the satellite of satellites，” is a kind of communication satellite used to transmit massive volumes of data. By providing data relay， telemetry， tracking and command （TT&C;） services for spacecraft and satellites， it greatly improves the efficiency and emergency response capabilities of various satellites. The technology enables real-time data transmission of resources satellites and environmental satellites， earning more warning time for major natural disasters.

Early on the morning of May 21， 2018， China successfully launched the worlds first relay satellite named Queqiao （“Magpie Bridge”） in orbit around the moon， which will provide a communication link between the earth and the planned Change-4 lunar probe that will soft-land on and explore the moons mysterious far side at the end of 2018.

The relay satellite will solve a major difficulty in lunar exploration. The tidal forces of the earth slowed the moons rotation to the point where the same side always faces the earth. The other side， most of which is never visible from the earth， is known as the “dark side” of the moon.

Due to shielding from the moon itself， the detector landing on the far side of the moon cannot directly realize TT&C; communication and data transmission with the earth.

The Queqiao relay satellite will assist the control center on the earth to enhance control of the lunar probe to ensure a smooth landing.