A rendering of the Queqiao satellite performing its communications relay beyond the moon. Photo: Chinese Academy of Sciences
A rendering of the Queqiao satellite performing its communications relay beyond the moon. Photo: Chinese Academy of Sciences
Queqiao relay satellite enters L2 orbit

A Chinese satellite with a huge golden umbrella-shaped antenna specifically designed for relaying signals between the moon and Earth is up and running in orbit more than 400,000 kilometers from Earth, biding its time for the launch of the fourth spacecraft of the Chang’e lunar-probe series this year, which is to land on the moon’s mysterious far side.

Since it catapulted its first probe to circle the moon more than a decade ago, Beijing now regards the up-and-coming fourth mission of the Chang’e program, named after the Chinese goddess of the moon in ancient folklore, as a source of national pride as no country has ever landed a probe on the hemisphere of the moon that always faces away from Earth because the moon’s revolution cycle is the same as its rotation cycle.

The satellite, named Queqiao (“Magpie Bridge” in Mandarin, referring to an arc in ancient mythology formed by birds that reunites two lovers separated by the heavens), will establish a communication link between ground control and Chang’e-4 once it sets foot on the moon’s far side.

A rendering of the Queqiao satellite performing its communications relay. Photo: Chinese Academy of Sciences

Launched on May 21, Queqiao is now in a halo orbit around the second Lagrangian (L2) point of the Earth-moon system, where it can “see” both the Earth and the moon’s far side.

Chang’e-4 will follow the path of Chang’e-3, launched at the end of 2013 as the first Chinese spacecraft to land on and explore an extraterrestrial body.

Xinhua revealed that after Chang’e-3, engineers and Communist Party cadres debated Chang’e-4‘s destination and some were in favor of the much closer and easier-to-reach near side, but eventually Beijing decided to venture into uncharted terrain with its ambitious lunar exploration scheme with the ultimate goal of sending its taikonauts there, an attempt to be made within 15 years.

Landing and roving on the far side require a relay satellite to transmit signals.

Profile of the communication links among the Chang’e-4 relay satellite Queqiao, the Earth ground station, and the lunar lander and rover.

China’s National Space Administration noted that Queqiao used relatively small amounts of fuel during its journey to the planned orbit as it was under precise control. It will remain in orbit for up to eight years to assist communications for probes from other countries.

A reliable long-distance data transmission link is a key technological goal for space experts around the world. Queqiao carries an umbrella-shaped antenna with a diameter of 4.2 meters, the largest of its kind ever used in deep space exploration.

Queqiao will also carry a radio antenna that researchers will use to study the early universe, what astronomers call the “cosmic dark ages” after the big bang and before the first stars in the universe were formed, while in the shadow of the moon, which blocks electromagnetic interference from Earth.