China launches relay satellite to explore Moon's far side

China successfully launched a relay satellite early today to set up a communication link between the Earth and a planned Chinese lunar exploration mission to explore the Moon's mysterious far side.

Named Queqiao (Magpie Bridge), the 400-kg satellite has a designed life of three years.

It was carried by a Long March-4C rocket that blasted off at 5:28 AM (local time) from southwest China's Xichang Satellite Launch Center, the China National Space Administration (CNSA) said.

"The launch is a key step for China to realise its goal of being the first country to send a probe to soft-land on and rove the far side of the Moon," said Zhang Lihua, manager of the relay satellite project.

About 25 minutes after lift-off, the satellite separated from the rocket and entered an Earth-Moon transfer orbit with the perigee at 200 kms and the apogee at about 400,000 kms. The solar panels and the communication antennas were unfolded.

Queqiao is expected to enter a halo orbit around the second Lagrangian (L2) point of the Earth-Moon system, about 455,000 kms from the Earth.

It will be the world's first communication satellite operating in that orbit, state-run Xinhua news agency reported.

The satellite carries several antennas. One, shaped like an umbrella with a diameter of five metre, is the largest communication antenna ever used in deep space exploration, said Chen Lan, deputy chief engineer of the Xi'an Branch of the China Academy of Space Technology (CAST).

The satellite could stay in the halo orbit around the L2 point of the Earth-Moon system for a long time by using relatively little fuel, thanks to the gravitational equilibrium at that point.

But the mission must overcome many challenges, including multiple adjustments to its orbit and braking near the Moon and taking advantage of the lunar gravity, Zhang said.

In a Chinese folktale, magpies form a bridge on the seventh night of the seventh month of the lunar calendar to enable Zhi Nyu, a weaver girl who is the seventh daughter of the Goddess of Heaven, to meet her beloved husband, cowherd Niu Lang. The couple were separated by the Milky Way.

Chinese scientists and engineers hope the Queqiao satellite will form a communication bridge between controllers on the Earth and the far side of the Moon where the Chang'e-4 lunar probe is expected to touch down later this year.

Today's launch was the 275th mission of the Long March rocket series.

Tidal forces of the Earth have slowed the Moon's rotation to the point where the same side always faces the Earth, a phenomenon called tidal locking.

The other face, most of which is never visible from the Earth, is the far side or dark side of the Moon, not because it's dark, but because most of it remains unknown.

With its special environment and complex geological history, the far side is a hot spot for scientific and space exploration.

The Aitken Basin of the lunar south pole region on the far side has been chosen as the landing site for Chang'e-4. The region is believed to have great research potential.

However, landing and roving require a relay satellite to transmit signals.

The Chang'e-4 mission will be more complicated than Chang'e-3, China's first soft landing on the Moon in 2013.

"We designed an orbit around the Earth-Moon L2 point where the relay satellite will be able to 'see' both the Earth and the far side of the Moon," Bao Weimin, director of the Science and Technology Commission of the China Aerospace Science and Technology Corporation said.

Establishing a communication link is essential for the success of the Chang'e-4 mission, Bao was quoted by Xinhua.