China will launch a data relay satellite to ensure communication between Earth and the lunar probe during an expedition to the far side of the moon, Ye Peijian, chief scientist with China's lunar exploration program, said Tuesday.

China in January announced plans to send the Chang'e-4 probe to the dark side of the moon around 2018. Due to gravitational forces, this part of the moon is not visible to Earth and has never been explored by humans. The data relay satellite will be launched six months before the probe.

Earth can contact Chang'e-4 with the help of a "communication station" on the Lagrange point L2 of the Earth-moon system, 80,000 kilometers away from the moon, according to Ye.

"The moon is too small to block the signal transmission between Earth and the data relay satellite," said Ye.

Chang'e-1 mission in 2007 began the era of China's lunar exploration, the launch of the Chang'e-2 and Chang'e-3 followed soon after. The latter marked completion of the second phase of China's lunar program, which includes orbiting, landing and returning to Earth.

Chang'e-3 delivered a rover and stationary lander to the moon in 2013, making China the third country after the Soviet Union and the United States to carry out such a mission.

China is preparing for its next lunar probe mission, Chang'e-5, which is expected to be launched around 2017.

The probe will be tasked with landing on the moon, collecting samples and returning to Earth.