Video: CNSA

China's Chang'e-5 lunar probe has officially embarked on the journey back to Earth amid earnest expectations from fans across the world, after the spacecraft carried out another successful maneuver that allowed it to break free from the moon's gravity and enter the lunar-Earth transfer orbit. 

The probe conducted the second lunar-Earth transfer projection on Sunday after seven days travelling around the moon. 

At 230 kilometers away from the lunar surface, the orbiter-returner combination broke free from the lunar gravitation force and was sent to the lunar-Earth transfer orbit by using four 150-newton thrust engines after 22 minutes of operation, Global Times learned from the China National Space Administration (CNSA). 

The probe will conduct several mid-course corrections during its journey, before the return capsule separates from the orbiter and heads back to Earth, carrying the precious parcel of lunar samples in a suitable time window, CNSA revealed. 

The latest operation marks the second-to-last stage of the Chang'e-5 mission. Wang Ya'nan, chief editor of Aerospace Knowledge magazine, told the Global Times on Sunday that the crucial factor for the probe's safe return lies in its upcoming development - separation of the orbiter-returner combination. 

"After the spacecraft enters the lunar-Earth transfer orbit, it will gradually come under the effect of Earth's gravitational force. During this time, the capsule must adjust its attitude and speed continuously, to ensure a suitable position for the separation," Wang noted. 

It also determines the capsule's initial state of the "stone-skipping" reentry, which plays a vital role in determining how smooth the bounce will be, he added. 

The separation of the returner and orbiter will take place about 5,000 kilometers away from Earth, according to a statement sent to the Global Times from the China Aerospace Science and Technology Corp.

The orbiter of the probe has shouldered the heaviest task and most complex maneuvers in China's aerospace history, involving eight of the 11 stages of the mission. It serves as a "space taxi," carrying its "siblings" to and fro. 

"The orbiter is meant to carry out five separations and six combinations during the whole journey, of which it has supported some key operations including docking and rendezvous, and sample transfer at the lunar orbit," Vice Chief Designer of the Chang'e-5 probe Zha Xuelei said. 

To perform its duties in a more reliable manner, the orbiter has perfected its thrust engine design and control systems, observers noted. There must be enough capacity for fuel to power the engines, which are adjustable to satisfy differentiated needs in various tasks. 

It has also improved the precision of attitude-control systems, and it is equipped with an automatic space guidance system, which could run on its own after receiving commands from the ground.

Before the latest action, the probe's ascender successfully docked with the orbital module in lunar orbit on December 6, at some 380,000 kilometers from the Earth, and completed the first lunar-Earth transfer projection on Saturday, which shifted path from near-circular orbit to a higher elliptical orbit.

China launched Chang'e-5 on November 24, the third stage of China's current lunar programs, which involves three phases - orbiting, landing and return. 

The mission, which is regarded one of the most complicated and challenging space exploration projects ever made by China, is expected to be completed in mid-December and land in North China's Inner Mongolia Autonomous Region.