Chang'e-3 to face five major difficulties

The Chang'e 3 lunar lander and moon rover is part of the second phase of China's three-step robotic lunar exploration program. [File photo]

The Chang'e 3 lunar probe will face five major difficulties during its moon landing mission, said Wu Weiren, chief designer of the Chinese lunar exploration project, the People's Daily reported.  [Special coverage]

Compared with its launch, perilunar braking and orbital transfer, the landing on the moon is far more crucial for the Chang'e 3 lunar exportation project. "It is completely new and [hence] is the most important test for us," said Wu.

Can it land on the specified Sinus Iridum?

Previously, Chang'e 1 and Chang'e 2 satellites had solved the technical problems of orbiting the moon. This time, Chang'e 3 lunar probe will solve the problem of whether it can land on the designated area after successfully orbiting the moon, Wu explained.

"This is just like driving a car on a highway. If you drive too slowly, you will lose time; if you drive too fast, you won't be able to stop the car immediately. Or miss the destination, or run into it, and won't complete its mission," said Wu, adding that a proper "braking" time and distance is key in the Chang'e 3 lunar exploration mission.

It's not easy to choose the final landing location

Scientists have chosen the Sinus Iridum, also known as the Bay of Rainbows, for the landing location of Chang'e 3. "The surface of the moon is macroscopically flat, but we're not very clear what its terrain is really like regionally. We don't know where the lunar probe will finally land," said Wu.

"Although we had taken a lot of measures, the risk is still big. There are numerous stones, rocks, craters and ditches on the moon, which the Chang'e 3 lunar probe will possibly encounter," Wu explained.

Lack of air friction can be used to slow down the landing

There's no air on the moon, which ensures that landing on the moon is completely different from doing so on earth. It is a soft landing in a vacuum state.

"No air means no air friction can be used to slow down the lunar probe, and a traditional rocket engine and propulsion system cannot complete this mission," said Sun Zezhou, chief designer of the Chang'e 3 lunar probe system.

Sun said that the newly developed 7500-type variable thrust engine is capable of continuously and precisely adjusting and controlling the landing speed. "But, as the new engine is used for the first time, a successful performance awaits further testing," said Sun.

Possibility of artificial intervention is almost zero

The landing process needs real-time measurements and adjustments of the lunar probe's speed and height. "The entire process must be completed within a very short period of time and it relies entirely on the lunar probe itself. Independent navigation control is very difficult," Sun said.

The 15-km landing process is described as the most "soul-stirring stage" by scientists. A series of crucial movements will be executed in this stage, including slowing down, designating the landing location and landing softly. The possibility of artificial intervention is almost zero at this point.

"No artificial intervention can keep up with it. We can do nothing but set the program in advance," said Tan Mei, vice general commander of the Chang'e 3 lunar probe system.

Dust may cling to the lunar probe and cause mechanical faults

Clouds of lunar dust may rise up during the Chang'e 3 landing. The dust clinging onto the surface of the lunar probe may cause decreased sensitivity of the optical system and cause for the mechanical structures to get stuck, Tan explained.

In addition, the huge impact energy from the surface of the moon and the plume from the lunar probe itself form the biggest threats to a safe soft landing. "Whether the Chang'e 3 buffer mechanism can stand the final test is still uncertain" said Tan.

Chang'e-3 lunar probe to land on the moon Saturday