There is no global dipolar magnetic field on the Moon, rendering compasses and GPS systems useless. The lunar rover could easily lose its direction, said Liu Jilin, a professor with the Information and Communication Engineering Institute of Zhejiang University.

"The computers will analyze the images collected by the cameras, and calculate the solar altitudes to locate the rover's position," he said.

Data collected by the cameras will be processed and reconstructed into a relief map in the rover's "mind", and steer it away from obstacles.

Soil on the Moon also poses a challenge. "The Moon's surface is blanketed with a large quantity of fine particles, and some have static charge. The dust can be as thick as 5 to 6 meters. Dust can enter the rover or even cover the equipment, making it work less efficiently and less accurately," said Chen Zonghai, a professor of the University of Science and Technology of China.

The Moon's gravity is only one sixth that of the Earth's, which means the friction coefficient is low, and the lunar rover may slide easily, Chen said.

To find solutions to the problem, scientists experiment in a simulated lunar environment. The Moon's soil was simulated with materials such as volcanic ash. Scientists also simulated extremely high and low temperatures on the Moon, its gravity, terrain and other aspects of its environment.

To choose the best landing site, the satellite carrying the lunar rover will contain a "laser eye," a high-precision laser distance measuring instrument. The Chang'e 2 satellite will provide high-resolution photo images of the prospective landing area for the Chang'e 3.

As the Moon has no atmosphere, its surface temperature is determined by the amount of sunlight it receives. During the night or in shaded areas, temperatures can drop to as low as minus 150 or even minus 180 degrees centigrade. When the sun rises, it quickly heats the surface to more than 100 degrees centigrade. The rover must be able to endure temperature difference ranging from minus to plus 150 degrees centigrade.

Gasoline engines cannot be used to power the rover as there is no air on the Moon. "Usually, land rovers are powered by solar energy and by batteries," Zhou said. Solar panels on both sides of the rover capture solar energy during the day. At night, the panels fold up and cover the body of the rover to shield the equipment from extreme cold, and the vehicle will be powered by energy stored in its batteries.

One night on the Moon is equivalent to 14 days on the Earth, Zhou said. So for about two weeks, the rover will not be able to collect solar energy. In extremely cold, long nights, the rover will "hibernate," waking up at sunrise the next day and resuming working.

The lunar rover will carry lithium batteries or nuclear batteries which are small but powerful, Chen said. One of these batteries, measuring 18 cubic millimeters and weighing 160 grams, can store as much energy as a normal chemical battery weighing as much as an adult.

The lunar rover will also be the most intelligent robot ever made in China, said Ouyang. It can select its own routes, work with mechanical arms and send data back to the Earth.

The rover's "arms and legs" are highly intelligent and probe as the vehicle proceeds. The bottom of the rover carries radar equipment which can "see" several kilometers under the Moon's surface. It is also equipped with seven sets of apparatus, including an astronomical telescope which will enable the first astronomical observations made by a rover on the Moon. n