Spudis says the Chang'e 3 lander's 1,700-kg (3,750-lb.) payload capacity is greater than a rover needs, and the spacecraft should easily be able to land a sample-return mission.
Taking advantage of technological advances since the last Soviet lunar landings 37 years ago, the Chinese engineers fitted Chang'e 3 with a system for autonomously evaluating its touchdown location during descent. The descent began with the main braking phase at an altitude of 15 km in which, according to the published plan, velocity was to be reduced from 2,000 meters per sec. to, at 2.4 km altitude, 70 meters per sec. Following further braking, at an altitude of 100 meters (330 ft.) the lander was to hover for less than 30 sec. to survey the terrain before dropping to 30 meters while maneuvering to avoid obstacles. At 30 meters, the 1,690-lb.-variable-thrust engine was expected to kick up dust from the surface; the rate of descent was then to be reduced to 2 meters per sec. At 3 meters, the engine was to shut down for a free-fall to the surface.
The rover, with six wheels, will move at 200 meters per hr. It has three pairs of sensors for navigation, panoramic imaging and obstacle avoidance. With solar panels folded, it is 1.5 meters long, 1 meter wide and 1.1 meter high.
The probe encountered unexpectedly extreme temperature disparities on the Moon's surface. The figures were not revealed, but mission managers had expected -180C to 120C (-360F to 250F). By Dec. 18, six of the mission's eight scientific instruments were activated and operating properly. The lander and rover each have four scientific instruments and their own individual communications channels to Earth.
The chief designer of the China Lunar Exploration Program, Wu Weiren, says that from launch to the initiation of observations on the lunar surface, the mission has gone more smoothly than expected. None of the more than 200 contingency plans prepared in case of failure has been needed.
Rocks apparently avoided by the lander are of high scientific interest because the Mare Imbrium site is covered by relatively fresh, thin lava that scientists such as Spudis believe flowed in a “flood,” with the viscosity of room-temperature motor oil, from a vent more than 700 km (430 mi.) to the south. In that sort of terrain, the boulders are probably remains of bedrock, now lying near the surface, that was kicked up by a meteor impact.
Scientists use meteor craters to estimate the age of a particular lunar surface—younger surfaces have fewer craters—while the bedrock can hold clues to the landing area's volcanic history. Chang'e 3 landed on a young surface that may help answer the long-standing question of when volcanism on the Moon ended.
Yutu carries a ground-penetrating radar that will help Chinese scientists find out how far down bedrock lies, while its spectral-image and alpha-particle X-ray spectrometers determine the composition of the regolith along the ground track. For Chang'e 4, Spudis and other lunar scientists have some priorities for where it should land, even if they do not have input on the decision.
“The obvious place to go, in my opinion, where the big unknowns are, are the poles,” Spudis says. “The whole thing about polar ice is very interesting. It's an enabling asset [for future human exploration]; it's a big scientific unknown. They could configure a rover with a slightly different instrument configuration to really get some first-order information about the polar deposits.”