After Chang'e 3, another probe will help prepare for a 2017 mission to return Moon rocks to Earth
With Chang'e 3's lander now on the Moon, its 140-kg (310-lb.) rover deployed and instruments on both working well, China is looking ahead to a sample-return mission to Earth's natural satellite in 2017.
The next mission, Chang'e 4, will be similar to the current effort, using a backup spacecraft and rover, but it will be adapted to prove technologies for the sample-return mission, Chang'e 5, says Wu Zhijian, a spokesman for the State Administration of Science, Technology and Industry for National Defense. Wu gave no schedule for Chang'e 4, but last year it was slated for 2015.
In 2017, Chang'e 5 will be China's first space expedition to collect samples from the Moon and return them to Earth. Chang'e 6 is designed to do the same, following China's habit of planning a pair of missions for each stage of its lunar exploration program, in case of failure. Stage 2 of the program, to land and deploy a rover, has been executed. Chang'e 3 touched down at 1:11 p.m. GMT on Dec. 14 at the eastern-most edge of its target zone, just short of the Bay of Rainbows in a scientifically promising region of the Sea of Rains (Mare Imbrium). Paul Spudis, an experienced lunar scientist based at the Lunar and Planetary Institute in Houston, says the touchdown spot suggests the Chinese lander succeeded in a safe descent on its first orbit.
“My sense is, one, they landed where they wanted to and, two, they landed safely because that objective had been built into the plan,” Spudis says. “It's quite impressive. It's a real tribute to them, I think.”
The rover rolled off the lander about 7 hr. later. It is intended to examine the Moon's geological structure and surface material and look for natural resources for the next three months. The lander, unable to move, is to observe its surroundings and the Earth's plasmasphere for a year.
China's lunar exploration program began in 2007 with the launch of Chang'e 1, a spacecraft built on a DFH-3 satellite bus; it was finally crashed onto the Moon. Chang'e 2, a basically similar spacecraft built as a back-up, improved on its predecessor in 2010, when it was launched directly into a lunar transfer orbit. Among the tasks of that mission was surveying possible landing sites for Chang'e 3. That completed Stage 1, although Chang'e 2 is still operational, heading into deep space and now 60 million km (37 million mi.) from Earth.
No details are available on how Chang'e 4 will be adapted to lay groundwork for the third-phase sample-return missions, but Wu tells state news agency Xinhua: “The program's third phase will be more difficult because many breakthroughs must be made in key technologies, such as Moon surface takeoff, sampling encapsulation, rendezvous and docking in lunar orbit and high-speed Earth reentry, which are all new to China.”
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.www.news.cn)">
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.”www.news.cn)">
Based on the Chang'e 3 landing, Spudis says China probably has the technical capability to put a rover down on the surface in the rugged polar terrain within “a kilometer or so” of a preselected landing site. Site selection for the planned Chang'e 5 sample-return mission will be more difficult. “I could come up with a list of 20 sites where it would be nice to have samples,” he says.
An initial Chinese sample-return mission probably would land on the Moon's near side to avoid the complexity of a communications-relay satellite. Beyond that, Spudis says, the most interesting results would come from a fresh lava flow not far from where Chang'e 3 is operating, or from the floor of a fairly young crater such as Copernicus. Nailing down its age would help determine when volcanic activity on the Moon shut down.
Scientists backed byare forbidden by law from cooperating with China, a situation that conceivably could change now that the author of that law, Rep. Frank Wolf (R-Va.), has announced he will not seek reelection next year. has three orbital missions operating at the Moon and, even without direct cooperation, has attempted to use the Chinese landing as an opportunity to collect data. So far, though, the cupboard has been bare.
Program scientists used NASA's new Lunar Atmosphere and Dust Environment Explorer (Ladee), launched Sept. 7 on a nominal 100-day orbital mission at the Moon, to try to detect the effects of Chang'e 3's arrival and landing, but at least initially without results. Ladee did not pick up gases from the Chinese mission's deorbit burn, nor did its dust instrument collect any unusual readings after the landing.
NASA has said it would make any data it gathers as a result of the Chinese landing “available to the international scientific community.” So far, China has kept its detailed lunar findings to itself. With the lunar landing, and the grand tour as far as the Earth-Sun L-2 Lagrangian point conducted by Chang'e 2, Spudis says China can go anywhere in cislunar space. Application of the capability is dual-use, as Wolf has warned in his legislative attacks on the Chinese government.