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China successfully lands robotic rover on the moon
BY STEPHEN CLARK
ASTRONOMY NOW

Posted: December 14, 2013


A Chinese robotic rover landed on the moon Saturday, becoming China's first outpost on another world after a rocket-powered descent to an unexplored barren volcanic plain.


Chang'e 3 returned real-time imagery of the moon from an on-board descent camera. Credit: CCTV
 
The ambitious Chang'e 3 mission also achieved the first "soft landing" on the moon in 37 years, and it made China the third country to pull off the feat after the United States and Russia.

Touchdown occurred at about 1311 GMT (8:11 a.m. EST; 9:11 p.m. Beijing time). China said the lander was aiming for a landing in the Bay of Rainbows, a dark basin on the moon's near side filled with lava that congealed billions of years ago.

The Chang'e 3 lander dropped from a low-altitude orbit, using its variable-thrust main engine to reduce its velocity from orbital speeds of 1.7 kilometers per second, or about 3,800 mph, to nearly zero.

Chinese media reports said the lander was designed to halt its descent about 300 feet above the lunar surface to ensure the landing zone was clear of hazards such as boulders or steep slopes.

Once the probe's autonomous hazard detection system was satisfied the landing site was safe, Chang'e 3 resumed its descent before shutting off its engine about 10 or 15 feet above the moon. Chinese officials said they designed the craft's landing sets with impact suppressors similar to shock absorbers.

Laser and radar ranging sensors supplied altitude and terrain data to Chang'e 3's computer, giving the lander navigation cues during the final descent.

Such on-board smarts have never been used on an unmanned lander before.

Chinese state television broadcast the landing live, showing animation and real-time imagery from Chang'e 3's camera.

Engineers at the Beijing Aerospace Command and Control Center, who appeared stoic and reserved before landing, erupted in applause and flashed smiles when the touchdown was announced.

A few minutes later, officials confirmed the 12-foot-diameter lander's solar panels deployed.


Artist's concept of the lander and rover on the lunar surface. Credit: Beijing Institute of Spacecraft System Engineering
 
A six-wheeled mobile rover was expected to detach from the lander later this weekend, perhaps as soon as a few hours after touchdown. Officials said the lander would first vent leftover propellant.

The rover will drive several miles around the landing site, surveying the dusty charcoal-colored landscape for several months.

China named the rover Yutu after soliciting suggestions from the public. Yutu translates as "Jade Rabbit" in English.

In Chinese mythology, Yutu is a rabbit who accompanies the goddess Chang'e to the moon.

Yutu will beam 3D imagery of the moon back to Earth and measure the composition of lunar soils and rocks.

The rover is also equipped with a ground-penetrating radar to survey the structures below the moon's surface.

"As the rover drives along the lunar surface, it will be as if it can cut and see 100 meters [328 feet] below," said Ouyang Ziyuan, a researcher at the China Academy of Sciences and senior advisor to China's lunar exploration program, in an interview with Chinese state television.

Ouyang said the rover will use nuclear batteries to keep warm during lunar nights. Temperatures dip as minus 292 degrees Fahrenheit (minus 180 degrees Celsius) during nights on the moon, exposing delicate electronics to cold conditions for two weeks.

Yutu is smaller than NASA's Curiosity rover currently exploring Mars. The Chinese lunar rover stands about 4.9 feet tall and has a mass of about 140 kilograms, or 308 pounds.

The lander and Yutu rover will snap photos of each other, and the mission's stationary lander will operate for up to a year doing its own investigations. The lander's instruments include an ultraviolet telescope to observe the Earth and other scientific targets.

It could take several days to pinpoint the probe's exact location on the moon.

An initial position estimate put the landing site at 44.12 degrees north latitude and 19.51 degrees west longitude. The estimate will be refined over the coming days.

Two European Space Agency tracking antennas were called up to receive signals from Chang'e 3 on Saturday. One of the European-owned ground stations in Australia tracked the lander throughout its descent, and another near Madrid was on standby to pick up a signal from Chang'e 3 a few hours after landing.

The New Norcia station near Perth received a strong signal from Chang'e 3 throughout its descent, according to an ESA official at the European Space Operations Center in Darmstadt, Germany.

Chang'e 3's ground team at the Beijing Aerospace Command and Control Center monitored the landing through China's own communications antennas, but ESA's ground stations were configured to provide navigation support.

Using quasars, bright beacons at the hearts of distant galaxies, ESA can attain precise position estimates for spacecraft flying through deep space. Chang'e 3 will be the first time the technique -- Delta-Differential One-Way Ranging, or delta-DOR -- has been used for a stationary probe on the surface of another celestial body.

In the delta-DOR technique, engineers compare the exact time a spacecraft's signals are received at two ground stations -- in Australia and Spain for the Chang'e 3 mission. The antennas simultaneously track a quasar, which have known locations, to correct for errors induced by radio signals passing through the Earth's atmosphere.

China's moon landing comes after the country launched two orbiters to the moon in 2007 and 2010.

One of the satellites, Chang'e 2, left the moon and became China's first interplanetary probe. Chang'e 2 flew by asteroid Toutatis in December 2012, returning the first close-up images of the potato-shaped object.

According to Ouyang, considered the father of the Chang'e lunar program, China will dispatch a robotic mission to the moon in a few years to return rock samples to Earth. The Chang'e 5 mission will launch in 2017, previous Chinese news reports said.

China has no public plans for a human mission to the moon, but scientists have said they are studying the possibility of manned expeditions in the future.

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