Emily LakdawallaMar 03, 2014

Brief Yutu update: Slightly more detail on what's keeping rover from roving

Over the weekend, Chinese state news agency Xinhua reported in both Chinese and English a little bit more information on what has stilled the Yutu rover's motions across the lunar surface:

China's Yutu (Jade Rabbit) moon rover suffered a control circuit malfunction in its driving unit, which troubled its dormancy in extremely low temperature, a scientist said on Saturday.

The control circuit problem prevented Yutu from entering the second dormancy as planned, Ye Peijian, chief scientist of the Chang'e-3 program, told Xinhua in an exclusive interview.

"Normal dormancy needs Yutu to fold its mast and solar panels," said Ye. "The driving unit malfunction prevented Yutu to do those actions."

Ye, a member of the National Committee of the Chinese People's Political Consultative Conference, the country's top political advisory body, added, "This means Yutu had to go through the lunar night in extremely low temperatures."

Yutu, named after the pet rabbit of the lunar goddess Chang'e in Chinese mythology, touched down on the moon's surface on Dec. 15, a few hours after lunar probe Chang'e-3 landed.

The rover was designed to roam the lunar surface for at least three months to survey the moon's geological structure and surface substances and look for natural resources.

But problems emerged before the rover entered its second dormancy on the moon on Jan. 25 as the lunar night fell. Experts had feared that it might never function again, but it "woke up" on Feb. 12, two days behind schedule.

At present every piece of equipment of Yutu, which is undergoing another dormancy, is getting back to normal, the state of the rover is not encouraging, Ye said.

"We all wish it would be able to wake up again," said Ye ahead of the annual session of the top advisory body, which is scheduled to open on Monday.

From what we know about the situation, it sounds like this "driving unit," which has had a "control circuit malfunction," operates both the rover's wheels and the motors that drive the motions of its solar panels. I would assume (but have no specific evidence) that it also drives the motor that would be used to fold the mast into the rover body, an action it is supposed to take in order to prepare for the lunar night. Clearly the mast is still in its vertical position, because the rover is able to take photos pointed at the lander.

One thing that does confuse me about all this is: the rover's high-gain antenna is also on the mast, pointed in the same direction as the cameras, and if the rover is southwest of the lander and looking northeast at the lander, then the high-gain antenna is not pointed at Earth (which would be in the southern part of the sky for Yutu). So how is it communicating with Earth? Is a low-gain antenna sufficient?

Yutu survived one lunar night; will she survive another? If she does, will her controllers manage to solve the motor control problems? It doesn't look good.

Postscript: China always seems to issue statements about Chang'e on Saturday, and I'm really trying not to work weekends, so it's always two days old by the time I get to blogging it. It's a consistent enough pattern to be intentional. Anybody got any ideas why China would prefer to issue these updates on Saturdays? Is that a good day for science news in China?

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