Despite the fact that it hasn't moved for 6 months, the plucky Yutu rover on the Moon is still alive. Its signal is periodically detected by amateur radio astronomers, most recently on July 19. A story posted today by the Chinese state news agency offers a new hypothesis to explain the failure of the rover's mobility systems: too many rocks. I don't mean to be flippant; this story, like that of Curiosity's wheels, shows how hard it is to reliably predict the physical properties of a landing site even when you have very good orbital data. For Yutu, rocks of a size that could damage the rover turned out to be more abundant than predicted, and they're now guessing that collisions with rocks may have damaged the vehicle. Here's the relevant part of the article:
Ailing Chinese moon rover Yutu, or "Jade Rabbit," might have been damaged by knocking against rocks on a lunar surface that is more complicated than expected, its designer has said.
Yutu, China's first moon rover, drove onto the lunar surface on Dec. 15 last year during the Chang'e-3 lunar mission, but in January it suffered a "mechanical control abnormality" which has continued to trouble it ever since.
The rover was tested in Beijing, Shanghai and the desert in northwestern China before its launch, but the terrain of the landing site proved to be much more rugged than expected, said Zhang Yuhua, deputy chief designer of the lunar probe system for the Chang'e-3 mission. "It is almost like a gravel field."
Data from foreign researchers projected that there would be four stones, each above 20 cm, on average every 100 square meters, but the quantity and size of the stones that Yutu has encountered has far exceeded this expectation, Zhang said in an exclusive interview with Xinhua.
"Experts' initial judgement for the abnormality of Yutu was that the rover was 'wounded' by colliding with stones while moving," she said.
Despite the unexpectedly early failure of its ability to rove, Yutu has proved surprisingly resilient in other ways. The rover was only expected to last three months, but it has now survived eight intense lunar days, although its capabilities are degenerating with time. After last contact on July 19, rover and lander have just hibernated for the eighth lunar night; they should awaken on August 8. (Here is a handy PDF calendar guide to the days and nights on the Chang'e 3 mission, courtesy of the International Lunar Observatory Association.)
Amateur radio astronomers have detected the lander's signal less frequently than the rover's. But, according to a presentation made to the U.N. Committee on the Peaceful Uses of Outer Space last month, the lander continues to operate normally; as of last month it had returned 120 Gigabits (or maybe Gigabytes? it's unclear) of data to Earth.
The presentation included a pair of images that Yutu fans had not seen previously. The photo of the rover must have been taken on the first lunar day, when the lander camera still functioned; I identified a couple of craters in the background and located them on Phil Stooke's route map to determine the date of the photo to be December 21, 2013.
This photo was taken by the rover.
And here's another image I hadn't seen before, showing the large boulder pile they called Dragon Rock, which Yutu approached on January 14:
Meanwhile, preparations are underway for follow-on missions Chang'e 4 and 5, although it's not quite clear yet what the plans are for Chang'e 4. There is a spacecraft -- Chang'e 4 is a backup spacecraft to Chang'e 3. Chang'e 3's landing and the deployment of the rover was perfect, so it's not clear they need to fly Chang'e 4 in order to continue with their lunar program. If they did fly Chang'e 4, presumably they would want to modify the rover design in order to avoid the problems they had with Yutu. Chang'e 5 has always been planned as a robotic sample return mission.
But there's actually a different Chang'e in the works. China plans a Chang'e 5 precursor mission to test out the Chang'e 5 sample return module. According to discussion on NASAspaceflight.com, it consists of a spacecraft like Chang'e 2, topped with a Chang'e 5 return module, which will loop around the Moon once and return to Earth. Launch is rumored to be scheduled for late October. I'm curious what will happen to the Chang'e-2-like spacecraft after it's separated from the return capsule! Watch that thread on NASAspaceflight.com for more news. In the meantime, here's a photo of the Chang'e 5 return capsule.
And, just for fun, an artwork of Chang'e 5's sample return capsule recently posted to the China Space Facebook page.