Yutu (rover)

The rover carried a ground-penetrating radar (GPR) on its underside, allowing for the first direct measurement of the structure and depth of the lunar soil down to a depth of 30 m (98 ft), and investigation of the lunar crust structure down to several hundred metres deep.[18]

The rover carried an alpha particle X-ray spectrometer (APXS)[22] and an infrared spectrometer, intended to analyze the chemical element composition of lunar samples. The APXS was the only payload on the robotic arm.[25]

There were two panoramic cameras and two navigation cameras on the rover's mast, which stands ~1.5 m (4.9 ft) above the lunar surface, as well as two hazard avoidance cameras installed on the lower front portion of the rover.[26] Each camera pair was used to capture stereoscopic images,[27] or for range imaging by triangulation.

The rover was successfully deployed from the lander and made contact with the lunar surface on 20:35 UTC, 14 December 2013.[33] On 17 December 2013, it was announced that all of the scientific instruments except the spectrometers were successfully activated, with both the lander and rover "functioning as hoped, despite the unexpectedly rigorous conditions of the lunar environment".[2] From 16 December 2013 to 20 December 2013, the rover remained immobile as its systems were partially powered down. Direct solar radiation raised the temperature on the exposed side of the rover to over 100 °C, while the shaded side simultaneously fell below 0 °C.[34]

By 22 December 2013, Yutu had completed its initial science mission: to photograph the lander from several different angles, following a roughly semi-circular route from north to south of the lander, while also being photographed and filmed at the same time by the lander. A number of these images have been released, including a stereoscopic view of the lander and videos of the rover in motion. The lander and rover then commenced their respective science missions.[27][35][36]

In addition to successfully deploying its robotic arm, Yutu completed diagnostic checks on 23 December 2013 to ensure that it was prepared for the upcoming lunar night, and moved about 40 metres south of the lander.[37] The lander also commenced diagnostics the following day. The lander first entered a low-power state at around 11:00 am, UTC+8 on 25 December 2013, later executed by the rover at 5:23 am on 26 December 2013 to conserve power as no sunlight will be received by the lander and rover's solar panels for 14 consecutive days. Both had to withstand the extreme cold of the two-week-long lunar nights.[23][38]

On 11 January 2014, following the lunar night, the rover exited sleep mode[10] and completed its first lunar soil inspection on 16 January 2014.[39] On 25 January 2014, near the end of the second lunar day, China's state media announced that the rover had undergone a "mechanical control abnormality", as caused by the "complicated lunar surface environment".[9] The Planetary Society reported that the rover was not responding to commands from Earth correctly, rendering it unable to "prepare for the oncoming night properly."[40][41][42][43] It later became evident that the rover suffered a control circuit malfunction in its driving unit, which prevented it from entering normal dormancy and folding its mast and solar panels.[44][45]

On 12 February 2014, Command Control listened for all transmissions from Yutu after enduring its second lunar night. Failure of communication attempts caused it to be declared permanently inoperative.[46] On 13 February, it unexpectedly re-established communication with Command Control.[47][48][49] China's lunar program spokesman Pei Zhaoyu declared that although Yutu was able to communicate, "it still suffers a mechanical control abnormality," rendering it immobile.[11]

The rover entered its third hibernation period on 22 February 2014 and continued to remain immobile, while serious technical difficulties persisted, further hampering science operations.[50] Chinese space scientists eventually ascertained that the control circuit had failed, and this prevented Yutu from entering normal dormancy as planned,[43][44] but stated that the GPR, panoramic and infrared imaging equipment were still functioning normally.[50][51]

While amateur observers were unable to detect transmissions from the lander, Chinese officials reported that the craft was still operating its UV Camera and Telescope as it entered its 14th lunar night on 14 January 2015.[52][53] On 18 April 2014, Wang Jianyu, deputy secretary general of the Chinese Society of Space Research stated that the failure was not mechanical, but electrical, and they were looking to bypass it. He also explained, "The temperature on the Moon is considerably lower than our previous estimation", adding that "certain components may be suffering from 'frostbite'".[54]

Yutu's solar panel alignment motors failed to respond, causing its solar panels to remain fully deployed as opposed to its planned insulating position to conserve heat as it entered low-power mode, exposing its internal electronics to the Moon's harsh outer environment. As Yutu progressed through consequent lunar nights, it lost certain capabilities,[55] but successfully exceeded its expected three-month operating life.[56] Yutu's scientific instruments may be functioning, but subsequent science data were very limited as the NIR spectrometer and the ground-penetrating radar were limited to the same observation as it was immobile. Mission Control planned to extend Yutu's mission until it ceased to communicate, as it would provide valuable data on its components' endurance to the lunar environment.[56]

The rover remained operational in December 2015 and continued to transmit data every lunar day.[57][58][59]

By the end of October 2015, Yutu had set the record for the longest operational period of a rover on the Moon, though most of its time was spent immobile.[60]

On 3 August 2016, it was reported that the rover had ceased to communicate with Chang'e 3 despite attempts to reestablish transmissions, effectively ending the mission.[61][62]