Chang'e 3

Chang'e 3 was launched at 17:30 UTC on 1 December 2013 (01:30 local time on 2 December) atop a Long March 3B rocket flying from Launch Complex 2 at the Xichang Satellite Launch Centre in the southwestern province of Sichuan.[29]

Homes downrange of the Launch Centre were damaged during liftoff when spent hardware wreckage from the rocket, including one piece the size of a desk, fell on a village in Suining County in neighbouring Hunan province. The county authorities had moved 160,000 people to safety before the liftoff, while more than 20,000 people near the launch site in Sichuan had been moved to a primary school auditorium. The expected wreckage zone for Long March rockets is 50 to 70 kilometres (31 to 43 mi) long and 30 km (19 mi) wide.[29]

Chang'e 3 entered a 100 km (62 mi)-high circular lunar orbit on 6 December 2013, 9:53 UTC. The orbit was obtained after 361 seconds (6 minutes) of variable thrust engine braking from its single main engine.[30] Later, the spacecraft adopted a 15 km (9.3 mi) × 100 km (62 mi) elliptic orbit. The landing took place one week later, on 14 December. At periapsis, its variable thrusters were again fired in order to reduce its velocity, descending to 100 m (330 ft) above the Moon's surface. It hovered at this altitude, moving horizontally under its own guidance to avoid obstacles, before slowly descending to 4 m (13 ft) above the ground, at which point its engine was shut down for a free-fall onto the lunar surface. The landing sequence took about 12 minutes to complete.

Topographic data from the Chang'e 1 and 2 orbiters were used to select a landing site for Chang'e 3. The planned landing site was Sinus Iridum,[31] but the lander actually descended on Mare Imbrium, about 40 km (24.9 mi) south of the 6 km (3.7 mi) diameter crater Laplace F,[32][33] at 44.1214°N, 19.5116°W (2640 m elevation) (1.6 mi),[34] on 14 December 2013, 13:11 UTC.[9][26][35]

With a landing mass of 1,200 kg (2,600 lb), it also carried and deployed the 140 kg (310 lb) rover.[3] It serves double-duty as a technology demonstrator to be further refined for the planned 2019 Chang'e 5 sample-return mission.[36][37]

The stationary lander is equipped with a radioisotope heater unit (RHU) in order to heat its subsystems and power its operations, along with its solar panels, during its planned one-year mission. It has a scientific payload of seven instruments and cameras. In addition to their lunar scientific roles, the cameras will also acquire images of the Earth and other celestial bodies.[1] During the 14-day lunar nights, the lander and the rover go into 'sleep mode'.[25]

The lander is equipped with a 50 mm (2.0 in) Ritchey–Chrétien telescope that is being used to observe galaxies, active galactic nuclei, variable stars, binaries, novae, quasars and blazars in the near-UV band (245–340 nm), and is capable of detecting objects at a brightness as low as magnitude 13. The thin exosphere and slow rotation of the Moon allow extremely long, uninterrupted observations of a target. The LUT is the first long term lunar-based astronomical observatory, making continuous observations of important celestial bodies to study their light variation and better improve current models.[38][39][40]

The lander also carries an extreme ultraviolet (30.4 nm) camera,[41] which will be used to observe the Earth's plasmasphere in order to examine its structure and dynamics and to investigate how it is affected by solar activity.[28]

Three panoramic cameras are installed on the lander, facing different directions. The lander is equipped with a single descent camera that was tested on the Chang'e 2 spacecraft.[38]

The Chang'e 3 lander also carries an extensible soil probe.[38][42]

Boulders near Ziwei crater. Image captured by Yutu rover

The development of the six-wheeled rover began in 2002 at the Shanghai Aerospace System Engineering Institute and was completed in May 2010.[43][44] The rover has a total mass of approximately 140 kg (310 lb), with a payload capacity of approximately 20 kg (44 lb).[1][45] The rover may transmit video in real time, and can perform simple analysis of soil samples. It can navigate inclines and has automatic sensors to prevent it from colliding with other objects.

Energy was provided by 2 solar panels, allowing the rover to operate through lunar days, as well as charging its batteries. At night the rover was powered down to a large extent, and kept from getting too cold by the use of several radioisotope heater units (RHUs) using plutonium-238.[46] The RHUs provide only thermal energy and no electricity.

The rover was deployed from the lander, and made contact with the lunar surface on 14 December, 20:35 UTC.[47] On 17 December it was announced that all of the scientific tools apart from the spectrometers had been activated, and that both the lander and rover were "functioning as hoped, despite the unexpectedly rigorous conditions of the lunar environment".[3] However, from 16 to 20 December the rover did not move, having shut down its subsystems. Direct solar radiation had raised the temperature on the sunlit side of the rover to over 100 °C (212 °F), while the shaded side simultaneously fell below zero. Since then, the lander and rover finished taking pictures of each other and commenced their respective science missions.[48]

The rover was designed to explore an area of 3 square kilometres (1.2 sq mi) during its 3-month mission, with a maximum travelling distance of 10 km (6.2 mi).

The rover demonstrated its ability to endure its first lunar night when it was commanded out of sleep mode on 11 January 2014.[49] On 25 January 2014, China's state media announced the rover had undergone a "mechanical control abnormality" caused by the "complicated lunar surface environment".[50]

The rover established contact with mission control on 13 February 2014, but it was still suffering from a "mechanical abnormality".[51] The rover was still intermittently transmitting as late as 6 September 2014[52] It ceased to transmit data in March 2015.[53]

The rover carries 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 meters deep.[28]

The rover carries an alpha particle X-ray spectrometer[54] and an infrared spectrometer, intended to analyze the chemical element composition of lunar samples.

There are 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.[38] Each camera pair may be used to capture stereoscopic images,[55] or for range imaging by triangulation.