Chinese Lunar Exploration Program

The first phase entailed the launch of two lunar orbiters, and is now effectively complete.

• Chang'e 1, launched on 24 October 2007 aboard a Long March 3A rocket, scanned the entire Moon in unprecedented detail, generating a high definition 3D map that would provide a reference for future soft landings. The probe also mapped the abundance and distribution of various chemical elements on the lunar surface as part of an evaluation of potentially useful resources.
• Chang'e 2, launched on 1 October 2010 aboard a Long March 3C rocket, reached the Moon in under 5 days, compared to 12 days for Chang'e 1, and mapped the Moon in even greater detail. It then left lunar orbit and headed for the Earth–Sun L₂ Lagrangian point in order to test the TT&C network. Having done that it completed a flyby of asteroid 4179 Toutatis on 13 December 2012, before heading into deep space to further test the TT&C network.

The second phase is ongoing, and incorporates spacecraft capable of soft-landing on the Moon and deploying lunar rovers.

• Chang'e 3, launched on 2 December 2013 aboard a Long March 3B rocket, landed on the Moon on 14 December 2013. It carried with it a 140 kilograms (310 pounds) lunar rover named Yutu, which was designed to explore an area of 3 square kilometers (1.2 square miles) during a 3-month mission. It was also supposed to conduct ultra-violet observations of galaxies, active galactic nuclei, variable stars, binaries, novae, quasars, and blazars, as well as the structure and dynamics of the Earth's plasmasphere.
• Chang'e 4 was launched on 7 December 2018. Originally scheduled for 2015, was a back-up for Chang'e 3. However, as a result of the success of that mission, the configuration of Chang'e 4 was adjusted for the next mission.[9] It landed on 3 January 2019 on the South Pole-Aitken Basin, on the far side of the Moon, and deployed the Yutu-2 rover.[10]

The third phase included a lunar sample-return mission.

• Chang'e 5-T1 was launched on 23 October 2014. It was designed to test the lunar return spacecraft.
• Chang'e 5, was launched on 23 November 2020, landed near Mons Rümker on the moon on 1 December 2020, and returned to earth with 2 kilograms of lunar soil on 16 December 2020.[11]

Development of a robotic research station near the Moon's south pole.[8][12][13]

• Chang'e 6, expected to launch in 2023 or 2024,[14][15] will investigate the topography, composition and subsurface structure of the landing site, and it will return south polar samples to Earth.[15][16]
• Chang'e 7, expected to launch in 2023, is a lander that will explore the south pole for resources.[17][15][16] The mission will include an orbiter, a lander, a rover, and a mini-flying probe.[17][12]
• Chang'e 8, expected to launch in 2027, will verify the utilization and development of natural resources.[15][16] It may include a lander, a rover, and a flying detector,[12] as well as a 3D-printing experiment using in-situ resource utilization (ISRU) to test-build a structure,[8] It will also transport a small sealed ecosystem experiment.[12] It will test technology necessary to the construction of a lunar science base.[18]

As of 2019, China was reviewing preliminary studies for a crewed lunar landing mission in the 2030s,[19][20] and possibly build an outpost near the lunar south pole with international cooperation.[8][19]

The biggest challenge in Phase I of the program was the operation of the TT&C system, because its transmission capability needed sufficient range to communicate with the probes in lunar orbit.[21] China's standard satellite telemetry had a range of 80,000 kilometers (50,000 miles), but the distance between the Moon and the Earth can exceed 400,000 kilometers (250,000 miles) when the Moon is at apogee. In addition, the Chang'e probes had to carry out many attitude maneuvers during their flights to the Moon and during operations in lunar orbit. The distance across China from east to west is 5,000 kilometers (3,100 miles),[22] forming another challenge to TT&C continuity. At present, the combination of the TT&C system and the Chinese astronomical observation network has met the needs of the Chang'e program,[23] but only by a small margin.

The complexity of the space environment encountered during the Chang'e missions imposed strict requirements for environmental adaptability and reliability of the probes and their instruments. The high-radiation environment in Earth-Moon space required hardened electronics to prevent electromagnetic damage to spacecraft instruments. The extreme temperature range, from 130 degrees Celsius (266 degrees Fahrenheit) on the side of the spacecraft facing the Sun to −170 degrees Celsius (−274 degrees Fahrenheit) on the side facing away from the Sun, imposed strict requirements for temperature control in the design of the detectors.

Given the conditions of the three-body system of the Earth, Moon and a space probe, the orbit design of lunar orbiters is more complicated than that of Earth-orbiting satellites, which only deal with a two-body system. The Chang'e 1 and Chang'e 2 probes were first sent into highly elliptical Earth orbits. After separating from their launch vehicles, they entered an Earth-Moon transfer orbit through three accelerations in the phase-modulated orbit. These accelerations were conducted 16, 24, and 48 hours into the missions, during which several orbit adjustments and attitude maneuvers were carried out so as to ensure the probes' capture by lunar gravity. After operating in the Earth-Moon orbit for 4–5 days, each probe entered a lunar acquisition orbit. After entering their target orbits, conducting three braking maneuvers and experiencing three different orbit phases, Chang'e 1 and Chang'e 2 carried out their missions.

Lunar orbiters have to remain properly oriented with respect to the Earth, Moon and Sun. All onboard detectors must be kept facing the lunar surface in order to complete their scientific missions, communication antennas have to face the Earth in order to receive commands and transfer scientific data, and solar panels must be oriented toward the Sun in order to acquire power. During lunar orbit, the Earth, the Moon and the Sun also move, so attitude control is a complex three-vector control process. The Chang'e satellites need to adjust their attitude very carefully to maintain an optimal angle towards all three bodies.

During the second phase of the program, in which the spacecraft were required to soft-land on the lunar surface, it was necessary to devise a system of automatic hazard avoidance in order that the landers would not attempt to touch down on unsuitable terrain. Chang'e 3 utilized a computer vision system in which the data from a down-facing camera, as well as 2 ranging devices, were processed using specialized software. The software controlled the final stages of descent, adjusting the attitude of the spacecraft and the throttle of its main engine. The spacecraft hovered first at 100 meters (330 feet), then at 30 meters (98 feet), as it searched for a suitable spot to set down. The Yutu rover is also equipped with front-facing stereo cameras and hazard avoidance technology.