The mission is the follow-up to Chang'e 3, the first Chinese landing on the Moon. The spacecraft was originally built as a backup for Chang'e 3 and became available after Chang'e 3 landed successfully in 2013. The configuration of Chang'e 4 was adjusted to meet new scientific objectives. Like its predecessors, the mission is named after Chang'e, the Chinese Moon goddess.
The Chinese Lunar Exploration Program is designed to be conducted in three phases of incremental technological advancement: the first is to reach lunar orbit, a task completed by Chang'e 1 in 2007 and Chang'e 2 in 2010; the second is to land and rove on the Moon, as Chang'e 3 did in 2013 and Chang'e 4 did in January 2019; the third is to collect lunar samples from the near-side and send them to Earth, a task for the future Chang'e 5 and Chang'e 6 missions. The program aims to facilitate a crewed lunar landing in the 2030s and possibly build an outpost near the south pole. The Chinese Lunar Exploration Program has started to incorporate private investment from individuals and enterprises for the first time, a move aimed at accelerating aerospace innovation, cutting production costs, and promoting military–civilian relationships.
The Chang'e 4 mission was first scheduled for launch in 2015 as part of the second phase of the Chinese Lunar Exploration Program. But the adjusted objectives and design of the mission imposed delays, and finally launched on 7 December 2018, 18:23 UTC. The spacecraft entered lunar orbit on 12 December 2018, 08:45 UTC. The orbit's perilune was lowered to 15 km (9.3 mi) on 30 December 2018, 00:55 UTC. Landing took place on 3 January 2019 at 02:26 UTC, shortly after lunar sunrise over the crater Von Kármán.
This mission will attempt to determine the age and composition of an unexplored region of the Moon, as well as develop technologies required for the later stages of the program.
An ancient collision event on the Moon left behind a very large crater, called the Aitken Basin, that is now about 13 km (8.1 mi) deep, and it is thought that the massive impactor likely exposed the deep lunar crust, and probably the mantle materials. If Chang'e 4 can find and study some of this material, it would get an unprecedented view into the Moon's internal structure and origins. The specific scientific objectives are:
The spacecraft took 24 days to reach L2, using a lunar swing-by to save fuel. On 14 June 2018, Queqiao finished its final adjustment burn and entered the L2 halo mission orbit, which is about 65,000 kilometres (40,000 mi) from the Moon. This is the first lunar relay satellite at this location.
As part of the Chang'e 4 mission, two microsatellites (45 kg or 99 lb each) named Longjiang-1 and Longjiang-2 (Chinese: 龙江; pinyin: Lóng Jiāng; literally: "Dragon River"), were launched along with Queqiao in May 2018. However, Longjiang-1 failed to enter lunar orbit, while Longjiang-2 succeeded and is currently operational in lunar orbit. These microsatellites were tasked to observe the sky at very low frequencies (1–30 MegaHertz), corresponding to wavelengths of 300 to 10 metres (984 to 33 ft), with the aim of studying energetic phenomena from celestial sources. Due to the Earth's ionosphere, no observations in this frequency range have been done in Earth orbit, offering potential breakthrough science.
Chang'e lander and Yutu-2 rover
Yutu-2 roving on the lunar surface photographed by Chang'e 4
As is the case with many of China's space missions, the details of the spacecraft and the mission have been limited. What is known is that much of the Chang'e 4 lander and rover design is modeled after Chang'e-3 and its Yutu rover. In fact, Chang'e 4 was built as a backup to Chang'e 3, and based on the experience and results from that mission, Chang'e 4 was adapted to the specifics of the new mission. The lander and rover were launched on 7 December 2018, 18:23 UTC, six months after the launch of the Queqiao relay satellite.
The total landing mass is 1,200 kg (2,600 lb). Both the stationary lander and Yutu-2 rover are equipped with a radioisotope heater unit (RHU) in order to heat their subsystems during the long lunar nights, while electrical power is generated by solar panels. After landing, the lander extended a ramp to deploy the Yutu-2 rover (literally: "Jade Rabbit") to the lunar surface. The rover measures 1.5 × 1.0 × 1.0 m (4.9 × 3.3 × 3.3 ft) and has a mass of 140 kg (310 lb).Yutu-2 rover was fabricated at Dongguan, Guangdong province; it is solar-powered, RHU-heated, and it is propelled by six wheels. The rover's nominal operating time is three months, but after the experience with Yutu rover in 2013, the rover design was improved and Chinese engineers are hopeful it will operate for "a few years."
The communications relay satellite, orbiting microsatellite, lander and rover each carry scientific payloads. The relay satellite is performing radio astronomy, whereas the lander and Yutu-2 rover will study the geophysics of the landing zone. The science payloads are, in part, supplied by international partners in Sweden, Germany, the Netherlands, and Saudi Arabia.
The primary function of the Queqiao relay satellite that is deployed in a halo orbit around the Earth–Moon L2 point is to provide continuous relay communications between Earth and the lander on the far side of the Moon.
Additionally, this satellite hosts the Netherlands-China Low-Frequency Explorer (NCLE), an instrument performing astrophysical studies in the unexplored radio regime of 80 kilohertz to 80 megahertz. It was developed by the Radboud University in Netherlands and the Chinese Academy of Sciences. The NCLE on the orbiter and the LFS on the lander will work in synergy performing low-frequency (0.1 MHz–80 MHz) radio astronomical observations.
The lander and rover carry scientific payloads to study the geophysics of the landing zone, with a modest chemical analysis capability. The lander is equipped with the following payloads:
Landing Camera (LCAM), mounted on the bottom of the spacecraft, the camera began to produce a video stream at the height of 12 km (7.5 mi) above the lunar surface.
Terrain Camera (TCAM), mounted on top of the lander and able to rotate 360°, is being used to image the lunar surface and the rover in high definition.
Low Frequency Spectrometer (LFS) to research solar radio bursts at frequencies between 0.1–40 MHz and to study the lunar ionosphere.
Lunar Lander Neutrons and Dosimetry (LND), a neutron dosimeter developed by Kiel University in Germany. It will gather radiation dosimetry for future human exploration of the Moon, and will contribute to solar wind studies.
Lunar Micro Ecosystem, is a 3 kg (6.6 lb) sealed biosphere cylinder 18 cm (7.1 in) long and 16 cm (6.3 in) in diameter with seeds and insect eggs to test whether plants and insects could hatch and grow together in synergy. The experiment includes six types of organisms: cottonseed, potato, rapeseed, Arabidopsis thaliana (a flowering plant), as well as yeast and fruit fly eggs. Environmental systems keep the container hospitable and Earth-like, except for the low lunar gravity and radiation. If the fly eggs hatch, the larvae would produce carbon dioxide, while the germinated plants would release oxygen through photosynthesis. It was hoped that together, the plants and fruit flies could establish a simple synergy within the container. Yeast would play a role in regulating carbon dioxide and oxygen, as well as decomposing processed waste from the flies and the dead plants to create an additional food source for the insects. The biological experiment was designed by 28 Chinese universities. Research in such closed ecological systems informs astrobiology and the development of biological life support systems for long duration missions in space stations or space habitats for eventual space farming.
Result: Within a few hours after landing on 3 January 2019, the biosphere's temperature was adjusted to 24°C and the seeds were watered. On January 15, 2019, it was reported that cottonseed, rapeseed and potato seeds had sprouted, but images of only cottonseed were released. However, on January 16, it was reported that the experiment was terminated due to an external temperature drop to −52 °C (−62 °F) as the lunar night set in, and a failure to warm the biosphere close to 24°C. The experiment was terminated after nine days instead of the planned 100 days, but valuable information was obtained.
Panoramic Camera (PCAM), is installed on the rover's mast and can rotate 360°. It has a spectral range of 420 nm–700 nm and it acquires 3D images by binocular stereovision.
Lunar penetrating radar (LPR), is a ground penetrating radar with a probing depth of approximately 30 m with 30 cm vertical resolution, and more than 100 m with 10 m vertical resolution.
Visible and Near-Infrared Imaging Spectrometer (VNIS), for imaging spectroscopy that can then be used for identification of surface materials and atmospheric trace gases. The spectral range covers visible to near-infrared wavelengths (450 nm - 950 nm).
Launches are separated by dashes ( – ), payloads by dots ( · ), multiple names for the same satellite by slashes ( / ). CubeSats are smaller. Manned flights are bolded. Launch failures are in italics. Payloads deployed from other spacecraft are (enclosed in brackets).
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