Chang'e 4

Chang'e 4 is a robotic spacecraft mission in the Chinese Lunar Exploration Program of the CNSA. It made a soft landing on the far side of the Moon, the first spacecraft to do so, on 3 January 2019.
A communication relay satellite, Queqiao relay satellite, was first launched to a halo orbit near the Earth–Moon L₂ point in May 2018. The robotic lander and Yutu-2 rover were launched on 7 December 2018 and entered lunar orbit on 12 December 2018, before landing on the Moon's far side. On 15 January it was announced that seeds had sprouted in the lunar lander's biological experiment, the first plants to sprout on the Moon. 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 and performance objectives. Like its predecessors, the mission is named after Chang'e, the Chinese Moon goddess.
In November 2019, the Chang'e 4 mission team was awarded a Gold Medal by the Royal Aeronautical Society. In October 2020, the team was awarded the World Space Award by the International Astronautical Federation. Both marked the first time that a Chinese mission had won their respective reward.

Overview

The Chinese Lunar Exploration Program is designed to be conducted in four phases of incremental technological advancement: The first is simply reaching lunar orbit, a task completed by Chang'e 1 in 2007 and Chang'e 2 in 2010. The second is landing and roving on the Moon, as Chang'e 3 did in 2013 and Chang'e 4 did in 2019. The third is collecting lunar samples from the near-side and sending them to Earth, a task Chang'e 5 completed in 2020, and Chang'e 6 that completed in 2024. The fourth phase consists of development of a robotic research station near the Moon's south pole.
The program aims to facilitate a crewed lunar landing in the 2030s and possibly the building of 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 militarycivilian relationships.
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.
The landing craft touched down at 02:26 UTC on 3 January 2019, becoming the first spacecraft to land on the far side of the Moon. Yutu-2 rover was deployed about 12 hours after the landing.

Launch

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.

Selenocentric phase

The spacecraft entered lunar orbit on 12 December 2018, 08:45 UTC. The orbit's perilune was lowered to on 30 December 2018, 00:55 UTC.
Landing took place on 3 January 2019 at 02:26 UTC, shortly after lunar sunrise over the Von Kármán crater in the large South Pole-Aitken basin.

Objectives

An ancient collision event on the Moon left behind a very large crater, called the Aitken Basin, that is now about 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:

Measure the chemical compositions of lunar rocks and soils
Measure lunar surface temperature over the duration of the mission.
Carry out low-frequency radio astronomical observation and research using a radio telescope
Study of cosmic rays
Observe the solar corona, investigate its radiation characteristics and mechanism, and explore the evolution and transport of coronal mass ejections between the Sun and Earth.
Components

''Queqiao'' relay satellite

Direct communication with Earth is impossible on the far side of the Moon, since transmissions are blocked by the Moon. Communications must go through a communications relay satellite, which is placed at a location that has a clear view of both the landing site and the Earth. As part of the Lunar Exploration Program, the China National Space Administration launched the Queqiao relay satellite on 20 May 2018 to a halo orbit around the Earth–Moon L₂ point. The relay satellite is based on the Chang'e 2 design, has a mass of, and it uses a antenna to receive X band signals from the lander and rover, and relay them to Earth control on the S band.
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 from the Moon. This is the first lunar relay satellite at this location.
The name Queqiao was inspired by and came from the Chinese tale The Cowherd and the Weaver Girl.

''Longjiang'' microsatellites

As part of the Chang'e 4 mission, two microsatellites named Longjiang-1 and Longjiang-2, were launched along with Queqiao in May 2018. Both satellites were developed by Harbin Institute of Technology, China. Longjiang-1 failed to enter lunar orbit, but Longjiang-2 succeeded and operated in lunar orbit until 31 July 2019 when it was deliberately directed to crash onto the Moon.
Longjiang 2's crash site is located at inside Van Gent crater, where it made a 4 by 5 metre crater upon impact.
These microsatellites were tasked to observe the sky at very low frequencies, corresponding to wavelengths of, 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

The Chang'e 4 lander and rover design was 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 by Long March 3B rocket on 7 December 2018, 18:23 UTC, six months after the launch of the Queqiao relay satellite.
The total landing mass is. Both the stationary lander and Yutu-2 rover are equipped with a radioisotope heater unit 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 to the lunar surface. The rover measures 1.5 × 1.0 × 1.0 m and has a mass of. Yutu-2 rover was manufactured by the China Academy of Space Technology; 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". On November 21, 2019, Yutu 2 broke the lunar longevity record, of 322 Earth days, previously held by the Soviet Union's Lunokhod 1 rover.

Science payloads

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.

Relay satellite

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.
The Queqiao launched on 21 May 2018. It used a lunar swing-by transfer orbit to reach the Moon. After the first trajectory correction maneuvers, the spacecraft is in place. On 25 May, Queqiao approached the vicinity of the L₂. After several small adjustments, Queqiao arrived at L₂ halo orbit on 14 June.
Additionally, this satellite hosts the Netherlands–China Low-Frequency Explorer, 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 work in synergy performing low-frequency radio astronomical observations.

Lunar lander

The lander and rover carry scientific payloads to study the geophysics of the landing zone, with a life science and modest chemical analysis capability. The lander is equipped with the following payloads:

Landing Camera, mounted on the bottom of the spacecraft, the camera began to produce a video stream at the height of above the lunar surface.
Terrain Camera, 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 to research solar radio bursts at frequencies between 0.1 and 40 MHz and to study the lunar ionosphere.
Lunar Lander Neutrons and Dosimetry, a dosimeter developed by Kiel University in Germany. It is gathering information about radiation dosimetry for future human exploration of the Moon, and will contribute to solar wind studies. It has shown that the radiation dose on the surface of the Moon is 2 to 3 times higher than what astronauts experience in the ISS.
Lunar Micro Ecosystem, is a sealed biosphere cylinder long and 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, 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.