Chang'e 4
Chang'e 4 is a robotic spacecraft mission, part of the second phase of the Chinese Lunar Exploration Program. It achieved humanity's first soft landing on the far side of the Moon, on 3 January 2019.
A communication relay satellite, #Queqiao, 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. 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.
, which is not visible from Earth due to tidal locking. The landing site in Von Kármán crater is at bottom center.
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 for the future Chang'e 5 and Chang'e 6 missions. 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 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 militarycivilian 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 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.
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.
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 to 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 is inspired 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. 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
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 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 in 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." In December 2019, Yutu 2 broke the lunar longevity record, 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 lunar swing-by transfer orbit to reach 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 0.1–40 MHz and to study the lunar ionosphere.
- Lunar Lander Neutrons and Dosimetry, 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 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.
Lunar rover
- Panoramic Camera, 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, 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, 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.
- Advanced Small Analyzer for Neutrals, is an energetic neutral atom analyzer provided by the Swedish Institute of Space Physics. It will reveal how solar wind interacts with the lunar surface, which may help determine the process behind the formation of lunar water.
Cost
Landing site
The landing site is within a crater called Von Kármán in the South Pole-Aitken Basin on the far side of the Moon that was still unexplored by landers. The site has symbolic as well as scientific value. Theodore von Kármán was the PhD advisor of Qian Xuesen, the founder of the Chinese space 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.
The Yutu-2 rover was deployed about 12 hours after the landing.
The selenographic coordinates of the landing site are 177.5991°E, 45.4446°S, at an elevation of -5935 m. The landing site was later named Statio Tianhe. Four other lunar features were also named during this mission: a mountain and three craters.
Operations and results
A few days after landing, Yutu-2 went into hibernation for its first lunar night and it resumed activities on 29 January 2019 with all instruments operating nominally. During its first full lunar day, the rover travelled, and on 11 February 2019 it powered down for its second lunar night. In May 2019, it was reported that Chang'e 4 has identified what appear to be mantle rocks on the surface, its primary objective. In January 2020, China released a large amount of data and high-resolution images from the mission lander and rover. In February 2020, Chinese astronomers reported, for the first time, a high-resolution image of a lunar ejecta sequence, and, as well, direct analysis of its internal architecture. These were based on observations made by the Lunar Penetrating Radar on board the Yutu-2 rover while studying the far side of the Moon.Cooperation with other countries
Chang'e 4 marks the first major US-China collaboration in space exploration since the 2011 Congressional ban. Scientists from both countries had regular contact prior to the landing. This included talks about observing plumes and particles lofted from the lunar surface by the probe's rocket exhaust during the landing to compare the results with theoretical predictions, but NASA's Lunar Reconnaissance Orbiter was not in the right position for this during the landing. The US also informed Chinese scientists about its satellites in orbit around the Moon, while China shared with the US scientists the longitude, latitude, and timing of Chang'e 4's landing.China has agreed to a request from NASA to use the Chang'e 4 probe and Queqiao relay satellite in future US Moon missions.