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, , 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.Notably, the rover was modified "to meet the demands of the far-side terrain, but also to avoid the fate of the robot's predecessor, which became immobilized after driving only 360 feet (110 meters)" 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 fourChang'e 4 press conference . CNSA, broadcast on 14 January 2019. 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.China's Planning for Deep Space Exploration and Lunar Exploration before 2030 . (PDF) XU Lin, ZOU Yongliao, JIA Yingzhuo. Space Sci., 2018, 38(5): 591-592. A Tentative Plan of China to Establish a Lunar Research Station in the Next Ten Years . Zou, Yongliao; Xu, Lin; Jia, Yingzhuo. 42nd COSPAR Scientific Assembly. Held 14–22 July 2018, in Pasadena, California, USA, Abstract id. B3.1-34-18.
The program aims to facilitate a crewed lunar landing in the 2030s and possibly the building of an outpost near the south pole.China lays out its ambitions to colonize the moon and build a "lunar palace" . Echo Huang, Quartz. 26 April 2018.China's moon mission to boldly go a step further . Stuart Clark, The Guardian 31 December 2017. 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.China's Moon Missions Are Anything But Pointless . Paul D. Spudis, Air & Space Smithsonian. 3 January 2017.
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.China launches historic mission to land on far side of the moon Stephen Clark, Spaceflight Now. 7 December 2018.
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:To the Far Side of the Moon: China's Lunar Science Goals . Leonard David, Space. 9 June 2016. 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 (CME) 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 (CNSA) 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,Future Chinese Lunar Missions: Chang'e 4 - Farside Lander and Rover . David R. Williams, NASA Goddard Space Flight Center. 7 December 2018. 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.Chang'e 4 relay satellite, Queqiao: A bridge between Earth and the mysterious lunar farside . Xu, Luyan, The Planetary Society. 19 May 2018. Retrieved on 20 May 2018
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 ("Magpie Bridge") 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 ( each) named Longjiang-1 and Longjiang-2 (;Radio Experiment Launches With China's Moon Orbiter . David Dickinson, Sky & Telescope. 21 May 2018. also known as Discovering the Sky at Longest Wavelengths Pathfinder or DSLWPChina Moon Mission: Lunar Microsatellite Problem? . Leonard David, Inside Outer Space. 27 May 2018.), 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 (1–30 megahertz), 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.Pioneering Chang'e-4 lunar far side landing mission to launch in December. Andrew Jones, Space News. 15 August 2018. 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 (RHU) in order to heat their subsystems during the long lunar nights,China Shoots for the Moon's Far Side . (PDF) IEEE.org. 2018. 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 . 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".China's Chang'e 4 spacecraft to try historic landing on far side of Moon 'between January 1 and 3' . South China Morning Post. 31 December 2018. 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 (November 17, 1970 to October 4, 1971).China's Farside Moon Rover Breaks Lunar Longevity Record. Leonard David, Space.com. 12 December 2019.
Science payloads The communications relay satellite, orbiting microsatellite, lander and rover each carry scientific payloads. The relay satellite is performing radio astronomy,Chang'e 4 Relay . Gunter Drunk Krebs, Gunter's Space Page. whereas the lander and Yutu-2 rover will study the geophysics of the landing zone.China's Journey to the Lunar Far Side: A Missed Opportunity? Paul D. Spudis, Air & Space Smithsonian. 14 June 2017.Plans for China's farside Chang'e 4 lander science mission taking shape . Emily Lakdawalla, The Planetary Society, 22 June 2016. 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 (TCMs), 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 (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 work in synergy performing low-frequency (0.1–80 MHz) 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 (LCAM), 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 (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 and 40 MHz and to study the lunar ionosphere.