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Chang'e 4

Coordinates:45°26′38″S177°35′56″E/ 45.444°S 177.599°E/-45.444; 177.599
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Chang'e 4
Top:Chang'e 4 lander on the surface of the Moon
Bottom:Yutu-2rover on lunar surface.
Mission typeLander,lunar rover
OperatorCNSA
COSPAR ID2018-103AEdit this at Wikidata
SATCATno.43845
Mission durationLander: 12 months (planned)
5 years, 6 months, 13 days(in progress)
Rover: 3 months (planned)[1]
5 years, 6 months, 13 days(in progress)
Spacecraft properties
Launch massTotal: 3,780 kg
Lander: 3,640 kg[2]
Rover: 140 kg[2]
Landing massTotal: ~1,200 kg; rover: 140 kg
DimensionsRover: 1.5 × 1.0 × 1.0 m[3]
Start of mission
Launch date7 December 2018, 18:23UTC[4]
RocketLong March 3B[5]
Launch siteXichang Satellite Launch Center,LA-2
Lunarlander
Landing date3 January 2019, 02:26 UTC[6]
Landing siteSpatio Tianhe[7]withinVon Kármán crater[8]in theSouth Pole-Aitken Basin[9]
45°26′38″S177°35′56″E/ 45.444°S 177.599°E/-45.444; 177.599
Lunarrover
Landing date3 January 2019, 02:26 UTC[10]
Landing siteSpatio Tianhe[7]withinVon Kármán crater[8]in theSouth Pole-Aitken Basin[9]
Distance driven1.596 km (0.992 mi)
as of 4 May 2024[11]
Chang'e probes

Chang'e 4(/ɑːŋˈə/;Chinese:Thường Nga số 4;pinyin:Cháng'é Sìhào;lit.'Chang'eNo. 4') is a robotic spacecraft mission in theChinese Lunar Exploration Programof theCNSA.China achieved humanity's firstsoft landingon thefar side of the Moonwith its touchdown on 3 January 2019.[12][13]

Acommunication relay satellite,Queqiao,was first launched to ahalo orbitnear the Earth–MoonL2pointin May 2018. The roboticlanderandYutu-2(Chinese:Thỏ ngọc số 2;pinyin:Yùtù Èrhào;lit.'Jade RabbitNo. 2')rover[14]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 toChang'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.[15]Like its predecessors, the mission is named afterChang'e,the ChineseMoon goddess.

In November 2019, Chang'e 4 mission team was awarded Gold Medal by theRoyal Aeronautical Society.[16]In October 2020, the mission was awarded theWorld Space Awardby theInternational Astronautical Federation.[17]Both were the first time for any Chinese mission to receive such awards.

Overview[edit]

Chang'e 4 landing zone location on thefar sideof theMoon,which is not visible from Earth due totidal locking.

TheChinese Lunar Exploration Programis designed to be conducted in four[18]phases of incremental technological advancement: The first is simply reaching lunar orbit, a task completed by Chang'e 1 in 2007 andChang'e 2in 2010. The second is landing and roving on the Moon, asChang'e 3did 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 taskChang'e 5completed in 2020, andChang'e 6that completed in 2024. The fourth phase consists of development of a robotic research station near the Moon's south pole.[18][19][20]

The program aims to facilitate a crewed lunar landing in the 2030s and possibly the building of an outpost near the south pole.[21][22]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.[23]

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.[24]

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-2rover was deployed about 12 hours after the landing.

Launch[edit]

The Chang'e 4 mission was first scheduled for launch in 2015 as part of the second phase of the Chinese Lunar Exploration Program.[25][26]But the adjusted objectives and design of the mission imposed delays, and finally launched on 7 December 2018, 18:23UTC.[4][27]

Selenocentric phase[edit]

The spacecraft entered lunar orbit on 12 December 2018, 08:45 UTC.[28]The orbit'sperilunewas lowered to 15 km (9.3 mi) on 30 December 2018, 00:55 UTC.[29]

Landing took place on 3 January 2019 at 02:26 UTC,[13]shortly after lunar sunrise over theVon Kármán craterin the largeSouth Pole-Aitken basin.[30]

Objectives[edit]

An ancient collision event on the Moon left behind a very large crater, called theAitken Basin,that is now about 13 km (8.1 mi) deep, and it is thought that the massive impactor likely exposed the deep lunarcrust,and probably themantlematerials. 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.[1]The specific scientific objectives are:[31]

  • Measure the chemical compositions oflunar rocksandsoils
  • Measure lunar surface temperature over the duration of the mission.
  • Carry out low-frequency radio astronomical observation and research using aradio telescope
  • Study ofcosmic rays
  • Observe thesolar corona,investigate its radiation characteristics and mechanism, and explore the evolution and transport ofcoronal mass ejections(CME) between the Sun and Earth.

Components[edit]

Queqiaorelay satellite[edit]

Communication with Chang'e 4 on the Moon's far side
Earth-Moon Lagrangian points: A satellite in ahalo orbitaround L2,which is behind the Moon, will have a view of both the Earth and the Moon's far side

Direct communication with Earth is impossible on thefar side of the Moon,since transmissions are blocked by the Moon. Communications must go through acommunications 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, theChina National Space Administration(CNSA) launched theQueqiao(Chinese:Cầu Hỉ Thước;pinyin:Quèqiáo;lit.'Magpie Bridge') relay satellite on 20 May 2018 to ahalo orbitaround the Earth–MoonL2point.[32][33][34]The relay satellite is based on theChang'e 2design,[35]has a mass of 425 kg (937 lb), and it uses a 4.2 m (14 ft) antenna to receiveX bandsignals from the lander and rover, and relay them to Earth control on theS band.[36]

The spacecraft took 24 days to reach L2,using a lunarswing-byto save fuel.[37]On 14 June 2018,Queqiaofinished its final adjustment burn and entered the L2halo mission orbit, which is about 65,000 kilometres (40,000 mi) from the Moon. This is the first lunar relay satellite at this location.[37]

The nameQueqiao( "Magpie Bridge" ) was inspired by and came from the Chinese taleThe Cowherd and the Weaver Girl.[32]

Long gian gmicrosatellites[edit]

As part of the Chang'e 4 mission, two microsatellites (45 kg or 99 lb each) namedLong gian g-1andLong gian g-2(Chinese:Long Giang;pinyin:Lóng Jiāng;lit.'Dragon River';[38]also known asDiscovering the Sky at Longest Wavelengths PathfinderorDSLWP[39]), were launched along withQueqiaoin May 2018. Both satellites were developed byHarbin Institute of Technology,China.[40]Long gian g-1failed to enter lunar orbit,[37]butLong gian g-2succeeded and operated in lunar orbit until 31 July 2019 when it was deliberately directed to crash onto the Moon.[41]

Long gian g 2's crash site is located at16°41′44″N159°31′01″E/ 16.6956°N 159.5170°E/16.6956; 159.5170(Long gian g-2 impact site)insideVan Gentcrater, where it made a 4 by 5 metre crater upon impact.[42] These microsatellites were tasked to observe the sky at very low frequencies (1–30megahertz), corresponding towavelengthsof 300 to 10 metres (984 to 33 ft), with the aim of studying energetic phenomena from celestial sources.[34][43][44]Due to the Earth'sionosphere,no observations in this frequency range have been done in Earth orbit,[44]offering potential breakthrough science.[24]

Chang'elander andYutu-2rover[edit]

Chang'e 4 lander and the ramp designed for theYutu-2rover deployment.

The Chang'e 4 lander and rover design was modeled after Chang'e-3 and itsYuturover.In fact, Chang'e 4 was built as a backup toChang'e 3,[45]and based on the experience and results from that mission, Chang'e 4 was adapted to the specifics of the new mission.[46]The lander and rover were launched byLong March 3Brocket on 7 December 2018, 18:23 UTC, six months after the launch of theQueqiaorelay satellite.[4]

The total landing mass is 1,200 kg (2,600 lb).[2]Both the stationary lander andYutu-2rover are equipped with aradioisotope heater unit(RHU) in order to heat their subsystems during the long lunar nights,[47]while electrical power is generated bysolar panels.

After landing, the lander extended a ramp to deploy theYutu-2rover (literally: "Jade Rabbit") to the lunar surface.[37]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).[2][3]Yutu-2rover was manufactured by theChina Academy of Space Technology;it is solar-powered, RHU-heated,[47]and it is propelled by six wheels. The rover's nominal operating time is three months,[1]but after the experience withYuturoverin 2013, the rover design was improved and Chinese engineers are hopeful it will operate for "a few years".[48]On November 21, 2019,Yutu 2broke the lunar longevity record, of 322 Earth days, previously held by the Soviet Union'sLunokhod 1rover (Nov. 17, 1970 to Oct. 4, 1971).[49]

Science payloads[edit]

The communications relay satellite, orbiting microsatellite, lander and rover each carry scientific payloads. The relay satellite is performingradio astronomy,[50]whereas the lander andYutu-2rover will study thegeophysicsof the landing zone.[8][51]The science payloads are, in part, supplied by international partners in Sweden, Germany, the Netherlands, and Saudi Arabia.[52]

Relay satellite[edit]

The primary function of theQueqiao relay satellitethat is deployed in ahalo orbitaround theEarth–Moon L2pointis to provide continuous relay communications between Earth and the lander on the far side of the Moon.[34][50]

TheQueqiaolaunched 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,Queqiaoapproached the vicinity of the L2.After several small adjustments,Queqiaoarrived at L2halo orbiton 14 June.[53][54]

Additionally, this satellite hosts theNetherlands–China Low-Frequency Explorer(NCLE), an instrument performingastrophysical studiesin the unexplored radio regime of 80 kilohertz to 80 megahertz.[55][56]It was developed by theRadboud Universityin Netherlands and theChinese 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.[43]

Lunar lander[edit]

The lander and rover carry scientific payloads to study the geophysics of the landing zone, with alife scienceand modest chemical analysis capability.[8][51][43]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)[43]to researchsolar radio burstsat frequencies between 0.1 and 40 MHz and to study the lunar ionosphere.
  • Lunar Lander Neutrons and Dosimetry (LND), a (neutron) dosimeter developed byKiel Universityin Germany.[57]It is gathering information about radiation dosimetry for future human exploration of the Moon, and will contribute tosolar windstudies.[58][59]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.[60][61]
  • Lunar Micro Ecosystem,[62]is a 3 kg (6.6 lb) sealedbiospherecylinder 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.[55]The experiment includes six types of organisms:[63][64]cottonseed,potato,rapeseed,Arabidopsis thaliana(a flowering plant), as well as yeast andfruit fly[65]eggs. Environmental systems keep the container hospitable and Earth-like, except for the low lunar gravity and radiation.[66]If the fly eggs hatch, the larvae would produce carbon dioxide, while the germinated plants would releaseoxygenthroughphotosynthesis.It was hoped that together, the plants and fruit flies could establish a simple synergy within the container.[citation needed]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.[63]The biological experiment was designed by 28 Chinese universities.[67]Research in suchclosed ecological systemsinformsastrobiologyand the development of biologicallife support systemsfor long duration missions inspace stationsorspace habitatsfor eventualspace farming.[68][69][70]
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 15 January 2019, it was reported that cottonseed, rapeseed and potato seeds had sprouted, but images of only cottonseed were released.[63]However, on 16 January, 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.[71]The experiment was terminated after nine days instead of the planned 100 days, but valuable information was obtained.[71][72]

Lunar rover[edit]

  • 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.[43]
  • Lunar penetrating radar (LPR), is aground penetrating radarwith a probing depth of approximately 30 m with 30 cm vertical resolution, and more than 100 m with 10 m vertical resolution.[43]
  • Visible and Near-Infrared Imaging Spectrometer (VNIS), forimaging spectroscopythat 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).
  • Advanced Small Analyzer for Neutrals (ASAN), is anenergetic neutral atomanalyzer provided by theSwedish Institute of Space Physics(IRF). It will reveal how solar wind interacts with the lunar surface, which may help determine the process behind the formation oflunar water.[57]

Cost[edit]

According to the deputy project director, who would not quote an exact amount, "The cost (of the entire mission) is close to building one kilometer ofsubway."[73]The cost-per-kilometre ofsubway in Chinavaries from 500 million yuan (about US$72 million) to 1.2 billion yuan (about US$172 million), based on the difficulty of construction.[73]

Landing site[edit]

The landing site is within a crater calledVon Kármán[8](180 km (110 mi) diameter) in theSouth Pole-Aitken Basinon thefar side of the Moonthat was still unexplored by landers.[9][74]The site has symbolic as well as scientific value.Theodore von Kármánwas the PhD advisor ofQian Xuesen,the founder of theChinese space program.[75]

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.[76]

TheYutu-2rover was deployed about 12 hours after the landing.[77]

Theselenographic coordinatesof the landing site are 177.5991°E, 45.4446°S, at an elevation of -5935 m.[78][79]The landing site was later (February 2019) namedStatio Tianhe.[7]Four other lunar features were also named during this mission: a mountain (Mons Tai) and three craters (Zhinyu,Hegu,andTianjin).[80]

Operations and results[edit]

A few days after landing,Yutu-2went 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 120 m (390 ft), and on 11 February 2019 it powered down for its second lunar night.[83][84]In May 2019, it was reported that Chang'e 4 has identified what appear to be mantle rocks on the surface, its primary objective.[85][86][87]

In January 2020, China released a large amount of data and high-resolution images from the mission lander and rover.[88]In February 2020, Chinese astronomers reported, for the first time, a high-resolution image of alunar ejecta sequence,and, as well, direct analysis of its internal architecture. These were based on observations made by theLunar Penetrating Radar(LPR) on board theYutu-2rover while studying thefar side of the Moon.[89][90]

International collaboration[edit]

Chang'e 4 marks the first major United States-China collaboration in space exploration since the2011 Congressional ban.Scientists from both countries had regular contact prior to the landing.[91]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'sLunar Reconnaissance Orbiter(LRO) was not in the right position for this during the landing.[92]The Americans informed Chinese scientists about its satellites in orbit around the Moon, while the Chinese shared with American scientists the longitude, latitude, and timing of Chang'e 4's landing.[93]

China has agreed to a request from NASA to use the Chang'e 4 probe and Queqiao relay satellite in future American Moon missions.[94]

International reactions[edit]

NASA AdministratorJim Bridenstinecongratulated China and hailed the success of the mission as "an impressive accomplishment".[95]

Martin Wieser of theSwedish Institute of Space Physicsand principal investigator on one of the instruments onboard Chang'e, said: "We know the far side from orbital images and satellites, but we don't know it from the surface. It's uncharted territory and that makes it very exciting."[96]

Gallery[edit]

The first panorama from the far side of the Moon by Chang'e 4 lander, with theYutu-2rover

See also[edit]

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