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Queqiao-2

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Queqiao 2
Rendering of Queqiao 2 satellite
Mission typeCommunication relay
Radio astronomy
OperatorCNSA
COSPAR ID2024-051AEdit this at Wikidata
SATCATno.59274
Mission durationPlanned: 8-10 years
3 months, 26 days(in progress)
Spacecraft properties
BusCAST-2000[1]
ManufacturerDFH Satellite Company LTD
Dry mass1,200 kilograms (2,600 lb)
DimensionsAntenna: 4.2 metres (14 ft) in diameter[1]
Power1350W[1]
Start of mission
Launch date20 March 2024, 00:31:28UTC[2]
RocketLong March 8[2]
Launch siteWenchang LC-201[2]
Orbital parameters
Reference systemSelenocentricfrozen orbit
Periselene altitude200 km (120 mi)[3]
Aposelene altitude16,000 km (9,900 mi)[3]
Inclination62.4°[4]
Period24 hours[3]
Lunarorbiter
Orbital insertion24 March 2024, 17:05UTC[5]
Instruments
  • Grid-based Energetic Neutral Atom imager (GENA)
  • ExtremeUltravioletCamera (EUC)
  • Lunar OrbitVLBIEXperiment (LOVEX)
Queqiao satellites

Queqiao-2relay satellite(Chinese:Cầu Hỉ Thước số 2 trung kế vệ tinh;pinyin:Quèqiáo èr hào zhōngjì wèixīng;lit.'Magpie Bridge2 relay satellite'), is the second communications relay and radio astronomy satellites designed to support the fourth phase theChinese Lunar Exploration Program,[6][7][8]afterQueqiao-1launched in 2018. TheChina National Space Administration(CNSA) launched the Queqiao-2 relay satellite on 20 March 2024 to an ellipticalfrozen orbitaround the Moon to support communications from thefar side of the Moonand theLunar south pole.[9][10][11][12]

The nameQueqiao(ch'wuh-ch'yow,"Magpie Bridge" ) was inspired by and came from the Chinese taleThe Cowherd and the Weaver Girl.[9][8][13]

Background and mission planning[edit]

The initial phase of theInternational Lunar Research Station(ILRS), consisting of theChang'e 7andChang'e 8probes, was scheduled to be built in 2026 and 2028 on the southern edge of theSouth Pole–Aitken basinlocated on thefar side of the Moon.[14]While theQueqiaoso far only had to connect with two probes on the far side of the Moon (Chang'e 4lander andYutu-2rover), future mission would include more workload, with up to ten robots being active on the moon for the ILRS project, which requires a complex and sophisticated communication network.[15]

TheQueqiao relay satellitewas inserted in ahalo orbitaround theEarth-Moon L2since 2018. China planned another relay satellite, calledQueqiao 2,to support and supplement Queqiao-1.[12][15]Originally, the idea was to design the relay satellite as an improved version of the Queqiao and launch it together with theChang'e 7probe. After a project revision,[16]theCenter for Lunar Exploration and Space Projectsat theCNSAdecided to launch it separately.[17]This allowed the building of a larger variant of the relay satellite that could be launched earlier and used in theChang'e 6sample return missionthat was also launched in 2024 to theApollo crateron thefar side of the Moon.[15]

Although the first Queqiao can provide the unique function of relaying constant communications to and from the far side of the Moon, aided byChinese Deep Space Network,its halo orbits around theEarth-Moon L1and L2were inherentlyunstable[18]and requires the satellite to consumes 80 g (2.8 oz) of fuel for asmall orbit correction maneuverapproximately every 9 days. Therefore, a frozenelliptic orbitaround the Moon itself was chosen for Queqiao 2 due to its more stable nature. The frozen elliptic orbit can provide visual contact with the Moon for eight hours, i.e., two-thirds of its 12-hour orbit, since the point of itsperiselenelies above the side of the southern polar region facing away from the Earth.[19]

When Queqiao-2 reaches a position about 200 km from the lunar surface, it will perform capture braking and enter a lunarparking orbitof 200 × 100,000 km with a period of about 10 days. Eventually, Queqiao-2 will enter a large ellipticalfrozen orbitof 200 × 16,000 km with a period of 24 hours, which is inclined at 62.4° to the equator, no further orbit correction maneuvers are necessary for a period of a good 10 years, i.e., in principle the assumed lifespan of the satellite.[3]

Design[edit]

Orbital regime of Queqiao-2 satellite

Queqiao 2 relay satellite and radio observatory is based on the CAST 2000 bus fromDFH Satellite,a subsidiary of theChinese Academy of Space Technology.[20]It carries a total of 488 kg (1,076 lb) of hydrazine and oxidizer in tanks with a total capacity of 606 L (133 imp gal; 160 US gal), giving it a take-off weight of around 1,200 kg (2,600 lb). The three-axis stabilized satellite has eight engines with a thrust of 20Neach for orbit correction maneuvers as well as eight engines with a thrust of 5Neach and four engines with a thrust of 1Neach for attitude control; it can be aligned with an accuracy of 0.03° (three times as good as the standard version of thesatellite bus). Two rotatablesolar cellwings, each with twosolar arrays,deliver a total output of 1350 W, the operatingvoltageis 30.5 V. During blackoutor eclipse period, it hasaccumulatorswith a charge storage capacity of 135Ah.The manufacturing company assumes that Queqiao 2 will work properly for at least 8 to 10 years.[21][22]

Adopted from the first Queqiao, aparabolic antennawith a diameter of 4.2 m and anantenna gainof 44dBiis permanently mounted on the top of the bus- the alignment is carried out via the satellite'sattitude control- and is used for radio communication with the lunar surface.[6]In order to be able to accommodate the satellite in thepayload fairingof thelaunch vehicle,the segments of thereflectorare folded together during launch. After separating from theupper stageof the rocket and unfolding the solar modules, the antenna is also unfolded at the beginning of thetransfer orbitto the Moon.[9][23][24][21][25][1]

Communication with the lunar surface is accomplished in theX band,using a high-gain 4.2 metres (14 ft) deployable parabolic antenna, the largest antenna used for adeep space explorationsatellite.[26]

The largeparabolic antennaprovides 10 simultaneously usableX-bandchannels forradio trafficdown to the Moon and 10 channels for traffic up to the satellite, as well as the possibility of communicating in the decimeter wave range. In the opposite direction, telemetry and payload data from the robots can be transmitted upwards at a speed of 50kbit/swhen using an omnidirectional antenna, and at 5Mbit/swhen using a parabolic antenna. The signals are thendemodulatedand decoded in the satellite.[6]

TheKabandis used to transmit payload data to theground stationsof theChinese Academy of Sciences,both from the surface probes on the Moon and from the satellite itself. Withquadraturephase shift keying,encryptionwithlow-density parity check codeand a traveling wavetube amplifierwith 55 W output power, thedata transferrate is on average 100 Mbit/s. The antenna used is a small parabolic antenna with a diameter of 0.6 m in a gimbal suspension, which is mounted on thenadirside of the satellite bus on a fold-out arm that allows it to protrude above the large parabolic antenna.[9][22]

Telemetryand control of the satellite is usually carried out on theS-band,for which there is an S-bandomnidirectional antennaat thefocal pointof the small parabolic antenna in addition to the Kabandtransceiver.Thedata transmissionrate for commands from the Earth to the satellite is 2000 bit/s, the telemetry data is transmitted from the satellite to the Earth at a speed of 4096 bit/s. This is twice as fast as the first Queqiao. The position is determined using a combination of the so-calledUnified S-Band Technology(USB), where the distance and speed of the satellite are calculated from theDoppler shiftof thecarrier wavefor thetelemetry signals,and long-baseinterferometry,where connectedradio telescopesare using the ChineseVLBInetwork to determine the exactangular position.[22]

The systems are alternately redundant. In the event of a failure of the S-band system, the telemetry and control signals can also be transmitted via the Kaband, and if the Kaband signals are subject to strongattenuationby thewater dropletsin the Earth'satmosphereduring thehot and wet season,the payload data can also be transmitted via the S-band, but only with a data transfer rate of a maximum of 6 Mbit/s. Similar to asatellite navigationsystem, thetime of arrival,i.e., atransit time measurementof the signals between the partners involved in communication, is used to determine their position in orbit or on thesurface of the Moonwith high accuracy.[8]

Scientific payloads[edit]

There are three scientific payloads on the spacecraft:[27][28]

Mission[edit]

Queqiao-2 was launched on 20 March 2024 at 00:31UTCby aLong March 8rocket from theWenchang Space Launch Site,[29][30]supporting China'sChang'e 6in 2024 and future7and8lunar missions scheduled for 2026 and 2028 respectively.[31][32]The upgraded Queqiao-2 entered lunar orbit on 24 March 2024 at 16:46UTC,[33]where it is expected to operate for 8–10 years and by using a ellipticalfrozen orbitof 200 km × 16,000 km with aninclinationof 62.4°,[3]instead of theL2halo orbit.[34][35]

The initial mission of Queqiao-2 is to provide relay communication support for Chang'e 6. After Chang'e 6 completed its mission, it adjusted its orbit to provide services for Chang'e-7, Chang'e-8 and subsequentlunar explorationmissions. In the future, Queqiao-2 will also work with Chang'e 7 and Chang'e 8 to build theInternational Lunar Research Station.[8]

Queqiao-2 also carries two smallerDeep Space Exploration Laboratorycommunication satellites,Tiandu-1andTiandu-2,to verify the technicality of the lunarcommunicationandnavigationconstellationbased on the Queqiao technology. After launch, the two satellites underwent lunar orbit insertion on 24 March 2024 at 17:43UTCand entered a largeelliptical orbitaround the Moon (Both were attached to each other and separated in lunar orbit on 3 April 2024).[36][33]Both are equipped with a communications payload and first one has a laser passive retroreflector and an in-space router, with another has navigational devices.[37]In a large elliptical orbit around the moon, satellite-to-groundlaser rangingareinter-satellite microwave rangingare to be carried out by these satellites via high-precisionlunar orbitdetermination technology.[38][8][39]

On 12 April 2024, CNSA announced that Queqiao-2 had successfully completed in-orbit communication tests withChang'e 4on the far side of the moon and the Chang'e 6 probe while still on the ground. The satellite entered its targeted elliptical orbit on 2 April after a correction midway, near-moon braking and orbital manoeuvre around the moon. It facilitates communication between Earth and lunar probes signaling China's commitment to space exploration and international cooperation.[40]

Comparison of relay satellites[edit]

Here is a comparison of some of the key differences of the two lunar relay satellites:[1][9][10][11][12][3][4]

Queqiao Queqiao 2
Bus CAST 100 CAST 2000
Mass 449 kg (990 lb) 1,200 kg (2,600 lb)
Power Supply 4 solar panels, total 800 W 4 solar panels, total 1350 W
Accumulator 45 Ah 135 Ah
Orbit Earth-Moon L2Halo orbit
at 65,000 km from Moon		 Elliptical orbit around moon of
200 × 16,000 km at 62.4°
orbital period 14 days 24 hours
Line of sight of surface
probes		 always every 20 in 24 hours
No. of surface probes
monitored		 2 10
Antenna X-band parabolic antenna 4.2 m
S-band spiral antenna		 X-band parabolic antenna 4.2 m
4 S-band omni-directional antennas
UHF omni-directional antenna
Ka-band parabolic antenna 0.6 m
Satellite to lunar surface
probes communication		 X-Band 125 bit/s X-Band 1 kbit/s
Satellite to lunar surface
probes communication		 X-Band 555 kbit/s X-Band 5 Mbit/s
Satellite to and fro
Earth communication		 S-Band 4 Mbit/s Ka-Band 100 Mbit/s
Start of operation 2018 2024
End of operation 2026 (expected) 2034 (expected)

See also[edit]

References[edit]

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