Queqiao 2

Rendering of Queqiao 2 satellite
Mission type	Communication relay Radio astronomy
Operator	CNSA
COSPAR ID	2024-051A
SATCATno.	59274
Mission duration	Planned: 8-10 years 1 year, 8 months, 7 days(in progress)
Spacecraft properties
Bus	CAST-2000[1]
Manufacturer	DFH Satellite Company LTD
Dry mass	1,200 kilograms (2,600 lb)
Dimensions	Antenna: 4.2 metres (14 ft) in diameter[1]
Power	1350W[1]
Start of mission
Launch date	20 March 2024, 00:31:28UTC[2]
Rocket	Long March 8[2]
Launch site	Wenchang LC-201[2]
Orbital parameters
Reference system	Selenocentricfrozen orbit
Periselene altitude	254.3 km (158.0 mi)[3]
Aposelene altitude	16,941.1 km (10,526.7 mi)[3]
Inclination	119.249°[3]
Period	26.18 hours[3]
Lunar orbiter
Orbital insertion	24 March 2024, 17:05UTC[4]
Instruments
Grid-based Energetic Neutral Atom imager (GENA) ExtremeUltraviolet Camera (EUC) Lunar OrbitVLBI EXperiment (LOVEX)
Chinese Lunar Exploration Program ← Chang'e 5 Chang'e 6 → Queqiao satellites ← Queqiao-1

Queqiao-2 relay satellite (Chinese:鹊桥二号中继卫星;pinyin:Quèqiáo èr hào zhōngjì wèixīng;lit. 'Magpie Bridge 2 relay satellite'), is the second of the communications relay and radio astronomy satellites designed to support the fourth phase theChinese Lunar Exploration Program,^[5][6][7] afterQueqiao-1 launched in 2018. TheChina National Space Administration (CNSA) launched the Queqiao-2 relay satellite on 20 March 2024 to an ellipticalfrozen orbit around the Moon to support communications from thefar side of the Moon and theLunar south pole.^{[8][9][10][11]}

The nameQueqiao (ch'wuh-ch'yow, "Magpie Bridge") was inspired by and came from the Chinese taleThe Cowherd and the Weaver Girl.^[8][7][12]

The initial phase of theInternational Lunar Research Station (ILRS), consisting of theChang'e 7 andChang'e 8 probes, was scheduled to be built in 2026 and 2028 on the southern edge of theSouth Pole–Aitken basin located on thefar side of the Moon.^[13] While theQueqiao so far only had to connect with two probes on the far side of the Moon (Chang'e 4 lander andYutu-2 rover), 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.^[14]

TheQueqiao relay satellite was inserted in ahalo orbit around theEarth-Moon L₂ since 2018. China planned another relay satellite, calledQueqiao 2, to support and supplement Queqiao-1.^[11][14] Originally, the idea was to design the relay satellite as an improved version of the Queqiao and launch it together with theChang'e 7 probe. After a project revision,^[15] theCenter for Lunar Exploration and Space Projects at theCNSA decided to launch it separately.^[16] This allowed the building of a larger variant of the relay satellite that could be launched earlier and used in theChang'e 6sample return mission that was also launched in 2024 to theApollo crater on thefar side of the Moon.^[14]

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 L₁ and L₂ were inherentlyunstable^[17] and requires the satellite to consumes 80 g (2.8 oz) of fuel for asmall orbit correction maneuver approximately every 9 days. Therefore, a frozenelliptic orbit around 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 itsperiselene lies above the side of the southern polar region facing away from the Earth.^[18]

When Queqiao-2 reaches a position about 200 km from the lunar surface, it will perform capture braking and enter a lunarparking orbit of 200 × 100,000 km with a period of about 10 days. Eventually, Queqiao-2 will enter a large ellipticalfrozen orbit of 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 10 years, the assumed lifespan of the satellite.^[19] However, it did not enter that orbit and instead entered a 119.25° 254 × 16941 km retrograde orbit.^[3]

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 20N each for orbit correction maneuvers as well as eight engines with a thrust of 5N each and four engines with a thrust of 1N each 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 cell wings, each with twosolar arrays, deliver a total output of 1350 W, the operatingvoltage is 30.5 V. During blackoutor eclipse period, it hasaccumulators with 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 antenna with a diameter of 4.2 m and anantenna gain of 44dBi is 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.^[5] In order to be able to accommodate the satellite in thepayload fairing of thelaunch vehicle, the segments of thereflector are folded together during launch. After separating from theupper stage of the rocket and unfolding the solar modules, the antenna is also unfolded at the beginning of thetransfer orbit to the Moon.^{[8][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 exploration satellite.^[26]

The largeparabolic antenna provides 10 simultaneously usableX-band channels forradio traffic down 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/s when using an omnidirectional antenna, and at 5Mbit/s when using a parabolic antenna. The signals are thendemodulated and decoded in the satellite.^[5]

TheK_a band is used to transmit payload data to theground stations of theChinese Academy of Sciences, both from the surface probes on the Moon and from the satellite itself. Withquadrature phase shift keying,encryption withlow-density parity check code and a traveling wavetube amplifier with 55 W output power, thedata transfer rate 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 thenadir side of the satellite bus on a fold-out arm that allows it to protrude above the large parabolic antenna.^[8][22]

Telemetry and control of the satellite is usually carried out on theS-band, for which there is an S-bandomnidirectional antenna at thefocal point of the small parabolic antenna in addition to the K_a bandtransceiver. Thedata transmission rate 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 shift of thecarrier wave for thetelemetry signals, and long-baseinterferometry, where connectedradio telescopes are using the ChineseVLBI network 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 K_a band, and if the K_a band signals are subject to strongattenuation by thewater droplets in the Earth'satmosphere during 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 navigation system, thetime of arrival, i.e., atransit time measurement of the signals between the partners involved in communication, is used to determine their position in orbit or on thesurface of the Moon with high accuracy.^[7]

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

• Grid-based Energetic Neutral Atom imager (GENA):Imagesparticle detector forneutral atoms for observing theterrestrialmagnetosphere, especially themagnetotail.^[27][28]
• ExtremeUltraviolet Camera (EUC).^[27][28]
• Lunar OrbitVLBI EXperiment: The intention is to use the 4.2 m antenna as aradio telescope during the four hours the satellite spends over the Moon'snorth pole during each orbit. The satellite will be used inconjunction withterrestrial telescopes for long-baseinterferometry with a baseline of 400,000 km. The aim is not only to determine the position and composition of radio sources outside theMilky Way, but also as part of theChinese deep space network, i.e, the position of spacecrafts such as the asteroid probeTianwen-2. For use as aradio telescope, a cooledX-band receiver for thefrequency range 8–9 GHz with anoise temperature of less than 50 K and four selectablebandwidths (64, 128, 256 and 512MHz) is mounted on the antenna. In order to be able to accurately determine thetransit time difference between the satellite and the terrestrial radio telescope for a given signal and thus calculate the position of the radio source or the spacecraft (the position of the satellite itself can be determined with an accuracy of 30 m), the satellite has anatomic clock with a maximum deviation of 10 −12 per second or 10 −14 per day. The receiver and clock together have a mass of 45 kg (99 lb) and have an average power consumption of 220 W.^[27][28]

Queqiao-2 was launched on 20 March 2024 at 00:31UTC by aLong March 8 rocket from theWenchang Space Launch Site,^[29][30] supporting China'sChang'e 6 in 2024 and future7 and8 lunar 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 orbit of 200 km × 16,000 km with aninclination of 62.4°,^[19] instead of theL₂ halo 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 exploration missions. In the future, Queqiao-2 will also work with Chang'e 7 and Chang'e 8 to build theInternational Lunar Research Station.^[7]

Queqiao-2 also carries two smallerDeep Space Exploration Laboratory communication satellites,Tiandu-1 andTiandu-2, to verify the technicality of the lunarcommunication andnavigationconstellation based on the Queqiao technology. After launch, the two satellites underwent lunar orbit insertion on 24 March 2024 at 17:43UTC and entered a largeelliptical orbit around 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 ranging areinter-satellite microwave ranging are to be carried out by these satellites via high-precisionlunar orbit determination technology.^[38][7][39]

On 12 April 2024, CNSA announced that Queqiao-2 had successfully completed in-orbit communication tests withChang'e 4 on 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]

On 23 September 2024, it was discovered by independent astronomer Scott Tilley that the satellite was instead in a 119.25° 1992 × 18679 km retrograde orbit.^[3]

Here is a comparison of some of the key differences of the two lunar relay satellites:^{[1][8][9][10][11][19][41]}

• Queqiao-1
• Chang'e 6
• Qianfan

• 2024 in China
• Chinese Lunar Exploration Program
• Chinese space probes
• Spacecraft launched by Long March rockets
• Spacecraft using halo orbits
• Satellites orbiting the Moon
• Space probes launched in 2024
• 2024 on the Moon

• CS1 Chinese-language sources (zh)
• CS1 Simplified Chinese-language sources (zh-hans)
• Webarchive template wayback links
• Articles with short description
• Short description is different from Wikidata
• Articles containing simplified Chinese-language text