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 the Chinese Lunar Exploration Program,[5][6][7] after Queqiao-1 launched in 2018. The China National Space Administration (CNSA) launched the Queqiao-2 relay satellite on 20 March 2024 to an elliptical frozen orbit around the Moon to support communications from the far side of the Moon and the Lunar south pole.[8][9][10][11]
 Rendering of Queqiao 2 satellite | |
| Mission type | Communication relay Radio astronomy |
|---|---|
| Operator | CNSA |
| COSPAR ID | 2024-051A |
| SATCAT no. | 59274 |
| Mission duration | Planned: 8-10 years 9 months, 6 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, 00:31:28 UTC[2] |
| Rocket | Long March 8[2] |
| Launch site | Wenchang LC-201[2] |
| Orbital parameters | |
| Reference system | Selenocentric frozen orbit |
| Periselene altitude | 1,991.69 km (1,237.58 mi)[3] |
| Aposelene altitude | 18,678.5 km (11,606.3 mi)[3] |
| Inclination | 119.249°[3] |
| Period | 26.18 hours[3] |
| Lunar orbiter | |
| Orbital insertion | 24 March 2024, 17:05 UTC[4] |
| Instruments | |
| |
Queqiao satellites | |
The name Queqiao (ch'wuh-ch'yow, "Magpie Bridge") was inspired by and came from the Chinese tale The Cowherd and the Weaver Girl.[8][7][12]
Background and mission planning
editThe initial phase of the International Lunar Research Station (ILRS), consisting of the Chang'e 7 and Chang'e 8 probes, was scheduled to be built in 2026 and 2028 on the southern edge of the South Pole–Aitken basin located on the far side of the Moon.[13] While the Queqiao so far only had to connect with two probes on the far side of the Moon (Chang'e 4 lander and Yutu-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]
The Queqiao relay satellite was inserted in a halo orbit around the Earth-Moon L2 since 2018. China planned another relay satellite, called Queqiao 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 the Chang'e 7 probe. After a project revision,[15] the Center for Lunar Exploration and Space Projects at the CNSA 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 the Chang'e 6 sample return mission that was also launched in 2024 to the Apollo crater on the far 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 by Chinese Deep Space Network, its halo orbits around the Earth-Moon L1 and L2 were inherently unstable[17] and requires the satellite to consumes 80 g (2.8 oz) of fuel for a small orbit correction maneuver approximately every 9 days. Therefore, a frozen elliptic 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 its periselene 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 lunar parking orbit of 200 × 100,000 km with a period of about 10 days. Eventually, Queqiao-2 will enter a large elliptical frozen 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° 1992 × 18679 km retrograde orbit.[3]
Design
edit
Queqiao 2 relay satellite and radio observatory is based on the CAST 2000 bus from DFH Satellite, a subsidiary of the Chinese 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 20 N each for orbit correction maneuvers as well as eight engines with a thrust of 5 N each and four engines with a thrust of 1 N each for attitude control; it can be aligned with an accuracy of 0.03° (three times as good as the standard version of the satellite bus). Two rotatable solar cell wings, each with two solar arrays, deliver a total output of 1350 W, the operating voltage is 30.5 V. During blackoutor eclipse period, it has accumulators with a charge storage capacity of 135 Ah. The manufacturing company assumes that Queqiao 2 will work properly for at least 8 to 10 years.[21][22]
Adopted from the first Queqiao, a parabolic antenna with a diameter of 4.2 m and an antenna gain of 44 dBi is permanently mounted on the top of the bus- the alignment is carried out via the satellite's attitude control - and is used for radio communication with the lunar surface.[5] In order to be able to accommodate the satellite in the payload fairing of the launch vehicle, the segments of the reflector are folded together during launch. After separating from the upper stage of the rocket and unfolding the solar modules, the antenna is also unfolded at the beginning of the transfer orbit to the Moon.[8][23][24][21][25][1]
Communication with the lunar surface is accomplished in the X band, using a high-gain 4.2 metres (14 ft) deployable parabolic antenna, the largest antenna used for a deep space exploration satellite.[26]
The large parabolic antenna provides 10 simultaneously usable X-band channels for radio 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 50 kbit/s when using an omnidirectional antenna, and at 5 Mbit/s when using a parabolic antenna. The signals are then demodulated and decoded in the satellite.[5]
The Ka band is used to transmit payload data to the ground stations of the Chinese Academy of Sciences, both from the surface probes on the Moon and from the satellite itself. With quadrature phase shift keying, encryption with low-density parity check code and a traveling wave tube amplifier with 55 W output power, the data 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 the nadir 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 the S-band, for which there is an S-band omnidirectional antenna at the focal point of the small parabolic antenna in addition to the Ka band transceiver. The data 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-called Unified S-Band Technology (USB), where the distance and speed of the satellite are calculated from the Doppler shift of the carrier wave for the telemetry signals, and long-base interferometry, where connected radio telescopes are using the Chinese VLBI network to determine the exact angular 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 Ka band, and if the Ka band signals are subject to strong attenuation by the water droplets in the Earth's atmosphere during the hot 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 a satellite navigation system, the time of arrival, i.e., a transit time measurement of the signals between the partners involved in communication, is used to determine their position in orbit or on the surface of the Moon with high accuracy.[7]
Scientific payloads
editThere are three scientific payloads on the spacecraft:[27][28]
- Grid-based Energetic Neutral Atom imager (GENA): Images particle detector for neutral atoms for observing the terrestrial magnetosphere, especially the magnetotail.[27][28]
- Extreme Ultraviolet Camera (EUC).[27][28]
- Lunar Orbit VLBI EXperiment: The intention is to use the 4.2 m antenna as a radio telescope during the four hours the satellite spends over the Moon's north pole during each orbit. The satellite will be used in conjunction with terrestrial telescopes for long-base interferometry with a baseline of 400,000 km. The aim is not only to determine the position and composition of radio sources outside the Milky Way, but also as part of the Chinese deep space network, i.e, the position of spacecrafts such as the asteroid probe Tianwen-2. For use as a radio telescope, a cooled X-band receiver for the frequency range 8–9 GHz with a noise temperature of less than 50 K and four selectable bandwidths (64, 128, 256 and 512 MHz) is mounted on the antenna. In order to be able to accurately determine the transit 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 an atomic 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]
Mission
editQueqiao-2 was launched on 20 March 2024 at 00:31 UTC by a Long March 8 rocket from the Wenchang Space Launch Site,[29][30] supporting China's Chang'e 6 in 2024 and future 7 and 8 lunar missions scheduled for 2026 and 2028 respectively.[31][32] The upgraded Queqiao-2 entered lunar orbit on 24 March 2024 at 16:46 UTC,[33] where it is expected to operate for 8–10 years and by using a elliptical frozen orbit of 200 km × 16,000 km with an inclination of 62.4°,[19] instead of the L2 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 subsequent lunar exploration missions. In the future, Queqiao-2 will also work with Chang'e 7 and Chang'e 8 to build the International Lunar Research Station.[7]
Queqiao-2 also carries two smaller Deep Space Exploration Laboratory communication satellites, Tiandu-1 and Tiandu-2, to verify the technicality of the lunar communication and navigation constellation based on the Queqiao technology. After launch, the two satellites underwent lunar orbit insertion on 24 March 2024 at 17:43 UTC and entered a large elliptical 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-ground laser ranging are inter-satellite microwave ranging are to be carried out by these satellites via high-precision lunar orbit determination technology.[38][7][39]
On 12 April 2024, CNSA announced that Queqiao-2 had successfully completed in-orbit communication tests with Chang'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]
Comparison of relay satellites
editHere is a comparison of some of the key differences of the two lunar relay satellites:[1][8][9][10][11][19][41]
| 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 L2 Halo orbit at 65,000 km from Moon |
Retrograde elliptical orbit around Moon of 1992 × 18679 km at 119.25° |
| orbital period | 14 days | 26.18 hours |
| Line of sight of surface probes |
always | |
| 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
editReferences
edit- ^ a b c d e Zhang, LiHua; Xiong, Liang; Sun, Ji; Gao, Shan; Wang, XiaoLei; Zhang, AiBing (2019-02-14). "Technical characteristics of the relay communication satellite "Queqiao" for Chang'e-4 lunar farside exploration mission". Scientia Sinica Technologica (in Chinese). 49 (2): 138–146. doi:10.1360/N092018-00375. ISSN 2095-946X. S2CID 88483165.
- ^ a b c "China launches Queqiao-2 relay satellite to support moon missions". Spacenews.com. 19 March 2024. Retrieved 20 March 2024.
- ^ a b c d e f Tilley, Scott [@coastal8049] (September 22, 2024). "QUEQIAO-2 is NOT in the orbit Chinese media sources or even Wikipedia claims it's in. SMA = 10335.1 km ECC = 0.807289 INC = 119.249° Claimed 200x16000km has an SMA of 9837.4km. Period = 26.18 hours. The observed orbit is retrograde NOT prograde. ⬇️ https://en.wikipedia.org/wiki/Queqiao-2" (Tweet). Retrieved September 23, 2024 – via Twitter.
- ^ "鹊桥二号中继星成功实施近月制动 顺利进入环月轨道飞行" (in Simplified Chinese). 新华网. 2024-03-25. Retrieved 2024-03-25.
- ^ a b c "微博". m.weibo.cn. Retrieved 2024-03-20.
- ^ "成功！". Weixin Official Accounts Platform. Retrieved 2024-03-20.
- ^ a b c d e Lihua, Zhang (2024-03-02). "Development and Prospect of Chinese Lunar Relay Communication Satellite". Space: Science & Technology. 2021. doi:10.34133/2021/3471608.
- ^ a b c d e Wall, Mike (18 May 2018). "China Launching Relay Satellite Toward Moon's Far Side Sunday". Space.com. Archived from the original on 18 May 2018.
- ^ a b "Queqiao". NASA.
- ^ a b "嫦娥六号或明年5月发射 实现月球背面采样返回 | 联合早报". www.zaobao.com.sg (in Simplified Chinese). Retrieved 2024-03-20.
- ^ a b c "Sina Visitor System". passport.weibo.com. Retrieved 2024-03-20.
- ^ "鹊桥二号中继星计划明年发射 --科技日报数字报". digitalpaper.stdaily.com. Retrieved 2024-03-20.
- ^ "嫦娥七号任务搭载机遇公告". www.cnsa.gov.cn. Retrieved 2024-03-20.
- ^ a b c "国家航天局：鹊桥二号2024年上半年发射-新华网". www.news.cn. Retrieved 2024-03-20.
- ^ "嫦娥七号设计再次改动，为搭载阿联酋月球车，将中继星挤下去了？_腾讯新闻". new.qq.com. 25 September 2022. Retrieved 2024-03-20.
- ^ "微博". m.weibo.cn. Retrieved 2024-03-20.
- ^ Lei, L. I. U.; Jianfeng, C. a. O.; Songjie, H. U.; Geshi, Tang (2015). "Maintenance of Relay Orbit About the Earth-Moon Collinear Libration Points" (PDF). Journal of Deep Space Exploration (in Chinese). 2 (4): 318–324. doi:10.15982/j.issn.2095-7777.2015.04.004. ISSN 2096-9287.
- ^ 周文艳; 高珊; 刘德成; 张相宇; 马继楠; 于登云 (2020). "月球极区探测轨道设计". 深空探测学报(中英文） (in Chinese). 7 (3): 248–254. doi:10.15982/j.issn.2095-7777.2020.20191109004. ISSN 2096-9287.
- ^ a b c Lihua Zhang (2024-03-20). "月亮之上"梦想绽放" 增强现实+AI生成技术揭秘鹊桥二号发射全程" (in Simplified Chinese). 央视网. Retrieved 2024-03-23.
- ^ "China Academy of Space Technology". www.cast.cn. Retrieved 2024-03-20.
- ^ a b Wu, Weiren; Tang, Yuhua; Zhang, Lihua; Qiao, Dong (2017-12-12). "Design of communication relay mission for supporting lunar-farside soft landing". Science China Information Sciences. 61 (4): 040305. doi:10.1007/s11432-017-9202-1. ISSN 1869-1919. S2CID 22442636.
- ^ a b c Jones, Andrew (2023-10-17). "China to launch Queqiao-2 moon relay satellite in early 2024". SpaceNews. Retrieved 2024-03-20.
- ^ Emily Lakdawalla (14 January 2016). "Updates on China's lunar missions". The Planetary Society. Archived from the original on 17 April 2016. Retrieved 24 April 2016.
- ^ Jones, Andrew (24 April 2018). "Chang'e-4 lunar far side satellite named 'magpie bridge' from folklore tale of lovers crossing the Milky Way". GBTimes. Archived from the original on 24 April 2018. Retrieved 28 April 2018.
- ^ Future Chinese Lunar Missions: Chang'e 4 - Farside Lander and Rover. David R. Williams, NASA Goddard Space Flight Center. 7 December 2018.
- ^ "鹊桥号发射成功 将成为世界首颗连通地月中继卫星". 2018-05-21. Archived from the original on 2018-05-27. Retrieved 2018-05-26.
- ^ a b c d "中国探月与深空探测网 - 通知公告". www.clep.org.cn. Retrieved 2024-03-20.
- ^ a b c d "NASA - NSSDCA - Spacecraft - Details". nssdc.gsfc.nasa.gov. Retrieved 2024-03-20.
- ^ "China launches Queqiao-2 relay satellite to support moon missions". Space.com. 20 March 2024. Retrieved 20 March 2024.
- ^ "我国成功发射鹊桥二号中继星-新华网". hq.news.cn. Retrieved 2024-03-20.
- ^ "探月工程四期中继星运抵海南文昌-新华网". www.news.cn. Retrieved 2024-03-20.
- ^ "鹊桥二号中继星任务星箭组合体垂直转运至发射区-新华网". www.news.cn. Retrieved 2024-03-20.
- ^ a b Jones, Andrew (2024-03-25). "China's Queqiao-2 relay satellite enters lunar orbit". SpaceNews. Retrieved 2024-03-26.
- ^ Jones, Andrew (23 January 2023). "China to launch relay satellite next year to support moon landing missions". SpaceNews.
- ^ "Queqiao 2". Space.skyrocket.de. 12 March 2024.
- ^ "探月工程里程碑：天都二号卫星成功应用冷气微推进系统". Weixin Official Accounts Platform. Retrieved 2024-04-04.
- ^ "China launches relay satellite to allow communication with far side of the moon". South China Morning Post. 2024-03-20. Retrieved 2024-03-20.
- ^ Jones, Andrew (10 May 2023). "China to launch communications relay satellite to the moon in early 2024". Space.com.
- ^ "我国将发射"天都一号""天都二号"探月卫星-新华网". www.news.cn. Retrieved 2024-03-20.
- ^ "China launch of relay satellite Queqiao-2 for lunar probe mission successful". Reuters. Retrieved 2024-04-12.
- ^ 周文艳、高珊、刘德成、张相宇、马继楠、于登云 (2020). "月球极区探测轨道设计" (PDF). 深空探测学报. 7 (3): 250.
