A rendering of the Tiangong Space Station in its current construction state as of June 2022, with the Tianhe core module in the middle, Tianzhou at two ends and the Shenzhou at the nadir.
Tiangong (Chinese: 天宮; pinyin: Tiāngōng; lit. 'Palace in the Sky'),[5][6] officially the Tiangong space station (Chinese: 天宫空间站; pinyin: Tiāngōng kōngjiānzhàn), is a space station being constructed by China in low Earth orbit between 340 and 450 km (210 and 280 mi) above the surface. Being China's first long-term space station, it is the goal of the "Third Step" of the China Manned Space Program. Once completed, Tiangong will have a mass between 80 and 100 t (180,000 and 220,000 lb), roughly one-fifth the mass of the International Space Station and about the size of the decommissioned Russian Mir space station.
The construction of the station is based on the experience gained from its precursors, Tiangong-1 and Tiangong-2.[7][8][9] The first module, the Tianhe ("Harmony of the Heavens") core module, was launched on 29 April 2021,[5][6] followed by multiple crewed and uncrewed missions and two more modules to be launched in 2022.[7] Chinese leaders have expressed the hope that the research conducted on the station will improve researchers' ability to conduct science experiments in space, beyond the duration and capacity offered by China's existing space laboratories.[10]
Nomenclature
It has been attributed to former paramount leaderDeng Xiaoping for the decision[citation needed] that the names used in the space program, previously all chosen from the revolutionary history of the People's Republic, would be replaced with mystical-religious ones. Thus, the new Long March launch vehicles were renamed Divine Arrow (神箭),[11][12] space capsule Divine Vessel (神舟),[13] spaceplane Divine Dragon (神龙),[14] land-based high-power laser Divine Light (神光)[15] and supercomputer Divine Might (神威).[16]
These poetic[17] names continue as the first, second, third, fourth and fifth Chinese Lunar probes are called Chang'e after the Moon goddess. The name "Tiangong" means "heavenly palace". Across China, the launch of Tiangong-1 was reported to have inspired a variety of feelings, including love poetry. The rendezvous of the space vehicles has been compared to the reunion of the cowherd and the weaver girl.[18]
Wang Wenbao, director of the China Manned Space Agency (CMSA), told a news conference in 2011: "Considering past achievements and the bright future, we feel the manned space programme should have a more vivid symbol, and that the future space station should carry a resounding and encouraging name. We now feel that the public should be involved in the names and symbols, as this major project will enhance national prestige and strengthen the national sense of cohesion and pride".[17][19][20]
On 31 October 2013, CMSA announced the new names for the whole space station program:[8]
The large modular space station would be called Tiangong as well, without number.[1]
The cargo transport spacecraft would be called Tianzhou (Chinese: 天舟; pinyin: Tiān Zhōu; lit. 'Heavenly Ship'), code TZ. The first Tianzhou mission successfully launched and deorbited in 2017. The first mission to the space station, Tianzhou 2, flew on 29 May 2021. Subsequently, Tianzhou 3 and Tianzhou 4 were launched respectively on 20 September 2021 and 9 May 2022.
The separate space telescope module would be called Xuntian (Chinese: 巡天; pinyin: Xún Tiān; lit. 'Touring the Heavens'), code XT (telescope), receiving the previously intended name for the Experiment Module II. Launch is planned for 2023.[26]
Purpose and mission
According to CMSA, which operates the space station, the purpose and mission of Tiangong is listed as: Further development of spacecraft rendezvous technology; Breakthrough in key technologies such as permanent human operations in orbit, long-term autonomous spaceflight of the space station, regenerative life support technology, and autonomous cargo and fuel supply technology; Test of next-generation orbit transportation vehicles; Scientific and practical applications at large-scale in orbit; Development of technology that can aid future deep space exploration.[27][28][29]
In addition, private sector commercial activities being encouraged, according to the designer of China's human spaceflight program: “When our space station is completed and running, we will actively encourage the private sector to engage in space through various ways.” “We hope there will be competitive, cost-efficient commercial space players to participate in areas including space applications and space resource development.”[30]
T-shaped early concept of the Chinese large modular space station
The space station will be a third generation modular space station. First generation space stations, such as early Salyut, Almaz, and Skylab, were single piece stations and not designed for resupply. Second generation Salyut 6 and 7, and Tiangong 1 and 2 stations, are designed for mid-mission resupply. Third generation stations, such as Mir and the International Space Station, are modular space stations, assembled on-orbit from pieces launched separately. Modularised design methods can greatly improve reliability, reduce costs, shorten development cycle, and meet diversified task requirements.[7]
The initial target configuration for the end of 2022 consists of three modules, which may be expanded to six in the future.[32]
The Tianhe Core Cabin Module (CCM) provides life support and living quarters for three crew members, and provides guidance, navigation, and orientation control for the station. The module also provides the station's power, propulsion, and life support systems. The module consists of three sections: living quarters, service section and a docking hub. The living quarters will contain a kitchen and toilet, fire control equipment, atmospheric processing and control equipment, computers, scientific apparatus, communications equipment to send and receive communications via ground control in Beijing, and other equipment.
An ISS Canadian-style SSRMS robotic arm, dubbed "Chinarm" was folded under the Tianhe core module. Additionally, the Wentian and Mengtian experiment modules (described below) will carry a duplicate stowed second SSRMS robotic arm. In 2018 fullscale mockup of CCM was publicly presented at China International Aviation & Aerospace Exhibition in Zhuhai. The video from CNSA revealed that two of these core modules have been built. Artist impressions have also depicted the two core modules docked together to enlarge the overall station.
The first of two Laboratory Cabin Modules, Wentian and Mengtian respectively, will provide additional navigation avionics, propulsion and orientation control as backup functions for the CCM. Both LCMs will provide a pressurised environment for researchers to conduct science experiments in freefall or microgravity which could not be conducted on Earth for more than a few minutes. Experiments can also be placed on the outside of the modules for exposure to the space environment, cosmic rays, vacuum, and solar winds.
Like Mir and the Russian orbital segment of the ISS, the Tiangong modules will be carried fully assembled into orbit, in contrast to the US Orbital Segment of the ISS, which required spacewalking to interconnect cables, piping, and structural elements manually. The axial port of the LCMs will be fitted with rendezvous equipment and will first dock to the axial port of the CCM. A mechanical arm dubbed, as Indexing robotic arm, looking a sort of Lyappa arm used on the Mir space station will then move the module to a radial port of the CCM.[33] It is different from Lyappa as it works on a different mechanism. Lyappa arm is needed to control the pitch of the spacecraft and redocking in a different plane. But the indexing robot arm where docking is needed in the same plane. In addition to this arm used for docking relocation, the Chinarm on Tianhe module can also be used as a backup.[34][35]
The initial lab module, which also serves as the backup platform of the core module with capability of space station control and management. It has its own airlock served as main exit for future spacewalking and a second mechanical arm for the station.[37]
The second lab module. It has its own airlock for supplement and equipment transportation.[37]
Systems
Power supply
Electrical power is provided by two steerable solar power arrays on each module, which use gallium arsenidephotovoltaic cells to convert sunlight into electricity. Energy is stored to power the station when it passes into the Earth's shadow. Resupply spacecraft will replenish fuel for the station's propulsion engines for station keeping, to counter the effects of atmospheric drag. The solar arrays are designed to last up to 15 years.[40]
Docking
Tiangong is fitted with Chinese Docking Mechanism used by Shenzhou spacecraft and previous Tiangong prototypes. The Chinese docking mechanism is based on the Russian APAS-89/APAS-95 system. Despite NASA describing it as a "clone" to APAS,[41] there have been contradictory claims on the compatibility of the Chinese system with both current and future docking mechanisms on the ISS, which are also based on APAS.[42][43][44] It has a circular transfer passage that has a diameter of 800 mm (31 in).[45][46] The androgynous variant has a mass of 310 kg and the non-androgynous variant has a mass of 200 kg.[47]
Chinese Docking Mechanism was used for the first time on Shenzhou 8 and Tiangong 1 space station and will be used on future Chinese space stations and with future CMSA cargo resupply vehicles.[48][42]
Propulsion
Tiangong space station is fitted with conventional chemical propulsion and ion thrusters to adjust and maintain the station's orbit. Four Hall-effect thrusters are mounted on the hull of Tianhe core module.[49] The development of the Hall-effect thrusters is considered a sensitive topic in China, with scientists "working to improve the technology without attracting attention". Hall-effect thrusters are created with manned mission safety in mind with effort to prevent erosion and damage caused by the accelerated ion particles.[50]
A magnetic field and specially designed ceramic shield was created to repel damaging particles and maintain integrity of the thrusters. According to a report by the Chinese Academy of Sciences, the ion drive used on Tiangong has burned continuously for 8,240 hours without a glitch during the testing phase, indicating their suitability for Tiangong's designated 15-year lifespan.[50] These are the world's first Hall thrusters to be used on a human-rated mission.[51]
Experiments
The space station will have more than 20 experimental racks with enclosed, pressurized environment. Over 1,000 experiments are tentatively approved by CMSA.[52] The programmed experiment equipment for the three modules as of June 2016 are:[9]
Planned Chinese space station telescope currently under development. It will feature a 2-meter (6.6 foot) diameter primary mirror and is expected to have a field of view 300–350 times larger than the Hubble Space Telescope. This will allow the telescope to image up to 40 percent of the sky using its 2.5 gigapixel camera over ten years. It will co-orbit with the space station in a slightly different orbital phase, which will allow for periodic docking with the station.
Construction
Planning
In 2011, it was announced that the future space station was planned to be assembled during 2020 to 2022.[54] By 2013, the space station's core module was planned to be launched earlier, in 2018, followed by the first laboratory module in 2020, and a second in 2022.[55] By 2018, it was reported that this had slipped to 2020-2023.[23][56] A total of 11 launches are planned for the whole construction phase, now beginning in 2021.[57][58]
The assembly method of the station can be compared with the Soviet-Russian Mir space station and the Russian orbital segment of the International Space Station. The construction of the modular station marks China to be the second nation to develop and use automatic rendezvous and docking for modular space station construction. The docking and assembly mechanisms of the Tiangong station are based on, or compatible with, Russian design due to two iterations of cross-agency cooperation in the past.[59]
During the cordial Sino-Soviet relations of the 1950s, the Soviet Union (USSR) had engaged in a cooperative technology transfer program with China, which helped kick-start the Chinese space program. However, the friendly relationship between the two countries soon turned to confrontation due to ideological differences on Marxism. As a consequence, all Soviet technological assistance was abruptly withdrawn after the 1960 Sino-Soviet split. The cooperation was only restarted after the fall of the Soviet Union.[59]
In 1994, Russia sold some of its advanced aviation and space technology to China. In 1995, a deal was signed between the two countries for the transfer of Russian Soyuz spacecraft technology to China. Included in the agreement were schedules for astronaut training, provision of Soyuz capsules, life support systems, docking systems, and space suits. In 1996, two Chinese astronauts, Wu Jie and Li Qinglong, began training at the Yuri Gagarin Cosmonaut Training Center in Russia. After training, these men returned to China and proceeded to train other Chinese astronauts at sites near Beijing and Jiuquan.[59]
The hardware and information sold by the Russians led to modifications of the original Phase One spacecraft, eventually called Shenzhou, loosely translatable as "divine vessel". New launch facilities were built at the Jiuquan launch site in Inner Mongolia, and in the spring of 1998 a mock-up of the Long March 2F launch vehicle with Shenzhou spacecraft was rolled out for integration and facility tests.[59]
A representative of the Chinese crewed space program stated that around 2000, China and Russia were engaged in technological exchanges regarding the development of a docking mechanism used for space station.[60] Deputy Chief Designer, Huang Weifen, stated that near the end of 2009, CMSA began to train astronauts on how to dock spacecraft.[61]
During the construction phase of the station in 2021, according to documents filed by CMSA with the United Nations Office for Outer Space Affairs and reported by Reuters, the station had two "close encounters" with Elon Musk's Starlink satellites on July 1 and October 21, with the station conducting evasive adjustment maneuvers.[62]
China's incentive to build its own space station was amplified after NASA refused Chinese participation in the International Space Station in 2011,[63] although China, Russia and Europe mutually vowed intentions to maintain a cooperative and multilateral approach in space.[64] Cooperation in the field of crewed space flight between the China Manned Space Agency (CMSA) and the Italian Space Agency (ASI) was examined in 2011 and participation in the development of China crewed space stations and cooperation with China in the fields such as visiting astronauts, and scientific research was discussed.[65]
An initial cooperative agreement with China National Space Administration and Italian Space Agency was subsequently signed in November 2011, covering areas of collaboration within space transportation, telecommunications, Earth observation, etc.[66] In 2019, an Italian experiment High Energy cosmic-Radiation Detection (HERD) was scheduled on board the Chinese station.[67] Tiangong also involved cooperation from France, Sweden, and Russia.[68]
On 22 February 2017, the CMSA and the Italian Space Agency (ASI) signed an agreement to cooperate on long-term human spaceflight activities.[69] The agreement holds importance due to Italy's leading position in the field of human spaceflight with regards to the creation and exploitation of the International Space Station (Node 2, Node 3, Columbus, Cupola, Leonardo, Raffaello, Donatello, PMM, etc.) and it signified Italy's increased anticipation in China's developing space station programme.[70] The European Space Agency (ESA) started human spaceflight training with CMSEO in 2017, with the ultimate goal of sending ESA astronauts to Tiangong.[71]
International experiments were selected by the CMSA and the United Nations Office for Outer Space Affairs (UNOOSA) in a UN session in 2019. 42 applications were submitted and nine experiments were accepted.[72] Some of the experiments are a continuation to the ones on Tiangong-2 such as POLAR-2, an experiment of researching Gamma-ray burst polarimetry, proposed by Switzerland, Poland, Germany and China.[73] Tricia Larose from the University of Oslo of Norway develops a cancer research experiment for the station. The 31-days experiment will test to see if weightlessness has a positive effect in stopping cancer growth.[74] Tiangong is also expected to host experiments from Belgium, France, Germany, India, Italy, Japan, Kenya, Mexico, the Netherlands, Peru, Russia, Saudi Arabia, and Spain.[73]
Regarding the participation of foreign astronauts, CMSA has repeatedly communicated their support for such proposals. During the press conference of the Shenzhou 12 mission, Zhou Jianping, the chief designer of China Manned Space Program explained that multiple countries had expressed their wish to participate. He told journalists that the future participation of foreign astronauts "will be guaranteed".[75] Ji Qiming, an assistant director at CMSEO told reporters that he believes "in the near future, after the completion of the Chinese space station, we will see Chinese and foreign astronauts fly and work together."[76]
Life aboard
Tiangong is currently staffed with a crew of 3 people. Once the construction is complete, the crew size will increase to a maximum of 6 people, beginning with Shenzhou 15, scheduled to launch before the end of 2022.[2]
The station possesses a Wi-Fi network for wireless connection and each astronaut wears a bone-conduction headphone and microphone for easy communication.[77] Meals consisting of 120 different types of food, selected based on astronauts' preference, are stored aboard. Staples including shredded pork in garlic sauce, kung pao chicken, black pepper beef, pickled cabbage and beverages, including a variety of teas and juices, are resupplied by trips of the Tianzhou-class cargo ship. Fresh fruits and vegetables are stored in coolers. Huang Weifen, chief astronaut trainer of CNSA, explains that most of the food is prepared to be solid, boneless, small-piece. Condiments such as pork sauce and Sichuan pepper sauce are used to compensate for the changes in the sense of taste in microgravity. The station is equipped with a small kitchen for food preparation and the first-ever microwave oven in spaceflight[78] so that astronauts can "always have hot food whenever they need."[79][80]
The station's core module, Tianhe, provides the living quarters for the crew members,[81][82] containing of three separate sleeping berths,[83] a toilet, shower facility, and gym equipment.[84] At least one berth features a small window, a headphone, ventilation and other amenities. Neuromuscular electrical stimulator is used to prevent muscle atrophy. The noise level in the working area is set at 58 decibels, while in the sleeping area, the noise is kept at 49 decibels.[85][86]
Space lectures
A new feature on the space station is the regular showcase of lessons and conducting of scientific experiments from space to educate, motivate and inspire Chinese younger generation in science and technology for the long term development of the nation. The lecture is then finally concluded by a Question-and-Answer (Q&A) session to answer schoolchildren's questions from the classrooms.[87] The first Tiangong space lesson was conducted on 9 December 2021, as a part of the Shenzhou 13 mission.
Operation
The station's resupply is planned to be conducted by visiting crewed and robotic spacecraft.
Crewed mission
Shenzhou is the spacecraft used to transfer astronauts between Earth and the space station.
Initial crewed missions to Tiangong, including its first mission Shenzhou 12 which lasted the planned 90 days, uses the Shenzhou spacecraft. Subsequent missions starting with Shenzhou 13 will last a planned 180 days, this then would become the normal duration of a mission cycle at Tiangong.[88]
CMSA announced the testing of a next-generation crewed spacecraft to eventually replace Shenzhou. It is designed to carry astronauts to Tiangong and offer the capability for lunar exploration. China's next-generation crew carrier is reusable with a detachable heat shield built to handle higher-temperature returns through Earth's atmosphere. The new capsule design is larger than the Shenzhou, according to CMSA officials. The spacecraft is capable of carrying astronauts to the Moon, and can accommodate up to six to seven crew members at a time, three more astronauts than Shenzhou.[89] The new crewed spacecraft has a cargo section that allows astronauts to bring cargo back to Earth, whereas the Tianzhou cargo resupply spacecraft is not designed to bring any cargo back to Earth.[89]
Tianzhou (Heavenly Vessel), a modified derivative of the Tiangong-1 spacecraft, is used as robotic cargo spacecraft to resupply this station.[90] The launch mass of Tianzhou is around 13,000 kg with a payload of around 6,000 kg.[91] Launch, rendezvous and docking shall be fully autonomous, with mission control and crew used in override or monitoring roles. This system becomes very reliable with standardisations that provide significant cost benefits in repetitive routine operations. An automated approach could allow assembly of modules orbiting other worlds prior to crewed missions.[92]
All dates are UTC. Dates are the earliest possible dates and may change.
Forward ports are at the front of the station according to its normal direction of travel and orientation (attitude). Aft is at the rear of the station, used by spacecraft boosting the station's orbit. Nadir is closest the Earth, zenith is on top. Port is to the left if pointing one's feet towards the Earth and looking in the direction of travel; starboard to the right.
Key
Uncrewed cargo spacecraft are in light blue colour
Tiangong is designed to be used for 10 years, though it could be extended to 15 years[109] and will accommodate three astronauts.[110] CMSA crewed spacecraft use deorbital burns to slow their velocity, resulting in their re-entry to the Earth's atmosphere. Vehicles carrying a crew have a heat shield which prevents the vehicle's destruction caused by aerodynamic heating upon contact with the Earth's atmosphere. The station itself has no heat-shield; however, small parts of space stations can reach the surface of the Earth, so uninhabited areas will be targeted for de-orbit manoeuvres.[55]
Notes
^Excludes visiting cargo like Tianzhou and crew vehicles like Shenzhou that are meant for supplementing the space station
^Duration is calculated from the moment of entry into the Tianhe core module to the time of undocking with the station.
^Initially docked to aft port, moved to forward port on 18 Sep 2021, and then again to portside port on 6 Jan 2022
^Initially docked to aft port, moved to forward port on 20 Apr 2022
References
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^Graham, William; Gebhardt, Chris (28 April 2021). "China readies launch of Tianhe module, start of ambitious two-year station construction effort". NASASpaceflight.com. This means the two future science modules, Wentian (“Quest for the heavens”) and Mengtian (“Dreaming of the heavens”), cannot dock directly to their planned radial port locations. [...] To account for this, each module will carry a Russian Lyappa robotic arm — like the ones used on Mir for the same purpose — to move the module from the forward port to its respective permanent location on a radial port of Tianhe's docking hub.
^Hong Yang (2020). Manned Spacecraft Technologies. China: Springer. p. 355. ISBN978-9811548970.
^Ping, Wu (23 April 2016). "空间站工程研制进展" [Space Station Project Development Progress] (PDF). China Manned Space Engineering. Archived from the original(PDF) on 14 September 2016. Retrieved 29 June 2016.
^John Cook; Valery Aksamentov; Thomas Hoffman; Wes Bruner (1 January 2011). ISS Interface Mechanisms and their Heritage(PDF). AIAA Space 2011 (Long Beach, CA). p. 26. JSC-CN-24225. Retrieved 31 March 2015 – via NTRS - NASA Technical Reports Server. The Chinese APAS is a clone of the Russian APAS. A view of the Chinese APAS is shown in Figure 19
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