China’s space station plan emerged in the mid-1980s in the wake of a global race to establish permanent human presence in space. The Soviet Union had already launched a number of Salyut/Almaz space stations and began to assemble a new multi-module station Mir. The United States government unveiled its ambitious plan to build Space Station Freedom. Japan and Europe also announced their plans to send human into space. Chinese space professionals believed that the country should have its own space station to avoid falling behind.
The goal of constructing an Earth-orbiting manned space station was set very early on in China’s manned space planning. Under Programme 863 (state high-tech R&D initiative), two expert groups were set up in February 1987 to draw up designs for the crew transportation system and manned space station respectively. While the choice for the crew transportation system between space shuttle and manned capsule sparked heated debates within the space community, having a space station as the ultimate goal for the manned programme was never a point of contention.
By 1991, the Chinese space industry had formulated a thirty-year plan to develop China’s human space flight technology in three phases: to send human into space aboard manned capsule in the first phase, to develop advanced spaceflight techniques including EVA and rendezvous docking and to launch 8 tonne temporarily man-tended space laboratories in the second phase, and to eventually build a 20 tonne manned space station in the third phase by 2020.
In September 1992, the Chinese leadership gave go-ahead to the initial phase of the manned programme, with the aim to send human into orbit aboard a manned capsule – the first step towards establishing human Chinese presence in space. The programme came to a conclusion in 2005 after having successfully launched four unmanned Shenzhou test flights and two crewed missions, making China the third country in the world to have the ability to send human into space independently.
In February 2005, the Chinese leadership approved the follow-up missions in the second phase of the manned programme, with the objective to develop advanced space flight techniques including extra-vehicular activity (EVA) and orbital rendezvous docking in support of the future space station programme. The first of these missions Shenzhou 7 was launched in 2008, which saw two Chinese astronauts performing a 20-minute spacewalk.
In October 2005, the State Council (central government) published the National Outline on Medium- and Long-Term Science and Technology Development (2006—2020), which put human space flight and lunar exploration as one of the China’s 16 key science and technology projects over the next fifteen years, effectively enshrining the space station programme into national strategy. Over the next three years, the PLA General Armaments Department (GAD) that oversees China’s manned space programme worked with the space industry and various relevant institutions to draw up a plan for the implementation of the space station programme.
The Chinese leadership officially approved the manned space station plan in September 2010. Chinese official writings described the objectives of the space station programme as “to build an operational manned space station in the low Earth orbit (LEO) around 2020, allowing the grasp of long-duration inhabitation of space, acquiring the capability to conduct long-duration, man-tended scientific and technological experiments in orbit, and enabling comprehensive exploration and utilisation of space resources”.
The original Project 921 writings called for the construction of a single-module station of 20 tonne orbital mass, essentially an enlarged space laboratory roughly comparable in size and capability to second-generation Salyut stations. By the time of the draft plan in 2010 this has evolved into a three-module configuration with a total orbital mass of 60 tonnes. In addition to serve as a scientific research facility in the low Earth orbit, Chinese space professionals also viewed the station as a platform to perfect and demonstrate long-duration life support, environment control, and resources recycle technologies required for future Chinese crewed deep space exploration missions including a temporarily-manned lunar base.
In October 2013, the China Manned Space Agency (CMSA) announced the naming of the Chinese space station. The station is named Tiangong (TG), the same name used by the two space laboratories launched during the second phase of the manned space programme but without a design number. The word Tiangong could be roughly translated as “Heavenly Palace” in English. The core module is named Tianhe (TH). The two laboratory modules are named Wentian (WT) and Xuntian (XT) respectively. The resupply cargo spacecraft is named Tianzhou (TZ).
Design
Tiangong is a third-generation modular space station, similar to the Russian Mir and the International Space Station but smaller in size. The space station in its basic configuration consists of a core module and two laboratory modules permanently docked together in a T-shape structure. Each of the three modules weighs about 20 tonnes. Together with two Shenzhou crew vehicles and a cargo resupply ship, the station will have a total mass of over 90 tonnes.
The three modules will be launched atop the Chang Zheng-5B launcher from the Hainan Satellite Launch Centre between 2018 and 2022. The station will station operates in a 42—43° inclined orbit 340—450 km above Earth, with a designed life of 10 years. If the International Space Station programme is to be retired in 2020 as currently scheduled, by the time it is fully assembled Tiangong may be the only operational space station in Earth orbit.
Between its three modules, the space station provides a total useable volume of 90 cubic metres for its crew. It is designed to support a three-man crew to live and work onboard continuously, though it can also operate with two astronauts only or completely autonomously. During its construction phase, the station will only be visited intermittently and remain unoccupied between visits. Once fully operational, the station will be continuously occupied. The station will also require at least one cargo resupply mission every 12 months to remain operational.
Modules
Tianhe Core Module
The core module, named Tianhe (“Heavenly Harmony”), is the backbone of the Tiangong space station, providing the main living quarters and also serving as the primary control element for the entire space station. The module is divided into three sections: an uninhabitable service compartment at rear, a pressurised living compartment in the middle, and a docking hub which also serves as an airlock at front. The module has a total of five passive APAS-type docking ports, four located on the docking hub at front and one on the rear end of the module.
The docking hub located at the forward end of the core module provides four docking ports. The two lateral docking ports are used as permanent attachment points for the two laboratory modules. The docking ports on the axis and Earth-facing directions are used for temporary docking of visiting Shenzhou crew vehicles. On the side of the hub facing away from the Earth a sealable hatch allows EVA astronauts to exit and re-enter the station. Externally the docking hub mounts a pair of solar panel wings and docking radar antennas and optical sensors.
The docking hub also doubles as an airlock to host EVAs, with a hatch located on the side facing away from the Earth to allow spacewalking astronauts to exit and re-enter the station. Spacesuits and other equipment will also be stored inside the hub. The docking hub provides the only EVA airlock for the core module during the initial construction phase. A permanent EVA airlock compartment will become available once the Wentian laboratory module is in place, after which the docking hub will only serves as a backup airlock.
The unpressurised service compartment accommodates the main engines, propellant tanks, power system, and communications system. A fifth docking port located at the rear end of the module is used for temporary docking of the Tianzhou resupply ship, though it can also be used as a backup docking point for the Shenzhou crew vehicle. A pressurised internal tunnel links the docking port through the service compartment to the living compartment to allow transfer of cargo and crew.
Wentian Laboratory Module
The first laboratory module, named Wentian (“Exploring the Sky”), will be designed and built by CAST in Beijing. The module divided into three sections: a fully pressurised working compartment at front, an airlock compartment in the middle, and an unpressurised service compartment at rear. The module is attached to the starboard side of the core module’s docking hub through an active APAS-type docking port at its front end. A pair of solar panel wings is mounted on a large boom with its centre attached to the rear end of the module.
The working compartment provides space for scientific and technological experiments, and is also used as a storage space for consumables and supplies used by the crew. The module is fitted with a secondary station control system as a backup to the main control system in the core module. The primary application payload onboard the Wentian module is a suite of Earth-observation instruments.
Xuntian Laboratory Module
The second laboratory module, named Xuntian (“Cruising the Sky”), will be designed and built by SAST in Shanghai. The module is also divided into three sections: a fully pressurised working compartment at front, an unpressurised application compartment in the middle, and an unpressurised service compartment at rear. It is attached to the port side of the core module’s docking hub through an active APAS-type docking port at its front end. A pair of solar panel wings is mounted on a large boom with its centre attached to the rear end of the module. The primary application system onboard the Wentian module is a space telescope mounted in the unpressurised application compartment, facing away from the Earth.
Spacecraft Systems
Power to the station is provided by an array of solar cells consisting of a pair of solar panel wings attached to the core module providing power supply during the initial flight demonstration and construction phase, and four large solar panels wings on the two laboratory modules as the main power source. The two solar panel wings on the core module are one-axis steerable, whereas the solar panel wings on the laboratory modules are two-axis steerable to track the Sun. The power management and distribution subsystem operates at a primary bus voltage of 100 volts.
There are two flight control systems providing most station control functions: a primary system on the core module and a backup system on the Xuntian module. The Tiangong space station will adopt an electrically-powered propulsion system using ion thrusters to reduce the amount of propellants being consumed for station keeping. All three modules of the space station are equipped with digital wireless communications. Information sharing and management is through three networks for spacecraft systems, communications, and payloads. Communication with the ground is via unified S-band (USB) links either directly to ground stations or through Tian Lian geostationary data relay satellites.
The space station is equipped with two robotic arms. The primary arm on the core module is developed by CAST and has a load capacity of 25 tonnes. The secondary arm on the Wentian laboratory module is developed by the Harbin Institute of Technology (HIT). The two robotic arms can be used either separately or jointly for assembling laboratory modules, installing and repairing external equipments and instruments, moving cargo and EVA astronaut around the station, and monitoring the station’s external conditions.
