China’s second Space Laboratory module, designed to demonstrate medium-term orbital living and in-orbit inrefuelling of propellants, and to carry out large-scale space science and applications experiments.
Type: Man-tended space laboratory. Crew size: 2. Programme: Project 921-II. Agency: CMSA. Primary contractor: CAST/CASC. Status: Deactivated. First launch: 2016-09-15. Last launch: 2016-09-15. Number: 1. Designed life: 2 Years. Launch vehicle: CZ-2F. Launch complex: Jiuquan–SLS2. Orbit: 380—400 km LEO, 42.77º inclination. Length: 10.4 m. Diameter: 3.35 m. Solar panel span: 18.4 m. Pressurised volume: 14 m3. Mass (orbital): 8,506 kg. Propellants: N2O4/MMH.
Five years after the launch of the first Space Laboratory module Tiangong 1, the China Manned Space Programme (CMSP, Project 921) was ready to launch a second module. Two identical modules were originally built for the Tiangong 1 mission. After the successful launch of Tiangong 1, its backup was modified into an improved module added with upgraded systems and new capabilities, most notably the ability to be resupplied and refuelled by a Tianzhou cargo vehicle.
To ensure the ‘new’ space module was still qualified for orbital flight after spending five years inside the spacecraft hangar at CAST, engineers had to carefully assess the conditions of nearly 300 components and parts on the module, either putting them through a life-extension process or replacing those that no longer met the requirements.
Unlike its predecessor Tiangong 1, which was mainly intended as a target vehicle for perfecting orbital rendezvous docking, Tiangong 2’s main objective was to “verify key technologies including cargo transportation, on-orbit propellant resupply, and medium-term stay of astronauts”, as well as “conducting space science and application experiments on a relatively large scale”, according to the programme’s official statement.
In February 2016, Chinese state media cited sources from the China Manned Space Agency (CMSA) that the country would orbit its second space laboratory Tiangong 2 in third quarter of this year, followed by a single expedition mission Shenzhou 11 in the fourth quarter of the same year and an experimental cargo resupply mission Tianzhou 1 in the first half of 2017.
The launch campaign began with the arrival of the Tiangong 2 module at the launch centre on 9 July, after a two-day train journey from its fabrication facility at the Beijing Space City. Upon its approval, the Tiangong 2 module was examined and assembled inside the Spacecraft Non-Hazard Operation Building, before being moved to the Spacecraft Hazard Operation Building for the irreversible process of fuelling with liquid propellants and loading of pressurised gases. The completed spacecraft inside its payload fairing was rolled to the Launch Vehicle Vertical Processing Building, where the CZ-2F launch vehicle was assembled. The spacecraft inside the payload fairing was then hoisted onto the top of the launch vehicle for payload integration.
On 9 September, the CZ-2F/Tiangong 2 launch vehicle stack sitting vertically atop the Mobile Launcher Platform (MLP) was rolled out to Pad 921 situated 1.5 km away from the processing building. Once the launch vehicle stack arrived at the pad, the rotating platforms of the umbilical tower were swung to ‘embrace’ the vehicle to allow the final checkout procedure to be conducted. After the mission managers gave a Go to the launch, fuelling of the CZ-2F launch vehicle with liquid propellants began in the morning of 14 September.
The CZ-2F (T2) launch vehicle, which lifted off from Jiuquan at 22:04 CST on 15 September, inserted the Tiangong 2 module into an initial 350 x 200 km parking orbit with an inclination of 42°. The next day, the space module used its own propulsions to make two orbit elevation manoeuvres, moving onto a 380 km near-circular orbit. Over the next few weeks, the ground mission control carried out various checks remotely to ensure that the space module is readied for the docking operation.
The Tiangong 2 module is almost identical to its predecessor in size and appearance, consisting of two cylinder-shaped sections: a habitable Experiment Compartment serving as the main living quarters and laboratory for the crew; and an inhabitable Service Compartment that houses propulsion, power, life support, and communications systems. A pair of solar wings each with 4 solar panels are attached to the Service Compartment. The space module is 10.4 m in length and 3.35 m in diameter, with an orbital mass of 8.6 t.
- The front Experiment Compartment is 5 m in length and 3.35 m in diameter, with a habitable internal volume of 14.4 cubic metres (2.0 x 1.8 x 4.0 m). The front end of the compartment, which provides a small free space for the crew to live and conduct experiment, is surrounded by heat pipes designed to conduct heat from internal systems to an external radiator. Inside the compartment is an instrument panel for flight controls and communications, a foldable table for eating and conducting experiments, and two sleep stations. There is a window on either side of the compartment allowing observation of outside. The remaining part of the compartment is packed with equipment and experiments.
- The module is connected to the visiting Shenzhou and Tianzhou spacecraft via an androgynous docking mechanism developed by Shanghai Academy of Spaceflight Technology (SAST). The system is believed to have derived from the Russian APAS-75, consisting of a docking port, radio beacons, transponders, communication antenna, UHF radar, laser rangefinder, and electro-optical tracking system. Visiting astronauts enter the Experimental Compartment via the hatch on the 0.8 m-diameter docking port. The docking port on Tiangong 2 has been modified in order to support in-orbit refuelling/resupply operations.
- Behind the experiment compartment is a 1.1 m-long transition section, tapered from 3.35 m diameter of the experiment compartment to the 2.25 m diameter of the aft service compartment. The section houses the nitrogen and oxygen tanks used for environmental control, and the water tank. The gases are stored in steel alloy spheres at a pressure of 21 Mpa.
- The aft Service Compartment is about 3.3 m in length and 2.5 m in diameter, and has been derived from the Shenzhou service module. The Space Laboratory is fitted with a different propulsion system to that of Shenzhou, with a 490-N dual-chamber high-expansion-ration main engine, four sets of two small aft-firing engines at the base to provide vernier thrust for fine manoeuvres, four sets of two small engines mounted around the external base of the module for pitch/yaw control, and four roll control thrusters. The unified propulsion system feeds both attitude control and main engines from four 230-litre propellant tanks loaded with up to 1,000 kg of N2O4/MMH propellants. The engines are pressure-fed using six 20-litre titanium cold gas tanks pressurised to 23 Mpa. This gas is used to force propellant at 2 Mpa using diaphragms within the propellant tanks.
- Two four-panel solar wings, with a total span of about 23 m, deploy from the sides of the Service Compartment. These can be rotated to obtain maximum solar insolation regardless of spacecraft attitude. Each wing, about 3.1 m x 10 m, provides about double the electrical power of the Shenzhou system (total about 7 kW peak, 2.5 kW average). The back surface filled silicon solar cells of the arrays have an efficiency of 14.8% on Shenzhou. Sun sensors between the panels measure the sunlight incidence angle which allows the panels to be automatically commanded to an optimum angle. Silver-zinc batteries in the service module provide emergency power in case of failure of the solar arrays. The spacecraft’s power bus operates at 28 V.
- The module is fitted with a robotic arm, developed by China Aacademy of Space Technology. The 10-m long robotic arm is designed to help the assembly and maintenance of the space station, move equipment and supplies around the station, and support astronauts in EVA.
- The Banxing 2 micro satellite, designed by Shanghai Academy of Spaceflight Technology (SAST), will be launched on the piggyback of Tiangong 2 and then released in orbit to demonstrate relevant technologies. Just like its predecessor Banxing 1 launched by the Shenzhou 7 mission in 2008, Banxing 2 will probably also carry an onboard camera to capture images of the mothership in orbit.
Tiangong 2 carries a total of 14 mission and experiment packages, including:
- The world’s first-ever in-space cold atomic fountain clock;
- Space-Earth quantum key distribution and laser communications experiment;
- A Gamma ray detector;
- Liquid bridge thermocapillary convection experiment;
- Space material experiment;
- Space plant growth experiment;
- Multi-angle wide-spectral imager;
- Multi-spectral limb imaging spectrometer;
- Stereoscopic microwave altimeter;
Shenzhou 11 — The sixth manned spaceflight mission to send a crew of two astronauts to the Tiangong 2 space laboratory module, where they will spend 30 days living and working in orbit.
Date Mission Type Crew Launch Site Launch Vehicle --------------------------------------------------------------------------------------------------- 2016-09-15 Tiangong 2 Space laboratory None Jiuquan CZ-2F (T2) 2016-10-17 Shenzhou 11 Crewed Jing Haipeng Jiuquan CZ-2F (Y11) Chen Dong 2017-04-20 Tianzhou 1 Fuel resupply None Wenchang CZ-7 (Y2)