China’s first cargo spacecraft, Tianzhou 1, has successfully docked with the Tiangong 2 space laboratory module for a six-month mission to demonstrate its design and technology, including on-orbit refuelling. The cargo spacecraft, carrying nearly 6 tonnes of equipment and supplies including 2 tonnes of liquid propellants, weighs 12.91 tonnes and is the heaviest spacecraft ever orbited by China. It launched aboard the Long March 7-Y2 launch vehicle from Wenchang Space Launch Centre last Thursday (20 April). After performing a number of orbit elevation and refinement burns, it docked with Tiangong 2 at midday Beijing Time on Saturday 22 April.
Tianzhou 1 Launch
The cargo resupply spacecraft programme was initiated in late 2010, and China Academy of Space Technology (CAST) was awarded the development contract in January 2011. By August 2014, the cargo spacecraft design had been finalised and the spacecraft was officially named Tianzhou (Sky Vessel). The first full-size prototype of the Tianzhou spacecraft was completed in April 2015. Production of the Tianzhou 1 vehicle began in April 2016 and the spacecraft was completed in January this year.
Tianzhou 1 launch campaign kicked off on 5 February, when the cargo spacecraft left Tianjin for the Wenchang Space Launch Centre aboard a cargo ship. After a week voyage the spacecraft arrived at Wenchang on 13 February for final assembly and testing. On 11 March, the Long March 7-Y2 launch vehicle also arrived at Wenchang. By 30 March, the various mission payloads had all arrived at the launch centre for testing and loading.
In the morning of 17 April local time, the assembled launch vehicle and spacecraft stack rolled out from the Vehicle Assembly Building at the Wenchang Space Launch Centre atop the Mobile Launcher Platform. After 2.5 hours of transit, the giant 1,800-tonne platform carrying the launch vehicle arrived at the launch pad.
Fuelling of the kerosene liquid fuel for the two-stage Long March 7 launch vehicle began at T minus 12 hours in the morning of 20 April, and fuelling of the liquid oxygen began at T minus 8 hours. The fuelling process lasted until about T minus 40 minutes.
At 19:41:35 CST (11:41:35 UTC) on 20 April, the Long March 7-Y2 launch vehicle carrying Tianzhou 1 lifted off from Pad 201 of Wenchang Space Launch Centre. After 10 minutes of flight, the second-stage engine shut down at 19:51:38 CST and the spacecraft was placed into a 200 x 383 km, 42.8° inclination initial parking orbit. Few moments later, the spacecraft’s two solar panel wings were successfully deployed, and the launch mission was declared a success.
Tianzhou 1 was China’s first orbital launch mission to have relied on the Tianlian tracking and data relay satellite as its primary tracking, telemetry and control (TT&C) system, while two Yuanwang tracking ships stationed in West and South Pacific provided secondary communications support during the ascent stage of the flight.
The Tianzhou cargo spacecraft was derived from the Tiangong space laboratory module, almost identical in appearance and size. The spacecraft consists of two cylinder-shaped sections: a habitable Cargo Compartment 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 spacecraft is 10.6 m in length and 3.35 m in diameter, and weighs nearly 13 tonnes (12.91 tonnes for the Tianzhou 1 mission) when fully loaded—the heaviest spacecraft China has ever launched. It is capable of carrying 6.5 tonnes of cargo, including 2 tonnes of liquid propellants.
The front Cargo Compartment is surrounded by heat pipes designed to conduct heat from internal systems to an external radiator. Equipment and supplies are packed in bags and strapped to wall-mounted racks and shelfs inside the compartment, with a small corridor in the middle to allow movement of the crew from the receiving space station. Future Tianzhou vehicles will also include both partially pressurized and non-pressurized variants to meet different mission requirements.
For the Tianzhou 1 mission, the spacecraft carried over 100 bags of equipment and supplies, including 90 man-days worth of supplies, an EVA space suit, a soft water tank and a rigid water tank, a pair of oxygen canisters, and a pair of nitrogen canisters. The spacecraft also carried about 2,000 kg of liquid propellants (both fuel and oxidiser), which will be used to demonstrate the on-orbit refuelling procedure. In addition, the spacecraft also carried 13 experiment packages. A scientific experiment CubeSat named Silu 1-01 was mounted on external pylon of the spacecraft and will be released during the mission.
The module is connected to the Tiangong 2 space laboratory module via an androgynous docking mechanism developed by Shanghai Academy of Spaceflight Technology (SAST). Tianzhou 1 is said to feature an improved second-generation docking system, which is capable of the faster 6-hour docking procedure and transferring liquid propellants through 4 refuelling nozzles on the docking port. Rendezvous and docking aids will likely consist of radio beacons, transponders, communication antenna, UHF radar, laser rangefinder, and electro-optical tracking system.
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.
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 Tianzhou cargo spacecraft features an improved 2nd-generation 490-N dual-chamber high-expansion-ration main engine, as well as 25-N, 120-N and 150-N control thrusters for pitch/yaw and roll control. 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.
The Tianzhou cargo spacecraft features a number of new technologies that have been put in use for the first time. It is the first Chinese spacecraft to have been developed completely using digital 3D simulation throughout design, manufacturing and testing; the spacecraft is equipped with an improved dual narrow/wide-band data communication terminal, which provides extra redundancy in tracking and communications via the Tianlian tracking and data relay satellites; It is also equipped with an improved Control Moment Gyroscope (CMG) platform for better navigation and orbit insertion accuracy.
Tianzhou 1 Mission
According to Chinese state media, the primary objectives of the Tianzhou 1 mission include:
- Demonstrating in-orbit refuelling procedure, and grasping on-orbit propellant refuelling technique;
- Demonstrating fast orbital rendezvous and docking;
- Carrying out scientific experiments with onboard experiment payloads;
- De-orbiting the spacecraft at the end of the mission;
- The entire mission is expected to last 5—6 months, during which the Tianzhou 1 spacecraft will perform three missions of rendezvous dockings and in-orbit refuelling with Tiangong 2, before finally performing a controlled de-orbit and burning up in the atmosphere.