Chinese space station freighter concludes refueling demo mission

Artist’s concept of the Tianzhou 1 freighter (left) and the Tiangong 2 space lab (right) docked together in orbit. Credit: China Manned Space Engineering Office

China’s Tianzhou 1 freighter, a pathfinder for regular resupply and refueling trips to the country’s planned space station, wrapped up a series of successful propellant transfer tests with the orbiting Tiangong 2 space lab Saturday and detached from the module for more standalone experiments and a destructive re-entry into Earth’s atmosphere.

Chinese space officials said in a statement that the Tianzhou 1 refueling and resupply craft completed its third transfer of propellant to the Tiangong 2 mini-space station in orbit at 0817 GMT (4:17 a.m. EDT) Saturday, pumping around 550 pounds (250 kilograms) of liquid fuel and oxidizer into the space lab nearly 250 miles (400 kilometers) above Earth.

The two spacecraft undocked Sunday to continue independent trials, with Tianzhou 1 set to eventually de-orbit and make a guided plunge into Earth’s atmosphere, where it will largely burn up and spread debris over a remote stretch of ocean. Chinese officials have not said when Tianzhou 1 will re-enter the atmosphere.

Tiangong 2 will continue its mission in orbit conducting experiments on several critical technologies necessary for China’s future space station, including a life support system. The space lab carried also carried an experiment to detect gamma-ray bursts, plus Earth observation, navigation and communications test equipment, when it launched in September 2016.

Two Chinese astronauts on the Shenzhou 11 mission lived aboard the Tiangong 2 space lab for one month late last year, the longest crewed spaceflight to date by China’s space program.

Tiangong 2 measures about 34 feet (10.4 meters) long and 11 feet (3.4 meters) wide. Its two solar array wings span 60 feet (18.4 meters) tip-to-tip. Tianzhou 1 is roughly the same size.

No more Chinese crews are planned to visit Tiangong 2. The next Shenzhou mission will launch astronauts to the Tianhe 1 module, the command section of China’s planned space station set for launch in 2019.

The Tianhe 1 module will be joined by China’s second supply ship, named Tianzhou 2, for a cargo delivery before the first astronaut crew visits the orbiting facility aboard the Shenzhou 12 spacecraft.

Two more modules will be added to the space station by 2022, completing assembly of a complex that is expected to have a mass of more than 60 metric tons, about one-seventh that of the International Space Station, and comparable to the mass of NASA’s Skylab station in the 1970s.

Tianzhou 1 is the first flight of a servicing craft designed to deliver cargo and fuel to the Chinese space station.

Designed to accommodate up to 14,300 pounds (6,500 kilograms) of payloads, the Tianzhou spacecraft is similar in purpose to cargo freighters that fly to the International Space Station, such as the Russian Progress supply ship and the commercial Cygnus and Dragon carriers built by Orbital ATK and SpaceX.

Tianzhou means “heavenly vessel” in Chinese.

In design and capability, the Tianzhou is most like Russia’s Progress and Europe’s now-retired Automated Transfer Vehicle, which carried dry goods, water and propellant to the orbiting outpost. The U.S. commercial supply ships and Japan’s HTV logistics vessel cannot refuel the space station.

While no crews were present during Tianzhou 1’s mission, the freighter hosted several experiments, including one on “non-Newtonian” gravity, according to Chinese media reports published when the cargo freighter launched in April. Other research investigations were launched to study the proliferation and differentiation of human embryonic stem cells into germ cells to gather data on the possibility of human reproduction in space, China’s state-run Xinhua news agency reported.

The stem cells and embryos of mice were also on-board Tianzhou 1 for an experiment into how animals and humans could regrow lost tissues and organs, Xinhua said. Researchers also sent up an experiment to test out a new medicine for osteoporosis.

Tianzhou 1 accomplished three automated dockings with Tiangong 2 after its April 20 launch aboard a Long March 7 rocket from the Wenchang space base, a spaceport on Hainan Island in southern China.

The final linkup occurred at 0458 GMT (12:48 a.m. EDT) on Tuesday, Sept. 12, after a simulated fast-track rendezvous profile to check out procedures for future cargo vehicles and crew ferry craft to dock with the Chinese space station as quickly as six hours after liftoff, China’s Manned Space Engineering Office said in a statement.

The expedited rendezvous sequence is similar to one used by Russian Progress and Soyuz spaceships launching to the International Space Station.

Chinese officials said Tianzhou 1 has been in “stable operation” for five months since its launch, including time spent in solo flight and docked with Tiangong 2. Tianzhou 1 released a small Chinese CubeSat in August while separated from the Tiangong 2 space lab.

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