Tianzhou 2 cargo ship docks with space station module

A Tianzhou cargo spaceship has two parts－a cargo cabin and a propulsion section. Such vehicles are 10.6 meters long and 3.35 meters wide. The craft, which has a liftoff weight of 13.5 metric tons, can transport up to 6.9 tons of supplies to the space station, according to Bai Mingsheng, Tianzhou's chief designer at the China Academy of Space Technology.

With a designed life of more than 1 year, Tianzhou 2, the country's second cargo spaceship, carried 6.8 tons of supplies for Tianhe, including 2 tons of propellants, more than 160 packages of living and experiment materials and two roughly 100-kilogram spacesuits for the astronauts to perform extravehicular activities outside the core module.

"Tianzhou 2 features a capability to conduct rapid autonomous docking with the space station. That is very significant for the station's operation because it ensures the timely delivery of time-sensitive items such as biological materials needed in experiments," Bai said. "Furthermore, such capability improves our readiness to respond to possible emergencies, as it can ferry urgently needed supplies to astronauts."

Beside refueling and resupplying tasks, the cargo ship will be used in scientific experiments and technology demonstrations during its linkup with Tianhe, but for most of its time in space, the craft will be dormant to save fuel and energy, Bai said.

The designer noted that when Tianzhou 2 departs from Tianhe, it will carry waste from the module and burn up during atmospheric reentry.

Lei Jianyu, a chief structural engineer of Tianzhou 2, said it is the world's best cargo ship when it comes to carrying capacity－before it, no cargo vehicle could transport as much as 6.9 tons of materials to space.

He said there are 18 cubic meters inside the vehicle for cargo and the shelves' shapes and arrangements were carefully calculated to make it easy for astronauts to move among them to get desired items.

Hao, from the manned space agency, said the Tianzhou 3 cargo ship will be launched in September to dock with Tianhe. In October, another three-astronaut team will fly to the core module on Shenzhou XIII to stay there for six months.

Two large space labs will be launched next year to connect with the module, and 2022 will also see two manned missions and two robotic cargo flights to further the construction of the Tiangong space station, which is scheduled to be completed around the end of next year.

Tiangong, China's most adventurous space endeavor, will consist of three main components－a core module attached to two space labs－with a combined weight of nearly 70 tons. The entire station is set to operate for about 15 years, mission planners have said.

Tianzhou 2's predecessor, Tianzhou 1, was China's biggest spacecraft when it entered service and was launched at the Wenchang launch center in April 2017.

It carried out several docking and in-orbit refueling maneuvers with a Chinese space laboratory in a low Earth orbit from April to September that year, making China the third nation with in-orbit refueling capability, after the former Soviet Union and the United States.

The world's first operational cargo spacecraft, Progress 7K-TG, was developed and launched by the Soviet Union in 1978. This type of transport vehicle conducted 43 cargo flights before being retired in 1990.

More than 200 cargo vehicles have been sent to deliver supplies to space stations. Currently, four models are in service－China's Tianzhou, Russia's Progress-MS and the US' Cargo Dragon and Cygnus.