Chinese cargo craft Tianzhou-2 docks with space station core module Tianhe

The combination of the Tianzhou-2 cargo spacecraft and a Long March-7 carrier rocket is transferred to the launching area, May 16. (Photo/Xinhua)

At 5:01 a.m. (Beijing Time) on May 30, Chinese cargo craft Tianzhou-2 successfully docked with the space station core module Tianhe, becoming the first spacecraft to visit the core module.

Rendezvous and docking is one of the basic technologies of manned space activities, as well as a prerequisite for in-orbit services of space stations and space transport systems, including assembly, recycling, replenishment, maintenance, astronauts substitution and rescue.

Dang Rong, deputy chief designer of Tianzhou-2 from the China Academy of Space Technology (CAST), introduced that it normally takes two to three days from the launch of a spacecraft to its rendezvous and docking, and the process also calls for much manned intervention.

Quickness was the highlight of the docking between Tianzhou-2 and Tianhe, said the deputy chief designer, adding that the whole process took around eight hours with no intervention from ground station, similar to driverless cars.

The Tianzhou-2 cargo freighter is composed of a pressurized cargo section and a propulsion section. Measuring 10.6 meters in length, it has a maximum takeoff weight of 13.5 tonnes and carries 6.8 tonnes of goods and materials. The cargo craft will operate in orbit for at least one year. Its power supply capacity is not less than 2,700 watts. Different from the Shenzhou manned spacecraft, the Tianzhou-2 cargo freighter only carries cargos.

In April 2017, Tianzhou-1, China’s first cargo spacecraft, successfully conducted automated docking with the orbiting Tiangong-2 space lab, and then carried out the first in-orbit refueling. As an important part of China’s space station, Tianzhou-2 is responsible for transporting materials to, refueling for, and taking away the waste from the space station.

According to Feng Yong, commander-in-chief of the Tianzhou-2 mission from the CAST, the carry-on onboard the cargo craft includes consumables that are designed to support three astronauts on their space missions for three months, space suits for missions outside cabin and other supplies. Apart from living materials, Tianzhou-2 also carries propellants to refuel the core cabinet.

Experiment devices and materials were also shipped by Tianzhou-2, and will be taken out and installed by astronauts when they are sent to the core module Tianhe by the Shenzhou-12 manned spaceship, Feng said.

Tianzhou-2 is loaded with some 160 parcels of goods and two tonnes of propellants, which account for over half of its total mass. There are two space suits for the astronauts’ outside-cabin activities, and each of them weighs over 100 kilograms.

Besides, a “space massager” and a “space refrigerator” also went into space with Tianzhou-2. The “space massager,” developed by the Sanjiang Group under the China Aerospace Science and Industry Corporation Limited (CASIC), can help astronauts alleviate muscle fatigue and reinforce muscle strength via electric pulse stimulation, so as to prevent amyotrophy, a possible result of long-term spaceflight. The “space refrigerator” manufactured by the 306th Research Institute under the CASIC is able to protect key medical materials and supplies in the cargo craft.

China has planned 11 missions in 2021 and 2022 to complete its space station construction, three for space station modules, four for cargo craft and four for manned spaceships.

The 11 missions scheduled for two years are like a relay race, and every mission concerns whether China can achieve a success in building the space station, said Xu Lijie, the chief designer of the country’s Long March-7 carrier rocket from the China Academy of Launch Vehicle Technology.