Credit: CCTV/Inside Outer Space screengrab

China has tested a key step in completing its space station by the end of this year.

A mechanical arm of China’s Tianhe core module shifted the Tianzhou-2 cargo spacecraft, then re-docked and locked the hardware to the core cabin.

The China Manned Space Agency (CMSA) said early Thursday morning that the experiment will be applied in the subsequent assembly and construction of the space station in orbit.

The process took about 47 minutes and was the first time that China has used the space station robotic arm to operate a large spacecraft in orbit for a “transposition” test. It is the first such maneuver of the robotic arm that measures 33-feet (10-meters) long and that’s able to lift objects weighing up to 20 tons.

Credit: GLOBALink/Inside Outer Space screengrab

Breakthrough technology

After being unlocked and separated from the Tianhe core module, the Tianzhou-2 cargo spacecraft was dragged by the mechanical arm, taking the sphere center of the core module’s node cabin as the center of the circle for plane transposition.

Then, a reverse operation was performed until the cargo spacecraft re-docked and locked with the core cabin, reports China Central Television (CCTV). The robotic arm is installed on the Tianhe core module.

The precursor evaluation will be utilized when China launches two lab modules – the Wentian and Mengtian lab modules — to the station construction site later this year.

Credit: CNSA/CMG/CCTV/Inside Outer Space screengrab

“If transposition fails or is unavailable, the whole scale will probably be limited. This is a technology in which we must make breakthrough in the course of building the entire space station,” Shi Jixin, deputy chief designer of the space station at the Fifth Academy under the China Aerospace Science and Technology Corporation (CASC) told CCTV. “The entire space station can be built on schedule only when we make the technological breakthrough,” Shi said.

First, the robotic arm crawled to its berth port near the node cabin of the core module two days ahead of schedule in preparation for the transposition test. After that, the Tianzhou-2 cargo spacecraft was grabbed by the robotic arm.

“I use a robotic arm to push the cargo spacecraft to unlock, and then reverse it and make it return to re-dock, and finally complete the lock,” said Shi.

Trial testing

Shi said that during the transposition test, one end of the robotic arm was connected to the core module and the other end to the Tianzhou-2 cargo spacecraft, which is unstable and might cause damage to the robotic arm just like a pole carrying two elephants. Therefore, technical researchers have carried out a dedicated design for the transposition test.

China’s space station is projected to be completed in late 2022.
Credit: CAST

“First, I set it upright, and then reverse it at a 90-degree angle, so that the windward side is the smallest and the operation in orbit has a minimal aerodynamic disturbance. It stands up like a pendulum, and the module is actually gradient-stable, which means that no matter which way I flip it, it will stay on its vertical axis,” Shi told CCTV.

Xu Xiaoping, deputy chief designer of the cargo spacecraft system of the Fifth Academy of China Aerospace Science and Technology Corporation (CASC) added: “Before carrying out the test in space, we had conducted trial tests on the ground to simulate the space test.”

Xu noted that he mechanical arm of the space station has assisted astronauts in four extravehicular activities. The test conducted Thursday was a test of the mechanical arm’s capability of transposition of the cargo spacecraft.

Large load

“The mechanical arm has never carried such a large load. In the past, an astronaut out of the spacecraft plus the space suit carried by a mechanical arm usually weighed about 300 kilograms. This time the load weighs nearly nine tons. Such a heavy load is also a test to the mechanical arm,” said Shi.

Shi said that the space station system is in good condition, and the maneuver will also prepare Tianhe to dock the Wentian and Mengtian lab modules.

Credit: CCTV/Inside Outer Space screengrab

“It is a joint validation of multiple systems,” Shi explained. “First, in the process of docking, the speed of the mechanical arm in fact is not high enough. Thus, the GNC [guidance, navigation and control] subsystem is needed to accelerate the speed, so that docking could be successfully completed. After docking, the cargo spacecraft needs to be re-docked and captured, and then the mechanical arm will withdraw after the locking [is] completed. Therefore, multiple systems involved in this process will be verified in the test.”

Two modes

“Astronauts control the cargo spacecraft in the core module, and carry out manual remote operation to conduct withdrawal and docking tests. At present, there are two modes of cargo spaceship rendezvous and docking. The automatic rendezvous and docking would be carried out if everything goes well. If any abnormality occurs, we also have the backup means of manual remote operation. So this operation in fact is mainly for the in-orbit verification of the backup means,” said Yang Sheng, general chief of the cargo-freighter system, Fifth Academy of CASC.

After completing all missions, Tianzhou-2 will separate from the space station core module, taking away stored waste and human excrement before eventually departing from orbit and burning up upon re-entry into the Earth’s atmosphere. This is also one of the key technologies of the space station construction.

Tianzhou-2 cargo spacecraft.
Credit: CCTV/Inside Outer Space screengrab

“Depending on its overall consumption and lifespan, Tianzhou-2 will choose the proper time to separate from the space station core module and burn up the waste upon re-entry into the Earth’s atmosphere. So, Tianzhou-2 is entrusted with the most and hardest tasks, and thus will stay relatively longer in orbit,” said Yang.

China sent the cargo craft Tianzhou-2 into space on May 29 last year from the southern island province of Hainan, to deliver life support supplies for astronauts, spacesuits for extra-vehicular activities, and space-science equipment among other supplies, and also to replenish Tianhe’s propellant.

On September 18 of last year, the Tianzhou-2 cargo craft separated from the rear docking port of Tianhe and docked with its front docking port.

The space station core module Tianhe was launched on April 29, 2021.

Shenzhou-13 crew members.
Credit: CNS/Inside Outer Space screengrab

Busy year

Upon its completion at the end of this year, Tiangong (Heavenly Palace) will consist of three main components; a core module attached to two space labs, and will have a combined weight of nearly 70 tons.

China’s station is scheduled to operate for 15 years in a low-Earth orbit about 250-miles (400-kilometers) above the planet.

Six launches this year involve Shenzhou-14 and Shenzhou-15 crewed missions to the Tiangong orbiting outpost, the Tianzhou-4 and 5 robotic cargo spaceships and the two large space labs that will be docked to the facility.

China Daily reports that the first of the six to be launched will be Tianzhou-4, which will be followed by the Shenzhou-14 piloted spacecraft. Then the two space labs — Wentian (Quest for the Heavens) and Mengtian (Dreaming of the Heavens) — will be launched to complete the station. The fifth launch will be Tianzhou-5 and the final will be the Shenzhou-15 crew.

To watch newly released videos of this testing phase of China’s space station construction and life onboard the facility, go to:

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