China's Shenzhou-16 spaceship, with three astronauts aboard, docked with the country's space station combination at 4:29 p.m. Beijing Time on Tuesday, finishing another important step of the country's latest manned space mission, according to the China Manned Space Agency (CMSA).

It took six autonomous orbit adjustments and about six and a half hours to complete the autonomous fast docking process.

Most difficult docking to date

Shenzhou-16's docking with the China Space Station was harder than previous Shenzhou missions because of the station's colossal size and mass, which exceeded 100 metric tonnes.

"This is the first time we performed radial docking after the T-shaped station was assembled," said Yao Jian, managing designer of the docking subsystem. "We had to add new dampers to reduce the impact on both the spaceship and the station."

They also upgraded the craft's light sensors, as the giant space station blocked too much sunlight, making it more difficult for the craft to determine the position of the space station's dock.

"The new sensors have improved abilities to recognize targets," said Zhang Yi, deputy managing designer of Shenzhou-16's navigation and control systems. "They can tell if an object is the target or just an obstacle blocking the way."

Multiple fallback plans

With all the improved parts and technologies, the Shenzhou-16 spaceship is still not perfect. The Chinese space engineers made multiple fallback plans to protect the taikonauts in case the mission went sideways.

"If the rocket fails, the automatic escape system in the spaceship will be activated and bring the taikonauts back to the ground safely," said Shao Limin, deputy manager of technologies of the Shenzhou-16. "We can also use emergency returning if the spaceship is breached."

Multiple navigation systems help ensure the spaceship knows precisely where the dock is.

"We have two systems for positioning: the BeiDou satellites and microwave radars," Shao explained. "The BeiDou system has a machine-A and a machine-B that are hot backups of each other – if one breaks, the other can go on working."

Shenzhou-16's docking with the China Space Station was automatic without human intervention. If the process had failed, there was a plan B.

"We can switch to manual docking and ask the taikonauts to finish the process," Shao said. "The two processes are completely independent of each other."