At 23:44 on October 31, 2025, the Shen Zhou-21 manned spaceship, carrying three astronauts, was successfully launched into its predetermined orbit by a Long March-2F carrier rocket. As astronauts Zhang Lu, Wu Fei, and Zhang Hongzhang will conduct an in-orbit rotation with the Shen Zhou-20 crew, six astronauts will stay temporarily together in orbit. This mission is the sixth manned flight during the application and development stage of the space station. The Shen Zhou-21 manned spaceship will, for the first time, adopt the 3.5-hour rapid autonomous rendezvous-docking mode, docking with the forward port of the space station.

SAST undertook a number of tasks for this mission, including development of the spaceship's power subsystem, docking mechanism subsystem, structure and assembly of the propulsion module, telemetry tracking and command (TT&C) communication subsystem, cable network of the propulsion module for the general circuit subsystem , and the power distributors for the three modules.

The "upgrading code" for precise docking

From the Shen Zhou-8, to the Shen Zhou-21, the time required for the first in-orbit rendezvous and docking has been shortened from 2 days to 3.5 hours. Behind this upgrade, SAST has additionally conducted more than 10 simulated flight tests for its products. It has also carried out multiple rounds of system-level joint drills in combination with dozens of fault response plans, which had fully verified the suitability and effectiveness of the contingency measures.

As a key component for rendezvous and docking, the docking mechanism has evolved significantly: the Shen Zhou-8 initially adopted a mechanical transmission and buffer system with fixed damping stiffness, while the prevailing version for Shen Zhou-21 has been optimized into a controlled damping and buffer system featuring both rigidity and flexibility. It can achieve flexible buffering and precise docking under different tonnages and docking scenarios, greatly improving the docking adaptability of the mechanism and laying a solid technical foundation for subsequent missions. As of now, the docking mechanism has completed 36 docking missions and 32 separation missions in orbit, all with great success.

“Service life extension upgrade” of the power supply system

With the expansion of China’s space station missions, the requirement to extend the total in-orbit flight time of the Shen Zhou spaceship has gradually been put on the agenda. As the "energy heart" of the Shen Zhou spaceship, the power supply subsystem has undergone a “key upgrade" on the zinc-silver batteries used in critical system components including the emergency power supply, return-and-landing power supply, pyrotechnic power supply for the return module, and pyrotechnic power supply for the orbital module. Improvements included enhancing the separator to increase battery strength and corrosion resistance, optimizing the zinc-silver ratio, and slowing separator oxidation to "extend the service life" of the batteries. Meanwhile, the power supply subsystem has further optimized its charging control method for lithium-ion batteries and a "triple protection mechanism" has been established to prevent overcharging, overheating, and over-discharging of the batteries. 

In addition, to adapt to this autonomous rapid rendezvous and docking mission, the emergency plans have been refined and 15 emergency response plans revised for power supply subsystem, further enhancing the reliability of this mission.

Meticulous escort for risk prevention and control

Based on the characteristics of this mission, SAST has dissected 32 specific elements from the four dimensions (technology, product, management, and operations) with a view to carrying out comprehensive risk analysis and control. By particularly focusing on analysis of mission characteristics, identification of key features, and analysis of the coverage and adequacy of testing, it has comprehensively verified and assessed all the risk-prone technical items of the products. This has resulted in the establishment of actionable, easy-to-implement digital management requirements and the creation of a risk control database, thereby further enhancing the risk identification and control capabilities of the manned spaceflight program.

Looking back, success has never been a smooth journey. The "upgrading" of the Shen Zhou series rockets has witnessed not only breakthroughs from zero to one, but also leaps from average to excellence. Every successful mission is backed by the hard work of countless aerospace workers who have interpreted the "space dream" with rigor, prudence, meticulousness, and practicality – enabling the Chinese people to take steadier and farther steps in exploring the universe.