China's Space Station Stabilizes Attitude During Astronaut EVAs

China's space station employs two primary methods to maintain stability and control its attitude during astronaut extravehicular activities (EVAs).

These methods include the use of thrusters, which adjust the station's orientation through reaction force, and Control Moment Gyroscopes (CMG). CMGs, acting as the space station's "balancing gyroscopes," regulate attitude via angular momentum exchange, offering more precise and smoother control compared to thruster-based adjustments.

During recent EVA missions, lasting approximately 5.5 hours, station personnel ensure the CMG system's stored angular momentum does not exceed its capacity. If the angular momentum nears its limit, the station temporarily switches to thruster control to offload excess momentum. This transition requires precise timing and safety protocols to prevent astronauts and robotic arms from being exposed to thruster plumes.

To manage angular momentum effectively during EVAs, China's space program has developed several strategies. These include reducing the initial angular momentum of the CMGs, increasing the maximum angular momentum capacity by engaging backup gyroscopes when necessary, and selecting an optimal nominal attitude to minimize the rate of angular momentum accumulation. Furthermore, momentum offloading is strategically timed during periods when robotic arms and astronauts are inactive, minimizing disruptions to EVA continuity.