Overview
- Yang Liwei, during China’s first human spaceflight Shenzhou 5, reported a repeating knocking sound that he said seemed to come from outside the capsule.
- Engineers inspected the spacecraft after landing and found no damage or hardware fault that accounted for the noise.
- Yang later described the tapping as a normal phenomenon and told future crews not to worry if they heard it.
- Chinese media reported similar knocks on later missions, including flights in 2005 and 2008, suggesting the effect recurred.
- Possible causes cited include tiny debris hits, metal flexing from rapid hot–cold cycles in low Earth orbit, or vibrations from valves, reaction wheels, or thrusters, and newer sensor suites now record such events for analysis.