Spacecraft vibration during first human flight

During the launch of China's Shenzhou 5 spacecraft in 2003, a low-frequency resonance occurred between 30 and 40 kilometers altitude, causing significant physical distress to the pilot, Yang Liwei. The vibration, below 10 Hz, combined with an acceleration of 8 G, froze Yang for 26 seconds, during which he was unable to move or see clearly.

Cause of the vibration

The resonance was not caused by the engines' thrust or noise but by a mechanical oscillation of the launcher, a phenomenon that was not anticipated by the engineers involved. The incident was not publicly acknowledged at the time, but it revealed a critical design flaw in the Long March 2F rocket.

Health risks of low-frequency vibrations

The resonance at such a low frequency posed a serious risk to human health, as vibrations in this range can damage internal organs. Despite the successful completion of the mission, with the spacecraft completing fourteen orbits around the Earth and traveling approximately 600,000 kilometers before returning to Earth safely, the incident highlighted the need for adjustments in the spacecraft's design.

Engineering modifications

Engineers made modifications to the engine piping and the pressure accumulator, which reduced the intensity of vibrations by more than half, significantly improving the comfort and safety of subsequent missions. Similar vibrations were reported during the Shenzhou 6 mission, indicating that the issue had not been fully resolved.

Design improvements and results

Jing Muchun, chief designer of the Long March 2F rocket, stated that the teams adjusted the engine piping to modify its natural frequency and rethought the design of the pressure accumulator. These changes led to a substantial reduction in vibration levels. Gao Xu, who later led the launcher design, noted that the levels of vibrations experienced by the crews became comparable to those of a car ride on a highway.

Improved crew experience

Chen Dong, a member of the Shenzhou 11 crew, described the flight as smooth, similar to a high-speed train ride, contrasting sharply with the experience of Yang Liwei during the Shenzhou 5 mission.