−252.8 °C Liquid Hydrogen Acoustic Emission Experiment in Simulated Aerospace Fuel Tank

With the increase of space activities, the safety detection of equipment in supercold environment becomes more and more important. However, the safety detection of equipment in liquid hydrogen environment is an unsolved worldwide problem. In this article, we present a new method to detect acoustic emission (AE) signals in liquid hydrogen environment, which can be used to confirm the safety and reliability of the equipment working in liquid hydrogen. First, the principle of mandrel-based fiber-optic ring (MBFOR) AE sensor and the corresponding demodulation method are introduced. Second, the effects of physical parameters, such as the length of the sensing fiber, the diameter and material of the mandrel, and the number of fiber winding layers on the sensor's sensitivity, are studied by experiment. Finally, the AE source localization accuracy test of the FOR AE detection system at low temperatures and the adaptability test of the proposed method in −252.8 °C liquid hydrogen are carried out. The results show that the proposed MBFOR sensor and the multichannel AE detection system can complete the defects detection of aerospace pressure vessel in liquid hydrogen. Certainly, it can be used for safety detection for other spacecraft equipment in harsh environments.