Anomaly Detection Method of Spacecraft Propulsion Using Multiplexed Fiber Bragg Gratings
Creators: name:  K. TOMINAGA 
name:   G. FUJII 
name:   T. NAGATA 
name:   D. WADA 
name:   S. HISADA 
name:   K. KAWATSU 
name:   T. KASAI 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: FUTURE SPACE OPERATIONS

description: To realize autonomous onboard fault detection and diagnostics for anomaly with spacecraft propulsion system in limited sensing resource, JAXA is currently conducting research on health monitoring technology focusing on dynamic response of pressure at the time of propellant valve operation [1,2]. The spacecraft propulsion system is equipped with only the minimum number of pressure sensors due to its weight and the limited number of sensor channels. Therefore, the amount of information that can be used for health monitoring is limited. To solve this problem, we thought that lightweight strain sensors, Fiber Bragg Gratings (FBGs), could be applied to the spacecraft propulsion system as a sensor to measure pressure changes at multiple points. However, it is not clear whether FBGs can measure pressure changes in the spacecraft propulsion system with the same accuracy as pressure sensors, and also whether they can be applied to detect anomalies in the propulsion system. In this study, the feasibility of the anomaly detection method was confirmed by conducting a water flow test in a branch piping system that simulates a spacecraft propulsion system configuration. First, we confirmed that the FBGs installed at the same position as the pressure sensor can capture the pressure change with the same accuracy as the pressure sensor. Comparing the pressure PFBG, which is the converted pressure of the strain due to water hammer measured by the FBGs, with the pressure P of the pressure sensor, the error of PFBG is about 2% of P at the maximum water hammer pressure and about 1% at the natural frequency obtained by FFT analysis. In addition, the accuracy of the PFBG in the area without a pressure sensor was evaluated in comparison with simulation results by using the analytical model. As a result, it was found that the FBGs had an error of about 4% in the maximum water hammer pressure and about 2% in the natural frequency from the calculated pressure values in the analytical model. Next, we changed the flow rate of the water flow test to detect the flow anomaly using the FBGs measurement data. As multiple points were measured by the FBGs, the frequency response function (FRF) was obtained between arbitrary FBGs, and the anomaly level was evaluated by confirming the difference in the gain spectrum due to the flow rate change. As a result, as the flow rate decreased due to some anomalies, the difference in the gain spectrum from that at normal flow rate tended to increase, which indicated the feasibility of the anomaly detection method by multipoint strain measurement in FBGs. In conclusion, we confirmed the feasibility of the FBGs-based anomaly detection method for spacecraft propulsion systems. The FBGs have the same level of measurement accuracy as a pressure sensor, and it could become a next-generation pressure sensing device in the spacecraft propulsion system. In addition, it is possible to determine the flow anomaly by comparing the FRF gain spectrum acquired between arbitrary FBGs. For the future, we will improve the determination method and try other method to determine the flow anomaly in more detail.