Structural health monitoring in low earth orbit environment using fiber bragg grating sensors

Abstract

The usage of composite materials in space structures are being expanded due to its excellent properties, but the problem of maintenance and management of composite material structures in the harsh space environment is still left unsolved. Low Earth orbit space structures experience gradual property degradation and damage in the exposed structural surface due to high-degree vacuum, ultraviolet radiation, thermal cycling, and atomic oxygen. In order to perform soundness monitoring using FBG sensors, appropriate separation technique of the strain and temperature is required in LEO’s thermal cycling with a range of $-150\degC \sim 150\degC$. The characteristics of FBG sensors and composites embedded FBG sensors from the harsh environment are studied to distinguish the real structural signals from all signals under LEO environment. And the impacts of small space debris or meteorites are considered to monitor damage in a short time period with in space. In this study, the study about the design of the FBG sensor head was carried out to separate strain and temperature simultaneously for structural health monitoring under the thermal cycle of low earth orbit space environment. The sensor head is formed by two adjacently located FBGs- a normal and a reverse index FBG-fabricated without fiber splicing by different laser exposure. It has some merits of the possibility of multiplexing and embedment, the simplicity of the measurement system, which is similar to that of commercial systems, higher reliability with no splicing, and measurement of the reflection of Bragg wavelength. The characteristics of FBG sensors and composites from the harsh environment were studied to distinguish the real structural signals from all signals under LEO environment. FBG sensors were embedded into the graphite/epoxy composite specimen. Through aging cycles simulating the LEO environment, the decreased range of wavelength change was compared with the degradation of material properties of gra...