Fibre optic sensor network for spacecraft health monitoring

Abstract

Close meshed instrumentation or sensor networks applyingconventional sensors for temperature and strain monitoring may result inexcessive penalties in terms of weight constraints, reliability andsensitivity to environmental conditions, and complex interfaces. Thefibre-optic sensor network described in this paper is a multiplexed system offibre Bragg grating (FBG) strain and temperature sensors and was designed anddeveloped for a demanding space environment, but it can also be emphasized asa promising sensor technology with high potential for non-space applications.The FBG sensor network measures both strain and temperature at the measuringconditions of the structural core of the X-38 spacecraft, by means ofwavelength shifts due to tensile stress on a Bragg grating. Dependent on thefixation of the fibre, either isolated from or mechanically coupled to thestructure, local thermal or mechanical loads can be determined in thetemperature range from -40 to +190 °C, and in the strainrange from -0.1% to +0.3%. Short-term resolution and repeatabilityof the strain measurement amount to 5 µε and25 µε, respectively.The FBG sensor network is very suitable for structural health monitoring oflarge structures, i.e. to determine thermal and mechanical load profilesduring operation, to assess residual strength of structural elements orto detect irregular working conditions. In comparison to conventional sensorslike thermocouples and strain gauges, an FBG sensor network significantlyreduces the amount of required front end electronics (FEE) and harness.