Fibre optic sensor network for spacecraft health monitoring

Close meshed instrumentation or sensor networks applying conventional sensors for temperature and strain monitoring may result in excessive penalties in terms of weight constraints, reliability and sensitivity to environmental conditions, and complex interfaces. The fibre-optic sensor network described in this paper is a multiplexed system of fibre Bragg grating (FBG) strain and temperature sensors and was designed and developed for a demanding space environment, but it can also be emphasized as a promising, sensor technology with high potential for non-space applications. The FBG sensor network measures both strain and temperature at the measuring conditions of the structural core of the X-38 spacecraft, by means of wavelength shifts due to tensile stress on a Bragg grating. Dependent on the fixation of the fibre, either isolated from or mechanically coupled to the structure, local thermal or mechanical loads can be determined in the temperature range from -40 to +190 degreesC, and in the strain range from -0.1 % to +0.3 %. Short-term resolution and repeatability of the strain measurement amount to 5 mu epsilon and 25 mu epsilon, respectively. The FBG sensor network is very suitable for structural health monitoring of large structures, i.e. to determine thermal and mechanical load profiles during operation, to assess residual strength of structural elements or to detect irregular working conditions. In comparison to conventional sensors like thermocouples and strain gauges, an FBG sensor network significantly reduces the amount of required front end electronics (FEE) and harness.