Innovative sensor networks for massive distributed thermal measurements in space applications under different environmental testing conditions

Optical fiber has seen significant development in the technical fields where it has been used in the last years. In the first place, obviously, for the Internet and, more broadly, to improve communication efficiency; but, more recently, for medicinal, structural, or lighting engineering applications. Furthermore, many optical solutions are beginning to be researched in the aerospace sector. The use of optical fiber, in particular, is strongly related to the employment of FBG type optical sensors, which may be particularly suitable for specific measurements of relevant physical parameters to be performed on specimens with typical aeronautical and/ or space employment. More specifically, the performance of several FBG sensors for temperature measurement in vacuum for validation tests of space products has been examined during this work. Unlike typical thermocouples, the adoption of this new type of sensor can provide substantial benefits, beginning with a significant gain in terms of the size of the fiber, which ensures a minimum disturbance on thermal data. Furthermore, if supplied with a suitable coating (in polyimide), the optical fiber may guarantee a very high operating temperature range, which is extensively compatible with the high-temperature range existent in space. The measurements were divided into two independent phases. First, a preliminary test was performed in the laboratory using a climatic chamber to evaluate several sensor network integration methodologies on the specimens and select the most effective one for the vacuum test. The test demonstrated that a simple adhesive bonding of the fiber to the specimens ensures a precise temperature measurement under vacuum and stable conditions. The following vacuum test program confirmed that FBGs could be used as temperature sensors even at very high temperatures. The good results of this test encourage us to consider FBG strategic for space applications and, particularly, for thermal characterizations, thanks to the high number of available sensors, combined with the minimal cable's size. However, further studies are required in cryogenic cases to validate the entire range of extreme temperatures that characterize the space environment.