Demonstration of strain independent temperature measurements using optical PM-FBG sensors for ground testing of satellite panels

Photonically wired spacecraft panels have been demonstrated within a recent ESA ARTES project by integrating mechanically packaged fiber Bragg grating (FBG) based optical temperature sensors into a honeycomb satellite test panel. Replacing electrical sensors with optical fiber sensors for testing satellites should have the advantage of reducing the harness mass and AIT. Fiber optic sensing also comes with clear benefits including immunity to electromagnetic interference and the capability of supporting arrays of sensors on a single fiber. However, standard FBG based temperature sensors are sensitive to both strain and temperature and in order to measure both strain and temperature simultaneously, two FBG sensors are required. An alternative solution using birefringent FBGs inscribed in Polarization Maintaining (PM) fiber (PM-FBG) in combination with high precision optical interrogators offers the same capabilities of standard FBG based optical sensors with high accuracy measurements, and can simultaneously measure both strain and temperature using only one sensor. PM-FBG sensors can also be multiplexed on a single fiber and therefore offer a simplified installation option by mounting them on the surface of the structure without the requirement for complex transducer packaging designs. With the support from an ESA GSTP project, we have developed an optical interrogator that measures PM-FBGs with high accuracy. The aim of the project is to demonstrate an optical strain independent temperature measurement system using PM-FBGs installed on a satellite test panel in atmospheric pressure and thermal vacuum environments with an operating temperature range from -20°C to + 80°C.