Fiber Optic Temperature Sensors for Thermal Protection Systems

In Phase 1, Intelligent Fiber Optic Systems Corporation (IFOS), in collaboration with North Carolina State University, successfully demonstrated a Fiber Bragg Grating (FBG)-based system for simultaneous, continuous, multipoint temperature measurements at different depths in a representative Thermal Protection System (TPS) material (Super Lightweight Ablator?SLA), with testing performed near its char temperature. Special high-temperature FBG sensors were also developed and tested to 1000¿C with an applied 7 kpsi tensile stress, and with an applied 18 kpsi after cooling to room temperature. A pure thermal loading calibration of these sensors in this temperature range was performed. The response of the FBG sensors was much faster than that of thermocouples, and all electrical wireswere replaced with a single optical fiber.In Phase 2, IFOS will embed 1000¿C-capable optical fiber sensors into a TPS material. Following an appropriate instrumentation development, we will demonstrate temperature profile measurements with a depth resolution of 250-¿m or better. We will also distinguish between temperature- and strain-induced responses in the FBG sensors, a critical consideration for embedded sensor arrays. Our Phase 2 base work plan is designed to advance the TRL to 5, with TRL 6 being obtained in a Phase 2-E program.