Description: This program addresses the need for interfacial and in-depth temperature monitoring of thermal protection systems (TPS). Novel, linear drive, eddy current methods are proposed that incorporate innovative sensor array constructs, physics-based models, and multivariate inverse methods to nondestructively assess temperatures for carbon-based TPS materials such as felts and PICA. The sensors can be mounted behind the TPS material or embedded within the TPS with sensing fields that are projected through the material to the far surface interface. Thermally induced changes in the electrical properties of the TPS material are then used to determine the temperatures. In Phase I, the focus is on establishing feasibility by demonstrating correlations between electrical properties measured by the eddy current sensors and the TPS temperature. It will also investigate adaptation of the sensor materials to support sustained and transient operation at high temperatures compared to typical operating conditions for standard eddy current sensors. JENTEK's physics-based methods for diagnostics of layered media using MWM-Array technologies have been demonstrated in scanning configurations for coating characterization, corrosion detection and sizing with and without interference layers, and condition and thickness assessment of felt-based TPS materials. These methods have also been extended to surface mounted sensing applications such as torque, fatigue, and heat treatment condition monitoring. JENTEK delivered the MWM-Array solution used by NASA KSC on the Space Shuttle leading edge to detect damage of the reinforced carbon-carbon (RCC) thermal protection tiles; thus after establishing the property correlations with temperature, JENTEK is well-positioned to deliver a novel method for temperature monitoring of TPS materials and material condition monitoring at elevated temperatures.

Benefits: If the program is successful, it will demonstrate the capability of the MWM-Array technology to monitor electrical conductivity and temperature of materials that are exposed to high temperature conditions. This type of monitoring tool could support monitoring during ground-based tests of thermal protection system materials; later versions with dedicated instrumentation designed for reduced size and weight with a potential implementation on spacecraft is also possible. Other structural applications that could take advantage of this type of projected-field, high-temperature, monitoring solution includes carbon-carbon rocket nozzles, Multi-Purpose Crew Vehicle, exhaust nozzles, and space probes. Other NASA customers which could use this technology include the Commercial Orbital Transportation Services (COTS) spacecraft manufacturers and other interplanetary programs such as science exploration mission vehicles and human crew vehicles.

There are numerous applications that could use a high temperature monitoring capability. One is manufacturing quality control and high temperature process monitoring. This includes heat treatment or annealing processes that are commonly performed on metals. In-situ monitoring of the electrical conductivity and/or magnetic permeability would offer a real-time assessment and process control capability. This could also be applied to TPS materials where the electrical conductivity and temperature of the carbon-base material is monitored during impregnation and curing of resins. A second application is structural health monitoring in challenging environments where conventional methods cannot be used. This includes monitoring of high temperature power plant combustion components and petrochemical plant piping for damage, such as fatigue or corrosion.