Surface temperatures in atmospheric reentry simulations range from 1500-2300 K, while stagnation temperature on the leading edge of a Mach 6 flight vehicle at 25 km altitude is 1817 K. Sensors that can operate at temperatures well above 1273 K are needed to provide reliable validation data for TPS modeling and design tools.We propose to develop a low-intrusive fiber-optical pyrometer capable of measuring temperature profiles within an ablating thermal protection system (TPS). In this concept a bundle of parallel sapphire fibers is embedded in a step-wise manner into a multilayered "plug" of TPS material. The sensing tip of each fiber consists of a metallic coating, forming an isothermal cavity; graybody emission from this cavity is transmitted through the fiber to a fiber-optic multiplexer, and thence to a compact near-infrared (NIR) spectrometer. By fitting the thermal spectrum from the shortest fiber to a Planck distribution (adjusted to account for spectral absorption in the sapphire fiber), a cold-side temperature can be inferred first. The next longest fiber can use this temperature to estimate the distorting effects of self-emission in the heated fiber. Sequential evaluation of fiber tip temperatures at known locations along the bundle will allow effective estimation of temperature gradient and subsequent calculation of heat flux.The proposed fiber-optic sensors are thermally and physically robust, lightweight, electrically passive, and immune to electromagnetic and radio-frequency interference. Additionally, our proposed fiber-optic pyrometer is optimized for high temperatures. As the TPS-embedded sensing tip temperature increases, the wavelength peak for the thermal emission spectrum moves from 2634 nm (at 1000 K) to 1260 nm (at the sapphire melting point of 2300 K), while the integrated spectral intensity increases as the 4th power of the temperature. Both effects improve the pyrometer signal-to-noise ratio.
Potential NASA Commercial Applications: (Limit 1500 characters, approximately 150 words) Heat shield technology is a critical component for re-entry and hypersonic vehicles The next generation of crew reentry vehicles being designed by NASA will require more advanced Thermal Protection System (TPS) designs than the conservative approaches currently used. While new TPS materials are under development, a key difficulty is the ability to predict and diagnose TPS materials with instrumentation capable of surviving the reentry environment
Potential NON-NASA Commercial Applications: (Limit 1500 characters, approximately 150 words) EDA's plan to pursue this technology beyond Phase-II is to develop production of flight hardware for DoD, NASA, and privately funded vehicles. Boeing has also expressed significant interest in transitioning our technology into their thermal protection systems as part of an integrated vehicle health monitoring system. As private sector space ventures continue to blossom, there will be significant opportunities for commercialization. This technology also has derivative terrestrial applications in high temperature industrial furnaces such as for cement manufacturing where temperatures in the Kiln can get up to 1450 Celsius and careful monitoring of temperature is critical.The target market for this technology is focused in re-entry vehicles but has secondary markets in any company that manufactures hypersonic vehicles as well as terrestrial applications in high power plasma processing, energy creation systems and industrial furnaces. Of particular note, the technology is of significant importance to DoD for terrestrial intercontinental hypersonic weapons systems. EDA expects to work closely with these agencies and their prime contractors to develop the fiber optic pyrometer system to provide mission critical capability.
Technology Taxonomy Mapping: (NASA's technology taxonomy has been developed by the SBIR-STTR program to disseminate awareness of proposed and awarded R/R&D in the agency. It is a listing of over 100 technologies, sorted into broad categories, of interest to NASA.) Diagnostics/Prognostics Entry, Descent, & Landing (see also Astronautics) Entry, Descent, & Landing (see also Planetary Navigation, Tracking, & Telemetry) Infrared Optical Spacecraft Design, Construction, Testing, & Performance (see also Engineering; Testing & Evaluation) Thermal
