Nonintrusive fiber interferometer for ablative TPS recession measurement

ABSTRACT: The next generation of hypersonic and reentry vehicles being designed for the Department of Defense (DoD) applications will require advanced Thermal Protection System (TPS). While new TPS shields are under development, a key difficulty is the ability to predict and diagnose TPS performance. ElectroDynamic Applications (EDA) has been developing an optical diagnosticfor use during testing and in flightthat will help address this need for experimental data. During an initial SBIR effort, we began the development of a low intrusive fiber optic plug insert for TPS materials that will enable spectrographic measurements of the reentry environment surrounding a TPS. This proposal seeks to modify the fiber optic plug to also permit interferometric measurement of surface recession rates for an ablative TPS. As the ablative surface recedes, light reflected from the fiber end alternates between constructive and destructive interference with light reflected from a similar (but unablated) fiber. The resulting fringe pattern permits sub-micron resolution of changes in the fiber length, and thus the TPS thickness. In addition, the optical fiber can simultaneously provide benchmark data for fundamental flow, radiation, and materials modeling as well as provide operational correlations between vehicle reentry drag and radiation. BENEFIT: EDA"s plan to pursue this technology beyond Phase-I is to develop production of flight hardware for DoD, NASA, and privately funded vehicles. Boeing has also expressed significant interest in transitioning the 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 may also have derivative terrestrial applications in high power plasma processing and energy creation systems.