Advanced Nozzle Materials and Concepts for High Mass Flux Boost Motors

Aluminized rocket motors impose a severe environment on nozzle materials, with pressures of 3000 psi and temperatures of 6300¿F. Thermodynamic calculations, supported by experimental data, indicate that only tungsten (W) and tantalum carbide (TaC) canprovide a non-eroding surface. Recent motor firings show that these materials can survive if the nozzle employs a thin liner over a high temperature sup-port. Unfortunately, not all designs are successful and their behavior is not well understood. Forexample, when a successful W nozzle is analyzed with today's tools, the stresses exceed the measured strengths indicating that the nozzle should have failed. Furthermore, if the models are revised to reflect the successful behavior and then applied to asomewhat different W liner design, the models indicate that the new design should survive when, in fact, it failed.These events indicate that the design tools, which were developed to analyze thick throats made primarily with ablative materials, are not directly applicable to non-eroding refractory materials used as thin, thermal stress-resistant liners. Review of theexisting design tools shows that they can be improved in three specific areas: 1) thermal boundary conditions and heat transfer analysis, 2) material models and structural analysis, and 3) failure criteria for brittle/ductile materials.The proposed program will systematically examine and improve the design methods used in present nozzles. The program will focus on the assumptions and tools used for 1) heat transfer analysis, 2) stress analysis, and 3) failure prediction. The improveddesign methodology will be integrated and verified by comparison with data from recent tests. The improved tools will then be exercised to design a TaC nozzle for an aluminized motor. Selected materials will be purchased and provided for characterization.The program will be performed by Materials Research & Design, Inc. (MR&D). Thermal Technologies, Inc. (TTI) will serve as a consultant in aerothermal behavior. The proposed design methods are directly applicable to improved boost motors, which will increase the capability of commercial communication satellites. Additionally, the technology is appropriate for a variety of high temperature structures includinghypersonic airframes, ramjet engines, and divert and altitude control systems.