Multidisciplinary Design of a RBCC SSTO using Taguchi Methods

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Olds, John R.
Walberg, Gerald D.
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This paper presents the results of an effort to optimize a conceptual design of a conical (winged- cone) single-stage-to-orbit launch vehicle. The vehicle employs a rocket-based combined-cycle (RBCC) engine capable of four different operating modes -- ejector, ramjet, scramjet, and rocket. The RBCC engine offers higher engine thrust-to-weight ratios than competing airbreathing engine cycles while maintaining an Isp advantage over rocket engines. The Taguchi method, a parametric multidisciplinary design method, was used to evaluate the effects of changing 8 design variables (2 of which were discrete) in an "all at the same time" approach rather than the traditional ³one variable at a time² trade study approach that is more typical of conceptual aerospace vehicle design. Design variables pertained to both the vehicle geometry (cone half-angle, engine cowl wrap around angle) and trajectory parameters (dynamic pressure limits, heating rate limits, and airbreathing mode to rocket mode transition Mach number). The vehicle payload was fixed at 10,000 lbs to 100 Nmi circular polar orbit. Vehicle dry weight and gross weight were determined for each of the 27 point designs performed. Using the method, a combination of design variables was found that produces a very attractive vehicle dry weight and gross weight. While not necessarily producing an optimum design, the Taguchi method has demonstrated considerable utility in characterizing the complex design space and identifying a vehicle with which to start a more detailed optimization process.
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