AIAA 93-1096 Multidisciplinary Design Of a Rocket-Based Combined Cycle SSTO Launch Vehicle using Taguchi Methods

This paper presents the results of an effort to optimize a conceptual design of a conical (wingedcone) 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 “one variable at a time” 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. Nomenclature Ac engine cowl annular capture area (ft2) ACCadvanced carbon-carbon thermal protection APAS Aerodynamic Preliminary Analysis System Ct airbreathing coef. of thrust, thrust/qAc ECLSS environmental control and life support sys. EMA electro-mechanical actuators GLOW gross lift-off weight (lbs) HTO horizontal take-off Isp specific impulse, thrust/prop flow rate (sec) LH2 liquid hydrogen LOX liquid oxygen MR mass ratio (GLOW/MECO weight) MECO main engine cut-off MER mass estimating relationship Mtr scramjet to rocket mode transition Mach OMS orbital maneuvering system PEEK polyether-ether ketone thermoset resin POST Program to Optimize Simulated Trajectories q dynamic pressure (1/2ρV2)(psf) RBCC rocket based combine cycle RCS reaction control system SSTO single stage to orbit STS Space Transportation System (shuttle) TPS thermal protection system T/Wo take-off vehicle thrust-to-weight ratio VTO vertical take-off α angle of attack (deg.) Θ cone half angle (deg.) Φ cowl wrap around angle (deg.) ξ propellant fraction, 1-1/MR