Combined-Cycle SSTO Design Using Parametric MDO Methods

This paper reports the results of the second phase of a research project to characterize and optimize the design of an advanced launch vehicle for human access to low earth orbit. The vehicle makes use of rocket-based combined-cycle (RBCC) propulsion — a concept combining operating modes of an ejector, ramjet, scramjet, and rocket in a single engine. This research builds on previous work focused on advanced multiple mode propulsion concepts and advanced conical acceleration-class single-stage-toorbit (SSTO) launch vehicles. Three systems level design variables of interest were optimized using multidisciplinary design optimization (MDO) techniques. Specifically, Taguchi’s method of robust design was used to identify a combination of variables that minimize the vehicle sensitivity to unpredictable changes in engine weights and performance. In addition, a second-order response surface method (RSM) was used to approximate the design space and predict the minimum dry weight vehicle. The optimized vehicle results (weights, dimensions, performance) are favorably compared with other SSTO designs including rocket and airbreathing concepts.