Visualization and Optimization of LE-X Engine System Margin

The LE-X is a new cryogenic booster engine with high performance, high reliability and low cost, designed for the next-generation Japanese launch vehicle, called H-X. It will be the first booster engine in the world with an expander cycle. In the LE-X engine design process, Taguchi method using L27 orthogonal array is applied to visualize quantitatively the margin and the correlation of engine system / components performance, reliability, and cost, and to determine the robust and optimum engine configuration. First, we extract the evaluation functions which affect the engine system performance, reliability and cost, and the control parameters which have a large impact on the evaluation parameters. Next, each control parameter is changed by three levels, and assigned to the orthogonal array L27. The margins of the evaluation functions and the sensitivities between the evaluation functions and the control parameters are calculated and visualized by engine system analysis for each case. Using the 27 engines in this L27 orthogonal array, the margins of the engine system and components will be visualized, and the control parameters which make the engine system be robust and match the system requirement of performance, reliability, and cost will be determined. JAXA is under study for the next booster rocket engine with higher reliability and significantly reduced cost, called LE-X. The LE-X will be applied to the next flagship Japanese launch vehicle. Last year, JAXA determined the LE-X engine cycle from the requirement of the reference next flagship launch vehicle and the trade study with respect to the performance, reliability, cost, and development risk. The next step of the LE-X engine design is to optimize the design parameters for adequate margins against the requirements of performance, reliability, and cost. Liquid rocket engine is huge and complex system with many components, such as combustion chamber, fuel/oxidizer injection elements, turbopumps, valves, pipelines and so on. They interact with each other in severe environment. For example, the life time of combustion chamber, turbine energy output and the total engine weight are strongly correlated in a expander cycle engine. Therefore it is important for liquid rocket engine designers to keep enough margins against the requirements in order to determine the robust and optimum engine configuration in the early phase of the development. In this paper, this systems engineering approach which is applied to the LE-X engine design is introduced.