Multidisciplinary Design Optimization of Reusable Launch Vehicles for Different Propellants and Objectives

Abstract

Identifying the optimal design of a new launch vehicle is most important because design decisions made in the early development phase limit the later performance of the vehicles and determine the associated costs. Reusing the first stage via retropropulsive landing increases the complexity even more. Therefore, an optimization framework for partially reusable launch vehicles is developed, which enables multidisciplinary design studies. The framework contains suitable mass estimates of all essential subsstems and a routine to calculate the needed propellant for the ascent and landing maneuvers. For design optimization, the framework can be coupled with a genetic algorithm. The overall goal was to reveal the implications of different propellant combinations and objective functions on the optimal design of the launcher for various mission scenarios. The results show that the optimization objective influences the most suitable propellant choice and the overall launcher design, concerning staging, weight, size, and rocket engine parameters. In terms of gross lift-off weight, liquid hydrogen seems to be favorable. When optimizing for a minimum structural mass or an expendable structural mass, hydrocarbon-based solutions show better results. Finally, launch vehicles using a hydrocarbon fuel in the first stage and liquid hydrogen in the upper stage are an appealing alternative, combining the benefits of both fuels.