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

TL;DR

This paper presents an optimization framework for designing reusable launch vehicles with various propellant options, revealing how objectives and propellants influence design choices and performance.

Contribution

It introduces a multidisciplinary optimization framework for partially reusable launch vehicles, incorporating subsystem mass estimates and propellant calculations, coupled with genetic algorithms for design exploration.

Findings

Liquid hydrogen favors lower lift-off weight.

Hydrocarbon fuels optimize structural mass.

Hybrid fuel configurations are promising for performance.

Abstract

Identifying the optimal design of a new launch vehicle is most important since design decisions made in the early development phase limit the vehicles' later performance and determines the associated costs. Reusing the first stage via retro-propulsive landing increases the complexity even more. Therefore, we develop an optimization framework for partially reusable launch vehicles, which enables multidisciplinary design studies. The framework contains suitable mass estimates of all essential subsystems 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 is to reveal the implications of different propellant combinations and objective functions on the launcher's optimal design 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 expandable 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 both fuels' benefits.