Evaluation of Exergy Efficiency Optimization of Space Launch Vehicles

Space launch vehicles are highly complex multidisciplinary systems with multiple subsystems. These subsystems vary significantly, complicating the selection of an objective function. Exergy efficiency has been suggested by some as a suitable objective function with relevance across a diverse set of subsystems; however, some characteristics of exergy efficiency may make it poorly suited for the task. At its core, exergy is the amount of work available from a system for a certain environment. In this paper, the use of exergy efficiency in the optimization of a space launch vehicle is explored. Exergy efficiency objective functions are constructed, including and excluding mass decreases from staging. These objective functions are used for the optimization of a physics-based rocket trajectory model. The results are compared to historical Saturn V data and analyzed to investigate the suitability of the metric. Due to the importance of mass in mechanical energy calculations, exergy efficiency can favor designs with more massive final stages, particularly when calculations include the staging-related mass decreases.