Liquid Rocket Analysis (LiRA)

Abstract

The need to increase specific impulse of rocket launcher engines has lead design engineers to start development of ever more complex engine cycles starting from simple gas pressure fed engines to the very complex staged combustion cycle engines. Currently a wide range of different cycles does exist. These cycles not only differ in terms of performance, but also in terms of mass, cost, reliability etc., which in general makes it difficult to quickly determine which cycle is best suited for a certain mission or task. For this a tool that is capable of analysing different cycles and the impact of design choices has been developed. The tool, named LiRA, has as goal giving the user better system level understanding of the different possible engine cycles and the functions of the components; it can therefore provide valuable and time saving assistance during design or in analysis and optimisation studies. A modular approach is applied where engine components are sized using a performance, dimension and mass model who make use of corrected ideal rocket theory and empirical relations. This work focuses mainly on the methodology and the construction of the models, and further includes the optimisation of an upper stage and a verification, validation and uncertainty and sensitivity analysis of the tool and the optimisation to assess its accuracy, precision and applicability. The completed program has proved to confirm known trends and known cycle characteristics like the mass savings that can be achieved when using turbo-pump fed engines instead of pressure fed engines for mid- to high-thrust booster applications. Further the superior performance of closed cycles, especially staged combustion cycles has been confirmed, and some cycle specific design choices like the need of bypasses in expander cycles have been explained. The tool however is not complete and should be expanded; the addition of a cost and reliability assessment model is for example strongly recommended. There also remain issues with the accuracy and uncertainty of certain estimates which make that the current version should only be used for comparative studies.