Launch Vehicles Multidisciplinary Optimization, a Step from Conceptual to Early Preliminary Design

A recent collaboration between Politecnico di Milano and Universität Bremen within ESA’s PRESTIGE PhD program has stemmed a significant research effort in the field of Multidisciplinary Design Optimization (MDO) for launch vehicles. This work is aimed at the development and integration of optimization algorithms and engineering methods in a software environment capable of assisting in the conceptual and early preliminary design of space launchers, potentially leading to relevant reductions in development effort and life cycle cost. The implemented MDO approach allows in fact efficient exploration of the design space throughout successive global and local, single and multi-objective optimization processes, guided by the engineering experience of the designer. The main obstacle to the successful application of MDO lays in the difficult task of finding a good compromise between models simplicity and accuracy. To tackle this issue, the engineering models were developed in two successive levels of detail, from conceptual to early-preliminary design. The paper is focused on this modelling effort, showing how a critical analysis of the first level’s results was exploited to improve fidelity and functionality. An overview of the conceptual design models is first presented, together with a quantitative assessment of their accuracy and of the impact of the disciplinary errors on global performance indexes. The models selection converged towards well-known disciplinary tools (NASA’s CEA and USAF’s Missile DATCOM), complemented by a set of ad hoc models in the following disciplines: propulsion, geometry, aerodynamics, weights, trajectory, guidance and control, costs and reliability assessment. The validation campaign showed how system-level errors in performance below 20% can be expected, and allowed identifying the most critical modelling aspects to be improved. In a second part, the paper focuses on the model enhancements stemming from the analysis of the conceptual design results, in particular: solid grain geometry and internal ballistics analysis, pressurization systems and engine cycles modelling, simplified structural sizing for all load bearing components, effect of wind and steering losses on the trajectories, and safety-related analyses (boosters/stages impact ellipse determination, upper stage end-of-life strategy). Validation results are presented with a comparison of the conceptual and early preliminary frameworks, highlighting the advantages in terms of accuracy (down to 12% of worst case system error on performance) with a limited increase in computational effort. The foreseen future research lines are finally discussed, especially those aimed at further increasing the design fidelity and at targeting less traditional launch systems, such as manned and reusable vehicles.