Beyond Gravitys approach to the multidisciplinary design, analysis and optimization of reusable payload fairings
Creators: name:  G. PIETRO 
name:   G. MOLINARI 
name:   M. RIGHI 
name:   A. SANCHEZ CEBRIAN 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: STRUCTURES
MATERIALS
DESIGN
OPTIMIZATION

description: The philosophy behind Space 2.0 is causing shifts in the paradigms at the basis of launch vehicle design. The pursue for maximum efficiency at all costs is no longer targeted, environmental concerns become predominant, and flexibility in launch rates and launch readiness is highly valued. The drivers for launch vehicle design are therefore vastly different with respect to few decades ago. Such change requires a radical re-thinking of the tools and approaches used throughout the entire product development. To this aim, RUAG has worked towards establishing a multi-disciplinary framework for the development of payload fairings. In addition to coupling the conventional disciplines of structural mechanics and aerothermodynamics, the framework considers additional aspects such as the costs of materials and labor associated with manufacturing, assembling, and refurbishing space structures. The inputs for the study are volumetric constraints, topology and structural concepts, and trajectory profiles. The associated design parameters span all disciplines: geometry, materials choice, structural sizing and refurbishment strategy. The computational complexity associated with coupling structural, thermal and fluid domains has been tackled by developing several multidisciplinary frameworks characterized by different levels of fidelity and computational costs. Two models were used to assess the aerothermodynamics: a simplified, semi-empirical approach using DKR formulas, and a steady-state RANS-based CFD simulation relying on Spalart-Allmaras turbulence model and ideal gas assumptions. The latter was also used in combination with a surrogate model developed on the basis of the CFD-generated aerothermal database. The impact of these simplifications has been validated with comparisons against reference simulations, permitting to estimate the introduced errors. Crucially, these models exhibit sufficient accuracy to capture the relevant phenomena and their limited computational cost permits executing global, multi-disciplinary optimizations in few hours. With this holistic approach, leveraging interactions between different disciplines, a global optimum can be reached. The possibility to execute such complex assessments in the early phases of a new product development, and of evaluating different scenarios in an accurate and unbiased manner, enables to effectively support critical decisions and identify truly optimal designs. As all disciplines are considered and evaluated, the goals can be expressed in a high-level manner: the fairing must exhibit the necessary strength and stiffness while requiring the lowest lifecycle costs possible within the chosen design space. These goals are conflicting hence a multi-objective optimization has been employed, permitting to quantify the impact of the tradeoffs. In this respect, reusability opens new financial scenarios once different strategies for reuse/refurbishment are considered. Notably, the optimizer does not prioritize only low weight solutions as more traditional engineering practices tend to do. In fact, the identified extremes are heavier designs, surviving numerous flights with minimum refurbishments between launches (thus having lower lifecycle costs) and lighter structures requiring significant refurbishment after each flight. Ultimately, this information will be crucial for the Launcher Prime to identify, based on the specific cadence and cost-per-kg information, the ideal solution for their specific business case. Further, this framework allows the analysis of the effects of market trends on the overall costs and performance of the fairings.