Hardware-Based Non-Optimum Factors For Launch Vehicle Structural Design

摘要

During aerospace vehicle conceptual and preliminary design, empirical non-optimum factors are typically applied to estimated structural weights to account for the weights of as-yet-undefined manufacturing and design details. Use of higher-fidelity and finer-granularity non-optimum factors in these early stages of design can result in greater understanding of and more accurate estimates of a concept vehicle's as-built weights and performance. To help achieve this objective, non-optimum factors are developed here for aluminum-lithium subcomponents of the liquid oxygen and liquid hydrogen tanks of the Space Shuttle Super-Lightweight Tank. Manufacturing drawings of the hydrogen tank orthogrid barrel panels and both tanks' monocoque bulkhead gores are assessed to determine minimum skin and stiffener thicknesses and other critical physical dimensions. These actual thicknesses are also compared to skin thicknesses estimated using classical structural mechanics and tank proof-test pressures. These thicknesses are then used to estimate subcomponent weights, which are then compared with actual weights to determine non-optimum factors at conceptual, preliminary, and detail levels of design. Evaluation of these non-optimum factors suggests that relatively simple models can improve estimation of large structural subcomponent weights for future launch vehicles. To demonstrate their utility, these calculated non-optimum factors are used to estimate structural weights for a proposed heavy-lift launch vehicle's propellant tank subcomponents.