Estimation of Launch Vehicle Propellant Tank Structural Weight Using Simplified Beam Approximation

Abstract

Many conceptual launch vehicles are designed through the integration of various disciplines, such as aerodynamics, propulsion, trajectory, weights, and aeroheating. In the determination of the total vehicle weight, a large percentage of the vehicle weight is composed of the structural weight of the vehicle subsystems, such as propellant tanks. Empirical mass estimating relations (MERs) and multi-dimensional finite element analysis (FEA) are two methods commonly used by the aerospace industry to estimate the loadbearing structural weight. MERs rapidly estimate the weight by evaluating empirical equations and the high-fidelity techniques of FEA accurately calculates the structural weight. The extreme inability for either method to provide both rapid and accurate weight estimations warrants an investigation into developing an improved, intermediate method. A methodology based on fundamental beam structural analysis has been developed for the rapid estimation of the load-bearing structural weight of the launch vehicle fuselage and integral propellant tanks. By creating a simplified beam approximation model of the vehicle, the method utilizes the vehicle component weights, load conditions, and basic material properties to analytically estimate the structural shell and stability frame weight. Implementation of this methodology into a fast-acting software tool allowed for rapid estimation of the component structural weight. Using statistical techniques, an empirical relationship between the estimated and actual load-bearing structure weights was determined. The method was utilized to estimate the liquid hydrogen (LH2) and liquid oxygen (LOX) propellant tanks for an existing Evolved Expendable Launch Vehicle (EELV) and the Space Shuttle External Tank (ET) for verification and correlation.