AIAA 98 - 5209 System Robustness Comparison of Advanced Space Launch Concepts

This research proposes two methods to investigate the robustness differences between competing types of advanced space launch systems. These methods encompass two different phases of the advanced design process and are used to compare the relative advantages of two concepts in these phases. The first is a Monte Carlo simulation during the conceptual phase of design, where mold lines can be changed to account for uncertainty in weight assumptions. This tests the vehicle weight growth for a fixed mission. Here, the all-rocket single stage to orbit (SSTO) shows a more narrow distribution of dry weight, suggesting higher concept robustness. A study of vehicle mass ratio and mixture ratio combinations for both vehicles show the relative location of the results. The second phase represents the transition to detailed design. An optimization based on length determines the appropriate size for detailed design. This optimization takes into account uncertainties placed on both weight relationships and performance requirements. Both of these analyses utilize Crystal Ball Pro® in conjunction with Microsoft Excel®. This gives the technique compatibility with commonly used computer platforms. While the all-rocket SSTO does show an advantage in the area of system weight growth, several other factors are important in determining the viability of a reusable launch system, not the least of which is mission flexibility. Here the runway-operated RBCC SSTO has a distinct advantage. NOMENCLATURE ACC advanced carbon-carbon c.g. center of gravity ESJ ejector scramjet LEO low-earth orbit LH2 liquid hydrogen LOX liquid oxygen MSE mean square error Mtr transition Mach number RBCC rocket-based combined cycle SSTO single stage to orbit T/W thrust to weight ratio TPS thermal protection system UHTC ultra high temperature ceramic VTO vertical takeoff WER weight estimating relationship