MITESD_77S10_paper05 (1)

MITESD_77S10_paper05 (1) - Space Shuttle External Tank...

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1 ESD.77 MSDO Spring 2010 Space Shuttle External Tank Optimization Anonymous MIT Students System Design and Management Massachusetts Institute of Technology Abstract A simplified model of the Space Shuttle External Tank was used to set up a Multidisciplinary System Design Optimization problem. First, Return of Investment (ROI) was established as single objective. Both gradient based and heuristic methods were used to solve this problem. Sequential Quadratic Programming (SQP) was the gradient based method chosen. In the other hand, a Genetic Algorithm was used as the heuristic optimization tool. In addition, sensitivity analysis was performed to the optimal solution found. Finally, a multi-objective problem was set up adding the total tank weight (TW) as second objective. Adaptive Weighted Sum (AWS) was the method selected to solve the problem. Introduction After the Cold war, and especially in times of economic crisis, manned space programs have been questioned per its high costs and the associated safety risks. Reusable launch vehicles (RLV’s) have emerged as an alternative to reduce expenses by reusing equipment and commercializing space flights. Recent discussions in Obama’s administration about the financials of future human space exploration have motivated us to explore the use of Multidisciplinary System Design Optimization (MSDO) as a tool to improve the business case of current space systems. The most successful RLV has been, without question, NASA’s Space Shuttle. At a high level, the elements of the Space Shuttle (at launch) are: the external tank, two solid rocket boosters and the orbiter vehicle. The external tank has several functions: to provide the fuel and the oxidizer for the main engines (liquid hydrogen and liquid oxygen) and to serve as structure to the system (the solid rocket boosters and the obiter vehicle are attached to the tank at launch). The tank is the only element that is not reused and is also the heaviest. Framing the optimization problem In this analysis we will use a simplified model of the external tank as described in Figure 1. This model assumes the tank is divided in three main sections: the hemisphere, the cylinder and the nose cone. Table 1 shows the six design variables considered in this problem and Table 2 shows the parameters assumed. Figure 1. Graphic representation of the External Tank simplified model Table 1. Design Variables Symbol Variable Variable name x 1 HR2 Height /radius ratio x 2 L Length of cylindrical body x 3 R Radius of the hemisphere H L R TCO TCY TH *HR2=H/R
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