(Georgia Institute of Technology, 2000-09)
Cormier, Timothy A.; Scott, Andrew; Ledsinger, Laura Anne; McCormick, David Jeremy; Way, David Wesley; Olds, John R.
Initial results are reported from an ongoing investigation into optimization techniques applicable to multidisciplinary reusable launch vehicle (RLV) design. The test problem chosen for investigation is neither particularly large in scale nor complex in implementation. However, it does have a number of characteristics relevant to more general problems from this class including (1) the use of legacy analysis codes as contributing analyses and (2) non-hierarchical variable coupling between disciplines. Propulsion, trajectory optimization, and mass properties analyses are included in the RLV problem formulation. A commercial design framework is used to assist data exchange and legacy code integration. The need for a formal multidisciplinary design optimization (MDO) approach is introduced by first investigating two or more conventional approaches to solving the sample problem. A rather naive approach using iterative sublevel optimizations is clearly shown to produce non-optimal results for the overall RLV. The second approach using a system-level response surface equation constructed from a small number of RLV point designs is shown to produce better results when the independent variables are judiciously chosen. However, the response surface method approach cannot produce a truly optimum solution due to the presence of uncoordinated sublevel optimizers in the three contributing analyses. Collaborative optimization (CO) appears to be an attractive MDO approach to solving this problem. Initial implementation attempts using CO have exhibited noisy gradients and other numerical problems. Work to overcome these issues is currently in progress.