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Daniel Guggenheim School of Aerospace Engineering
Daniel Guggenheim School of Aerospace Engineering
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ItemStarsaber: A Small Payload-Class TSTO Vehicle Concept Utilizing Rocket-Based Combined Cycle Propulsion(Georgia Institute of Technology, 2001-07) St. Germain, Brad David ; Olds, John R. ; McIntire, James ; Nelson, Douglas K. ; Weglian, John E. ; Ledsinger, Laura AnneThis paper introduces Starsaber, a new conceptual launch vehicle design. Starsaber is a two-stage-to-orbit (TSTO) vehicle capable of putting a 300 lb class payload into low Earth orbit (LEO). The vehicle is composed of a reusable winged booster, powered by two hydrocarbon fueled ejector ramjet (ERJ) engines, and a LOX/RP-1 expendable upper stage. The vehicle utilizes advanced structural and thermal protection system (TPS) materials, as well as advanced subsystems. Details of the conceptual design process used for Starsaber are given in this paper. Disciplines including mass properties, internal and external configuration, aerodynamics, propulsion, trajectory simulation, aeroheating, and cost estimation are used in this study. A baseline design was generated, and a 2-level 15-variable Taguchi L16 array was used to determine key system variables' influence on vehicle weight and cost. Based on these preliminary results, the Starsaber vehicle was optimized for both minimum weight (gross and dry weight) and recurring cost. The lowest recurring cost vehicle was estimated to have a recurring cost per flight of $2.01M, a gross liftoff weight of 168,000 lb and a booster length of 77 ft.
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ItemOptimized Solutions for the Kistler K- 1 Branching Trajectory Using MDO Techniques(Georgia Institute of Technology, 2000-09) Ledsinger, Laura Anne ; Olds, John R.Fully reusable two-stage-to-orbit vehicle designs that incorporate 'branching' trajectories during their ascent are of current interest in the advanced launch vehicle design community. Unlike expendable vehicle designs, the booster of a reusable system must fly to a designated landing site after staging. Therefore, both the booster return branch and the orbital upper stage branch along with the lower ascent trajectory are of interest after the staging point and must be simultaneously optimized in order to achieve an overall system objective. Current and notable designs in this class include the U. S. Air Force Space Operations Vehicle designs with their 'pop-up' trajectories, the Kelly Astroliner, the Kistler K-l, the two-stage-to-orbit vehicle Stargazer, and NASA's proposed liquid flyback booster designs (Space Shuttle booster replacement). The solution to this problem using an industrystandard trajectory optimization code (POST) typically requires at least two separate computer jobs — one for the orbital branch, from the ground to orbit, and one for the flyback branch, from the staging point to the landing site. These jobs are coupled and their data requirements are interdependent. These requirements must be taken into consideration when optimizing the entire trajectory. This paper analyzes the results of branching trajectory optimization for the Kistler K-l launch vehicle with respect to computational efficiency and data consistency for various solution methods. In particular, these methods originate from the field of Multidisciplinary Design Optimization (MDO).
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ItemComparison of Collaborative Optimization to Conventional Design Techniques for a Conceptual RLV(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.