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Daniel Guggenheim School of Aerospace Engineering
Daniel Guggenheim School of Aerospace Engineering
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ItemIn-Space Deployment Options for Large Space Solar Power Satellites(Georgia Institute of Technology, 2000-10) Olds, John R. ; Way, David Wesley ; Charania, Ashraf ; Budianto, Irene Arianti ; Marcus, Leland R.This research was performed at the Space Systems Design Lab at the Georgia Institute of Technology, Atlanta, GA, with the charter of identifying economically attractive candidate space transfer vehicle systems for ferrying components of Space Solar Power (SSP) satellites from Low Earth Orbit (LEO) to Geostationary Earth Orbit (GEO). An aggressive price goal of only $400/kg of payload was established in order to control the cost of transportation for the SSP satellite developer. A multi-step decision process was employed to down-select from a large number of candidate systems to four. The final four concepts were Nuclear Thermal Rocket (NTR), Solar Thermal Rocket (STR), a rotating tether, and Solar Electric Propulsion (SEP). Additional concepts considered were Dual-Mode (Chemical/SEP) and All-Chemical. Results show that the most economical concept is one which is highly reusable, has a short turn-around time, a long vehicle life, and small propellant requirements. These characteristics result in a low fleet size and therefore lower debt requirements. These characteristics also lower the Initial Mass in Low Earth Orbit (IMLEO) and therefore lower deployment costs. The goal of $400/kg, or 2.5cents/kW-hr, for in-space transportation costs is very aggressive and difficult to achieve.
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ItemA Collaborative Optimization Approach to Design and Deployment of a Space Based Infrared System Constellation(Georgia Institute of Technology, 2000-03) Budianto, Irene Arianti ; Olds, John R.Collaborative optimization, as a design architecture, has been used successfully in solving large-scale multidisciplinary optimization problems related to aircraft and space vehicle designs. The study presented in this paper attempts to demonstrated yet another application for this architecture, i.e., to satellite constellation designs. As an example, it is implemented for the design and deployment problem of a space based infrared system placed at a low earth orbit. Preliminary results on a simplified problem are presented as a proof-of-concept. The constellation configuration is fixed to be a 28/4/2 Walker delta pattern (four planes with seven satellites per plane and relative phasing of two). The mission orbit, spacecraft design, and deployment strategy are varied to determine the optimal system (i.e., one with the minimum cost to deployment). Problem reformulation required by the collaborative optimization architecture and some implementation issues are discussed. The three analysis tools used in this study are also described in this paper. The constellation design module finds orbit parameters and constellation configurations that satisfy the coverage requirements. The spacecraft model performs the payload and bus design. Finally, the launch manifest module finds the best strategy, in terms of total launch cost, to deploy the constellation system.
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ItemDemonstration of CLIPS as an Intelligent Front-End for POST(Georgia Institute of Technology, 1999-01) Budianto, Irene Arianti ; Olds, John R. ; Baker, Nelson C.Most of the analysis codes used in the design of aerospace systems are complex, requiring some expertise to set up and execute. Usually the Program to Optimize Simulated Trajectories (POST) fails to converge when its control variables are given a bad set of initial guesses, causing the trajectory to remain in the infeasible design region throughout the computations. The user then analyzes the output produced and relies on a set of heuristics, typically gained from experience with the program, to determine the appropriate modification to the problem setup that will guide POST in finding a feasible region and eventually converge to a solution. The potential benefits of employing knowledge-based system within a design environment have long been well known. Various methods of utilization have been identified. As a postprocessing guide, an expert system can distill information obtained from an analysis code, such as POST, into knowledge. The system then can emulate the human analyst's decision-making capability based on this collected knowledge. This paper describes the implementation of POST expertise in a knowledge-based system called CLIPS and demonstrates the feasibility of utilizing this integrated system as a design tool.
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ItemConstant Dynamic Pressure Trajectory Simulation in POST(Georgia Institute of Technology, 1998-01) Olds, John R. ; Budianto, Irene AriantiFuture space transportation vehicles may well rely on high speed airbreathing propulsion (ramjets and scramjets) to supply much of their motive power. Because of the tradeoff relationship between engine thrust and vehicle airframe weight, ascent trajectories are typically simulated using a constant dynamic pressure phase during airbreathing acceleration; dynamic pressure is increased to benefit vehicle thrust up to some fixed limit imposed by the vehicle structure. The constant dynamic pressure portion of the trajectory typically begins around Mach 2-3 and continues to the maximum airbreathing Mach number or until some convective aeroheating limit is reached. We summarize comparative research on three candidate guidance methods suitable for simulating constant dynamic pressure trajectories. These are generalized acceleration steering, linear feeedback control, and cubic polynomial control. All methods were implemented in POST (Program to Optimize Simulated Trajectories), an industry standard trajectory simulation code. Both quantitative and qualitative comparisons of these methods (i.e. in terms of computer processing time, number of required iterations for convergence, sensitivity to quality of initial values, accuracy and program robustness) are presented. Of the three methods, the linear feedback control approach is found to be the most efficient and robust, with good accuracy.