John R. Olds

Evaluation of multidisciplinary OPtimization techniques applied to a reusable launch vehicle

Three multilevel multidisciplinary optimization techniques, Bi-Level Integrated System Synthesis, Collaborative Optimization, and Modified Collaborative Optimization, are applied to the design of a reusable launch vehicle, evaluated, and compared in this study. In addition to comparing the techniques against each other, they are also compared with designs reached via fixed-point iteration of disciplines with local optimization and the industry accepted multidisciplinary optimization technique, All-at-Once. The new multidisciplinary optimization techniques, particularly Bi-Level Integrated System Synthesis, showed greater ability than fixed-point iteration to design for a global objective and were more applicable to complex systems than All-at-Once. This study was the first time that the novel multidisciplinary optimization methods were compared qualitatively and quantitatively under controlled experimentation practices. It is still impossible to statistically determine whether any one of the novel multidisciplinary optimization techniques is better than another, because more studies using different test problems corroborating the conclusions made here are needed.

Design and deployment of a satellite constellation using collaborative optimization

A study of collaborative optimization as a systematic, multivariable, multidisciplinary method for the conceptual design of satellite constellations is presented. Collaborative optimization was selected because it is well suited to a team-oriented environment, such as often found in the constellation design process. The method provides extensive and formal exploration of the multidisciplinary design space and a scalable formulation of the problem without compromising its subsystems’ flexibility or eliminating opportunities for collaboration. The feasibility and benefits of the collaborative optimization architecture are highlighted by the successful convergence of an application notional problem to design and deploy elements of a space-based infrared system that provides early missile warning. Furthermore, this study contributes to the existing knowledge of the collaborative optimization method by verifying the feasibility of nongradient optimization algorithms as both system and subsystem optimizers within the architecture. Finally, the demonstrated convergence of this problem, which involves integer variables, also demonstrates the flexibility of the architecture for handling mixed-discrete nonlinear multidisciplinary problems.

Constant Dynamic Pressure Trajectory Simulation in POST

NOMENCLATURE Future 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. That is, 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 or 3 and continues to the maximum airbreathing Mach number or until some convective aeroheating limit is reached. This paper summarizes comparative research on three candidate guidance methods suitable for simulating constant dynamic pressure trajectories. These are generalized acceleration steering, linear feedback 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. * Assistant Professor, School of Aerospace Engineering, Senior member AIAA. Palace Knight Fellow, School of Aerospace Engineering, Student member AIAA. Copyright

A collaborative optimization approach to design and deployment of a space based infrared system constellation

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 demonstrate 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 low earth orbit.

A Quantitative Methodology for Identifying Evolvable Space Systems

*† With the growing emphasis on spiral development, a system’s ability to evolve is becoming increasingly critical. This is especially true in systems designed for the exploration of space. While returning to the Moon is widely regarded as the next step in space exploration, our journey does not end there. Therefore, the technologies, vehicles, and systems created for near-term lunar missions should be selected and designed with the future in mind. Intelligently selecting evolvable systems requires a method for quantitatively measuring evolvability and a procedure for comparing these measurements. This paper provides a brief discussion of a quantitative methodology for evaluating space system evolvability and an in-depth application of this methodology to an example case study. Nomenclature e = event s = state vector of original mission requirements s’ = state vector of evolved mission requirements S(X) = possible state space of system SL(X) = lawful state space of system W = evolvability vector wi = difficulty rating for i-th state variable along most efficient path of evolvability

A CONCEPTUAL DESIGN TOOL FOR RBCC ENGINE PERFORMANCE ANALYSIS

Future reusable launch vehicles will depend on new propulsion technologies to lower system operational costs while maintaining adequate performance. Recently, a number of vehicle systems utilizing rocket-based combined-cycle (RBCC) propulsion have been proposed as possible low-cost space launch solutions. Vehicles using RBCC propulsion have the potential to combine the best aspects of airbreathing propulsion (high average Isp) with the best aspects of rocket propulsion (high propellant bulk density and engine T/W). Proper conceptual assessment of each proposed vehicle will require computer-based tools that allow for quick and cheap, yet sufficiently accurate disciplinary analyses. At Georgia Tech, a spreadsheet-based tool has been developed that uses quasi-1D flow analysis with component efficiencies to parametrically model RBCC engine performance in ejector, fan-ramjet, ramjet and pure rocket modes. The technique is similar to an earlier RBCC modeling technique developed by the Marquardt Corporation in t...

The Technology Roadmapping and Investment Planning System (TRIPS)

In the past significant effort has been placed on the identification of key technologies through evaluation of the impacts that they will have on a system. However, this is usually done under the premise that once a technology has been identified, the next step is to simply go out and develop the technology. That is, little consideration is given to the behavior of a developing technology or the management of its development. These issues become magnified when one considers the management of an entire portfolio of technologies, much as NASA is presently tasked with. This paper focuses on the development of a system (TRIPS) to assist in the management and optimization of a large technology portfolio for the purpose of developing a particular system or architecture. The TRIPS methodology focuses on first modeling the uncertainty of a developing technology and then optimizing an investment portfolio around that uncertainty. A probability based technology model is first outlined and then a framework that operates on a suite of technology models in discussed.

Tempest: Crew Exploration Vehicle Concept

41st AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit nJuly 10-13, 2005, Tucson, AZ.

Demonstration of CLIPS as an Intelligent Front-End for POST

Most of the analysis codes used in the design of aerospace systems are complex, requiring some expertise to set up and execute. POST, which is used in many conceptual design studies to compute space vehicle performance characteristics, often encounters numerical difficulties in solving the defined trajectory problem. Usually 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. 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. The automation of POST executions and CLIPS’ output evaluation and decision-making is shown to potentially reduce design cycle time. In addition, verification of the decision process and of the quality of the results is easily attained in CLIPS. The potential benefits of employing knowledgebased system within a design environment have long been well known. Various methods of utilization have been identified. As a post-processing 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. CLIPS CPU ctha HTI-IL ICBS LH2 LOX P2 POST 9 RBCC SSDL SST0 wopt a C Language Integrated Production System Central Processing Unit optimization indicator from POST Horizontal Take-off Horizontal Landing Knowledge-Based System Liquid Hydrogen Liquid Oxygen weighted constraint error from POST Program to Optimize Simulated Trajectories dynamic pressure (psf) Rocket-Based Combined Cycle Space Systems Design Laboratory Single-Stage-to-Orbit weighting factor for optimization variable angle of attack t Palace Knight Fellow, School of Aerospace Engineering, Student member AIAA m Assistant Professor, School of Aerospace Engineering, Senior member AIAA t Associate Professor, School of Civil & Environmental Engineeting Background Copyright

Probabilistic cost, risk, and throughput analysis of lunar transportation architectures

The Presidents vision for space exploration presents a need to determine the best architecture and set of vehicle elements in order to achieve a sustained human lunar exploration program. The Lunar Architecture Stochastic Simulator and Optimizer (LASSO), a new simulation-based capability based on discrete-event simulation, was created to address this question by probabilistically simulating lunar transportation architecture based on cost, reliability, and throughput figures of merit. In this study, two competing lunar transportation architectures are examined for a variety of launch vehicle scenarios to determine the best approach for human lunar exploration. Additionally, the two architectures are also compared for varying available ground infrastructure and desired flight rates. It is concluded that an expendable architecture is favored, using man-rated versions of existing evolved expendable launch vehicles (EELVs) for crew launches and developing a heavy-lift launch vehicle for cargo launches