A prototype computerized synthesis methodology for generic space access vehicle (SAV) conceptual design.

This dissertation presents the development steps required towards a generic (configuration independent) hands-on flight vehicle conceptual design synthesis methodology. This process is developed such that it can be applied to any flight vehicle class if desired. In the present context, the methodology has been put into operation for the conceptual design of a tourist Space Access Vehicle. The case study illustrates elements of the design methodology & algorithm for the class of Horizontal Takeoff and Horizontal Landing (HTHL) SAVs. The HTHL SAV design application clearly outlines how the conceptual design process can be centrally organized, executed and documented with focus on design transparency, physical understanding and the capability to reproduce results. This approach offers the project lead and creative design team a management process and tool which iteratively refines the individual design logic chosen, leading to mature design methods and algorithms. As illustrated, the HTHL SAV hands-on design methodology offers growth potential in that the same methodology can be continually updated and extended to other SAV configuration concepts, such as the Vertical Takeoff and Vertical Landing (VTVL) SAV class. Having developed, validated and calibrated the methodology for HTHL designs in the 'hands-on' mode, the report provides an outlook how the methodology will be integrated into a prototype computerized design synthesis software AVDS-PrADOSAV in a follow-on step.Today's and especially tomorrow's competitive launch vehicle design environment requires the development of a dedicated generic Space Access Vehicle (SAV) design methodology. A total of 115 industrial, research, and academic aircraft, helicopter, missile, and launch vehicle design synthesis methodologies have been evaluated. As the survey indicates, each synthesis methodology tends to focus on a specific flight vehicle configuration, thus precluding the key capability to systematically compare flight vehicle design alternatives. The aim of the research investigation is to provide decision-making bodies and the practicing engineer a design process and tool box for robust modeling and simulation of flight vehicles where the ultimate performance characteristics may hinge on numerical subtleties. This will enable the designer of a SAV for the first time to consistently compare different classes of SAV configurations on an impartial basis

Aeronautical Engineering: A continuing bibliography, supplement 120

This bibliography contains abstracts for 297 reports, articles, and other documents introduced into the NASA scientific and technical information system in February 1980

Proceedings, MSVSCC 2013

Proceedings of the 7th Annual Modeling, Simulation & Visualization Student Capstone Conference held on April 11, 2013 at VMASC in Suffolk, Virginia

Developing 3D Virtual Safety Risk Terrain for UAS Operations in Complex Urban Environments

Unmanned Aerial Systems (UAS), an integral part of the Advanced Air Mobility (AAM) vision, are capable of performing a wide spectrum of tasks in urban environments. The societal integration of UAS is a pivotal challenge, as these systems must operate harmoniously within the constraints imposed by regulations and societal concerns. In complex urban environments, UAS safety has been a perennial obstacle to their large-scale deployment. To mitigate UAS safety risk and facilitate risk-aware UAS operations planning, we propose a novel concept called \textit{3D virtual risk terrain}. This concept converts public risk constraints in an urban environment into 3D exclusion zones that UAS operations should avoid to adequately reduce risk to Entities of Value (EoV). To implement the 3D virtual risk terrain, we develop a conditional probability framework that comprehensively integrates most existing basic models for UAS ground risk. To demonstrate the concept, we build risk terrains on a Chicago downtown model and observe their characteristics under different conditions. We believe that the 3D virtual risk terrain has the potential to become a new routine tool for risk-aware UAS operations planning, urban airspace management, and policy development. The same idea can also be extended to other forms of societal impacts, such as noise, privacy, and perceived risk.Comment: 33 pages, 19 figure

Variable-Drift Diffusion Models of Pedestrian Road-Crossing Decisions

Peer reviewe

Reynolds number influences in aeronautics

Reynolds number, a measure of the ratio of inertia to viscous forces, is a fundamental similarity parameter for fluid flows and therefore, would be expected to have a major influence in aerodynamics and aeronautics. Reynolds number influences are generally large, but monatomic, for attached laminar (continuum) flow; however, laminar flows are easily separated, inducing even stronger, non-monatomic, Reynolds number sensitivities. Probably the strongest Reynolds number influences occur in connection with transitional flow behavior. Transition can take place over a tremendous Reynolds number range, from the order of 20 x 10(exp 3) for 2-D free shear layers up to the order of 100 x 10(exp 6) for hypersonic boundary layers. This variability in transition behavior is especially important for complex configurations where various vehicle and flow field elements can undergo transition at various Reynolds numbers, causing often surprising changes in aerodynamics characteristics over wide ranges in Reynolds number. This is further compounded by the vast parameterization associated with transition, in that any parameter which influences mean viscous flow development (e.g., pressure gradient, flow curvature, wall temperature, Mach number, sweep, roughness, flow chemistry, shock interactions, etc.), and incident disturbance fields (acoustics, vorticity, particulates, temperature spottiness, even electro static discharges) can alter transition locations to first order. The usual method of dealing with the transition problem is to trip the flow in the generally lower Reynolds number wind tunnel to simulate the flight turbulent behavior. However, this is not wholly satisfactory as it results in incorrectly scaled viscous region thicknesses and cannot be utilized at all for applications such as turbine blades and helicopter rotors, nacelles, leading edge and nose regions, and High Altitude Long Endurance and hypersonic airbreathers where the transitional flow is an innately critical portion of the problem

Mission Analysis and Design of MECSE Nanosatellite

Since the moment humankind started venturing into the realms of space, the problems associated with Radio Frequency (RF) blackout period due to plasma sheath interactions with the spacecraft have been an unsolved issue. During this period, the spacecraft loses all the communication with the control center or satellite including voice, real-time data telemetry and GNSS navigation. Considering that continuous communication during atmospheric re-entry is crucial to ensure safety and accomplishment of manned and unmanned space missions, solutions for the mitigation of RF blackout are of high priority and a requirement for the design of future space vehicles. One solution is the use of an electromagnetic field to manipulate the plasma layer surrounding the vehicle. In this M.Sc. thesis, an innovative CubeSat mission for the manipulation of ionospheric plasma is proposed and designed. MECSE (Magneto/Electro hydrodynamics CubeSat Experiment) aims to confirm in space that the electron density of the plasma layer can be reduced through the generation of an electromagnetic field. From a systems engineering perspective, the early phases of MECSE mission are fully designed (phases 0, A and B1 of ESA’s project lifecycle). Starting with mission characterization, the scientific case is presented and the feasibility of the mission is studied based on tradespace exploration methods. Then, the mission objectives, requirements and figures of merit are defined. The mission analysis is performed considering a reference orbit from a launch survey. In the end, a preliminary design of the spacecraft is presented including the analyses performed for the subsystems, the concept of operations and the definition of system requirements. This M.Sc. thesis also focusses on the study of orbital lifetime predictions for a CubeSat. The impact of using different solar and geomagnetic activity models proposed by standard guidelines is investigated using STK and DRAMA software and compared against historical data from already decayed CubeSats. It is concluded that there are still large deviations between the results provided by different models and that the satellite parameters recommended by the guidelines are not suitable when predicting accurately the orbital lifetime of a CubeSat. The orbital lifetime of MECSE nanosatellite is predicted and the effects of variations in orbital and satellite parameters are evaluated.Desde o começo da aventura da humanidade no espaço que os problemas associados ao período de blackout de comunicações são uma questão por resolver. Durante este período, o veículo espacial perde toda a comunicação com o centro de controlo ou satélite, incluindo voz, dados de telemetria em tempo real e navegação GNSS. Uma vez que a comunicação contínua é um fator crítico para garantir a segurança e o sucesso de missões espaciais tripuladas e não tripuladas, torna-se essencial encontrar soluções para a mitigação do blackout de comunicações. De facto, estas soluções são de extrema importância e já consideradas um requisito no desenvolvimento de futuros veículos espaciais. Uma solução é a utilização de um campo eletromagnético para manipular a camada de plasma que se forma em volta do veículo. Nesta tese de mestrado, uma inovadora missão CubeSat para a manipulação do plasma ionosférico é proposta e projetada. MECSE (Experimento de Magneto/Electro hidrodinâmica em Cubesat) tem o objetivo de provar no espaço que a densidade eletrónica da camada de plasma pode ser reduzida através da geração de um campo eletromagnético. De uma perspetiva de engenharia de sistemas, as fases inicias da missão MECSE são projetadas (fases 0, A e B1 do ciclo de vida da ESA). Começando por uma caracterização da missão, o caso científico é apresentado e a viabilidade da missão é estudada com base em métodos de exploração científica e tecnológica. De seguida, os objetivos de missão, requisitos e figuras de mérito são definidos. A análise de missão é feita considerando uma órbita referência baseada em pesquisa de lançamentos. No fim, um design preliminar do satélite é apresentado incluindo as análises realizadas para os subsistemas, o conceito de operações e a definição dos requisitos de sistema. Esta tese de mestrado foca-se ainda em estudar a previsão do tempo de vida orbital de um CubeSat. O impacto de usar diferentes modelos recomendados pelas diretrizes standard para a atividade solar e geomagnética é investigado usando STK e DRAMA softwares e comparado com dados históricos de CubeSats que já reentraram. É concluído que ainda existem enormes variações nos resultados de diferentes modelos e que os parâmetros de satélite recomendados pelas directrizes não são adequados para prever o tempo de vida orbital com precisão. O tempo de vida do satélite MECSE é previsto e os efeitos de variações em parâmetros orbitais e de satélite são avaliados

A Controller Development Methodology Incorporating Unsteady, Coupled Aerodynamics and Flight Control Modeling for Atmospheric Entry Vehicles

Atmospheric entry vehicle aerodynamics, flight dynamics, and control mechanisms are inherently coupled and unsteady. The state-of-the-art disciplinary models used for Mars entry vehicle simulation do not directly account for these time-dependent interactions, resulting in increased model fidelity uncertainty that can negatively affect controller performance. This can be especially detrimental given the more rigorous landing precision requirements and increased technological and volitional uncertainty expected for future missions. This work seeks to formulate and implement an entry controller tuning methodology that directly accounts for coupled, unsteady entry vehicle aerodynamic and control system behavior. The methodology uses a 6-degree-of-freedom coupled CFD-rigid body dynamics (RBD) model, extended to include flight control system modeling, for flight simulation while preserving unsteady flow history. This is capable of high-fidelity simulation to evaluate the performance of a controller, but the high cost makes it infeasible to directly use the state-of-the-art methodology for controller tuning which relies on thousands of short-duration simulations. Instead, multifidelity optimization is used. The coupled model is run to evaluate promising designs at high fidelity, while a lower-fidelity model is used to rapidly explore the design space. Crucially, each time the coupled model is executed, it produces new time-accurate trajectory and aerodynamic data that can be added to the training data for the low-fidelity aerodynamic surrogate model. A multifidelity surrogate is then constructed to provide a correction between the low- and high-fidelity results. As tuning proceeds, knowledge of the model is thus gained both by data fusion of the controller performance metrics, and by decreasing aerodynamic error in the low-fidelity surrogate. The methodology was developed through numerical experimentation with an entry vehicle equipped with a single-axis internal moving mass actuator for pitch control. A feed-forward neural network architecture with better performance than a state-of-the-art database was identified for use as the low-fidelity aerodynamic surrogate. A fusion-based multifidelity optimization method is implemented to leverage the quasi-hierarchical nature of the coupled and low-fidelity models. The methodology is demonstrated for tuning an angle of attack controller, yielding a controller that has better performance than one that is tuned using the state-of-the-art methodology.Ph.D