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Daniel Guggenheim School of Aerospace Engineering
Daniel Guggenheim School of Aerospace Engineering
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ItemLES of Turbulent Premixed Flame Kernel Formation and Development(Georgia Institute of Technology, 2020-12-17) Lambert, AlexanderSpark ignition of flammable mixtures is highly sensitive to early and local conditions. Kernel formation and subsequent flame development are largely governed by turbulent conditions and interactions with igniter geometry. In order to investigate this phenomenon, the use of Large Eddy Simulation (LES) is examined for (1) modelling spherical turbulent flame development, and (2) simulating spark ignition in a channel with either laminar or turbulent inflow. A comparison between LES spherical flame simulation is made to FSD-LES results as well as experimental measurements from previous studies. For spark ignition experiments, we characterize the temporal evolution of the ignition process, and demonstrate the dependence on early velocity fluctuations and local conditions.
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ItemAn acoustical based approach to conceptual design of non-traditional rotorcraft configurations(Georgia Institute of Technology, 2020-07-31) Huelsman, SaraAs interstate and highway traffic increases, commute times become drastically large. Such large commute times create fatigue and take away from productive hours at work, or joyful hours at home. The idea of urban air mobility becomes increasingly more attractive and viable as technology improves. These more advanced rotor concepts have opened up the design space in order to satisfy a very different mission profile. Nontraditional rotor concepts can provide performance benefits within a new use of the design. Noise becomes an increasing concern since the mission profile allows these vehicles flying much closer to communities. This research investigates three configurations of rotorcraft: coaxial rotors, ducted rotors, and ducted coaxial rotors, to provide insight on how design configuration changes the acoustics of these vehicles. The methodology developed is a parametric environment to provide detail on influential parameters for a model to be created for use within the conceptual design stage. This provides designers a process for capturing acoustic changes early on in the design process, while these new vehicles are still being developed.
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ItemA systems of systems methodology for conceptual studies of in-situ resource utilization for near earth object applications(Georgia Institute of Technology, 2020-07-28) Kitson, Christopher CurticeNear Earth Objects (NEO) have historically been neglected as an object of study relative to other celestial bodies. Interest has been increasing as more recognize the potential value of NEO resources represented by ‘asteroid mining’, especially as a supporting role in a Systems of Systems (SoS) context. After all, reusable rockets require refueling before reuse. That propellant needs to come from somewhere. Still, a feasible means to harness NEO resources has proven elusive. In-Situ Resource Utilization (ISRU) is a broad field with literature siloed by both disciplines and use cases. This is especially apparent for existing NEO ISRU concepts, with wildly varying levels of detail between systems in the same concept, including omission of key functions. Pet projects given context imply ‘technology push’ instead of ‘mission pull’. This thesis aims to show NEO ISRU is more feasible than previously believed, by providing a more comprehensive treatment of the required functionality and the means to deliver it. This boils down to permitting better comparisons via enabling trade studies at the conceptual level (NASA pre-phase A). A sample return mission using propellant produced from NEO resources for the return trip is formulated to contextualize the analysis. A program to develop a design that accomplishes this mission could be named “Sample return from Near earth object with In-situ Propellant production Technology demonstrator” (SNIPT). Both qualitative and quantitative design aspects are considered herein. Qualitative aspects are considered first. By reconciling commonalities between concepts, standardized terminology is proposed through a functional decomposition along with a morphological matrix of alternatives. A streamlined technology readiness assessment is performed to rank these morphological options. This information is used to select four concepts, one for each propellant type considered. Both impulsive (methalox and hydrolox) and continuous (hydrogen and steam) propulsion are considered as possible customers of an In-Situ Propellant Production (ISPP) SoS. Another significant part of this effort is quantifying alternatives sufficiently to permit comparisons beyond subject matter expert opinions. A modular sizing code is developed from scratch in line with the selected morphological options for each propellant, and verified at the module level using analog test data. By establishing baseline design(s), perturbations can be compared with directionally correct results. Input parameters for NEO orbital characteristics and then NEO composition are varied to ascertain effects upon sizing results. These results inform a trade study between the four propellant types considered. It was found that previous modeling efforts for NEO ISRU concepts have grossly underestimated the overall plant mass, likely due to neglecting indirect ISRU functionality and energy use. This includes sized values for mass payback ratio (MPR ≈ 5) and mass-specific regolith throughput (f_REG ≈ 0.3 day^(-1) ) which were previously overestimated by orders of magnitude. Methalox works better above 5 C: 1 H atoms by mass, a restrictive niche. Steam had the highest MPR but also heaviest plant mass. Hydrolox was found to be lightest on average for low Δv, with hydrogen lighter for high values, though hydrogen had MPR < 1 due to low volatile utilization. Increasing the proportion of volatiles used to make the propellant was found to reduce specific energy intensity, which in turn increases MPR.
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ItemA methodology to reduce dimensionality of a commercial supersonic transport design space using active subspaces(Georgia Institute of Technology, 2020-04-28) Crane, Nathan ThomasAs the commercial aviation industry continues to grow, the next technological leap is speed, and commercial supersonic transports are reappearing from multiple companies. Although this problem has been solved before, supersonic design is still difficult as it is highly interdisciplinary, lacks historical data, and requires additional design considerations earlier in the design cycle. Without historical data, higher fidelity analysis is needed early in the design process. The large number of design variables and the need for high fidelity analysis creates large computational costs, limiting design space exploration. To address this, the dimensionality of the design space needs to be reduced without removing the effects from the design variables. A recent technique called Active Subspaces has accomplished this goal by rotating a design space into the most active direction and taking surrogates in this active direction. Through rotation, the effects of each design variable are still present, but less impactful directions can be removed from the surrogate model, reducing dimensionality. This research applies this method to a commercial supersonic design space and asks additional questions about active subspace implementation into a design methodology. These questions address the gradient oversampling needed for good active subspace surrogate fits, if a better active subspace could be found in a partition of the full design space, and how the goodness of an initial surrogate, used to calculate gradients, affects the active subspace surrogate. Finally, the research compares computational cost between a traditional surrogate and an active subspace surrogate. These questions were addressed using aerodynamic data of various aircraft configurations at supersonic cruise conditions. Beginning with a design of experiments of 20 planform variables, the configurations were input into Engineering Sketch Pad to generate the geometry. The geometry was taken into an inviscid computational fluid dynamics (CFD) tool to calculate coefficients of lift and drag at the cruise condition, and these were tabulated. The results were post processed, and a traditional surrogate was created. From this surrogate, gradients were taken to develop active subspace variables. These variables were used to generate a sweep of active subspace surrogates starting from a single variable to a surrogate made from all 20 variables. From these surrogates, it was concluded that oversampling gradients beyond the published range does not decrease error while undersampling increases error at a lower significance than expected. An active subspace in a local partition of a design space initially reduced error, but error reduction decreased as more variables were included in the active subspace surrogate. The number of cases per design variable of an initial surrogate used to calculate gradients was significant. The error of the active subspace surrogate created from these gradients decreased until 50 cases per design variable, when the decrease in error plateaued. Finally, active subspaces saw a large potential to reduce computational time. A small reduction in dimensionality could greatly reduce computational time, especially if gradients are found within a tool. Using these results, a design methodology was presented incorporating active subspaces into the design loop.
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ItemDevelopment of a methodology for technology requirement assessment for space habitats(Georgia Institute of Technology, 2020-04-28) Deguignet, MarieThere recently has been a renewed focus on space exploration and space habitats all over the world. Future lunar developments should focus on reusability, sustainability and affordability. To comply with these objectives, deep space exploration will be faced with technical and human limitations. New technologies must be developed to overcome these challenges. Because technology development is a long and onerous process, it is important to be able to identify the requirements early in the design process to reduce the risk of new developments. A clear methodology to evaluate the requirements of a technology to meet future goals must be provided to innovative companies. This work aims at establishing a clear and consistent methodology to evaluate future space technologies and compare their impact on several factors of a campaign to define the conceptual requirements. To prove that the developed methodology answers all the targeted requirements of the research objective, it will be tested on a technology: cryocoolers, and the space logistics framework FOLLOW. The proposed methodology uses Technology Impact Forecasting and applies and modifies it to take into consideration the specificity of the problem at hand: a smaller data set, long computation times and the goal of the thesis. The methodology can be used by companies to prove the worth of new innovative ideas and encourage investment. It is a rather safe process to help technology advancement.
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ItemOptimal Phasing and Performance Mapping for Translunar Satellite Missions across the Earth-Moon Nodal Cycle(Georgia Institute of Technology, 2020-01-10) Hunter, Richard Anthony JohnFast, high-cadence translunar pathfinder missions hold great promise for advancing NASA's scientific observation, prospecting, and technology validation objectives through increased lunar exploration. This research applies high-performance computing to characterize direct injection lunar trajectories over a broad parameter space, and in so doing, demonstrates the viability of lunar pathfinder missions using the near-future commercial launch market. The results are intended to provide mission designers with an accurate, versatile reference for preliminary planning, including optimal departure epochs, and pertinent performance dependencies. Characterized herein are statistical distributions for the performance demands of optimally phased translunar missions, over an 18.6 year Earth-Moon nodal cycle, to a range of tailored lunar arrival architectures, for 0 – 24 kg small satellite payloads capable of supporting pathfinder objectives. This characterization is based upon a TLI stage with flight proven propulsion technology, high fidelity orbital dynamics, and direct injection flyby, orbit insertion and landing architectures compatible with both dedicated and ride share commercial launches.
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ItemMulti-mission sizing and selection methodology for space habitat subsystems(Georgia Institute of Technology, 2019-12-11) Boutaud, Agathe KathiaFuture space missions aim to set up exploration missions in further space and establish settlements on other celestial bodies like the Moon or Mars. In this context, subsystem sizing and selection is crucial, not only because resource management is critical for the astronauts’ survival, but also because subsystems can account for more than 20% of the total mass of the habitat, so reducing their size can greatly impact the cost of the mission. A few tools already exist to size space habitat subsystems and assess their performance. However, these tools are either very high-fidelity and very slow or instantaneous but steady-state. Steady-state tools do not allow to take risks or mission variations into account and the dynamic, slower tools are less performing at helping stakeholders evaluate the impact of technology trade-offs because of their long running time. Faster sizing tools would also allow to implement additional capabilities, such as multi-mission sizing, which could be used to develop lunar or martian settlements. These tools are also used in the context of point-based design, which focuses on the development of one design throughout the process. Such approach can lead to a sub-optimal design because the selection of an alternative is made early in the design process, based on low-fidelity analyses. In addition, because the costs and design choices are committed early in the design process, requirements or design changes can have very significant cost consequences. This research proposes a new sizing capability, developed using HabNet [1], a dynamic space habitat simulation tool. It is faster than existing dynamic sizing tools and it allowed to develop a multi-mission sizing methodology using Design Space Exploration. Finally, leveraging the faster sizing tool developed to create surrogate models for the size of the elements in the habitat, it was shown that trade-off analyses can be used to support set-based design during the conceptual design phase. Consequently, the methodology proposed is faster than what is currently used to size and select space habitat subsystem technologies. It gives more insight to the user because it can perform instantaneous trade-offs. However, the quality of the surrogate models generated is not sufficient to validate the multi-mission sizing method and environment developed during this thesis. This methodology could be used as a basis for the development of a set-based design method for space habitats. Numerous capabilities, including the evaluation of the impact of disruptions or the level of uncertainty associated with the various alternatives considered, could be easily implemented and added to the existing tool.
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ItemX-ray Pulsar Navigation Instrument Performance and Scale Analysis(Georgia Institute of Technology, 2019-12-06) Payne, Jacob HurrellThis thesis investigates instruments for autonomous satellite navigation using measurements of X-ray emissions from millisecond pulsars. A manifestation of an instrument for this purpose, called the Neutron star Interior Composition Explorer (NICER), was launched to the International Space Station in 2017. The NICER instrument was designed to observe X-ray emissions from neutron stars for astrophysics research, and is out of scale in terms of volume, power consumption, mass and mechanical complexity to be useful for small satellite missions. This work surveys the range of existing X-ray observation missions to tabulate collecting areas, focal lengths, and optical configurations from milestone missions which describe the evolution of the state of the art in X-ray observatories. A navigation demonstration experiment, called the Station Explorer for X-ray Timing and Navigation Technology (SEXTANT), was conducted using the NICER instrument. The experimental performance observed from NICER through the SEXTANT navigation demonstration is compared to theoretical predictions established by existing formulations. It is concluded that SEXTANT benefits from soft band (0.3-4 keV) exposure to achieve better accuracy than predicted by theoretical lower bounds. Additionally, investigation is presented on the readiness of a navigation instrument for small satellites using compound refractive lensing (CRL) and derived designs. X-ray refraction achieves a much shorter focal length than grazing incidence optics at the expense of signal attenuation in the lens material. Performance estimates and previous experimental results are presented as a baseline for physical prototypes and hardware testing to support future development of a physical instrument. The technological hurdle that will enable this tool is manufacturing precise lenses on a 3-micron scale from materials like beryllium with low atomic mass. Recent X-ray concentrator concepts demonstrate progress towards an implementation that can support a CubeSat scale navigation instrument optimized for soft band (0.3-4 keV) X-rays.
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ItemDevelopment of a Multidisciplinary Design Analysis Framework for Unmanned Electric Flying Wings(Georgia Institute of Technology, 2019-12-03) Whitmore, William ValentinSmall-scale subsonic unmanned aerial vehicles have become common tools in both military and civil applications. A vehicle configuration of special interest is the flying wing (aka all-wing or tailless aircraft). This configuration can potentially reduce drag, increase structural efficiency, and decrease detectability. When combined with an electric propulsion system, it produces no observable emissions and possesses fewer maintenance issues. Unfortunately, strong couplings between disciplinary analyses hinder the design of unmanned electric flying wings. In particular, achieving adequate stability characteristics degrades the aerodynamic efficiency of the vehicle, and constrains the available volume in which subsystem components may be placed. Exploiting the potential advantages of electric flying wings therefore necessitates a multidisciplinary perspective. In order to overcome the identified challenges of unmanned electric flying wing design, a multidisciplinary design analysis framework was conceptualized, implemented, and evaluated. The Python-based framework synthesizes automated analysis modules that model geometry, weight distribution, electric propulsion, aerodynamics, stability, and performance. Virtual experiments demonstrated the framework’s utility in quickly exploring a wide design space and assessing design robustness. Two important stand-alone contributions developed for the framework are (1) an algorithm for densely packing battery cells within a wing shape and (2) a parametric electric propulsion analysis code. In short, the framework supports the design of small-scale (i.e. 0-55lb weight range) subsonic unmanned electric flying wings with a host of valuable capabilities that were previously unavailable within traditional design methods.
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ItemDecentralized allocation of safety-critical applications on parallel computing architecture(Georgia Institute of Technology, 2019-08-26) Sutter, LouisThis work presents a decentralized task allocation algorithm for an abstract parallel computing architecture made of a set of Computational Units connected together, each of them being prone to fail. Such an architecture can represent for example a multi-core processor with each Computational Unit standing for one core. The aim of the algorithm is to find the best mapping between Computational Units and the different applications we want to execute on the architecture, while taking into account faulty Computational Resources and the priority of the applications. The proposed approach consists in formulating the allocation problem as an Integer Linear Program (ILP), that is solved thanks to a state-of-the-art ILP solver. The second main aspect of this work is the decentralization the allocation process, in the sense that no central element decides alone of the allocation for the rest of the network. Redundant copies of the allocation algorithm are executed on the architecture itself, meaning that the copies must reallocate themselves. Then, the proposed allocation process is implemented on an experimental setup reproducing the multi-core architecture that inspired this work. Each core is represented by a Raspberry Pi single board computer. The model is used to demonstrate the capabilities of the proposed allocation process to maintain operation of a physical system in a decentralized way, while individual components fail.