Master of Science in Aerospace Engineering

Series

Master of Science in Aerospace Engineering

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https://hdl.handle.net/1853/73269

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Degree Series

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Organizational Unit

Daniel Guggenheim School of Aerospace Engineering

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Now showing 1 - 10 of 16

Multi-mission sizing and selection methodology for space habitat subsystems

(Georgia Institute of Technology, 2019-12-11) Boutaud, Agathe Kathia

Future 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.
X-ray Pulsar Navigation Instrument Performance and Scale Analysis

(Georgia Institute of Technology, 2019-12-06) Payne, Jacob Hurrell

This 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.
Development of a Multidisciplinary Design Analysis Framework for Unmanned Electric Flying Wings

(Georgia Institute of Technology, 2019-12-03) Whitmore, William Valentin

Small-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.
Decentralized allocation of safety-critical applications on parallel computing architecture

(Georgia Institute of Technology, 2019-08-26) Sutter, Louis

This 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.
Investigation of ODE-based non-equilibrium wall shear stress models for large eddy simulation

(Georgia Institute of Technology, 2019-07-30) Dzanic, Tarik

For high Reynolds number flows, wall modeling is essential for performing large eddy simulation at a reasonable computational cost. In this work, a novel low-cost ODE-based non-equilibrium wall model is introduced for wall shear stress modeling in LES. Using polynomial approximations of the pressure gradient and convective terms obtained from interpolation of the LES solution, as opposed to direct evaluation of these gradients within the wall model, the governing wall model equations reduce from coupled PDEs to uncoupled ODEs that do not require an embedded wall model grid within the LES grid. Additionally, the steady form of the wall model equations was utilized, feasible due to the spatial decoupling of the wall model equations, and the effects of the temporal evolution on the wall shear stress were modeled. The effects of polynomial degree on the accuracy of the wall shear stress predictions were explored, and an empirical lag model was built to model the unsteady effects without requiring the solution of a time-stepping problem. Wall resolved large eddy simulations of separated flow around the NASA wall mounted hump and an iced NACA 63A213 airfoil were performed and used as a reference for the comparison of the non-equilibrium wall model to a commonly used equilibrium wall model. The proposed non-equilibrium wall model was able to predict separated flow and laminar flow regions in much better agreement with the wall resolved results than the equilibrium wall model. Underpredictions in the skin friction coefficient in non-equilibrium flow regimes were reduced from 20-50% to less than 10% between the equilibrium and the non-equilibrium wall modeled approaches. Minor improvements in the pressure coefficient predictions were observed with the non-equilibrium model in the separated flow region of the iced airfoil. The results suggest that the proposed wall model can offer better predictions of separated and/or laminar flows compared to equilibrium wall models with negligible computational cost increase.
Context dependent total energy alerting system for the detection of low energy unstabilized approaches

(Georgia Institute of Technology, 2019-07-05) Portman, Michael Aaron

This thesis examines context dependent total energy alerting to protect against low energy unstable approaches in commercial aviation operations. Currently, many individual states are monitored independently to identify unstable approaches, rather than an integrated single assessment of total energy. An alert would also have to be context dependent, integrating the individual states with awareness of phase of flight, approach profile modeling, and expected pilot response to individualize the alert’s activation threshold for each approach. This thesis details a design of such a context dependent total energy alerting system. First, a preliminary analysis examines when such an alert would have been given in a case study of Asiana Airlines Flight 214. This flight’s crash on approach into San Francisco International Airport was attributed to lack of pilot situational awareness and understanding of the aircraft’s autoflight systems, leading to the aircraft having sufficiently low total energy that it stalled into the seawall just before the runway threshold. Analysis shows the total energy alert would have sounded roughly 14-41 seconds before impact, earlier than any currently installed system and potentially early enough for corrective action. Next, the context dependent total energy alert is analyzed to assess its performance in real flight as captured by Flight Operations Quality Assurance (FOQA) data. The analysis examines how alerting parameters impact when and how often the alert is triggered, and the thesis concludes with recommendations for the design and application of a context dependent total energy alert, along with recommendations for future work.
A multi-UAV trajectory optimization methodology for complex enclosed environments

(Georgia Institute of Technology, 2019-05-02) Barlow, Sarah

Unmanned Aerial Systems (UAS) have become remarkably more popular over the past decade and demonstrate a continuous upward market trend. As UAS become more accessible and advanced, they are able to be incorporated into a broader range of applications and provide substantial operational benefits. In addition to exterior use cases, UAS are being investigated for interior use cases as well. An area that has great potential for UAV involvement are manufacturing and warehouse environments, as these typically occupy vast spaces. Warehouse logistics and operations are very complex and could significantly benefit from the integration of UAVs. Many companies are already exploring using UAS as a means to perform inventory audits to reduce labor costs and time, and improve accuracy and safety. To achieve the maximum benefit from this technology in these environments, multiple vehicles would be essential. The purpose of this thesis is to optimize the operations of multiple UAVs in complex and confined environments, using a warehouse model as a test case. There are added complexities when working with multiple vehicles; for example, ensuring that there are no collisions between vehicles. A great deal of research has been done on vehicle routing and trajectory optimization, but very little has been done with UAV optimization in confined spaces. This thesis further develops these algorithms and focuses in on the impact UAV involvement could have on operations in environments that are similar to warehouses. The proposed improvements from the current methods will help uncover the most optimal results by changing the process for finding solutions, the criteria under which solutions are ranked, and the operational/experimental setup. The new methodologies seek to resolve the sub-optimality issues from the existing approach to significantly reduce the mission time required to perform a warehouse inventory audit. An existing inventory scanning algorithm generates sub-optimal, collision free paths for multi-UAV operations, which has two sequential processes: solving a vehicle routing problem and determining optimal deployment time without any collisions. To improve the sub-optimal results, this thesis introduces three possible improvements on the multi-UAV inventory tracking scenario. First, a new algorithm logic which seeks to minimize the total mission time once collision avoidance has been ensured rather than having separate processes. Next, an objective function that seeks to minimize the maximum UAV mission time rather than minimizing the total of all UAV mission times. Last, an operational setup consisting of multiple deployment locations instead of only one. These proposed improvements are assessed based on their degree of impact on the overall mission time compared to the current methods. They are also analyzed in comparison to one another and in combination with one another to better understand the effectiveness and sensitivities of the presented changes.
A methodology for conducting design trades related to advanced in-space assembly

(Georgia Institute of Technology, 2018-12-07) Jara de Carvalho Vale de Almeida, Lourenco

In the decades since the end of the Apollo program, manned space missions have been confined to Low Earth Orbit. Today, ambitious efforts are underway to return astronauts to the surface of the Moon, and eventually reach Mars. Technical challenges and dangers to crew health and well-being will require innovative solutions. The use of In-Space Assembly (ISA) can provide critical new capabilities, by freeing designs from the size limitations of launch vehicles. ISA can be performed using different strategies. The current state-of-the-art strategy is to dock large modules together. Future technologies, such as welding in space, will unlock more advanced strategies. Advanced assembly strategies deliver smaller component pieces to orbit in highly efficient packaging but require lengthy assembly tasks to be performed in space. The choice of assembly strategy impacts the cost and duration of the entire mission. As a rule, simpler strategies require more deliveries, increasing costs, while advanced strategies require more assembly tasks, increasing time. The effects of these design choices must be modeled in order to conduct design trades. A methodology to conduct these design trades is presented. It uses a model of the logistics involved in assembling a space system, including deliveries and assembly tasks. The model employs a network formulation, where the pieces of a structure must flow from their initial state to a final assembly state, via arcs representing deliveries and assembly tasks. By comparing solutions obtained under different scenarios, additional design trades can be performed. This methodology is applied to the case of an Artificial Gravity Space Station. Results for the assembly of this system are obtained for a baseline scenario and compared with results after varying parameters such as the delivery and storage capacity. The comparison reveals the sensitivities of the assembly process to each parameter and the benefits that can be gained from certain improvements, demonstrating the effectiveness of the methodology.
A scalable hardware-in-the-Loop simulation for satellite constellations and other multi-agent networks

(Georgia Institute of Technology, 2018-04-30) Degraw, Christopher F.

Given the plans for satellite mega-constellations, there is a lack of rigorously tested operations and control methods for constellations larger than 30 to 50 spacecraft. The purpose of this thesis is to propose the principles behind a robust, modular, and scalable system able to provide software-in-the-loop (SWIL) and hardware-in-the-loop (HWIL) simulation capabilities for the advancement of formation and constellation system Technology Readiness Levels (TRL). Additionally, this thesis will develop a first generation system demonstrating these principles called Constellation Simulation on a Massive Scale, or COSMoS. The preliminary goals of COSMoS are to 1) simulate multiple or more satellites in a constellation to demonstrate scalable capability; and 2) connect to external hardware devices in real-time to demonstrate HWIL capability. The simulation framework behind COSMoS is the Multi-Agent Distributed Network Simulator, or MADNS. MADNS is a real-time hardware-in-the-loop (RT-HWIL) simulator capable of communicating with independent agents and external hardware and software elements. This framework will encapsulate the COSMoS simulation but will be designed to work with any multi-agent network simulation designed within the constraints of the MADNS API. This thesis will show the results of the preliminary development of both MADNS and COSMoS and will present a direction for the further development of both a satellite constellation simulator and general real-time hardware-in-the-loop simulators.
A combined feedback controller design for active vibration suppression

(Georgia Institute of Technology, 2018-04-30) Manghaipathy, Pavithra

To prevent failure due to fatigue, especially in high-performance aircraft, there is a significant amount of interest in vibration suppression methods with a special focus on active vibration control methods. This thesis demonstrates vibration controller designs, by using a combination of acceleration & positive position feedback (PPF), acceleration & velocity feedback and positive position feedback (PPF) & velocity feedback, along with smart actuators based on piezoelectric stacks in order to address the issue. While several feedback and controller methods exist, this previously unexplored design was chosen to emphasize the effects of two types of combined feedback over a single feedback. Noting the work by Caughey & Goh (1983) and Fanson (1984) for the controller design process, this thesis aims to perform a stability analysis and expand on the use of the method designed by Hanagud & de Noyer (1998); a control method which uses a single specified closed frequency and a preset closed loop damping ratio to control the damping. Therefore, the new research presented in this thesis includes the following: 1. Study combinations of two feedbacks (Acceleration & Velocity, Position & Velocity and Acceleration & Position) to design controllers that yield a single closed loop frequency for specified closed loop damping ratio and a new solution technique of equating coefficients of the transfer function denominator. 2. Modifying the design to include frequencies other than the single closed loop frequency by adding perturbations about a single closed loop frequency ωf. 3. Search for a design that uses minimum energy required by the controller to suppress and control vibrations. 4. Search for the best combination; Acceleration & Velocity, Position & Velocity or Acceleration & Position Feedback design.