Mavris, Dimitri N.

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Now showing 1 - 5 of 5
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    Optimal Deployment Strategies for Cislunar PNT+C Architectures
    (Georgia Institute of Technology, 2024-01) Gabhart, Austin ; Drosendahl, Madilyn ; Robertson, Bradford E. ; Steffens, Michael J. ; Mavris, Dimitri N.
    Cislunar operations are expected to rise dramatically within the next decade, requiring a comparable increase in PNT and communications services. However, current PNT systems are at capacity and need to be augmented to serve a cislunar space domain, specifically in the form of novel cislunar PNT architectures. This paper studies the problem of the deployment of PNT and communications satellites, specifically, the problem of deployment strategies spanning multiple stages over extended periods of time. A set of stage definitions will be determined along with areas of potential user activity. A novel application of the hidden gene genetic algorithm to the constellation optimization problem is presented. A design space exploration is presented with comparisons of circular and elliptical constellations. Optimization results from the first stage are also provided. It is shown that acceptable performance can be achieved with a low number of deployed satellites and that strong trade-offs exist between performance and stability.
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    A Reduced Order Modeling Approach to Blunt-Body Aerodynamic Modeling
    (Georgia Institute of Technology, 2024-01) Dean, Hayden V. ; Decker, Kenneth ; Robertson, Bradford E. ; Mavris, Dimitri N.
    Blunt-body entry vehicles display complex flow phenomena that results in dynamic instabilities in the low supersonic to transonic flight regime. Dynamic stability coefficients are typically calculated through parameter identification and trajectory regression techniques using both physical test data and Computational Fluid Dynamics (CFD) simulations. This methodology can generate dynamic stability coefficients, but the resulting data points are limited, and have high degrees of uncertainty due to the nature of data reduction methods. With increased computational capabilities, new methods for dynamic stability quantification have been explored that seek to leverage the high-dimensional aerodynamic data produced from CFD simulations to compute dynamic stability behavior and address the limitations of linearized aerodynamics. The objective of this work is to advance the quantification of dynamic stability behavior of blunt-body entry vehicles by leveraging high-fidelity CFD data through Reduced Order Modeling (ROM). ROMs are capable of leveraging high-fidelity aerodynamic data in a cost effective manner by finding a low-dimensional representation of the Full Order Model (FOM). ROMs based on Proper Orthogonal Decomposition (POD) have shown success in recreating CFD analyses of parametric ROM applications and time-varying ROM applications. Results of this research demonstrated success in constructing two ROMs of a notional blunt-body entry vehicle to recreate heatshield and backshell pressure distributions from forced oscillation trajectories. The ROM was more successful at reconstructing the heatshield pressure distribution, with challenges arising in predicting the chaotic response of backshell latent coordinates.
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    Unsteady Aerodynamic Uncertainty Quantification of a Blunt-Body Entry Vehicle in Free-Flight
    (Georgia Institute of Technology, 2024-01) Willier, Brenton J. ; Hickey, Alexandra M. ; Robertson, Bradford E. ; Mavris, Dimitri N.
    The design process of blunt-body entry vehicles balances atmospheric heating and drag to ensure crucial payloads can safely traverse through entry, descent, and landing. However, the blunt shape leads to a chaotic recirculating wake. Currently, uncertainties in the vehicle design process are captured through scalars and multipliers, and these conservative estimations lead to over-engineered vehicles, reduced payload capacity, and less accurate landings. To supplement the data gathered through physical testing, CFD-in-the-loop free-flight trajectories can be simulated throughout the flight regime. While CFD performance has improved significantly, the number of cases required to produce a meaningful sample for an uncertainty analysis remains computationally intense. Parametric uncertainty can be captured with traditional uncertainty methods like Monte Carlo analysis. However, the non-parametric uncertainty due to the unsteady nature of the chaotic wake has yet to be studied for free-flight analysis. This paper presents and implements an ensemble sampling initialization approach to determine the impact of unsteady wake structures imparted on CFD-in-the-loop data produced using replicated trajectory simulations. To enable this data generation, the Genesis vehicle gridding process is detailed, along with an overview of the free-flight CFD simulation setup for a supersonic flight regime. While running a static unsteady simulation, ten flow fields were saved at various times to capture different instantaneous structures in the wake. After initializing identical free-flight simulations with the ten different flow fields, results of vehicle aerodynamic angles, aerodynamic force and moment coefficients, inertial velocity, and vehicle trajectory in multiple reference frames showed identifiable trends with diverging behavior. The uncertainty on these variables due to unsteady flow is also quantified throughout the motion. It is concluded that this aspect of uncertainty must be carefully considered when CFD-in-the-loop is used to model the flight characteristics of a blunt-body vehicle.
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    Analysis of Infrastructure to Support a Future Space Economy
    (Georgia Institute of Technology, 2024-01) Roohi, Zayn A. ; Robertson, Bradford E. ; Mavris, Dimitri N.
    Beginning with the Artemis-I mission in late 2022, NASA is embarking upon a series of increasingly complex missions to establish a permanent presence on the surface of the Moon, potentially leading to manned Mars missions within the next few decades. Several private companies have also announced that they have begun work on space tourism projects with the goal of launching within this same time-frame. Supporting this expansion will require advanced space logistics and the development of dedicated space-based supply chains in order to reduce cost and increase resiliency. Previous research has focused on studying the impact that a specific technology, vehicle, or type of infrastructure has on supporting a single space campaign or mission; this paper takes a wider view by examining the impact that several types of infrastructure concepts together will have on the entire set of operations that could take place within the next decade. Lunar in-situ resource utilization, space depots, and space tugs are considered as infrastructure concepts, and a Lunar space station, Lunar habitat, Earth space stations, and Mars missions are considered as the operations to support. A time expanded mixed-integer nonlinear programming model is used to solve traditional network flow and supply chain problems, the results of which are used to propose future resupply missions and supply chain architectures.
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    Multidisciplinary Design Analysis and Optimization of a Hypersonic Inflatable Aerodynamic Decelerator
    (Georgia Institute of Technology, 2023-01) Dean, Hayden V. ; Robertson, Bradford E. ; Mavris, Dimitri N.
    Human missions to Mars will require advanced entry, descent, and landing (EDL) technology to safely land payloads onto the planet’s surface. With rapidly increasing mass requirements, and stagnant geometry constraints set by current launch vehicles, non-heritage EDL vehicles must be considered to safely land human-scale payloads on Mars. The hypersonic inflatable aerodynamic decelerator (HIAD) is an EDL architecture being evaluated for human-scale payloads to Mars. Parameterization of a HIAD using important geometry variables is generated and used to explore the feasible design space of the entry architecture. The design space is evaluated using GT-Hypersonics, a multidisciplinary design analysis and optimization environment that combines ESP, CBAero, a Dymos-based trajectory optimizer, TPSSizer, and FIAT to perform trajectory, aerodynamic, and aerothermodynamic analysis on a given entry vehicle geometry, and prescribed flight parameters. This analysis is used to size the vehicle’s TPS system, and determine loads experienced by the vehicle during entry. Ranges for geometric inputs were selected and implemented to explore the design space of the HIAD architecture for a use case on Mars using uncrewed and crewed mission constraints. The design spaces for both the uncrewed and crewed missions demonstrated flexibility of inputs, allowing for multiple configurations to be used successfully in a mission to Mars. This study was useful in understanding the future of using the HIAD architecture in space exploration. This study demonstrates the ability to rapidly generate vehicle designs and evaluate their feasibility, a capability that will be useful in the growing space industry.