Doctor of Philosophy with a Major in Aerospace Engineering

Series

Doctor of Philosophy with a Major in Aerospace Engineering

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https://hdl.handle.net/1853/72952

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Degree Series

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Organizational Unit

Daniel Guggenheim School of Aerospace Engineering

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Publication Search Results

Now showing 1 - 10 of 21

Design and manufacturing of conformal ablative heatshields

(Georgia Institute of Technology, 2019-06-10) Sidor, Adam Thomas

Conformal ablators, first introduced in the early 2000s under the NASA Hypersonics Project, are a type of rigid ablative thermal protection system that uses flexible, rather than rigid, fibrous substrates. These materials are impregnated with resin in a mold to yield a part that is close to the final geometry and requires little post-process machining (a near net shape part). The lack of fiber connectivity through the thickness enables the TPS to tolerate larger strains than comparable rigid substrate ablators facilitating larger tiles and installation on most aeroshells without strain isolation. Reduced part count and simplified integration drive reductions in labor, cost and complexity –advancements which are enabling for planetary and human missions. Conformal ablators are currently fabricated using an open liquid impregnation process adapted from a technique developed for Lightweight Ceramic Ablators, such as Phenolic Impregnated Carbon Ablator, which leads to design and manufacturing inefficiencies. This work advanced a new manufacturing technique for conformal ablators, vacuum infusion processing, that reduces resin consumption and streamlines clean up. The closed process also eliminates an expensive atmosphere-controlled oven or vacuum chamber. A design methodology, centered around a simulation of the mold filling process, was developed to tailor a conformal ablative heatshield to vacuum infusion processing. A constitutive model, combining properties of individual components, was formulated to estimate the properties of the composite TPS material. The methodology leverages this model, integrated with material selection, tile layout, and the mold filling simulation, to automate a conceptual conformal heatshield design. The approach allows rapid iteration on TPS composition and manufacturing constraints.
Magnetohydrodynamic energy generation and flow control for planetary entry vehicles

(Georgia Institute of Technology, 2019-05-03) Ali, Hisham K.

Proposed missions such as a Mars sample return mission and a human mission to Mars require landed payload masses in excess of any previous Mars mission. Whether human or robotic, these missions present numerous engineering challenges due to their increased mass and complexity. To overcome these challenges, new technologies must be developed, and existing technologies advanced. Resource utilization technologies are particularly critical in this effort. This thesis aims to study the reclamation and harnessing of vehicle kinetic energy through magnetohydrodynamic (MHD) interaction with the high temperature entry plasma. Potential mission designs, power generation and power storage configurations are explored, as well as uses for the reclaimed energy. Furthermore, the impact and utility of MHD flow interaction for vehicle control is assessed. The state of the art for analysis of MHD equipped planetary entry systems is advanced, with the specific goals including: development of performance analysis capabilities for potential MHD equipped systems, identification of systems or configurations that show promise as effective uses of MHD power generation, experimental designs for developing technologies applicable to MHD power generation systems, assessment of MHD flow interaction and beneficial use for entry vehicle control through drag modulation, and increasing the technology readiness level of MHD power generation architectures for entry, descent and landing.
Conceptual thermal response modeling, testing, and design of flexible heatshield insulation materials

(Georgia Institute of Technology, 2018-01-12) Rossman, Grant Andrew

Flexible Thermal Protection Systems (FTPS) have been investigated to support many applications, including thermal protection of inflatable atmospheric entry vehicles. This flexible blanket is composed of a stack of material sheets, including heat rate resistant outer fabrics, heat load resistant insulation, and an air-tight gas barrier to prevent pressure leaks. This dissertation advances the state-of-the-art of thermal modeling, material property testing, and design of FTPS. In this investigation, a one-dimensional (1D) thermal response model is used to predict in-depth temperatures of FTPS layups during arc-jet ground testing. An extended inverse multi-parameter estimation methodology is developed to improve thermal model prediction accuracy. This method utilizes concepts from inverse heat transfer analysis, parameter estimation, and probabilistic analysis. Thermal response model input parameters are adjusted to minimize the error between temperature predictions and in-depth temperature measurements from arc-jet ground testing. Some FTPS insulators experience decomposition under extreme heating conditions, while others do not. In this investigation, a thermogravimetric analysis (TGA) experimental campaign was designed and executed to further characterize fibrous insulators that undergo decomposition. This material testing methodology was developed to obtain the approximate distribution of activation energy. Associated activation energies were inserted into corresponding thermal response models to improve temperature prediction accuracy. In this investigation, a simulation-based FTPS insulator design methodology is developed to obtain a final FTPS insulator configuration. This design process uses inputs such as candidate insulators, insulator material properties, and a nominal mission profile. Candidate insulators are designed efficiently using an improved thermal response model, providing FTPS insulator stackup configurations that satisfy mission requirements.
Use of the Mars atmosphere to improve the performance of supersonic retropropulsion

(Georgia Institute of Technology, 2017-05-23) Gonyea, Keir C.

NASA has landed seven vehicles on the surface of Mars using parachutes for supersonic descent. These parachutes are unsuited to future high mass missions due to inflation, drag, and aerothermodynamic complications. Supersonic retropropulsion is a candidate technology to replace supersonic parachutes, but is hindered by its large associated propellant mass. Atmospheric-breathing propulsion systems may reduce this mass constraint by ingesting oxidizer from the surrounding atmosphere. However, the Martian atmosphere, which is composed of primarily carbon dioxide, necessitates that metal fuels be used in order to combust the available oxidizer. This thesis advances the state of the art of atmospheric-breathing supersonic retropropulsion (ABSRP) by providing the first exploration into the feasibility and potential performance of ABSRP as a technology solution for high-mass Mars missions. Specific advancements include the development of modeling methods and tools, the evaluation of conceptual ABSRP performance and sensitivities, and the formulation of vehicle concepts. Model development targeted components and subsystems most relevant to ABSRP in order to capture the necessary physics and provide a preliminary integrated vehicle simulation for future conceptual design efforts. Models were developed to assess metal – CO2 combustion performance and sensitivity to both the engine design and operating regime. These tools include an equilibrium combustion simulation to evaluate engine efficiency, a finite-rate kinetics simulation to investigate the time-dependent phenomena, and a particle burning simulation to assess diffusion effects. Case studies are presented for ABSRP relevant mixtures and conditions to predict propulsion performance of the ABSRP engine across a range of conditions and verify that reasonably sized combustion chambers can provide complete combustion of the propellant. Exploration of the performance results indicate that ABSRP systems have promising propulsive performance relative to comparative rocket systems and do not have unacceptable burning timescale constraints. The propulsion system results are used in an ABSRP vehicle model, which accounts for the variable engine performance across different flight regimes. This model is used to search the design space and determine the performance and sensitivity of multiple proposed ABSRP vehicle concepts relative to competing propulsive solutions. The investigation includes an assessment of feasible and unfeasible regions of the design space in addition to design trends for optimal configurations. Mass favorable vehicles of multiple architectures are compared to understand their relative performance. Vehicle architectures involving ABSRP are seen to have optimal mass performance, which demonstrates the potential applicability of atmospheric-breathing propulsion for Mars descent.
Mechanical property determination for flexible material systems

(Georgia Institute of Technology, 2016-04-12) Hill, Jeremy Lee

Inflatable Aerodynamic Decelerators (IADs) are a candidate technology NASA began investigating in the late 1960’s. Compared to supersonic parachutes, IADs represent a decelerator option capable of operating at higher Mach numbers and dynamic pressures. IADs have seen a resurgence in interest from the Entry, Descent, and Landing (EDL) community in recent years. The NASA Space Technology Roadmap (STR) highlights EDL systems, as well as, Materials, Structures, Mechanical Systems, and Manufacturing (MSMM) as key Technology Areas for development in the future; recognizing deployable decelerators, flexible material systems, and computational design of materials as essential disciplines for development. This investigation develops a multi-scale flexible material modeling approach that enables efficient high-fidelity IAD design and a critical understanding of the new materials required for robust and cost effective qualification methods. The approach combines understanding of the fabric architecture, analytical modeling, numerical simulations, and experimental data. This work identifies an efficient method that is as simple and as fast as possible for determining IAD material characteristics while not utilizing complicated or expensive research equipment. This investigation also recontextualizes an existing mesomechanical model through validation for structures pertaining to the analysis of IADs. In addition, corroboration and elaboration of this model is carried out by evaluating the effects of varying input parameters. Finally, the present investigation presents a novel method for numerically determining mechanical properties. A sub-scale section that captures the periodic pattern in the material (unit cell) is built. With the unit cell, various numerical tests are performed. The effective nonlinear mechanical stiffness matrix is obtained as a function of elemental strains through correlating the unit cell force-displacement results with a four node membrane element of the same size. Numerically determined properties are validated for relevant structures. Optical microscopy is used to capture the undeformed geometry of the individual yarns.
Automated trajectory control for proximity operations using relative orbital elements

(Georgia Institute of Technology, 2015-04-02) Spencer, David Allen

This dissertation develops a methodology for automated trajectory control of a spacecraft about a non-maneuvering target. The methodology utilizes relative orbital elements (ROEs), combined with guidance laws based upon artificial potential functions (APFs), to perform automated trajectory planning and maneuver design. The investigation provides a definitive reference on the definition and use of ROEs for relative proximity operations. The detailed derivation of ROEs is provided, along with transformations between ROEs and relative Cartesian state elements, characteristics of unforced motion in terms of ROEs, and the effect of impulsive maneuvers on ROEs. Operationally-useful guidance algorithms utilizing ROEs are developed and demonstrated. These ROE-based algorithms for rendezvous, circumnavigation and station-keeping provide a toolkit for relative proximity operations mission planning. A new approach for APF formulation using ROEs as the target variables is developed. While previous approaches allowed targeting of a specified relative position, the present approach allows the targeting of relative orbit geometries. The approach capitalizes upon the orbital dynamics represented through the ROEs, and retains the computational simplicity offered by the APFs. Formulations for the APF targeting of individual ROEs, as well as simultaneous targeting of a set of ROEs, are established. An approach for combining ROE targeting using APFs with obstacle avoidance is presented. The trajectory guidance algorithm performance is evaluated using a flight-like guidance, navigation and control simulation environment, including orbital perturbations. Algorithm performance is established through a set of operationally relevant scenarios. The guidance algorithms are shown to be capable of correcting for environmental disturbances, while meeting the targeted relative orbits in an automated fashion.
Improved analytical methods for assessment of hypersonic drag-modulation trajectory control

(Georgia Institute of Technology, 2015-04-01) Putnam, Zachary Reed

During planetary entry, a vehicle uses drag generated from flight through the planetary atmosphere to decelerate from hyperbolic or orbital velocity. To date, all guided entry systems have utilized lift-modulation trajectory control. Deployable aerodynamic devices enable drag-modulation trajectory control, where a vehicle controls its energy and range during entry by varying drag area. Implementation of conventional lift-modulation systems is challenging for deployable systems. In contrast, drag-modulation trajectory control may be simpler and lower-cost than current state-of-the-art lift-modulation systems. In this investigation, a survey of analytical methods for computing planetary entry trajectories is presented and the approximate analytical solution to the entry equations of motion originally developed by Allen and Eggers is extended to enable flight performance evaluation of drag-modulation trajectory control systems. Results indicate that significant range control authority is available for vehicles with modestly sized decelerators. The extended Allen-Eggers solution is closed-form and enables rapid evaluation of nonlifting entry trajectories. The solution is utilized to develop analytical relationships for discrete-event drag-modulation systems. These relationships have direct application to onboard guidance and targeting systems. Numerical techniques were used to evaluate drag-modulation trajectory control for precision landing and planetary aerocapture missions, including development of prototype real-time guidance and targeting algorithms. Results show that simple, discrete-event drag-modulation trajectory control systems can provide landed accuracies competitive with the current state of the art and a more benign aerothermal environment during entry for robotic-scale exploration missions. For aerocapture, drag-modulation trajectory control is shown to be feasible for missions to Mars and Titan and the required delta-V for periapsis raise is insensitive to the particular method of drag modulation. Overall, results indicate that drag-modulation trajectory control is feasible for a subset of planetary entry and aerocapture missions. To facilitate intelligent system selection, a method is proposed for comparing lift and drag-modulation trajectory control schemes. This method applies nonlinear variational techniques to closed-form analytical solutions of the equations of motion, generating closed-form expressions for variations of arbitrary order. This comparative method is quantitative, performance-based, addresses robustness, and applicable early in the design process. This method is applied to steep planetary entry trajectories and shows that, in general, lift and drag-modulation systems exhibit similar responses to perturbations in environmental and initial state perturbations. However, significant differences are present for aerodynamic perturbations and results demonstrate that drag systems may be more robust to uncertainty in aerodynamic parameters. Finally, the results of these contributions are combined to build a set of guidelines for selecting lift or drag-modulation for a Mars Science Laboratory-class planetary entry mission.
Computational fluid dynamics and analytical modeling of supersonic retropropulsion flowfield structures across a wide range of potential vehicle configurations

(Georgia Institute of Technology, 2013-11-15) Cordell, Christopher E.

For the past four decades, Mars missions have relied on Viking heritage technology for supersonic descent. Extending the use of propulsion, which is required for Mars subsonic deceleration, into the supersonic regime allows the ability to land larger payload masses. Wind tunnel and computational experiments on subscale supersonic retropropulsion models have shown a complex aerodynamic flow field characterized by the interaction of underexpanded jet plumes exhausting from nozzles on the vehicle with the supersonic freestream. Understanding the impact of vehicle and nozzle configuration on this interaction is critical for analyzing the performance of a supersonic retropropulsion system, as deceleration will have components provided by both the aerodynamic drag of the vehicle and thrust from the nozzles. This investigation focuses on the validity of steady state computational approaches to analyze supersonic retropropulsion flowfield structures and their effect on vehicle aerodynamics. Wind tunnel data for a single nozzle and a multiple nozzle configuration are used to validate a steady state, turbulent computational fluid dynamics approach to modeling supersonic retropropulsion. An analytic approximation to determine plume and bow shock structure in the flow field is also developed, enabling rapid assessment of flowfield structure for use in improved grid generation and as a configuration screening tool. Results for both the computational fluid dynamics and analytic approaches show good agreement with the experimental datasets. Potential limitations of the two methods are identified based on the comparisons with available data. Six additional geometries are defined to investigate the extensibility of the analytical model and determine the variation of supersonic retropropulsion performance with configuration. These validation geometries are split into two categories: three geometries with nozzles located on the vehicle forebody at varying nozzle cant angles, and three geometries with nozzles located on the vehicle aftbody at varying nozzle cant angles and number of nozzles. The forebody nozzle configurations show that nozzle cant angle is a significant driver in performance of a vehicle employing supersonic retropropulsion. Aerodynamic drag preservation for a given thrust level increases with increasing cant angle. However, increasing the cant angle reduces the contribution of thrust to deceleration. The tradeoff between these two contributions to the deceleration force is examined, noting that performance improvements are possible with modest nozzle cant angles. Static pitch stability characteristics are investigated for the lowest and highest cant angle configurations. The aftbody nozzle configuration results show that removing the plume flow from the region forward of the vehicle results in less interaction with the bow shock structure. This impacts aerodynamic performance, as the surface pressure remains relatively undisturbed for all thrust values examined. Static pitch stability characteristics for each of the aftbody nozzle configurations are investigated; noting that supersonic retropropulsion for these configurations exhibits a transition point from static stability to instability as a function of this center of mass location along the axis.
Statistical methods for reconstruction of entry, descent, and landing performance with application to vehicle design

(Georgia Institute of Technology, 2013-11-06) Dutta, Soumyo

There is significant uncertainty in our knowledge of the Martian atmosphere and the aerodynamics of the Mars entry, descent, and landing (EDL) systems. These uncertainties result in conservatism in the design of the EDL vehicles leading to higher system masses and a broad range of performance predictions. Data from flight instrumentation onboard Mars EDL systems can be used to quantify these uncertainties, but the existing dataset is sparse and many parameters of interest have not been previously observable. Many past EDL reconstructions neither utilize statistical information about the uncertainty of the measured data nor quantify the uncertainty of the estimated parameters. Statistical estimation methods can blend together disparate data types to improve the reconstruction of parameters of interest for the vehicle. For example, integrating data obtained from aeroshell-mounted pressure transducers, inertial measurement unit, and radar altimeter can improve the estimates of the trajectory, atmospheric profile, and aerodynamic coefficients, while also quantifying the uncertainty in these estimates. These same statistical methods can be leveraged to improve current engineering models in order to reduce conservatism in future EDL vehicle design. The work in this thesis presents a comprehensive methodology for parameter reconstruction and uncertainty quantification while blending dissimilar Mars EDL datasets. Statistical estimation methods applied include the Extended Kalman Filter, Unscented Kalman Filter, and Adaptive Filter. The estimators are applied in a manner in which the observability of the parameters of interest is maximized while using the sparse, disparate EDL dataset. The methodology is validated with simulated data and then applied to estimate the EDL performance of the 2012 Mars Science Laboratory. The reconstruction methodology is also utilized as a tool for improving vehicle design and reducing design conservatism. A novel method of optimizing the design of future EDL atmospheric data systems is presented by leveraging the reconstruction methodology. The methodology identifies important design trends and the point of diminishing returns of atmospheric data sensors that are critical in improving the reconstruction performance for future EDL vehicles. The impact of the estimation methodology on aerodynamic and atmospheric engineering models is also studied and suggestions are made for future EDL instrumentation.
Inverse estimation methodology for the analysis of aeroheating and thermal protection system data

(Georgia Institute of Technology, 2013-11-06) Mahzari, Milad

Thermal Protection System (TPS) is required to shield an atmospheric entry vehicle against the high surface heating environment experienced during hypersonic flight. There are significant uncertainties in the tools and models currently used for the prediction of entry aeroheating and TPS material thermal response. These uncertainties can be reduced using experimental data. Analysis of TPS ground and flight data has been traditionally performed in a direct fashion. Direct analyses center upon comparison of the computational model predictions to data. Qualitative conclusions about model validity may be drawn based on this comparison and a limited number of model parameters may be iteratively adjusted to obtain a better match between predictions and data. The goal of this thesis is to develop a more rigorous methodology for the estimation of surface heating and TPS material response using inverse estimation theory. Built on theoretical developments made in related fields, this methodology enables the estimation of uncertainties in both the aeroheating environment and material properties from experimental temperature data. Unlike direct methods, the methodology developed here is capable of estimating a large number of independent parameters simultaneously and reconstructing the time-dependent surface heating profile in an automated fashion. This methodology is applied to flight data obtained from thermocouples embedded in the Mars Pathfinder and Mars Science Laboratory entry vehicle heatshields.